i

GA-Al4690 uc-77

ASSESSMENT OF GRADE H-451 GRAPHITE FOR REPLACEABLE FUEL

AND REFLECTOR ELEMENTS IN HTGR

bY G. B. ENGLE

Prepared under Contract EY-76-C-03-0167

Project Agreement No. 17 for the San Francisco Operations Office

Department of Energy

\

DATE PUBLISHED: DECEMBER 1977

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

This report wan prepared an an account of work sponsored by the United States Government. Neither the United States nor the Department of Energy, nor any of their employees, nor any of their contractors, subcontradarn, or their employees, makes any warranty, expreas or implied, or assumes any legal liability or responsibility for the accuracy, completeneee or usefulness of any information, apparatus, product or pmceee disclosed, or represents that ita use would not infringe privately owned rights.

Printed in the United States of America Available from

National Technical Information Service U . S . Department of Commerce

5285 Port Royal Road Springfield, Virginia 22161

Price: Printed Copy $8.00; Microfiche $3.00

’

NOTICE

rponrored by the United Stater Government. Neither t h e United States nor the Uluted Stater Department of Energy. nor any of their employees, nor any of thetr contractors, subcontractors. or their employees, maker any warranty. express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus. product or process disclosed, or reprerenu that its usc would not

GA-A14690 uc-77

ASSESSMENT OF GRADE H-451 GRAPHITE FOR REPLACEABLE FUEL

AND REFLECTOR ELEMENTS IN HTGR

Prepared under Contract EY-76-C-03-0167

Project Agreement No. 17 for the San Francisco Operations Office

Department of Energy

GENERAL ATOMIC PROJECT 3224 DATE PUBLISHED: DECEMBER 1977

GENERAL ATOMIC COMPANY

ABSTRACT

Experimental d a t a f o r grade H-451 g r a p h i t e are presented and assessed

t o suppor t l i c e n s i n g of H-451 g r a p h i t e f o r use as f u e l element b locks i n a

high-temperature gas-cooled r e a c t o r (HTGR). Addi t iona l d a t a from t h e l i t e r -

a t u r e on g r a p h i t e grades similar t o grade H-451 are presented t o supplement

t h e H-451 d a t a . Evaluat ion programs a t General Atomic Company (GA) cover ing

c h a r a c t e r i z a t i o n , i r r a d i a t i o n , and o x i d a t i o n s t u d i e s , a long wi th s t u d i e s

c a r r i e d o u t i n t h e Great Lakes Carbon Corporat ion H-451 development program,

are repor t ed .

Grade H-451 i s a h igh-pur i ty g r a p h i t e manufactured by e x t r u s i o n as l o g s

432 mm i n d iameter by 864 mm i n l eng th from a s p e c i a l blend of nea r - i so t rop ic

petroleum coke us ing convent ional g r a p h i t e manufacturing processes .

type, p reproduct ion , and product ion l o g s have been eva lua ted by systemat-

i c a l l y measuring phys ica l and mechanical p r o p e r t i e s , impur i ty con ten t , and

f a t i g u e behavior . Cont ro l led i r r a d i a t i o n experiments , c a r r i e d o u t i n i n s t r u -

mented capsu le s , w e r e u t i l i z e d t o provide d a t a over t h e temperature and

f luence l i f e of f u e l elements i n an HTGR.

c i e n t s were t aken from l i t e r a t u r e va lues on H-451 and g r a p h i t e s s i m i l a r t o

H-451. Oxidat ion rates i n helium-water mixtures and t h e e f f e c t of ox ida t ion

burnoff on s t r e n g t h and e l a s t i c modulus of H-451 are r epor t ed .

Proto-

I r rad ia t ion- induced creep c o e f f i -

Grade H-451 shows an improvement i n r a d i a l s t r e n g t h and thermal con-

d u c t i v i t y over H-327, a needle-coke g r a p h i t e , which i s c u r r e n t l y used f o r

HTGR r e p l a c e a b l e f u e l and r e f l e c t o r e lements .

an i so t ropy f a c t o r . Overa l l , H-451 w i l l provide b e t t e r s a f e t y margins i n t h e

For t S t . Vrain (FSV) r e a c t o r and more f l e x i b i l i t y i n des ign f o r f u t u r e HTGRs.

Grade H-451 a+o has a lower

iii.

n

Q

.

CONTENTS 8

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

1 . SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . 1-1

1.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.2. Concept and Need for a Near-Isotropic Fuel Element Graphite . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.3. Development Program at GLCC . . . . . . . . . . . . . . . 1-2 1.4. Characterization Program . . . . . . . . . . . . . . . . . 1-5

Distribution of Properties Within Individual Logs and Between Logs Within a Lot . . . . . . . . 1-5 Statistical Distribution of Strength Within aLog . . . . . . . . . . . . . . . . . . . . . . 1-6 Definition of Minimum Strength and Strength Distribution Among Logs . . . . . . . . . . . . . 1-7

1.4.4. Fatigue Behavior . . . . . . . . . . . . . . . . . 1-8

1.5. Irradiation Program . . . . . . . . . . . . . . . . . . . 1-9 1.5.1. Dimensional Changes . . . . . . . . . . . . . . . 1-9 1.5.2. Tensile Strength and Elastic Modulus . . . . . . . 1-9 1.5.3. Fatigue Behavior . . . . . . . . . . . . . . . . . 1-10 1.5.4. Thermal Expansivity . . . . . . . . . . . . . . . 1-10 1.5.5. Thermal Conductivity . . . . . . . . . . . . . . . 1-10 1.5.6. Irradiation-Induced Creep . . . . . . . . . . . . 1-11

1.6. Oxidation Program . . . . . . . . . . . . . . . . . . . . . 1-12 1.6.1. Oxidation Rate of H-451 Graphite . . . . . . . . . 1-12 1.6.2. Effect of Oxidation on Tensile Strength and

Elastic Modulus . . . . . . . . . . . . . . . . . 1-12

1.4.1.

1.4.2.

1.4.3.

2 . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 3 . CONCEPT AND NEED FOR A NEAR-ISOTROPIC FUEL ELEMENT GRAPHITE . . 3-1 4 . DEVELOPMENT PROGRAM AT GLCC . . . . . . . . . . . . . . . . . . 4-1

4.1. Filler Cokes . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.2. Processing . . . . . . . . . . . . . . . . . . . . . . . . 4-4

V

4.3. Pro to type and Preproduct ion Development . . . . . . . . . . 4.4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 . CHARACTERIZATION PROGRAM . . . . . . . . . . . . . . . . . . . . 5 . 1 . I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . 5 . 2 . D i s t r i b u t i o n of P r o p e r t i e s Within I n d i v i d u a l Logs and

Between Logs Within a Lot

5.2 .1 . Sampling . . . . . . . . . . . . . . . . . . . . . 5.2.2. Bulk Densi ty . . . . . . . . . . . . . . . . . . . 5 .2 .3 . Mechanical P r o p e r t i e s . . . . . . . . . . . . . . . 5 . 2 . 4 . Thermal P r o p e r t i e s . . . . . . . . . . . . . . . . 5 .2 .5 . Impurity Content . . . . . . . . . . . . . . . . . 5 .2 .6 . Conclusions . . . . . . . . . . . . . . . . . . . .

5.3 . S t a t i s t i c a l D i s t r i b u t i o n of S t r eng th Within a Log . . . . . 5 . 3 . 1 . Sampling . . . . . . . . . . . . . . . . . . . . . . 5 .3 .2 . Conclusions . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

5 .4 . D e f i n i t i o n of Minimum S t reng th and S t r e n g t h D i s t r i b u t i o n Among Logs . . . . . . . . . . . . . . . . . . . . . . . . 5 . 4 . 1 . Sampling . . . . . . . . . . . . . . . . . . . . . 5 . 4 . 2 . Experimental R e s u l t s . . . . . . . . . . . . . . . 5.4 .3 . Appl i ca t ion of R e s u l t s t o Acceptance T e s t i n g . . . 5.4.4. Conclusions . . . . . . . . . . . . . . . . . . . .

5.5 . Fa t igue Behavior . . . . . . . . . . . . . . . . . . . . . 5 . 5 . 1 . Sampling . . . . . . . . . . . . . . . . . . . . . 5 .5 .2 . Experimental Procedure . . . . . . . . . . . . . . 5 .5 .3 . Experimental R e s u l t s . . . . . . . . . . . . . . . . 5 . 5 . 4 . Conclusions . . . . . . . . . . . . . . . . . . . .

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 . IRRADIATION PROGRAM . . . . . . . . . . . . . . . . . . . . . . .

6 .1 . I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . 6 . 2 . Sampling . . . . . . . . . . . . . . . . . . . . . . . . . 6 . 3 . Dimensional Changes . . . . . . . . . . . . . . . . . . . .

6.3 .1 . 873 t o 1673 K (600" t o 1400°C) . . . . . . . . . . 6 .3 .2 . 5 7 3 t o 873 K (300" to 600°C) . . . . . . . . . . .

4-4

4-6

4-6

5-1

5-1

5-1

5-1

5-2 5-2

5-4

5-6

5-14

5-15

5-16

5-16

5-17

5-17

5-18

5-20

5-26

5-27

5-28

5-28

5-28

5-31

5-31

6-1

6-1

6-3

6-3

6-3

6-7

vi

6.4. Tensile Strength. Elastic Modulus. and Strain at Fracture . . 6-9

6.4.1. 823 to 1623 K (550' to 1350°C) . . . . . . . . . . . 6-9 6.4.2. 627 to 873 K (350" to 600°C) . . . . . . . . . . . . 6-10

6.4.3. Between-Log and Within-Log Variations in Strength Increase . . . . . . . . . . . . . . . . . . 6-11

6.5. Fatigue Behavior . . . . . . . . . . . . . . . . . . . . . . 6-13

6.5.1. Sampling and Procedures . . . . . . . . . . . . . . . 6-13

6.5.2. Experimental Results and Discussion . . . . . . . . . 6-13

6.6.1. 823 to 1623 K (550" to 1350°C) . . . . . . . . . . . 6-15

6.6. Thermal Expansivity . . . . . . . . . . . . . . . . . . . . . 6-15

6 .6 .2 . 623 to 823 K (350" to 550°C) . . . . . . . . . . . . 6-17

6 . 7 . Thermal Conductivity . . . . . . . . . . . . . . . . . . . . 6-17

6.7.1. 923 to 1623 K (650" to 1350°C) . . . . . . . . . . . 6-17

6.7.2. 523 to 923 K (250" to 650°C) . . . . . . . . . . . . 6-19

6 .7 .3 . Effect of Change in Temperature . . . . . . . . . . . 6-20

6.8. Irradiation-Induced Creep . . . . . . . . . . . . . . . . . . 6-20

6 .8 .1 . Conclusions . . . . . . . . . . . . . . . . . . . . . 6-21

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21

7 . OXIDATION PROGRAM . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1. Oxidation Rate of H-451 Graphite . . . . . . . . . . . . . . 7-1

7.1.1. Reaction Rate Theory . . . . . . . . . . . . . . . . 7-1

7.1.2. Experimental Procedure and Sampling . . . . . . . . 7-3

7.1.3. Determination of Reaction Rate Constants . . . . . . 7-4

7 . 1 . 4 . Application of Rate Constants . . . . . . . . . . . 7-6 Effect of Steam Oxidation on Tensile Strength and Elastic Modulus . . . . . . . . . . . . . . . . . . . . . . 7-8

7.2.1. Experimental Procedure and Sampling . . . . . . . . 7-8

7.2.2. Experimental Results . . . . . . . . . . . . . . . . 7-9

7.2.

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-22

8 . ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

APPENDIX A: SAMPLING DIAGRAMS . . . . . . . . . . . . . . . . . . . . A-1 APPENDIX B: RESULTS OBTAINED DURING ASSESSMENT PROGRAM . . . . . . . B-1

FIGURES

1.1 . Comparison of dimensional changes for H-451 and H-327 graphites: (a) axial. (b) radial . . . . . . . . . . . . . . . . . . . . . 1-4

vii

6-1.

6-2.

6-3.

6-4.

7-1.

7-2.

7-3.

7-4.

7-5.

7-6.

7-7.

7-8.

7-9.

A-1.

A-2.

A-3.

A-4.

A-5.

H-451 graphite irradiation data . . . . . . . . . . . . . . . . 6-2

Irradiation-induced dimensional change in H-451 graphite (design curves): (a) axial direction, (b) radial direction . . 6-5

Dimensional changes in H-451 graphite irradiated with

Fatigue stress limits for survival of H-451 graphite to 105 cycles, normalized to the unirradiated tensile strength, versus the fast neutron fluence at an irradiation temperature of 1173 to 1263 K (900" to 990°C) . . . . . . . . . . . . . . . 6-16

Comparison of rate constants as a function of PH 0 (from Ref. 7-2). . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

Tensile strength versus burnoff for H-451 graphite (log 6484-34, quarter-length axial edge and center specimens)

Tensile strength versus burnoff for H-451 graphite (log 6484-34, quarter-length axial specimens) oxidized at

Tensile strength versus burnoff for H-451 graphite (log 6484-34, quarter-length axial center specimens) . . . . . . . . 7-16 Tensile strength versus burnoff for H-451 graphite (log 6484-34, quarter-length radial specimens) oxidized at

Tensile strength versus burnoff for H-451 graphite (log 6484-34, quarter-length radial specimens) oxidized at

Elastic modulus versus burnoff for H-451 graphite (log 6484-34, quarter-length axial center specimens) . . . . . . . . 7-19

Elastic modulus versus burnof f for H-451 graphite (log 6484-34, quarter-length axial specimens) oxidized at

Elastic modulus versus burnoff for H-451 graphite (log 6484-34, quarter-length radial edge specimens) oxidized at 1273 K (1000°C). . . . . . . . . . . . . . . . . . . . . . . . . 7-21

Sampling diagram of H-451 for within-log property measurements: slabs and sections . . . . . . . . . . . . . . . A-3

Sampling diagram of H-451 for within-log property measurements: center section showing specimen locations . . . . A-4 Sampling diagram of H-451 for within-log property measurements: edge section showing specimen locations . . . . . A-5

Orientation of orthogonal axes for definition of Poisson's ratio data in Table B-4 . . . . . . . . . . . . . . . . . . . . A-6

Locations of slabs (shaded) for statistical strength testing H-451 graphite (log 5651-90) . . . . . . . . . . . . . . A-7

changes in temperature (from Ref. 6-3) . . . . . . . . . . . . . 6-6

2

oxidized at 1073 K (800°C) . . . . . . . . . . . . . . . . . . . 7-14

1 2 7 3 K ( 1 0 0 0 ° C ) . . . . . . . . . . . . . . . . . . . . . . . . 7-15

1 0 7 3 K ( 8 0 0 ° C ) . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

1273 K (1000°C) . . . . . . . . . . . . . . . . . . . . . . . . 7-18

1273 K (1000°C) . . . . . . . . . . . . . . . . . . . . . . . . 7-20

n

viii

A-6. Coring p lan f o r cen te r zone of A and B s e c t i o n s of s l a b s ( see F ig . A-5) . . . . . . . . . . . . . . . . . . . . . . . .

A-7. Coring p lan f o r edge zone of A and B s e c t i o n s of s l a b s (see Fig. A-5) . . . . . . . . . . . . . . . . . . . . . . . .

A - 8 . Sampling diagram of H-451 l ogs for t e n s i l e s t r e n g t h . . . . . . A-9. Sampling diagram of H-451 l og sample core ( see Fig. A-8):

a x i a l specimens . . . . . . . . . . . . . . . . . . . . . . . A-10. Sampling diagram of H-451 l o g s l a b ( see Fig. A-8):

r a d i a l specimens . . . . . . . . . . . . . . . . . . . , . . A-11. Coring diagram f o r u n i r r a d i a t e d H-451 f a t i g u e specimens;

edge zone, from s l a b 2 ( see F ig . A-5) . . . . . . . , . . . . A-12. Sampling diagram f o r i r r a d i a t i o n specimens: c e n t e r zone,

from s l a b 3 (see Fig. A-1) . . . . . . . . . . . . . . . . . . A-13. Sampling diagram f o r i r r a d i a t i o n specimens: o u t e r zone,

edge s e c t i o n from s l a b 3 ( see Fig. A-1) . . . . . . . . . . . A-14. Sampling p l an of g r a p h i t e log showing s l a b des igna ted

f o r ox ida t ion tests. . . . . . . . . . . . . . . . . . . . . . A-15. Sampling p lan of H-451 showing s e c t i o n i n g of a s l a b

A-16. Sampling diagram of H-451 graph i t e : c e n t e r s e c t i o n of

A-17. Sampling diagram of H-451 graph i t e : edge s e c t i o n of

B-1. Fat igue test da ta : i n a i r log-log p l o t of normalized

from Fig. A-14 . . . . . . . , . . . . . . . . . . . . . . . . s l a b from Fig . A-15 . . . . . . . . , . . . . . . . . . . . . s l a b from Fig. A-15 . . . . . . . . . . . . . . . . . . . . . peak stress versus number of cyc le s t o f a i l u r e wi th R = - 1 ; lower x/y to l e rance l i m i t s r ep resen t l i m i t s above which x% of a l l d a t a would f a l l , w i t h y% confidence; a x i a l specimens; open c i r c l e s r ep resen t run-outs (from Ref. 5-10). .

B-2. Constant life fatigue diagram (Goodman diagram) for H-451 graph i t e : a x i a l d i r e c t i o n (from Ref, 5-10). . . . . . . . . . i r r a d i a t i o n temperatures 875 K t o 975 K and 1075 K t o 1175 K (602" t o 702°C and 802" to 902°C) (from Ref. 6-3) . , . , . . i r r a d i a t i o n temperatures 1275 K t o 1375 K and 975 K t o 1075 K (1002" to 1102°C and 702" t o 802°C) (from Ref. 6-3) . . , , . i r r a d i a t i o n temperatures 1175 K t o 1275 K (902' t o 1002°C) ( f romRef . 6-3). . . . . , . . . , . :. . . . . . . . . . . .

B-3. Dimensional change i n H-451 graph i t e : axial d i r e c t i o n ;

B-4. Dimensional change i n H-451 graph i t e : a x i a l d i r e c t i o n ;

B-5. Dimensional change i n H-451 graph i t e : axial d i r e c t i o n ;

A- 8

A- 9

A-10

A-11

A-12

A-13

A-14

A-15

A-16

A-17

A-18

A-19

B-22

B-23

B-24

B-25

B-26

' \

i x

B - 6 .

B-7.

B-8.

B-9.

B-10.

B-11.

B-12.

B-13.

B-14.

B-15.

B-16.

B-17.

Dimensional change i n H-451 g r a p h i t e : a x i a l d i r e c t i o n ; i r r a d i a t i o n temperatures 1475 K t o 1575 K and 1575 K t o 1675 K (1202" t o 1302°C and 1302" t o 1402°C) (from R e f . 6 - 3 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . B-27

Dimensional change i n H-451 g r a p h i t e : r a d i a l d i r e c t i o n ; i r r a d i a t i o n temperatures 875 K t o 975 K and 1475 K t o 1575 K (602' t o 702°C and 1202" t o 1302°C) (from Ref. 6-3) . . . . . . B-28

Dimensional change i n H-451 g r a p h i t e : radial . d i r e c t i o n ; i r r a d i a t i o n temperatures 975 K t o 1075 K and 1275 K t o 1375 K (702" t o 802°C and 1002" t o 1102°C) ( f r o m Ref . 6 - 3 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . B-29

Dimensional change i n H-451 g r a p h i t e : r a d i a l d i r e c t i o n ; i r r a d i a t i o n temperatures 1175 K t o 1275 K (902" t o 1002°C) ( f r o m R e f . 6 - 3 ) . . . . . . . . . . . . . . . . . . . . . . . . B - 3 0

Dimensional change i n H-451 g r a p h i t e : r a d i a l d i r e c t i o n ; i r r a d i a t i o n temperatures 1075 K t o 1175 K (802" t o 902OC and 1302" t o 1402OC) (from Ref. 6-3) . . . . . . . . . . . . . B-31

Dimensional changes i n n e a r - i s o t r o p i c g r a p h i t e i r r a d i a t e d a t 633 K t o 773 K (360" t o 500°C) ( d a t a from Refs , 6-4 a n d 6 - 6 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . R-32

Dimensional changes i n n e a r - i s o t r o p i c g r a p h i t e i r radiated a t 773 K t o 873 K (500" t o 600°C) ( d a t a from Refs. 6-4 a n d 6 - 6 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-33

Changes i n t e n s i l e s t r e n g t h and e las t ic modulus of H-451 g r a p h i t e as a f u n c t i o n of f a s t neu t ron f luences . E r r o r b a r s denote 5 one s t a n d a r d d e v i a t i o n (from Ref. 6-3). . . . . . B-34

F r a c t i o n a l changes i n s o n i c e las t ic modulus of extruded n e a r - i s o t r o p i c p i t c h coke g r a p h i t e (Dragon code No. 100) (from Ref. 5-7) . . . . . . . . . . . . . . . . . . . . . . . . B-35

Change i n t h e s o n i c e las t ic modulus (E) and s t r e n g t h (S) of n e a r - i s o t r o p i c g r a p h i t e i r r a d i a t e d a t 623 K t o 973 K a t (350" t o 700°C) (from Ref. 6-8). . . . . . . . . . . . . . . B-36

Ca lcu la t ed p e r c e n t i n c r e a s e s i n s t a t i c e las t ic modulus of n e a r - i s o t r o p i c g r a p h i t e s ( s o l i d p a r t s of cu rves correspond t o d a t a i n Refs. 6-6 and 6-8; broken p a r t s are e x t r a p o l a t e d ) . . B-37

Fa t igue test d a t a i r r a d i a t e d t o 3.0 x 1025 N/m2 ( E > 29 fJlHTGR a t 1173 K (900°C). Log-log p l o t of normalized peak stress v e r s u s number of c y c l e s to f a i l u r e , w i t h stress r a t i o , R = -1. Lower x/y t o l e r a n c e l i m i t s r e p r e s e n t t h e l i m i t s above which x% of a l l d a t a would f a l l , w i t h y% confidence; a x i a l specimens; open circles r e p r e s e n t run-outs (from Ref. 5-10). . . . . . . . . . . . . . . . . . . . . . . . . . . B-38

X

B-18. Percent change i n thermal expans iv i ty E295 K t o 773 K (22" t o 500°C)] of nea r - i so t rop ic g r a p h i t e s as a func t ion of f a s t neut ron f luence : i r r a d i a t i o n temperature 865 K t o 1205 K (592" t o 932OC) (from Ref. 6-3) . . . . . , . . . . . . B-39

B-19. Percent change i n thermal expans iv i ty [295 K t o 773 K (22" t o 500°C)] of near i s o t r o p i c g r a p h i t e s as a func t ion of f a s t neut ron f luence : i r r a d i a t i o n temperature 1250 K t o 1705 K (592" t o 932°C) (from Ref. 6-3) . . . . . . . , , . . . B-40

B-20. Change i n thermal expans iv i ty of nea r - i so t rop ic g r a p h i t e i r r a d i a t e d a t 350" t o 550°C ( d a t a from Ref. 6-4) . . . . . . . B-41

B-21. Thermal conduc t iv i ty a t t h e i r r a d i a t i o n temperature f o r H-451 and o t h e r nea r - i so t rop ic g r a p h i t e s as a func t ion of f a s t neut ron f luence (from Ref. 6-3) . . . . . . . . . . . . . B-42

n e a r - i s o t r o p i c g r a p h i t e (da t a p o i n t s from Refs. 6-6 and 6-8; curves from Ref. 6-10). . . . . . . . , . . . . . . . . . B-43

B-22. I r rad ia t ion- induced changes i n thermal r e s i s t i v i t y of

TABLES

1-1. Comparison of H-451 and H-327 p r o p e r t i e s . . . . . . . . . . . 4-1. M i c r o s t r u c t u r a l ana lys i s of ca l c ined cokes used t o

manufacture H-451 g r a p h i t e . . . . . . . . . . . . . . . . . . 4-2. H-451 lots manufactured by (;LCC ,ind l o g d i s t r i b u t i o n s

dur ing development program . . . . . . . . . . . . . . . . . . 4-3. Programs u t i l i z i n g H-451 g r a p h i t e l o g s . . . . . . . . . . . . 5-1.

l o t 426, l o g 6484-34 . . . . . . . . . . . . . . . . . . . . . 5-2. Impuri ty con ten t : H-451, l o t 426 . . . . . . . . . . . . . . 5-3. Summary of l i t h i u m analyses : H-451 . . . . . . . . . . . . . 5-4. Impuri ty conten t : H-451 . . . . . . . . . . . . . . . . . . . 5-5. S t a t i s t i c a l ana lyses of GA and GLCC a x i a l s t r e n g t h da t a . . . . 5-6. S t a t i s t i c a l a n a l y s i s of r a d i a l s t r e n g t h d a t a . . . . . . . . . 5-7. Components of var iance : a x i a l s t r e n g t h d a t a . . . . . . . . . 5-8. Criteria f o r a s s ign ing logs t o s t r e n g t h c a t e g o r i e s A , B , o r

C ( a x i a l d a t a ) . . . . . . . . . . . . , . . , . . . . . . . . 5-9. Yie lds of l ogs i n each s t r e n g t h ca tegory (based on a x i a l

s t r e n g t h s ) . . . , . . . . . . . , . . . . . . . , . . . . . . 5-10. S t a t i s t i c a l ana lyses of f a t i g u e d a t a f o r u n i r r a d i a t e d H-451

g r a p h i t e . . . . , . . . . . . . , . . . . . . . . . . . . . .

Summary of boron equ iva len t t es t d a t a on H-451,

1-3

4-3

4-5

4-7

5-8

5-1 2 5-1 3

5-1 4

5-19

5-20

5-21

5-24

5-25

5-30

x i

n 6-1. Within-log variation in irradiation-induced shrinkage of

Between-log variations in irradiation-induced shrinkage of H-451 graphite, Lot 426 . . . . . . . . . . . . . . . . H-451 graphite, Lot 426 . . . . . . . . . . . . . . . . . .

6-2.

6-3. Between-log variations in irradiation-induced strength

6-4.

6-5. Results of statistical analysis of fatigue data for H-451

increase of H-451 graphite, Lot 426 . . . . . . . . . . . . Within-log variations in irradiation-induced strength increase of H-451 graphite, axial direction . . . . . . . . graphite irradiated at 1173 to 1263 K (900' to 990°C)

6-6. Increase in thermal expansivity of near-isotropic graphite

7-1. Experimentally determined Langmuir-Hinshelwood constants

7-2.

7-3. Reduction in ultimate tensile strength and elastic modulus with oxidation . . . . . . . . . . . . . . . . . . . . . .

B-1. Bulk density: H-451, Lot 426 . . . . . . . . . . . . . . . B-2. Ultimate tensile strength: H-451, Lot 426 . . . . . . . . B-3. Elastic modulus in tension: H-451, Lot 426 . . . . . . . . B-4. Poisson's ratio: H-451, Lot 266 . . . . . . . . . . . . . B-5. Flexural strength: H-451, Lot 426 . . . . . . . . . . . . B-6. Ultimate compressive strength and elastic modulus in

B-7. Thermal expansivity: H-451, Lot 426 . . . . . . . . . . . B-8. Anisotropy factor: H-451, Lot 426 . . . . . . . . . . . . B-9. Thermal conductivity: H-451, Lot 426, MLC . . . . . . . . B-10. Mean tensile strength of unirradiated H-451 graphite

specimens used in fatigue study . . . . . . . . . . . . . . B-11. Irradiation conditions and mean tensile strength of

irradiated H-451 graphite used in fatigue study (all

(stress ratio, R = -1) . . . . . . . . . . . . . . . . . . irradiated between 623 and 823 K (350" and 550°C) . . . . . for H-451 graphite. . . . . . . . . . . . . . . . . . . . . Summary of UTS and elastic modulus data and comparison of population means of nonoxidized and oxidized specimens. . .

compression: H-451, Lot 478. . . . . . . . . . . . . . . .

specimens MLC location) . . . . . . . . . . . . . . . . . . B-12. Summary of irradiation-induced changes in thermal

expansivity of H-451 graphite irradiated in capsules OG-1, OG-2, and OG-3 . . . . . . . . . . . . . . . . . . . expansivity of H-429 graphite irradiated in capsules OG-1, OG-2, and OG-3 . . . . . . . . . . . . . . . . . . .

B-13. Summary of irradiation-induced changes in thermal

6-8 . . 6-8 . .

. .

. . 6-1 2

6-12

6-14 . . 6-1 8 . . 7-4 . . 7-1 1 . . 7-1 2

B- 3 B-4

B-5

B-6

B- 7

. .

. .

. .

. .

. .

. . B- 8 B-9 B-10

B-11

. .

. .

. .

. . B-11 . .

B-12 . .

B-13 . .

B-14 . .

xii

U - 1 4 . Summary o f irradintion-induced cliniiges In thermal expansivlty of T S - 1 2 4 0 graphite irradiated in capsules OG-2 and OG-3 . . . . B-15

B - 1 5 . Summary of irradiation-induced changes in thermal expansivity of S O 8 1 8 graphite irradiated in capsule OG-3 . . . . . . . . . . B-16

B - 1 6 . Summary of frradiation-induced changes in thermal conductivity of H-451 graphite irradiated in capsules OG-1, OG-2, and OG-3 (all specimens from MLC of parent log) . . . . . . . . . . B-17

B - 1 7 . Summary of irradiation-induced changes in thermal conductivity of T S - 1 2 4 0 graphite irradiated in capsules OG-2 and OG-3 (all specimens from MLC of parent log) . . . . . . . . . . . . . B-18

B - 1 8 . Summary of irradiation-induced changes in thermal conductivity of S O 8 1 8 graphite irradiated in capsule OG-3 (all specimens from MLC of parent log). . . . . . . . . . . . . . . . . . . . . B-19

B - 1 9 . Calculated thermal conductivity at irradiation temperature of near-isotropic graphite irradiated between 573 and 873 K

B - 2 0 . Allocation of graphite samples for oxidation studies

(300" and 6 0 0 O C ) . . . . . . . . . . . . . . . . . . . . . . . . B-20

(number of specimens) . . . . . . . . . . . . . . . . . . . . . B-21

xiii

1 . SUMMARY ANI) CONCLUSIONS

1 . 1 . INTRODUCTION

Grade H-451 g r a p h i t e , developed e x c l u s i v e l y by t h e Great Lakes Carbon

Corpora t ion (GLCC) f o r HTGR f u e l element b locks , has been eva lua ted exten-

s i v e l y i n p repa ra t ion f o r i t s i n t r o d u c t i o n i n t o t h e high-temperature gas-

cooled r e a c t o r (HTGR). Th i s r e p o r t summarizes t h e d a t a on grade H-451 and

d a t a from t h e l i t e r a t u r e on g r a p h i t e s s imi la r t o H-451 t h a t were used as a

b a s i s f o r p repa r ing t h e Graphi te Fuel Element s e c t i o n of t h e Fuel Design Data

Manual (GA-AI 44 29) .

The f i v e major s e c t i o n s of t h i s r e p o r t desc r ibe : (1) t h e concept and

need f o r a nea r - i so t rop ic f u e l element g r a p h i t e , (2) t h e development program

a t GLCC, ( 3 ) t h e c h a r a c t e r i z a t i o n program, (4) t h e i r r a d i a t i o n program, and

(5) t h e o x i d a t i o n program. Appendix A con ta ins sampling p l ans f o r t h e pro-

gram, and d a t a obta ined are presented i n t h e f i g u r e s and t a b l e s of Appendix B .

This r e p o r t i s supplemental t o t h e Materials S p e c i f i c a t i o n f o r Replaceable

Fuel and R e f l e c t o r Element Graphi tes (Number 900739) and t h e Graphi te Fuel

Element s e c t i o n of t h e Fuel Design Data Manual (GA-A14429).

1.2. CONCEPT AND NEED FOR A NEAR-ISOTROPIC FUEL ELEMENT GRAPHITE

T h e primary i n c e n t i v e f o r developing a nea r - i so t rop ic g r a p h i t e t o

r ep lace needle-coke g r a p h i t e grade H-327 f o r HTGR f u e l e lements w a s t o

improve dimensional s t a b i l i t y , s t r e n g t h , and thermal conduc t iv i ty and thus

improve performance, s a f e t y margins i n FSV, and f l e x i b i l i t y i n des ign f o r

f u t u r e HTGRs .

1- 1

The d a t a i n Table 1-1 show a comparison of p r o p e r t i e s between grades

H-451 and H-327 i n t h e u n i r r a d i a t e d s ta te and a f t e r i r r a d i a t i o n t o end-of-

l i f e HTGR f luences .

thermal conduc t iv i ty i n t h e i r r a d i a t e d state. The thermal expans iv i ty of

H-451 i s h igher than t h a t of H-327 i n t h e u n i r r a d i a t e d state, bu t t h e

thermal expans iv i ty of H-451 dec reases wi th i r r a d i a t i o n whereas i t remains

unchanged f o r H-327.

H-451 bu t H-327 has a h igher modulus i n t he a x i a l d i r e c t i o n . A comparison

of dimensional changes i s shown i n Fig. 1-1. Grade H-451 h a s a lower aniso-

t ropy f a c t o r f o r dimensional change, and r a d i a l expansion i s delayed t o

beyond t h e end-of- l i fe HTGR f luences a t peak HTGR temperatures .

The major improvement i s i n t h e r a d i a l s t r e n g t h and

Grade H-327 h a s a lower r a d i a l e l a s t i c modulus than

I n a d d i t i o n t o t h e improved p r o p e r t i e s and i r r a d i a t i o n behavior , t h e

near - i so t ropy i n p r o p e r t i e s and dimensional changes g r e a t l y s i m p l i f i e s

des ign c a l c u l a t i o n s over t h e more a n i s o t r o p i c needle-coke grade H-327.

1.3. DEVELOPMENT PROGRAM AT GLCC

GLCC developed two similar n e a r - i s o t r o p i c petroleum cokes, des igna ted

A and C , from two sources f o r product ion of nea r - i so t rop ic g r a p h i t e s . The

cokes were examined by meta l lographic techniques a t GA and judged t o have

s a t i s f a c t o r y mic ros t ruc tu res f o r f u e l element g r a p h i t e s . A pro to type grade

H-429 w a s prepared wi th coke A and submit ted f o r e a r l y i r r a d i a t i o n expe r i -

ments. Cokes A and C were blended wi th coke B , a r e g u l a r product ion coke,

t o develop grade H-451. A number of preproduct ion l o t s were manufactured,

u s ing cokes A through A i n combination wi th cokes B1 through B and

eva lua ted a t GA. Preproduct ion l o t 426, manufactured w i t h cokes A and B

w a s chosen f o r product ion. Approximately 98 H-451 product ion l o g s were

eva lua ted f o r s t r e n g t h , and about 300 H-451 l o g s have been d i spe r sed f o r

v a r i o u s s t u d i e s on programs a t GA, ORNL, BNL, and t h e European HTGR programs.

1 3 3’

2’ 3

1-2

I

Y

12.8 12.0

7.9 6.9

A

I W

11.2 6.4

10.3 4.0

Property

U 1 t ima te t ens i l e strength,

Axial Rad i a1

Elastic modulus,

Axial Radial

Thermal conductivity, Axial Radial

Thermal expansivity

a x 10 [295 to 1273 K (22' to

6

10OO0C) J Axial Radial -

TABLE 1-1 COMPARISON OF H-451 AND H-327 PROPERTIES

Units

MPa

GPa

W/m*K

c-l ( O f ' )

Unirradiated H-451 1 H-327

I

58 65 I ::

Irradiated (4 1

1073 H-45 1

23.0 21.5

19.7 17.2

39 34

3.4 4 .O

17.5 8.4

20.1 7.8

37 28

1.9 3.6

(a)End-of-life fluence f o r HTGR: 8 x N/m 2 (E > 29 fJ)HTGR

* ":

K ("C) 1273

H-451

21.5 20.2

17.8 15.5

41 3 7

2.7 3.1

1000) H-327

16.7 8.1

18.6 7.2

41 29

1 . 8 3.4

‘:I

0

-1.0

- ae - 2 -2.0

a -l

w a z

0 -I

z v)

9 -3.0

a El 5 -4.0 I 0

-5.0

-6.0

H-327

J 6 1 a I I I I I I I

2 3 4 5 0 1

FAST NEUTRON FLUENCE X

(b) RADIAL)

N/m2 (E > 29 FJ~HTGR

I 6 7 a I I I I I I I

3 4 5 0 1 2

FAST NEUTRON FLUENCE (loz5 N d ) (E > 29 FJ)HTGR

Fig. 1-1. Comparison of dimensional changes f o r H-451 and H-327 graphites: (a) axial, (b) radial.

1-4

n

1 . 4 . CHARACTERIZATION PROGRAM

1.4.1. D i s t r i b u t i o n of P r o p e r t i e s Within Ind iv idua l Logs and Between Logs Within a Lot

A number of H-451 product ion l o t s were eva lua ted t o determine t h e

d i s t r i b u t i o n of p r o p e r t i e s w i t h i n s i n g l e l o g s and between l o g s i n a s i n g l e

l o t . P r o p e r t i e s measured were bulk d e n s i t y , mechanical p r o p e r t i e s includ-

ing s t r e n g t h , e l a s t i c modulus, s t r a i n - a t - f r a c t u r e , and Po i s son ' s r a t i o i n

t ens ion , f l e x u r a l s t r e n g t h , s t r e n g t h and e l a s t i c modulus i n compression,

thermal expans iv i ty , thermal conduc t iv i ty , and impuri ty con ten t . Measure-

ments were made a t four l o c a t i o n s wi th in a log :

midlength edge (MLE), end center ( E C ) , and end edge (EE) . midlength c e n t e r (MLC),

Mean proper ty va lues a long wi th s tandard d e v i a t i o n s and d i s t r i b u t i o n s

of t h e va lues w i t h i n t h e l o g s and l o t s are given i n Sec t ion 5. The H-451

l o g s are weakest a t t h e i r midlength c e n t e r l o c a t i o n . This c h a r a c t e r i s t i c

makes i t mandatory t o sample t he H-451 g r a p h i t e f o r acceptance s t r e n g t h

t e s t i n g a t o r near t h e midlength c e n t e r of each log .

The r a d i a l s t r e n g t h of H-451 is about 80% g r e a t e r than t h a t of H-327

( t h e needle-coke g r a p h i t e used t o manufacture FSV f u e l e lements ) . The

thermal conduc t iv i ty i n the r a d i a l d i r e c t i o n is a l s o h ighe r than t h a t of

H-327. These b e n e f i t s r e s u l t i n g from t h e u s e of nea r - i so t rop ic coke w i l l

improve in-serv ice s a f e t y margins involv ing secondary stresses.

The impur i ty conten t w a s found t o be h i g h e s t i n t h e c e n t e r of t h e log ;

t hus , t e s t i n g f o r acceptance should p a r a l l e l t he procedure o u t l i n e d f o r

s t r e n g t h . The impuri ty conten t is a func t ion of t h e degree of p u r i f i c a t i o n

i n each g r a p h i t i z a t i o n furnace run du r ing manufacture. Mean a sh con ten t s

were found t o vary from 25 t o 300 ppm depending on t h e g r a p h i t i z a t i o n

furnace run.

1-5

I n genera l , i m p u r i t i e s t h a t c a t a l y z e ox ida t ion r e a c t i o n s , such as i r o n ,

t i t an ium, and vanadium, fol low t h e a sh con ten t . Lithium could no t be

de t ec t ed i n H-451 g r a p h i t e a t t h e lowes t l e v e l of s e n s i t i v i t y of t h e ana-

l y t i c a l techniques used (0.005 ppm) .

An a n a l y t i c a l technique w a s worked o u t i n c o l l a b o r a t i o n among four

l a b o r a t o r i e s , under t h e guidance of t h e ASTM Committee on Nuclear Graphi te ,

f o r measuring t h e nonburnable boron equ iva len t impur i ty conten t i n H-451

g raph i t e .

ppm of nonburnable boron equ iva len t con ten t i n a sample from a h igh ly pur i -

f i e d l o g .

The r e s u l t s of round-robin tests provide a va lue of about 0.04

1.4.2. S t a t i s t i c a l D i s t r i b u t i o n of S t r eng th Within a Log

A log of H-451 g r a p h i t e w a s d e s t r u c t i v e l y t e s t e d t o determine t h e

sys t ema t i c v a r i a t i o n of s t r e n g t h w i t h i n a l o g , t h e r e l a t i o n s h i p between

tens i le and f l e x u r a l s t r e n g t h , and t h e de te rmina t ion of a model a p p l i c a b l e

t o H-451 s t r e n g t h d i s t r i b u t i o n . The d a t a were analyzed us ing Weibul l ' s

s t a t i s t i c a l model f o r b r i t t l e materials.

The H-451 g r a p h i t e w a s found, as i n t h e earlier c h a r a c t e r i z a t i o n work,

t o b e s t r o n g e r i n t h e a x i a l d i r e c t i o n than i n t h e r a d i a l , and weaker a long

t h e c e n t r a l a x i s than a t t h e edges. The v a r i a t i o n of s t r e n g t h w i t h i n a

tes t zone w a s lowest f o r a x i a l specimens. Var i a t ion i n f l e x u r a l s t r e n g t h s

was less than t h e v a r i a t i o n i n t e n s i l e s t r e n g t h s .

Within experimental scat ter , t h e d a t a were e q u a l l y w e l l r epresented by

normal (Gaussian) d i s t r i b u t i o n o r by a d i s t r i b u t i o n p red ic t ed by t h e Weibull

model. The va lue o f t h e Weibull modulus, m, w a s lower f o r tensi le d a t a than

f o r f l e x u r a l d a t a . Such a d i f f e r e n c e i s con t r a ry t o p r e d i c t i o n s based on

the Weibull model. Small specimens averaged 3% and 8% s t r o n g e r than t h e

l a r g e r specimens f o r a x i a l and r a d i a l d i r e c t i o n s , r e s p e c t i v e l y . The

observed " s i z e e f f e c t " w a s much lower than expected from t h e Weibull model,

1-6

which would p r e d i c t d i f f e r e n c e s of 29% and 38% f o r a x i a l and r a d i a l d i r e c t -

i ons , r e s p e c t i v e l y . The mean f l e x u r a l s t r e n g t h showed good c o r r e l a t i o n

wi th t h e mean t e n s i l e s t r e n g t h of companion specimens ( c o r r e l a t i o n c o e f f i -

c i e n t 0 .9 ) . F l exura l s t r e n g t h averaged 52% and 55% higher than the corre-

sponding t e n s i l e s t r e n g t h f o r a x i a l and r a d i a l d i r e c t i o n s , r e s p e c t i v e l y .

These va lues are i n good agreement wi th va lues of 51% a x i a l and 64% r a d i a l

p red ic t ed by t h e Weibull model.

While t h e r e i s agreement between t h e experimental f l e x u r a l - t o - t e n s i l e

s t r e n g t h r a t i o s and the r a t i o s p red ic t ed by t h e Weibull model, t he exper i -

menta l ly der ived s i z e e f f e c t and t h e d i f f e r e n c e i n Weibull modulus between

t e n s i l e and f l e x u r a l d a t a are i n c o n s i s t e n t w i th t h e Weibull model. Thus i t

w a s concluded t h a t t h e H-451 g r a p h i t e l o g t e s t e d d i d n o t meet t h e c r i t e r i a

which would p e r m i t i t t o be t r e a t e d as a Weibull s o l i d .

1 .4 .3 . D e f i n i t i o n of Minimum S t reng th and S t r eng th D i s t r i b u t i o n Amone. Logs

Tensile s t r e n g t h w a s measured on e i g h t a x i a l specimens taken from t h e

midlength c e n t e r from each of 98 product ion logs which were taken from

t h r e e product ion l o t s . The a x i a l s t r e n g t h s showed cons ide rab le l o t - t o - l o t

and log-to-log v a r i a t i o n s .

Acceptance c r i te r ia were der ived f o r a s s ign ing l o g s t o a minimum s t r e n g t h ca tegory based on a x i a l t e n s i l e tests, i f each l o g i s sampled .

A s t a t i s t i c a l model i nco rpora t ing a s e p a r a t e l o t - t o - l o t va r i ance , log-to-

l o g va r i ance , and within- log va r i ance was adopted f o r t h i s purpose.

Acceptance c r i t e r i a which can be used f o r a s s ign ing a l o t t o s t r e n g t h

ca tegory A (minimum s t r e n g t h 10.3 MPa), B (minimum s t r e n g t h 8.3 MPa), o r C

(minimum s t r e n g t h 5.5 m a ) were der ived . Ca lcu la t ions w e r e made f o r e i t h e r

fou r o r e i g h t r e p l i c a t e specimens p e r log,, and two a l t e r n a t i v e d e f i n i t i o n s

of "minimum s t r eng th" were cons idered . The f i r s t d e f i n i t i o n would r e q u i r e

1-7

90% of t h e material a t t h e midlength c e n t e r of t h e l o g t o exceed t h e s p e c i -

f i e d minimum s t r e n g t h , w i th 90% confidence (90/90); t h e second would r e q u i r e

99% of t h e material t o exceed t h e s p e c i f i e d minimum, wi th 95% confidence

(99/95) .

Applicat ion of t h e s e c r i t e r i a t o t h e a x i a l test d a t a from t h e 98 l o g s

provided information f o r a c c e p t a n c e / r e j e c t i o n of t h e l o g s , f o r a s s i g n i n g each

l o g t o a s t r e n g t h ca t egory , and subsequent ly f o r a s s i g n i n g each l o g t o a

s p e c i f i c l o c a t i o n w i t h i n t h e r e a c t o r c o r e , i .e . , s t r o n g l o g s t o p o s i t i o n s

of high stress and weak l o g s t o p o s i t i o n s of low stress. It a l s o Frovided

a c r i t e r i o n f o r r e j e c t i n g weak o r d e f e c t i v e l o g s du r ing q u a l i t y t e s t i n g a t

a confidence l e v e l t o be e s t a b l i s h e d by t h e d e s i g n e r s .

Analysis of t h e d a t a , u s ing t h e acceptance c r i t e r i a , showed t h a t 5 l o g s

w o u l d be rejected f o r a 4 - s p e c i m e n test a t 90/90 confidence l e v e l whereas 18

logs would be r e j e c t e d f o r an 8-specimen test a t 99/95 confidence l e v e l .

When t h e a n a l y s i s w a s app l i ed t o s p e c i f i c l o t s t h e r e s u l t s showed t h a t most

of t h e r e j e c t e d l o g s were i n one weak l o t which had a mean s t r e n g t h s i g n i -

f i c a n t l y below t h e o t h e r two.

1 .4 .4 . Fa t igue Behavior

Grade H-451 g r a p h i t e w a s t e s t e d t o determine i t s f a t i g u e l i f e . Fa t igue

tes ts were run over a range from compression/ tension c y c l i n g (R va lues -1

and -0.5) and i n t e n s i o n ( R va lues 0 and 0.5) .

The H-451 g r a p h i t e showed c y c l i c f a t i g u e l i f e cu rves (S-N curves)

g e n e r a l l y resembling t h o s e of metals, b u t w i th more scatter.

stress c y c l i n g (R = - l ) , t h e homologous stress l i m i t s (maximum app l i ed

f a t i g u e stress d iv ided by t h e t e n s i l e s t r e n g t h ) f o r 50% specimen s u r v i v a l 5 t o 10 c y c l e s averaged 0.63 i n t h e a x i a l d i r e c t i o n and 0.74 i n t h e r a d i a l

d i r e c t i o n . Corresponding homologous stress l i m i t s f o r 99% specimen su r -

v i v a l (99 /95 t o l e r a n c e l i m i t s ) w e r e 0.48 and 0.53. The f a t i g u e l i f e and

the homologous stress l i m i t s i nc reased as R i nc reased .

For reversed

1-8

.

1.5.2. Tensile Strength and Elastic Modulus

1.5. IRRADIATION PROGRAM

1.5.1. Dimensional Changes

Dimensional changes were measured from 873 to 1623 K (600' to 1350OC)

in a series of capsules irradiated in the to 9 x N/m (E > 29 fJ)HTGR ORR. Additional data at 573 to 873 K (300" to 6OOOC) on graphites similar

to H-451 were taken from the literature. The dimensional data cover the

temperature and fluence range of the HTGR.

2

The dimensional changes of H-451 graphites at 573 to 1623 K (300" to 1350OC) fall within an envelope of 0% and -3% in the axial direction and 0% and -1.5% in the radial direction up to 9 x 10

which is about 10% above the lifetime fluence of the H-451 graphite in an HTGR.

irradiation period, the shrinkage rate increased to that of the higher

temperature.

irradiation period, the shrinkage rate also was reduced, but remained

higher than the isothermal rate at the lower temperature.

25 2 N/m (E > 29 fJ)HTGR,

When the irradiation temperature was increased after an initial

When the irradiation temperature was reduced after an initial

Differences in shrinkage between MLC and MLE specimens from the same log were not satistically significant, nor were there statistically signi-

ficant differences in shrinkage among specimens taken from the same location in the log but from different logs.

Tensile strength increased and elastic modulus increased during irra- diation at 823 to 1623 K (550" to 135OOC). There was an increase in the

1-9

s t anda rd d e v i a t i o n of s t r e n g t h v a l u e s b u t no change i n t h e c o e f f i c i e n t of

v a r i a t i o n . The i n c r e a s e i n s t r e n g t h i s r e l a t e d t o t h e i n c r e a s e i n e las t ic

modulus by

0 . 6 4

0

Within-log v a r i a t i o n and log-to-log v a r i a t i o n of f r a c t i o n a l s t r e n g t h

i n c r e a s e w e r e n o t s i g n i f i c a n t .

1 . 5 . 3 . Fa t igue Behavior

n

I r r a d i a t i o n inc reased t h e homologous stress l i m i t s f o r f a t i g u e endur-

ance of H-451 by about a f a c t o r of 2 when t h e stresses were normalized by

d i v i d i n g by t h e u n i r r a d i a t e d s t r e n g t h .

1 . 5 . 4 . Thermal Expansivi ty

I r r a d i a t i o n induced a n i n c r e a s e of about 20% i n thermal e x p a n s i v i t y of

H-451 a t 623 t o 823 K (350' t o 550OC) over t h e l i f e of t h e f u e l e lement .

The thermal e x p a n s i v i t y inc reased by about 10% a t 873 t o 973 K (600' t o

7OOOC) a t low f l u e n c e s and r e t u r n e d t o t h e o r i g i n a l v a l u e s a t HTGR end-of-

l i f e . A t 923 t o 1673 K (700" t o 1400°C) t h e thermal e x p a n s i v i t y decreased

20% t o 50% over t h e l i f e of t h e fuel element.

1 . 5 . 5 . Thermal Conduct ivi ty

Changes i n thermal c o n d u c t i v i t y of H-451 g r a p h i t e due t o i r r a d i a t i o n

were measured a t 923 t o 1623 K (650O t o 135OOC) t o HTGR end-of- l i fe

f luences , and d a t a a t 523 t o 923 K (250" t o 65OOC) were obtained from

UKAEA d a t a on g r a p h i t e s similar t o H-451. 2 r a p i d l y a t f l u e n c e s of 0 t o 2 x

Thermal conduc t iv i ty decreased

and then showed N/m (E > 29 fJ)HTGR

1-10

Ir, .8

2 only a small decrease between 2 and 9 x

I r rad ia t ion- induced r educ t ion i n thermal conduc t iv i ty w a s temperature-

dependent, wi th t h e l a r g e s t reduct ion occur r ing a t t he lowest i r r a d i a t i o n

temperatures .

N/m ( E > 29 fJ)HTGR.

A method i s descr ibed f o r c a l c u l a t i n g the i r r a d i a t e d thermal conduc-

t i v i t i e s a t the temperature of i r r a d i a t i o n . When t h e i r r a d i a t i o n tempera-

t u r e was e i t h e r increased o r decreased a f t e r an i n i t i a l per iod, t h e new

c o n d u c t i v i t i e s assumed t h e s a t u r a t i o n l e v e l of t h e new i r r a d i a t i o n tempera-

t u r e .

1.5.6. I r r ad ia t ion - Induced Creep

A sys temat ic program designed t o measure i r rad ia t ion- induced creep

c o e f f i c i e n t s of H-451 g raph i t e i s i n progress a t ORNL, bu t only one capsule

has been completed t o da t e . Therefore , the c reep c o e f f i c i e n t s have been

der ived from the l i t e r a t u r e .

A wide v a r i e t y of g r a p h i t e s have been measured i n a v a r i e t y of exper i -

ments dur ing t h e p a s t 20 years .

experiments a t RCN P e t t e n i n the Nether lands, where a number of g r a p h i t e

grades were measured i n a r e s t r a i n e d shr inkage experiment; t hus , a few

H-451 d a t a p o i n t s were a v a i l a b l e f o r comparison. RCN and JRC Euratom,

Pe t t en , have completed t h e f i r s t phase of an experiment where the c reep coef-

f i c i e n t of an H-451 specimen w a s measured i n tens ion . I n t h i s experiment,

A few H-451 specimens were included i n

a t 1123 K (850"C)l , N/m [ ( E > 29 fJ)HTGR 2 which w a s taken t o about 3.3 x

both t h e t ransient and s t eady- s t a t e c reep c o e f f i c i e n t were measured.

An equat ion f o r c a l c u l a t i n g t h e c reep s t r a i n i n

der ived t h a t covers t h e range 773 t o 1473 K (500" t o

and c reep s t ra ins up t o 2.5% i n N/m (E > 29 fJIHTGR compression.

2

des ign has been 26 1200OC) up t o 10

t ens ion and 2% i n

1-1 1

n 1.6. OXIDATION PROGRAM

1.6.1 Oxidation Rate of H-451 Graphi te

The chemical r e a c t i o n s of water vapor wi th H-451 are rep resen ted by

t h e Langmuir-Hinshelwood equat ion.

t h e Langmuir-Hinshelwood equa t ion f o r l o w water c o n c e n t r a t i o n s (5300 Pa)

and high water concen t r a t ions (2300 or 13300 Pa)

Rate c o n s t a n t s were de r ived t o s a t i s f y

The OXIDE computer code i s used t o determine t h e o x i d a t i o n rates f o r

r e a c t o r s e r v i c e . Rate c o n s t a n t s de r ived f o r H-451 by t h e Langmuir-

Hinshelwood equa t ion are used as i n p u t f o r t h e OXIDE c a l c u l a t i o n s .

water l e v e l rate c o n s t a n t s have been de r ived f o r a c c i d e n t c o n d i t i o n s , where

h igh moisture l e v e l s are p o s s i b l e .

been de r ived and should b e used f o r normal s t e a d y - s t a t e r e a c t o r o p e r a t i o n ,

High

Low water level rate c o n s t a n t s have

where

1.6.2

water c o n c e n t r a t i o n s i n t h e range 10 t o 1000 Pa are expected.

E f f e c t o f Oxidat ion on Tensile S t r e n g t h and Elast ic Modulus

A l a r g e number of small specimens taken from a p a r e n t log of H- 5

g r a p h i t e were oxidized t o b u r n o f f s up t o 20%, and t h e changes i n t e n s i l e

s t r e n g t h and e l a s t i c modulus were determined.

The t e n s i l e s t r e n g t h and e las t ic modulus of H-451 g r a p h i t e were

decreased by an average of 3.6% i n c e n t e r axial specimens when ox id ized

t o bu rnof f s up t o 2.0% a t e i t h e r 1073 K o r 1273 K (800' o r lOOO'C), and

no s i g n i f i c a n t r e d u c t i o n i n e l a s t i c modulus i n t h e s e same specimens was

observed when they were ox id ized t o b u r n o f f s o f up t o 2.0% a t 1273 K

(100O'C) . These r e s u l t s are o f p a r t i c u l a r importance because t h e maximum

l o c a l i z e d burnoff i n t h e HTGR f u e l element blocks has been c a l c u l a t e d t o

be 1%.

1-12

The r a t e of reduct ion of t e n s i l e s t r e n g t h and e l a s t i c modulus f o r

c e n t e r a x i a l specimens i s g r e a t e r a t 1073 K (800°C) than a t 1273 K (lOOO°C).

This conclus ion i s no t important f o r des ign because the maximum burnoff of

t h e f u e l element b locks i n an HTGR i s c a l c u l a t e d t o occur a t approximately

1273 K (1000°C). About 0.1% t o 0.2% burnoff is c a l c u l a t e d f o r f u e l element

blocks o p e r a t i n g a t 1073 K (8OOOC).

I n gene ra l , t h e r educ t ion ra te of e l a s t i c modulus wi th burnoff w a s

g r e a t e r than t h a t of u l t i m a t e t e n s i l e s t r e n g t h (UTS). The h igher r educ t ion

rate of t h e e l a s t i c modulus i s important i n des ign because a lower e l a s t i c

modillus decreases t h e secondary stresses, i . e . , thermal stresses r e s u l t i n g

from g r a d i e n t s and d i f f e r e n t i a l i r r ad ia t ion - induced s t r a i n . The rate of

r educ t ion of t e n s i l e s t r e n g t h and e l a s t i c modulus f o r a x i a l specimens

oxid ized a t 1273 K (lOOO°C) i s g r e a t e r a t t h e edge than a t t h e c e n t e r of a

l o g . This does not impose a l i m i t a t i o n i n des ign because t h e t e n s i l e

s t r e n g t h f o r acceptance of a l o g f o r f u e l element b locks is always measured

a t t h e c e n t e r of t h e l o g where i t i s a minimum.

edge of a l o g oxid ized up t o 2% burnoff i s never less than t h e t e n s i l e

s t r e n g t h a t t h e c e n t e r a t 0 t o 2% burnof f . I n gene ra l , t h e r educ t ion i n

t e n s i l e s t r e n g t h and e l a s t i c modulus of r a d i a l specimens w a s h ighe r than

t h a t of a x i a l specimens. The h ighe r seismic-induced stresses i n an HTGR

f u e l element are i n t h e r a d i a l d i r e c t i o n and t h i s phenomenon could a f f e c t

des ign . However, t h e r educ t ion i n e l a s t i c modulus of t h e r a d i a l specimens

w a s greater than the strength loss, and, thus, the overa l l e f f e c t on s e i s m i c

performance should be n e g l i g i b l e .

The t e n s i l e s t r e n g t h a t t h e

1-13

2 . INTRODUCTION

Grade H-451 nea r - i so t rop ic g r a p h i t e is t h e r e fe rence candida te graph-

i t e f o r r ep laceab le f u e l and r e f l e c t o r e lements i n HTGRs. Grade H-451

g r a p h i t e has been under development a t GLCC f o r approximately 7 yea r s .

Concurrent wi th GLCC's development program, an i n t e n s i v e e v a l u a t i o n program

has been c a r r i e d ou t on H-451 a t GA. The r a w material type , formula t ion ,

and process ing have been f rozen , and s e v e r a l product ion l o t s have been

manufactured and eva lua ted .

The d a t a generated from t h e e v a l u a t i o n programs have been publ ished i n

a series of GA r e p o r t s . The purpose of t h i s r e p o r t i s t o c o l l e c t , ana lyze ,

and s o r t t h e d a t a from t h e GA r e p o r t s , i nc lud ing d a t a on g r a p h i t e s similar

t o H-451 from o t h e r U . S . o r European programs and the open l i t e r a t u r e , and

t o p re sen t t h e t o t a l a v a i l a b l e d a t a set on H-451 g r a p h i t e f o r use i n pre-

pa r ing t h e H-451 s e c t i o n of t h e Fuel Design Data Manual (GA-A14429), which i s

requ i r ed f o r des ign and s a f e t y a n a l y s i s of HTGRs. The fol lowing t o p i c s are

d iscussed:

Concept and Need f o r a Near-Isotropic Fuel Element Graphi te

Sec t ion 3 exp la ins t h e l o g i c and need f o r developing a nea r - i so t rop ic

g r a p h i t e i n t h e U . S . f o r HTGR f u e l elements.

Development Program a t GLCC

Sec t ion 4 d e s c r i b e s the scope of t he H-451 development program a t

GLCC .

2- 1

Characterization Program

In Section 5, the characterization program is described. An extensive

characterization program was required to (1) confirm that a suitable

material was available for use in the core of HTGRs and (2) provide a

data set on properties, purity, and fatigue. The characterization

program was designed to evaluate the various development products from

the GLCC program and select a formulation and process for production.

The quality of the selected grade was established by determining the

properties and distribution of properties representative of the grade. A materials specification has been written that defines requirements

for fuel element graphite in HTGRs and it will be applied to ensure

that future H-451 production meets the quality required.

Irradiation Program

Section 6 discusses the irradiation program, which was designed to

provide the mean and distribution of properties of H-451 that are

representative of the material in the fast neutron flux present dur-

ing the service life of the fuel elements.

directly to design the fuel elements and to calculate the thermal and

stress gradients that occur in the fuel element graphite during its

life in the reactor core. Tests on the filler cokes have been included

in the materials specification to aid in standardizing the quality of

the raw material and ensure that future H-451 production will exhibit

the same irradiation behavior as that of the preproduction logs used

to obtain the irradiation data set presented here.

These data are used

Oxidation Proeram

The oxidation program is discussed in Section 7. element blocks may be exposed to steam oxidation during their life in the reactor; therefore, it is necessary to determine the effect of

oxidation on their properties.

The H-451 fuel

The oxidation program was designed to

2-2

determine t h e rate o f ox ida t ion i n H O-He m i x t u r e s and t h e e f f e c t of

ox ida t ion burnoff on mechanical p r o p e r t i e s , p r imar i ly s t r e n g t h and

e l a s t i c modulus. The ox ida t ion d a t a are r equ i r ed f o r des ign and

s a f e t y a n a l y s i s .

2

Two documents are c l o s e l y r e l a t e d t o t h i s r e p o r t .

S p e c i f i c a t i o n f o r Replaceable Fuel and Ref l ec to r Element Graphi tes

(Number 900739), which con ta ins r a w material, process ing , and property

l i m i t s t h a t must be m e t by t h e manufacturer t o q u a l i f y H-451 f o r

acceptance and subsequent use i n HTGRs.

s p e c i f i c a t i o n i s t o prevent t h e i n c l u s i o n of d e f e c t i v e o r out-of-

s p e c i f i c a t i o n l o g s i n t h e manufacture of f u e l e lements o r r ep laceab le

r e f l e c t o r s . The s p e c i f i c a t i o n a l s o r e q u i r e s t e s t i n g t o ensure uni-

formi ty i n r a w materials from ba tch t o ba t ch over a long per iod, t hus

ensu r ing p r o p e r t i e s and i r r a d i a t i o n behavior c o n s i s t e n t w i th those of

t h e materials u t i l i z e d i n t h e c u r r e n t e v a l u a t i o n programs.

One i s t h e Materials

The o b j e c t i v e of t h e materials

The o t h e r document t o be used w i t h t h i s r e p o r t i s t h e H-451 g r a p h i t e s e c t i o n

of t he Fuel Design Data Manual (GA-A14429), which con ta ins H-451 proper ty

d a t a de r ived from t h i s r e p o r t , o t h e r domest ic and European g r a p h i t e programs,

and t h e open l i t e r a tu re . The material i n t h e Fuel Design Data Manual i s

presented i n a form s u i t a b l e f o r use f o r the des ign and safety analyses of

HTGR f u e l elements.

2-3

3 . CONCEPT AND NEED FOR A NEAR-ISOTROPIC FUEL ELEMENT GRAPHITE

The primary i n c e n t i v e f o r developing a nea r - i so t rop ic g r a p h i t e i n t h e

U.S. f o r HTGR f u e l e lements w a s t o improve t h e dimensional s t a b i l i t y and

s t r e n g t h over t he convent ional HTGR needle-coke g r a p h i t e (grade H-327). The development of H-451 w a s aimed a t providing more f l e x i b i l i t y i n des ign ,

b e t t e r s a f e t y margins f o r stresses, and s t r e t c h c a p a b i l i t y f o r f u t u r e

des igns . The i s o t r o p y imparted t o the g raph i t i zed l o g s by t h e use of near-

i s o t r o p i c petroleum coke was aimed a t minimizing t h e dimensional c o n t r a c t i o n

and de lay ing the subsequent expansion t o f luences w e l l beyond the s e r v i c e

l i f e i n an HTGR. An a d d i t i o n a l goa l of t he program w a s t o i n c r e a s e the

thermal conduc t iv i ty of t h e g r a p h i t e , e s p e c i a l l y i n t h e r a d i a l d i r e c t i o n

which i s pa ra l l e l t o t h e th i ckness o f t he t h i n l igaments t h a t s e p a r a t e t h e

f u e l and t h e coo lan t i n t h e f u e l element b locks .

3- 1

4. DEVELOPMENT PROGRAM AT GLCC

Based on the incen t ives descr ibed i n Sec t ion 3 , t he development of a

nea r - i so t rop ic g r a p h i t e w a s i n i t i a t e d i n 1969. To minimize the impact of

development c o s t s and t o keep t h e pr ice of t h e new product compet i t ive , a

d e c i s i o n w a s t aken j o i n t l y by GA and GLCC t o u t i l i z e commercially a v a i l a b l e

materials wi th convent iona l e x t r u s i o n and process ing as i n t h e manufacture

of H-327, whi le a t the same t i m e emphasizing improved i s o t r o p y i n t h e f i l l e r

coke s t r u c t u r e . Thus, t h e development work and f u t u r e product ion could be

accomplished employing e x i s t i n g r a w materials, equipment, and p l a n t s .

The s t r u c t u r e of Gilsocoke w a s used as a guide i n procur ing a new

petroleum-based, s p e c i a l , nea r - i so t rop ic coke f o r t h e GLCC development

program. Gilsocoke w a s used i n Europe t o manufacture g r a p h i t e s f o r t h e

UK Advanced Graphi te Reactors .

shown s a t i s f a c t o r y i r r a d i a t i o n behavior . However, Gilsocoke i s a s i n g l e -

source r a w material t h a t i s no longe r commercially a v a i l a b l e . Also, Gilso-

coke presented d i f f i c u l t i e s when used t o f a b r i c a t e large-diameter l ogs ,

impar t ing a high degree o f hardness t o t h e g r a p h i t i z e d products .

Graphi tes manufactured wi th Gilsocoke have

4 .1 . FILLER COKES

GLCC procured a s p e c i a l ba t ch of nea r - i so t rop ic coke and des igna ted

i t coke A Subsequent ba tches from s u p p l i e r A w e r e procured and are 1 ' des igna ted A and A 3' 2

A commercial coke t h a t is used r o u t i n e l y i n t h e product ion o f o t h e r

commercial g r a p h i t e art icles i n GLCC p l a n t s w a s a l s o considered f o r blend-

i n g wi th Coke A. This coke is a s p e c i a l type of sponge coke and has a

s t r u c t u r e t h a t i s less i s o t r o p i c than coke A , bu t i t i s n o t a needle coke.

4-1

1 The second coke, des igna ted B 1 , w a s considered f o r blending wi th coke A

t o improve the manufacturing c h a r a c t e r i s t i c s and t h e m i c r o s t r u c t u r e of t h e

f i n a l product .

A second s p e c i a l n e a r - i s o t r o p i c coke was procured from a second

s u p p l i e r .

type feedstock, t he a i m be ing t o e s t a b l i s h a coke similar t o coke A b u t

from a d i f f e r e n t s u p p l i e r .

prototype l o g s du r ing l a t e r s t a g e s o f t he development program.

This coke, des igna ted C , w a s produced from t h e same g e n e r i c

Th i s coke was used a long wi th coke B t o make 1

The m i c r o s t r u c t u r e s of t h e c a l c i n e d cokes descr ibed above were classi-

f i e d a t GA us ing me ta l log raph ic techniques desc r ibed by White and P r i c e

(Ref. 4-1) .

i n grade H-429 and t h e e a r l y p ro to type H-451 l o g s , c o n s i s t e d of on ly 65% of t h e d e s i r a b l e heterogeneous f i n e i s o t r o p i c (HFI) material, whereas cokes

The r e s u l t s are given i n Table 4-1. Coke A I , which w a s used

A2 and A c o n s i s t e d of 90% o r more of the HFI material. Coke C is compar- 3 1 a b l e t o cokes A and A i n m i c r o s t r u c t u r e . Coke B i s c l a s s i f i e d as a

r e g u l a r o r sponge coke; t h e a n a l y s i s shows a range of c o n s t i t u e n t s from

HFI t o c o a r s e f i b r o u s (CF) c o n s t i t u e n t s . None of t h e cokes used i n H-451

development and subsequent product ion l o g s contained f i n e f i b r o u s (FF)

c o n s t i t u e n t s , and they c o n t a i n on ly small amounts of CF material. However,

t h e r e i s some degree of an i so t ropy i n t h e f i n a l g r a p h i t i z e d product due t o

t h e s m a l l c o n t e n t of o r i e n t e d c o n s t i t u e n t s i n t h e f i l l e r cokes.

2 3 1

Cokes t h a t have n e a r - p e r f e c t i s o t r o p y were n o t considered because they

impart h igh thermal e x p a n s i v i t y t o t h e g r a p h i t i z e d product and are even more

d i f f i c u l t t o process i n t o large-diameter l ogs wi th convent ional equipment.

Needle-like c o n s t i t u e n t s , on t h e o t h e r hand, impart low s t r e n g t h and aniso-

t r o p i c dimensional changes du r ing s e r v i c e i n a fas t neutron environment.

Thus, t he near i s o t r o p i c petroleum cokes used i n H-451 appear t o be optimum

f o r HTGR f u e l element g r a p h i t e s .

4- 2

TABLE 4-1 MICROSTRUCTURAL ANALYSIS OF CALCINED COKES

USED TO MANUFACTURE H-451 GRAPHITE

Coke No.

536 1-60

5361-61

5361-65

(4 Percent of Cons t i tuent Coke D e s igna t i o n HFI FI C I CF FF

65 0 15 20 0

95 0 5 0 0

97 0 3 0 0

A 1

A2

A3

52

90

B 1

c1

5361-62

5361-67

(" 'Descr ipt ions from Ref. 4-1 : HFI = heterogeneous f i n e i s o t r o p i c

FI = f i n e i s o t r o p i c C I = coarse i s o t r o p i c CF = coa r se f i b r o u s FF = f i n e f i b r o u s

7 12 29 0

0 4 6 0

4-3

4.2. PROCESSING

Details of t he manufactur ing processes of H-451 are p r o p r i e t a r y t o

GLCC.

i n l e n g t h us ing convent iona l g r a p h i t e manufacturing processes common t o t h e

manufacture of e lec t r ic s teel furnace e l e c t r o d e s . The ca l c ined coke is

crushed and s i z e d and a s p e c i f i c formulat ion s e l e c t e d c o n s i s t i n g of m u l t i -

s i z e d f r a c t i o n s o f t h e coke par t ic les , wi th coa l t a r p i t c h as t h e b inder .

This formula t ion of ca l c ined cokes and c o a l t a r p i t c h is mixed thoroughly

i n t h e range 393 t o 453 K (120" t o 180"C), extruded i n t o green logs, and

baked s lowly t o about 1073 K (800°C) t o carbonize t h e b inde r p i t c h . The

baked l o g s are then impregnated w i t h petroleum p i t c h and t h e l o g s hea ted

t o 2973 K (2700°C) o r above t o g r a p h i t i z e t h e s t r u c t u r e .

l o g s i s improved by conduct ing t h e g r a p h i t i z a t i o n process i n t h e presence

of c h l o r i n e gas . The r e s u l t a n t product is a h igh p u r i t y , nea r - i so t rop ic ,

medium-grained n u c l e a r g r a p h i t e s u i t a b l e f o r use i n an HTGR core.

I n gene ra l , H-451 i s produced as l o g s 432 mm i n diameter by 864 mm

The p u r i t y of t h e

.

4.3. PROTOTYPE AND PREPRODUCTION DEVELOPMENT

Grade H-429 w a s formulated wi th Coke A and ex t ruded i n t h e GLCC p i l o t 1 p l a n t as a 52-mm-diameter log.

d i a t i o n t e s t i n g by Ch dur ing 1970-1972.

H-429, GLCC manufactured a number of f u l l - s i z e experimental grades.

H-451 ( l o t 266), i n i t i a l l y f a b r i c a t e d wi th coke A1, was s e l e c t e d j o i n t l y

by GA and GLCC as t h e most promising material f o r f u r t h e r development.

chronology of t h e development program is given i n Table 4-2.

p reproduct ion development, l o t s 408, 424, and 426 were f a b r i c a t e d us ing a

blend of e i t h e r cokes A2 and B1 o r A3 and B

a blend of cokes C1 and B

r a t e d i n t o GA's c h a r a c t e r i z a t i o n and i r r a d i a t i o n programs.

Grade H-429 was committed t o e a r l y irra-

Concurrent w i th the i r r a d i a t i o n of

Grade

A

I n subsequent

Two l o t s were produced us ing

Logs from l o t s 266, 408, and 426 were incorpo- 2 '

3'

I n 1975, t h e formula t ion and process ing methods of l o t 426 were j o i n t l y

s e l e c t e d by GLCC and GA as models f o r t h e i n i t i a l product ion of 350 logs of

4-4

4-5

n H-451 f o r p o s s i b l e use i n FSV as r e load elements . Product ion l o t s 472, 474,

4 7 6 , 4 7 8 , and 482 were produced f o r t h e For t S t . Vrain r e load segments using

a blend of coke A and B and t h e same formulat ion and process ing as f o r

preproduct ion l o t 426 . Ninety-eight l o g s from product ion l o t s 4 7 2 , 4 7 8 , and

482 were sampled a t t h e midlength c e n t e r (MLC) of each l o g , and t e n s i l e

s t r e n g t h w a s measured on e i g h t axial and four r a d i a l specimens from each.

3 1

During t h e development program a number of t h e l o g s from each l o t were

The programs d i s t r i b u t e d t o e v a l u a t i o n programs w i t h i n and e x t e r n a l t o GA.

u t i l i z i n g H-451 g r a p h i t e are given i n Table 4-3. The use o f H-451 prepro-

duc t ion l o g s f o r experiments involv ing f u e l development, ox ida t ion , r e c y c l e ,

FSV f u e l test elements , l a r g e - s c a l e mechanical t e s t i n g , fo re ign programs,

ORNL programs, and BNL programs occurred concur ren t ly wi th t h e GLCC develop-

ment program and t h e c h a r a c t e r i z a t i o n and i r r a d i a t i o n programs a t GA. Thus,

s e l e c t i o n of material f o r each program depended on the availability of logs

a t t h e t i m e of t h e i r need; i.e., e v a l u a t i o n d id n o t wait u n t i l the develop-

ment program was complete.

4.4 . CONCLUSIONS

GLCC developed p r o p r i e t a r y sou rces of nea r - i so t rop ic cokes f o r use i n developing grade H-451 as a cand ida te f o r advanced HTGR f u e l e lements .

Grade H-451 w a s developed us ing convent iona l g r a p h i t e process ing and a

blend of a n e a r - i s o t r o p i c coke and a s p e c i a l sponge coke.

product ion l o t s and one product ion ba tch were manufactured f o r e v a l u a t i o n

by GA and o t h e r r e a c t o r programs i n t h e U.S. and Europe.

A number of pre-

REFERENCE

4-1. White, J. L , , and R. J. P r i c e , “The ‘Formation of Mesophase Micro-

s t r u c t u r e s During the P y r o l y s i s of Se lec t ed Coker ‘Feedstocks,”

Carbon 12, - 321 (1974).

4-6

TABLE 4 - 3 PROGRAMS U T I L I Z I N G H-45 1 GRAPHITE LOGS

Program

C h a r a c t e r i z a t i o n

I r r a d i a t i o n

Fuel element development

Oxida t i o n s t u d i e s

Recycle f u e l element s t u d i e s

Large-scale mechanical tests

ORNL programs

BNL program

Foreign programs: KFA, CEA, RCN P e t t e n , and Dragon

Use o r Measurements

Measurement of phys i ca l , mechanical, and chemical p r o p e r t i e s on s m a l l specimens c u t from f u l l - s i z e l o g s . w i t h i n l o g s , from log-to-log w i t h i n l o t s , and from l o t - t o - l o t were i n v e s t i g a t e d . Fa t igue c h a r a c t e r i s t i c s were determined.

Same as above except fewer specimens measured due t o l i m i t e d r e sources and high cos t of i r r a d i a t i o n experiments .

Fu l l - s i ze machined b locks used t o determine c h a r a c t e r i s t i c s of H-451 g r a p h i t e and i t s i n t e r - a c t i o n wi th f u e l s t i c k s dur ing carboniza t ion- in-place (CIP) experiments .

Measurement of r e a c t i o n rates of H-451 i n He-H20 mixtures . of H 2 0 and H2 concen t r a t ion , f low rate , and temperature . S tud ie s of t h e e f f e c t of oxida- t i o n on s t r e n g t h reduct ion .

Fu l l - s i ze machined b locks used t o determine e f f e c t of material on c rushing , burning, and f u e l s epa ra t ion .

Use of f u l l - s i z e o r s ca l ed machined b locks f o r se i smic t e s t i n g . In t e rmed ia t e - s i ze specimens used f o r dowel p in , thermal stress, and miscel laneous mechanical tests.

Oxidat ion, i r r a d i a t i o n creep, and f u e l r e c y c l e t e s t s . Oxidat ion tests.

Oxidat ion and i r r a d i a t i o n tests inc lud ing creep , i n - r eac to r thermal stress tes ts , f u l l - s i z e machined elements f o r s t r e n g t h proof t e s t i n g , and machining tests.

Var i a t ions of p r o p e r t i e s

Paramet r ic s t u d i e s of e f f e c t

4- 7

5. CHARACTERIZATION PROGRAM

5.1. INTRODUCTION

Charac t e r i za t ion of grade H-451 inc ludes de te rmina t ion o f : (1) d i s -

t r i b u t i o n of p r o p e r t i e s w i t h i n i n d i v i d u a l l ogs and between l o g s w i t h i n a

l o t , ( 2 ) s t a t i s t i c a l d i s t r i b u t i o n of s t r e n g t h w i t h i n a log , ( 3 ) s t r e n g t h

d i s t r i b u t i o n among logs , and ( 4 ) f a t i g u e behavior .

5.2. DISTRIBUTION OF PROPERTIES W I T H I N I N D I V I D U A L LOGS AND BETWEEN LOGS WITHIN A LOT

5.2.1 . Sampling

Sampling diagrams are shown i n Appendix A. P r o p e r t i e s were measured

on specimens taken para l le l t o t h e e x t r u s i o n d i r e c t i o n ( a x i a l ) * and per-

pendicular t o t h e e x t r u s i o n d i r e c t i o n ( r a d i a l ) * . I n t h e experiments t o

determine proper ty d i s t r i b u t i o n s w i t h i n a l o g , t h e l o g s were sampled a t

four d i f f e r e n t l o c a t i o n s w i t h i n each log: midlength c e n t e r (MLC), end

c e n t e r (EC), midlength edge (MLE), and end edge (EE) . P r o p e r t i e s measured

on l o g s i n the u n i r r a d i a t e d state w e r e ( 1 ) bulk d e n s i t y , (2) tensile prop-

erties, inc lud ing s t r e n g t h , e las t ic modulus, s t r a i n a t f r a c t u r e , and

Poisson ' s r a t i o i n tens ion , ( 3 ) f l e x u r a l s t r e n g t h , ( 4 ) s t r e n g t h and e l a s t i c

modulus i n compression, (5) thermal expans iv i ty , (6) thermal conduc t iv i ty ,

and ( 7 ) impuri ty conten t .

* The terms a x i a l and r a d i a l are used throughout t h i s r e p o r t t o d e s i g n a t e specimens whose l o n g i t u d i n a l a x i s ( a x i s a long which measurement w a s made) w a s para l le l t o the l o n g i t u d i n a l a x i s of t h e pa ren t l o g and p a r a l l e l t o t he r a d i u s of t he pa ren t l og , r e s p e c t i v e l y .

5-1

5.2 .2 . Bulk Density

The bulk d e n s i t y of g r a p h i t e is de f ined as t h e weight of t h e l o g

d iv ided by the bu lk volume ( o u t e r dimensions of t he l o g ) .

t i o n , the bulk d e n s i t y was determined on t h e tens i le s t r e n g t h specimens

p r i o r t o t h e i r u se i n s t r e n g t h tests.

on whole a s -g raph i t i zed logs a t the GLCC product ion p l a n t .

acceptance w i l l be based on whole l o g d e n s i t i e s measured a t GLCC.

For c h a r a c t e r i z a -

Density measurements were a l s o made

Product ion

The d e n s i t i e s of f o u r l o g s from preproduct ion l o t 426 are p resen ted i n

The d a t a inc lude measured and c a l c u l a t e d Appendix B, Table B-1 (Ref. 5-1).

whole l o g d e n s i t y v a l u e s .

va lues from t h e c e n t e r and edge specimens.

whole l o g s i n the manufacturer ' s p l a n t were about 0.01 Mg/m3 h ighe r than

those measured a t GA on small specimens l o c a t e d throughout t h e log.

w a s a s m a l l but significant increase in d e n s i t y from t h e c e n t e r t o t h e edge

of some logs . However, several l o g s had no g r a d i e n t . The d e n s i t y w a s , i n

g e n e r a l , lowest a t t h e MLC p o s i t i o n and inc reased s l i g h t l y n e a r t h e edges

and ends of t h e l o g s . Again a few excep t ions w e r e observed.

i n d e n s i t y f o r H-451, l o t 426, ranged from 1.695 t o 1.753 Mg/m ,

The la t ter were ob ta ined by averagipg t h e mean

The bulk d e n s i t i e s measured on

There

The v a r i a t i o n 3

The mean of t h e small-specimen measurements a g r e e s w e l l w i th t h a t of

3 measurements by GLCC on whole logs .

l o g s from l o t 426 w a s 1.73 5 0.01 Mg/m . va lues were ob ta ined on 98 l o g s from product ion l o t s 472, 478, and 482.

The mean bulk d e n s i t y of t hese l o g s w a s 1.74 ? 0.025 Mg/m .

The mean bulk densi ty f o r t h e fou r

Add i t iona l whole l o g d e n s i t y

3

5.2.3. Mechanical Proper t ies

The mechanical p r o p e r t i e s measured were u l t i m a t e t e n s i l e s t r e n g t h ,

e l a s t i c modulus i n t e n s i o n , s t r a i n a t f r a c t u r e i n t ens ion , Po i s son ' s r a t i o

i n t ens ion , u l t i m a t e f l e x u r a l s t r e n g t h , u l t i m a t e compressive s t r e n g t h ,

e l a s t i c modulus i n compression, and f a t i g u e behavior .

5-2

5.2.3.1. Tens i l e S t r eng th , E las t ic Modulus, and S t r a i n a t F r a c t u r e . The

u l t i m a t e t e n s i l e s t r e n g t h d a t a f o r preproduct ion l o t 426 a r e summarized i n

Appendix B , Table B-2 (Ref. 5-1). The t e n s i l e s t r e n g t h of H-451 i s h i g h e s t

i n t h e a x i a l d i r e c t i o n , lowest a t MLC f o r a x i a l and r a d i a l d i r e c t i o n s , and

i n c r e a s e s from t h e c e n t e r t o the edge. The mean t e n s i l e s t r e n g t h of H-451,

l o t 426, ranged from 13.65 f 1.60 MPa a t MLC t o 19.00 _+ 1.85 MPa a t MLE i n

t h e a x i a l d i r e c t i o n and from 10.75 ? 2.10 MPa a t MLC t o 15.22 _+ 2.25 MF'a a t

EE i n t h e r a d i a l d i r e c t i o n .

The observed p a t t e r n of lowest a x i a l o r r a d i a l s t r e n g t h a t t h e MLC of

each l o g makes i t mandatory t o test each l o g as near t h e MLC as p o s s i b l e

du r ing a c c e p t a n c e / r e j e c t i o n t e s t i n g , as r equ i r ed by S p e c i f i c a t i o n 900739

(wi th in s l a b 3, s e c t i o n AC/BC; see Appendix A, F ig . A-1). Th i s ensu res

t h a t each l o g i s t e s t e d a t i t s weakest l o c a t i o n . Tes t ing specimens of e i t h e r

a x i a l o r r a d i a l d i r e c t i o n i s accep tab le . V a r i a t i o n s i n t e n s i l e s t r e n g t h were

observed from l o t t o l o t a t the same l o c a t i o n i n each l o g ( s e e Sec t ion 5 .4 ) .

Data on e l a s t i c modulus measured i n t ens ion f o r preproduct ion l o t 426

are given i n Appendix B, Table B-3 (Ref. 5-1). The e l a s t i c modulus followed

the same p a t t e r n w i t h i n l o g s as t h e t e n s i l e s t r e n g t h .

H-451, l o t 426, ranged from 7 . 9 3 GPa a t MLC t o 8.82 GPa a t MLE i n t h e a x i a l

d i r e c t i o n and from 6.89 GPa a t MLC t o 7.45 GPa a t EE i n t h e r a d i a l d i r e c t i o n .

The mean modulus of

The s t r a i n a t f r a c t u r e f o r H-451 w a s i n t he range 0.25 t o 0 . 3 5 % (Ref.

5-1). The s t r a i n a t f r a c t u r e w a s lowest f o r both a x i a l and r a d i a l specimens

a t t h e MLC of a l l logs and inc reased from t h e c e n t e r t o t h e edges. A

sys t ema t i c v a r i a t i o n i n t h e s t r a i n a t f r a c t u r e from l o g t o l o g o r l o t t o

l o t w a s n o t observed i n H-451.

5.2.3.2. Po i s son ' s Rat io . Po i s son ' s r a t i o d a t a are summarized i n Appendix

B, Table B-4 (Ref. 5-1). Po i s son ' s r a t i o v a l u e s , v are i d e n t i f i e d i n

s t anda rd t e n s o r n o t a t i o n according t o t h e or thogonal axes (Ref. 5-2) w i t h i n i j '

a l o g ( s e e Appendix A, Fig. A-4). P o i s s o n ' s r a t i o w a s measured on H-451 i n

t h e a x i a l and r a d i a l d i r e c t i o n s a t s e v e r a l l o c a t i o n s w i t h i n a l o g .

5-3

Poisson ' s r a t i o decreased wi th i n c r e a s i n g stress dur ing i n i t i a l loading

and reached a cons t an t va lue , independent of stress, a f t e r two o r t h r e e load-

i n g s . o r u2) t o MLX

specimens, v = v = 0.110 ? 0.009 and v = w = 0.108 2 0.008. When

stresses were app l i ed i n t h e a x i a l d i r e c t i o n (a ) t o MLC specimens, v = - 3 31 v = 0.127 ? 0.013. When stresses were app l i ed i n t h e a x i a l d i r e c t i o n (u )

t o MLE specimens, u

When stresses were app l i ed i n a r a d i a l d i r e c t i o n (a 1 - - - -

- 13 23 1 2 21

3 - 32 = 0.121 _+ 0.005 and J = 0.114 _+ 0.006. When stresses

32 31 - were app l i ed i n t h e a x i a l d i r e c t i o n (a ) t o EE specimens, v = 0.110 ? 0.010 - 3 32 and v = 0.117 _+ 0.006. 31

5.2.3.3. F l exura l S t r eng th . The f l e x u r a l s t r e n g t h d a t a f o r H-451 l o t 426

are summarized i n Appendix B, Table B-5 (Ref. 5-3). The f l e x u r a l s t r e n g t h

ranged from 20.2 t o 25.3 MPa i n t h e a x i a l d i r e c t i o n and from 1 7 . 4 t o 21.7

MPa i n t h e r a d i a l d i r e c t i o n .

5.2.3.4. Compressive S t r eng th and Elast ic Modulus. Data on t h e compressive

s t r e n g t h and e l a s t i c modulus are summarized i n Appendix B, Table B-6. The

mean u l t i m a t e compressive s t r e n g t h measured on a l o g from product ion l o t

478 w a s 4 7 MPa i n t h e a x i a l and r a d i a l d i r e c t i o n s .

w a s 2.5 MPa and t h e log-to-log v a r i a t i o n w a s 1.5 MPa. Elas t ic modulus i n

compression averaged 7.6 MPa.

The within- log v a r i a t i o n

5.2.4. Thermal P r o p e r t i e s

5.2.4.1. Thermal Expansivi ty and Anisotropy Fac tor . Thermal expans iv i ty

d a t a are summarized i n Appendix B, Table B-7 (Ref. 5-1). The mean thermal

expans iv i ty between 300 and 773 K (27' and 5 0 O o C ) of H-451, l o t 426,

ranged from 3.9 t o 4 .1 x 10 K ( ' C - ' ) i n t h e a x i a l d i r e c t i o n and 4.5 t o

4.6 x 10 K ("C-l) i n t h e r a d i a l d i r e c t i o n . There w a s no s i g n i f i c a n t

v a r i a t i o n of thermal expans iv i ty as a func t ion of specimen l o c a t i o n w i t h i n

t h e l o g s of l o t 426.

-6 -1

-6 -1

5-4

The an i so t ropy f a c t o r i s def ined as

a ( r a d i s 1 )

cr(axia1) an i so t ropy f a c t o r (AF) =

where a ( r a d i a 1 ) is t h e thermal expans iv i ty i n the r a d i a l d i r e c t i o n and

cc(axia1) i s t h e thermal expans iv i ty i n t h e a x i a l d i r e c t i o n .

d a t a are shown i n Appendix B, Table B-8 (Ref. 5-1, 5-3). The mean a n i s o t -

ropy f a c t o r f o r t h e l o g s i n l o t 426 i s 1.15.

The an i so t ropy

5.2.4.2. Thermal Conduct ivi ty . Data on thermal conduc t iv i ty are summarized

i n Appendix B , Table B-9 (Ref. 5-1). The mean thermal conduc t iv i ty a t t h e

MLC of l o g s from l o t 426 w a s 65 f 4 W/m*K i n t h e a x i a l d i r e c t i o n and 63 +_ 4

W/m*K i n t h e r a d i a l d i r e c t i o n a t 1073 K (8OOOC).

5.2.3.3. S p e c i f i c Heat. The s p e c i f i c h e a t of H-451 g r a p h i t e is g iven by

the equat ion (Ref. 5-4)

1 -1 = (0.54212 - 2.42667 x T - 9.02725 x 10 T cP

- 4.34493 x lo4 T-’ + 1.59309 x lo7 T-3

9 -4 - 1.43688 x 10 T ) x 4186

C = s p e c i f i c heat at constant pressure (J/kg-K), P

T = temperature ( K ) .

where

5-5

5.2.5. Impuri ty Content

5.2.5.1 . Neutron-Absorbing I m p u r i t i e s . Two t y p e s of neupron-absorbing

impuri ty e lements , burnable* and nonburnable*, are of importance t o the

neu t ron ic des ign and ope ra t ion of H T G R s .

burnable poison elements i s expressed i n boron equ iva len t s :

The impuri ty conten t of t h e non-

'xAB

Ax5B

BE (boron equ iva len t ) = - (5-2)

where CS = e f f e c t i v e neut ron cap tu re c r o s s s e c t i o n of impur i ty X element x,

boron,

- u = e f f e c t i v e neut ron cap tu re c r o s s s e c t i o n of n a t u r a l

Ax = atomic weight of impurity element x ,

AB = atomic weight of n a t u r a l boron.

B

The boron equ iva len t va lues f o r each element are then m u l t i p l i e d by t h e i r

r e s p e c t i v e concen t r a t ions i n the g r a p h i t e , and t h e products are summed t o

o b t a i n t h e boron equ iva len t l e v e l , i n p a r t s per m i l l i o n , f o r t h e g raph i t e :

Y E C = BEG

i x x

where BE =

c = X

X

boron equ iva len t of impur i ty element x,

boron equ iva len t concen t r a t ion of a l l impur i ty e lements i n g r a p h i t e .

(5-3)

* Nonburnable impur i ty e lements are those t h a t remain i n some propor t ion t o t h e i r o r i g i n a l conten t a t t he end-of- l i fe f o r the f u e l element block, whereas t h e burnable i m p u r i t i e s are completely transmuted t o o t h e r i so topes .

5-6

The neu t ron ic des igne r s of HTGRs r e q u i r e knowledge of t h e nonburnable

i m p u r i t i e s l i s t e d i n Table 5-1, column 8. Those def ined as burnable poisons

are: boron, cadmium, europium, gadolinium, samarium, and l i t h ium; t h e

balance are def ined as nonburnable. I t i s d e s i r a b l e t o keep t h e t o t a l non-

burnable impuri ty con ten t below 0.5 ppm. However, i t i s a formidable and

expensive t a s k t o perform chemical ana lyses f o r a l l r equ i r ed nonburnable

e lements and o b t a i n t h e s e n s i t i v i t y requi red t o d e t e c t t h e elements a t a

l e v e l s a t i s f y i n g the requirement of 0.5 ppm. A recommended p r a c t i c e f o r

determining BE involv ing low-temperature ash ing of t h e g r a p h i t e and subse-

quent a n a l y s i s of t h e ash by emission spectroscopy i s under development by

ASTM Committee C5:05, "Nuclear Appl ica t ions ," a subcommittee of C-5,

" I n d u s t r i a l Carbon and Graphite." A round-robin specimen of H-451 taken

from l o g 6484-34 of l o t 426 w a s prepared by GA and analyzed by AirCo Speer ,

OWL, BNL, and GA, who have r e p r e s e n t a t i v e s on Committee C5:05. The r e s u l t s

of t h e round-robin tests are presented i n Table 5-1, columns 4 through 7 ,

wi th the permission of t h e o rgan iza t ions l i s t e d above.

4

The agreement among t h e four l a b o r a t o r i e s was e x c e l l e n t . The GA d a t a

(column 7) w e r e ob ta ined by emission spectroscopy on t h e ash of a 0.100-kg

sample . The ash w a s prepared a t about 473 t o 523 K (200" t o 25OOC) over a

258-hr per iod . Low-temperature ash ing prevents t h e evapora t ion of v o l a t i l e

i m p u r i t i e s , t hus improving t h e accuracy of t h e d a t a . The va lues f o r each

element r e p r e s e n t , i n most ca ses , t h e lower l i m i t of d e t e c t i o n and, i n some

cases, t h e a c t u a l v a l u e of t h e impur i ty e lement . Thus, t h e c a l c u l a t e d boron

equ iva len t concen t r a t ion r e p r e s e n t s an upper l i m i t of d e t e c t i o n ; i .e. , t h e

boron equ iva len t concen t r a t ion , i n most cases, is less than t h e va lue shown.

An a t tempt w a s made t o select and e l i m i n a t e e lements t h a t have e i t h e r

(1) a low boron equ iva len t f a c t o r (equal t o o r less than O.OOOl), o r ( 2 ) a

high p r o b a b i l i t y o f ' occu r r ing a t i n s i g n i f i c a n t concen t r a t ions .

Using the GA d a t a (Table 5-1, column 7 ) , a boron equ iva len t of 0.131

ppm w a s ob ta ined f o r nonburnable e lements . This excludes c h l o r i n e , which

i s included i n column 8 b u t no t i n column 7 because no d a t a were a v a i l a b l e .

5-7

TABLE 5-1 SIMNARY OF BORON EQUIVALWT TEST DATA ON H-451, LOT 426, LOG 6484-34

4 5

column

6 7 8 -

2 -

Symbol

Al Sb A AS Ba Be B i B Br cd ca C Ce CS cl cr Co cu Dy EK Eu F Gd G a G e Au Hf He Ho H I n I Ir Fe KK La Pb L i Lu m Mn Hg Ma Nd N e N i Nb N OS 0 Pd P

-

9 10 1 1 14 13

Elements DI Boron u lva len t a lysescd)

1 12

Elements d i t h Boron Equivalent

< 0.0001

3

Boron equivalent

Factor

Clements NO' Recomendei :or Analyse:

by ASTH C o m i t t e d C5:05

Analyses )r Purposes

Other Than Boron luivalent(c)

X

Equivalent Boron

( p e d

Elements Requested

+or Analyses(b l e n t N T equestedyb) I I1 I11 Element

Aluminum Ant iwny Argon Arsenic Barium Beryl l ium Bismuth Bomn Bromine cadmium Calcium Carbon Cerium cesium Chlorine Chromium Cobal t

Dysprosiun Erbium Europium F luor ine Gadoliniun Gallium Germanium Cold Hafnium Helium Holmium Hydrogen Indium Iod ine I r id ium I r o n Krypton Lanthanum Lead Lithium Lutet ium Magnesium Manganese Mercury Molybdenum Neodymium Neon Nickel Niobium Nitrogen Osmium

Pal ladium Phosphorus

Copper

O m e n

X X

X

X

X X

X X

X

X

X

X X

X

X X

0.000036 0.0001 2

0.000025 0.000000016 0.000000016 0.18

0.02565 0.00006

0.0000005 0.038

0.00015 0.0001 4 0.000030 0.0000 0.00014 0.0023

0.0079

0.0029

0.000044

0.0004 1

0.0012

0.0000057 0.000000018 0.00051 0.00024 0.000003 0.0001 2

0.000034 0.00029

0.00014 0.00001 6 NA

NA

0.0001

0.0001 2 0.0062 -- -- 0.00042 0.00001 6 0.000026 1 .woo 0.855 0.00020

0.0001 0.0127 0.0136 0.00086 0.0114 0.00099 0.1048 0.0692 0.459

1.57

--

--

- -- - -_

0.0475

0.0222

0.135

-- -- -- --

0.00068

0.00114 0.000001 0.171 0.048 0.00005 0.0041

0.0014 0.00573

0.00114 0.00088 0.002

0.000004

0.0001

--

-

-

- --

0.3 - -- --

0.02 0.005 0.01 0.2

0.03 0.2

0.2

--

-- - --

0.2 0.02 0.07 0.05 0.02 0.01

0.01 0.01 0.02

0.05

0.02

--

-- -- I -- - --

4.0

0.01 0.07 0.005

0.1 0.1

0.06 0.03

0.2

_-

-

-

-- -- - -- - - --

0.45 0.45

0.45 0.045

0.045 0.45

4.5 0.45

--

--

--

- -- - -- 0.14 0.45 0.14 4.5 4.5 4.5

4.5

0.045

0.45

4.5

-- - -- -- L - -- --

2.2

4.5 0.45 0.45 4.5 0.045 0.045

0.045 4.5

0.14 0.045

-

--

--

-_ -- - -- --

0.2 - -- - 0.009 - -- 0.05

0.007 0.2

-- -- -

0.02

0.2 0.04 0.001 0.018 0.004 0.002

0.007

-

-

-- - - 0.004

0.018

0.007

-_ -- -- --

2.6 -- - 0.014 0.007 0.001 0.07 0.07 0.002 -- - -- 0.2 --

-- 0.004

0.001 -- --

X X

X X X X

X X

X X X X X X X X X

X

X

X

X

X

X X X X X X

X X

X X X X X

X

X X

X

X

X

X X X

X

X

X X

X

X

X

X

X

X

X X X

X

X

X

X

X

X

X

TABLE 5-1 (Continued)

1

Element

Plat inum Po tassium Praseodyniu P r o t a c t i n i u Radium Redon Rhenium Rhodium Rubidium Ruthenium Samarium Scandium Selenium S i l i c o n S i l v e r Sodium s t ron t ium S u l f u r Tantalum Tel lur ium Terbium Thallium Thorium Thulium T in Titanium Tungsten Uranium Vanadium Xenon Ytterbium Y t t r i u m Zinc

2

Symbol

P t K P I Pa Ra Rn Re Rh Rb Ru Sm SC Se si Ag N a Sr s Ta T e Tb TS Th Tm Sn T i W U V Xe Yb Y Zn

3

Boron Equivalent

Factor

-_ 0.00081 0.00156 -_ - - - -

0.00033

0.941 0.0074

0.000085 0.0322 0.00034 0.000836 0.00029 0.0159

0.0137 0.0004 3

0.0487 0.00029 0.0018 0.00857

0.00147

0.00715

0.00027 0.0001 0.053

--

-

--

I

-- - __

4 5 6 7

Round Robin Test Dataca) ( p p d

Laborator ies

I Ill - :0.001 :0.017 - - -- - :0.001 :O.W)4 :O .004 :o .002 :0.007

L-

I

26.0 0.028 0.10 0.006

:O .007 - -- --

0.2

:0.004 0.07

:0.004 :0.004 0.001

- --

-- -- _-

0.070 0.070 _- -

IV

<0.012 <0.030 C0.050 --

-- __ -- <0.024 <0.120

<O .050 <0.002

3.0 0.001 0.90 <0.012

<0.120 <O .060 <0.050 0.060

<O .005 0.060 0.180 <0.120 <0.060 0.018

<0.002 C0.003 t0.060 0.060

--

--

--

--

-

-_

Colurrm

8

Elements Requested

>r Analyses (b)

X X

X

X X

X X X X X X

X X

X

X X

X

X

X X X

‘a)Work done by ASTM Ana ly t i ca l Task Force; C5:05 Nuclear Graphi te Committee.

(b)Elements requested by neu t ron ic designers .

(C)Neasured f o r purpose of c o n t r o l l i n g oxidat ion. but included i n BE c a l c u l a t i o n .

(d)Elements no t l i s t e d i n columns 10. 11, and 12.

(e)NZ measured on l og 6884-34 = 45 ppm

Note: Ash content of a n a l y t i c a l specimen used for t h i s experiment - 60 ppm.

9

:lement N .eques t e d x )

X

X X X X X

X

X

X

X

X

X

X

x

10

Analyses or Purposes

Other Than Boron quivalent(c:

X

X

C5:05

X

X X

X

X

X

X

1 1

lements NOT ecomended o r Analyses

by ASTU Committee

12

Elements d i th Boron lquivalent < 0.0001

X

X

Elements for Boron

Squivalent malyses(d)

- -

X X

X

X

X X

X X

X

X

14

Boron Equivalent

( p p d ~

0.000024 0.000078

0.000040

0.047 0.000075

0.00026 0.000032 0.0031 0.00001 0.00046 0.0019

0.00069 0.000026

0.00024

0.00032 0.0010

0.000026

0.00001 4

0.000016 0.000006

No a n a l y s i s w a s done f o r phosphorus o r n i t rogen , b u t va lues of 1.6 pprn f o r

phosphorus (Ref. 5-1) and 45 ppm f o r n i t r o g e n ( s e e Table 5-1, foo tnote e )

were obta ined on d i f f e r e n t specimens and included i n t h e BE c a l c u l a t i o n . A

BE va lue of 0.238 ppm was obta ined f o r burnable e lements (boron, calcium,

europium, ga l l ium, l i t h i u m , and samarium). The only element t h a t con t r ibu ted

s i g n i f i c a n t l y t o t h e nonburnable BE va lue was cadmium, whereas f o r t h e

burnable BE va lue boron and samarium w e r e t h e b i g c o n t r i b u t o r s . It w a s

assumed t h a t ch lo r ine (BE f a c t o r = 0.0136) d id no t c o n t r i b u t e g r e a t l y t o t h e

t o t a l BE.

By e l i m i n a t i n g elements i n Table 5-1, column 9 (not requested by t h e

n e u t r o n i c des igne r s ) , column 10 ( t o be determined f o r purposes of checking

on ox ida t ion r e s i s t a n c e ) , column 1 1 (not recommended f o r ana lyses by ASTM

C5:05 work due t o low p r o b a b i l i t y of occur rence) , and column 12 (BE f a c t o r

<0.0001), w e arrive at the r e m a i n i n g l i s t of e l e m e n t s i n column 13 which

are requ i r ed . Again us ing data from Table 5-1, column 7 , a BE of 0.093

ppm w a s c a l c u l a t e d f o r nonburnable e lements and 0.18 ppm f o r burnable . The

e l i m i n a t i o n of cadmium i n accordance wi th t h e ASTM Committee C5:05 recom-

mendation accounts f o r t he l a r g e r educ t ion i n nonburnable BE. I f cadmium

i s inc luded i n column 13, t h e va lue becomes 0.128 ppm, i n e x c e l l e n t agree-

ment wi th t h e va lue of 0.131 when a l l e lements are inc luded .

The nonburnable BE concen t r a t ion i s w e l l below t h e d e s i r e d l i m i t of

0.5 ppm f o r t h i s specimen and i t made l i t t l e d i f f e r e n c e whether i t w a s cal-

c u l a t e d us ing impuri ty d a t a f o r e lements i n column 8 o r column 13.

va lue c a l c u l a t e d from t h e round-robin d a t a s i g n i f i c a n t l y i n c r e a s e s t h e

s e n s i t i v i t y of a n a l y s i s and g ives an upper l i m i t o f 0.131 ppm on t h e

nonburnable BE i n comparison wi th an upper l i m i t va lue of 0.9486 ppm

repor t ed i n Ref. 5-1 and 0.238 ppm f o r t h e round-robin d a t a ve r sus 3.2922

ppm from Ref. 5-1 f o r burnable BEs .

The BE

I t should be noted t h a t t h e r e s u l t s r epor t ed on t h e boron equ iva len t

impuri ty con ten t were obta ined on a preproduct ion l o g of h igh p u r i t y (ash

con ten t = 60 pprn). Impuri ty con ten t w i l l be d i s t r i b u t e d among l o g s w i t h i n

5-3 0

a product ion ba tch , t h e p u r i t y depending on t h e degree of p u r i f i c a t i o n with-

i n each g r a p h i t i z a t i o n furnace l o t . The d i s t r i b u t i o n of impuri ty con ten t i s

d i scussed f u r t h e r i n Sec t ion 5.2.5.2.

l o t 4 2 6 , i s of h igh p u r i t y and would e a s i l y q u a l i f y as a f u e l element i n t h e

co re of an HTGR.

Based on t h i s experiment, log 6848-34,

5.2.5.2. Ash, I m p u r i t i e s Af fec t ing Oxidat ion Rate, and Lithium. The t o t a l

ash con ten t , i m p u r i t i e s t h a t c a t a l y z e o x i d a t i o n r e a c t i o n s , and l i t h i u m are

important f o r des ign and s a f e t y ana lyses . The d a t a f o r H-451 g r a p h i t e , l o t

4 2 6 , are summarized i n Tables 5-2 , 5 -3 , and 5-4.

Impuri ty con ten t f o r four l o g s of l o t 426 are shown i n Table 5-2 . The

ash con ten t f o r t h e s e l o g s averaged 45 ppm and ranged from <25 t o 8 9 ppm

wi th s m a l l v a r i a t i o n s w i t h i n t h e l o g (Ref. 5 - 1 ) . Elements known t o c a t a l y z e

o x i d a t i o n r e a c t i o n s , such as i r o n , vanadium, t i t an ium, aluminum, s i l i c o n ,

and calcium, ranged from 0.5 t o 22 ppm. S u l f u r con ten t w a s about 1 ppm.

The d i s t r i b u t i o n of t h e s e elements w a s uniform w i t h i n each l o g and p a r a l -

l e l e d t h e d i s t r i b u t i o n of t h e ash. Lithium (see Table 5-3 ) w a s n o t d e t e c t e d

us ing t h e most s e n s i t i v e methods a v a i l a b l e . The l i t h i u m con ten t w a s w e l l

below 1 ppm and may be below 0.005 ppm.

A s mentioned p rev ious ly , t h e p u r i t y of t he l o g s i s a f u n c t i o n of t h e

degree of p u r i f i c a t i o n imparted i n each g r a p h i t i z a t i o n furnace.

ash con ten t f o r a number of t h e preproduct ion l o t s as a f u n c t i o n of t h e i r

g r a p h i t i z a t i o n run are given i n Table 5-4. The mean a sh c o n t e n t i n fu rnace

runs 6399-C and 6003-C w a s 23 and 50 ppm, r e s p e c t i v e l y , whereas i t w a s 255

Data on

ppm i n run 5698-C.

3 l o t s ; l o t 426 l o g s contained coke A , and l o t s 438 and 440 l o g s contained

coke C; however, a l l l o g s were low i n a sh . Product ion l o t s 4 7 2 , 478 and

482 were r e l a t i v e l y h igh i n ash con ten t .

d i f f e r e n t and less e f f i c i e n t p u r i f i c a t i o n f a c i l i t y than t h e preproduct ion

l o t s .

G r a p h i t i z a t i o n furnace run 6399-C contained l o g s from

These l o g s w e r e g r a p h i t i z e d i n a

Since the d a t a presented h e r e show t h a t t h e manufacturing p rocess i s

5-1 3

bl I ir

Mg Pb

~ 0 . 5 6.0

~0.6 <10.3

2.0 < 6.0

~ 0 . 5 < 6.0

to

x o . of Replicates

8

8

8

8

Log No. I Ash

GA (b 1 GLCC GLCC

C 1 . 0

~ 2 . 1

c1.0

q l . 0

<1.3

6484-40

6484-4 1

Mean lot ( 4

1

C2.0 4.0 <20 213.8 < i o

<2.1 11.3 ~ 2 7 . 5 36.3 <11.3

<1.0 C 1 . 0 c20.0 c10.0 C10.0

C1.0 < 1.0 C 2 0 . 0 <10.0 c10.0

c 1 . 5 < 4 . 3 c21.9 c 2 1 . 3 <10.3

6484-33

6484-34

logs)

92 34

198 24

- GA

5 5

84

<25

<25

89

41

<45

42

13

TABLE 5-2 IMPURITY CONTENT: H-451, LOT 426 ' " )

I

- B

3 . 0

4.8

~0.8

~ 1 . 4

~ 2 . 5

Fe

4 . 0

C 7 . 4

<1 .o < 1 .o

~ 3 . 2

Va

<0.5

~ 0 . 5

~ 0 . 5

<O. 5

<0.5

(a)From R e f . 5 - 1 .

(b)Measured by GLCC; 1 specimen per l o g .

Mean Value (MLC, MLE, EC, EE) (pprn)

<0.9 I ,: 7 . 1 j 32

,

TABLE 5-3 SUMMARY OF L I T H I U M ANALYSES : H-45 1 ( a )

GA Log N o . / ( G L C C Log No./GLCC L o t N o . )

565 1-861 521408

6484-331 921426

64 84 - 34 1 1 9 8 / 4 2 6

6484-40/ 1551426

6484-41 / 1841426

N o . of K e p 1 i c a t es

4

1

1

8

2

2

8

1

1

1

1

1

1

1

8

1

1

3

1

(a)From Ref. 5-1 .

( b ) A l l specimens have this v a l u e .

C o n t e n t (ppm)

<O .07

<o .02

<1 .o (b 1

<O. 005

0.074

<O .005

<0.01

<0.01

5-3 3

Q -

Ash (ppm) CLCC Graph i t i za t ion GLCC Lot ._

Furnace Run No. No. X U

TABLE 5-4 IMPURITY CONTENT : H-451

( a ) No. Logs Tested

1 2 7 2 472(b) 304

4 7 8 ( b )

5698-C

6399-C

6003-C

6399-C

6399-C

258

426

426

4 26

4 38

440

23

50

21

26

n 4 38

6.5

75

9.1

1 3

45

31

51

25

23

98

(a)One specimen t e s t e d per l og .

(b)Lots 472, 478, and 482 va lues averaged toge the r .

capable of producing material w i th extremely low impuri ty con ten t , i t i s

t h e f u n c t i o n of t h e m a t e r i a l s p e c i f i c a t i o n to main ta in t h e impur i ty con ten t

r equ i r ed f o r r e a c t o r des ign and s a f e t y analyses i n f u t u r e product ion.

5 .2 .6 . Conclusions

3 The bulk d e n s i t y averaged 1.74 2 0.02 Mg/m f o r product ion logs. The

mechanical p r o p e r t i e s e x h i b i t e d nea r - i so t rop ic c h a r a c t e r i s t i c s wi th t h e

lowest s t r e n g t h va lues a t t h e MLC of t h e logs .

Thermal expans iv i ty va lues were in t e rmed ia t e between needle-coke

g r a p h i t e s and h igh-s t rength i s o t r o p i c g raph i t e s .

w a s 1 .15. The in t e rmed ia t e thermal expans iv i ty and t h e an i so t ropy f a c t o r

The an i so t ropy f a c t o r

5-1 4

r e s u l t from t h e s t r u c t u r e of the f i l l e r coke used. The nea r - i so t rop ic cokes

improve t h e thermal conduc t iv i ty i n t h e r a d i a l d i r e c t i o n (major d i r e c t i o n of

h e a t flow i n r e a c t o r s e r v i c e ) over needle-coke g r n p h i t e s .

The impur i ty con ten t of l ogs from each g r a p h i t i z a t i o n l o t depends on

t h e thoroughness of p u r i f i c a t i o n dur ing the g r a p h i t i z a t i o n process . The ash

con ten t can range from <50 t o 300 ppm, depending on t h e degree of p u r i f i c a -

t i o n .

0.131 ppm and t h e burnable boron equ iva len t va lue 0.238 ppm.

The nonburnable boron equ iva len t va lue of a h igh ly p u r i f i e d l o g w a s

5.3. STATISTICAL DISTRIBUTION OF STRENGTH WITHIN A LOG

A d e t a i l e d knowledge of t h e s t a t i s t i c a l d i s t r i b u t i o n of t e n s i l e and

f l e x u r a l s t r e n g t h w i t h i n an H-451 l o g w a s ob ta ined by d e s t r u c t i v e l y t e s t i n g

a complete l o g (Ref. 5-5). Fac tors sought were (1) t he sys temat ic v a r i a t i o n

of s t r e n g t h wi th o r i e n t a t i o n and l o c a t i o n throughout a l o g , (2) f o r a given

o r i e n t a t i o n and l o c a t i o n , t h e s t a t i s t i c a l d i s t r i b u t i o n of s t r e n g t h s , t h e

mean, s tandard d e v i a t i o n , and the c o e f f i c i e n t of v a r i a t i o n which c h a r a c t e r i z e

the specimen populat ion, (3 ) t he r e l a t i o n between f l e x u r a l s t r e n g t h and

t e n s i l e s t r e n g t h , and ( 4 ) t h e v a l i d i t y of t h e Weibull s t a t i s t i c a l theory

(Ref. 5-61, i nc lud ing t h e dependence o f s t r e n g t h on specimen s i z e and the

Weibull modulus, i f app l i cab le . The Weibull theory , i n which the s t r e n g t h

of a b r i t t l e s o l i d i s assumed t o be c o n t r o l l e d by f laws, has p o t e n t i a l u ses

i n the engineer ing des ign of load-bearing s t r u c t u r e s m a d e f r o m b r i t t l e

materials because i t relates the p r o b a b i l i t y of f a i l u r e t o t h e volume of

material under load , t he stress g r a d i e n t , and m u l t i a x i a l stress states. It

can be combined wi th f i n i t e element stress a n a l y s i s t o p r e d i c t t h e prob-

a b i l i t y of f a i l u r e as a func t ion of p o s i t i o n i n components under complex

stress s ta tes . Previous s t u d i e s of t h e s t r e n g t h of H-327 g r a p h i t e (Ref.

5-7) and nea r - i so t rop ic Gilsocoke-based g r a p h i t e s (Ref. 5-8) showed t h a t

whi le t h e r a t i o s r e l a t i n g the s t r e n g t h of f l e x u r a l specimens and i n t e r n a l l y

p re s su r i zed tubes t o t h e t e n s i l e s t r e n g t h were c o r r e c t l y p red ic t ed by t h e

Weibull model, t h e dependence of s t r e n g t h on specimen volume w a s over-

es t imated .

5-35

n 5.3.1 . Sampling

Sampling diagrams are shown i n Appendix A, Figs . A-5 , A-6, and A-7.

A l og from preproduct ion l o t 408, log 5651-90, was w e d .

of two s i z e s and f l e x u r a l specimens w e r e taken i n both a x i a l and r a d i a l

d i r e c t i o n s from l o c a t i o n s cover ing most of t h e log.

mens were t e s t e d t o f a i l u r e .

'I'ensilc specimens

More than 2000 spec i -

5.3.2. Conclusions

Complete d a t a sets are r epor t ed i n Ref. 5-5. The fo l lowing paragraphs

summarize t h e r e s u l t s .

Axial t e n s i l e specimens averaged 19% s t ronge r than r a d i a l specimens,

and a x i a l f l e x u r a l specimens averaged 13% s t r o n g e r than radial specimens.

Axial specimens taken near t h e edge of t h e l o g averaged 16% and f l e x u r a l

specimens 7% s t r o n g e r than those taken nea r t h e center.

v a r i a t i o n f o r ax ia l t e n s i l e s t r e n g t h s from t h e same zone i n t h e pa ren t l o g

averaged 11.2%, compared wi th 14.7% f o r r a d i a l t e n s i l e s t r e n g t h s .

t h e c o e f f i c i e n t o f v a r i a t i o n averaged 7.9% and 9.0% i n t h e axia l and r a d i a l

d i r e c t i o n s , r e s p e c t i v e l y .

The c o e f f i c i e n t of

I n f l e x u r e ,

Within exper imenta l scatter, t h e d a t a were e q u a l l y w e l l r ep resen ted by

a normal (Gaussian) d i s t r i b u t i o n o r by a d i s t r i b u t i o n p red ic t ed by t h e

Weibull model. The va lue of t h e Weibull modulus m was lower f o r t e n s i l e

tests (mean va lues of 10.7 f o r ax i a l specimens and 8.1 f o r r a d i a l spec i -

mens) than f o r f l e x u r a l tests (mean va lues of 15.8 f o r axial specimens and

1 3 . 6 f o r r a d i a l specimens).

based on t h e Weibull model.

mm and 724 mm ) were t e s t e d .

s t r o n g e r than t h e l a r g e specimens f o r t h e axial and r a d i a l d i r e c t i o n s ,

r e spec t ive ly .

t h e Weibull model, which p red ic t ed d i f f e r e n c e s of 28% and 38% f o r t h e axial

and r a d i a l d i r e c t i o n s , r e s p e c t i v e l y .

Such a d i f f e r e n c e is con t ra ry t o p r e d i c t i o n s

Tens i l e specimens of two s i z e s (volumes 9847,

The small specimens averaged 3% and 8% 3 3

The observed s i z e e f f e c t w a s much lower than expected from

n

5-3 6

The mean f l e x u r a l s t r e n g t h showed good c o r r e l a t i o n w i t h t h e mean ten-

s i l e s t r e n g t h of companion specimens ( c o r r e l a t i o n c o e f f i c i e n t 0 .9) . Flex-

u r a l s t r e n g t h averaged 52% and 55% h ighe r than t h e corresponding t e n s i l e

s t r e n g t h s f o r t h e a x i a l and r a d i a l d i r e c t i o n s , r e spec t ive ly . These va lues

a r e i n good agreement wi th va lues of 51% a x i a l and 64% r a d i a l p red ic t ed by

t h e Weibull model. While t h e r e i s agreement between t h e exper imenta l

f l exure - to - t ens i l e s t r e n g t h r a t i o s and t h e r a t i o s p r e d i c t e d by t h e Weibull

model, t h e exper imenta l ly der ived s i z e e f f e c t and t h e d i f f e r e n c e i n Weibull

modulus between t e n s i l e and bend da ta are i n c o n s i s t e n t w i t h t h e Weibull

model. Thus, t h e H-451 g r a p h i t e l o g t e s t e d does no t meet t h e c r i t e r i a which

would permit i t t o be t r e a t e d as a Weibull s o l i d .

When cons ide r ing t h e minimum s t r e n g t h of H-451 l o g s f o r acceptance/

r e j e c t i o n tests, t h e d a t a i n Ref. 5-5 conf i rmthe r e s u l t s from Ref. 5-1 t h a t

t h e l o g s are weakest a t t h e midlength c e n t e r (MLC). Thus, t e s t i n g spec i -

mens from t h e MLC zone c o n s t i t u t e s t h e most conse rva t ive c r i t e r i o n f o r

e l i m i n a t i n g weak o r d e f e c t i v e logs .

5.4. DEFINITION OF M I N I M U M STRENGTH AND STRENGTH DISTRIBUTION AMONG LOGS

Ninety-eight f u l l - s i z e (432 mm diameter by 813 mm long) product ion

l o g s were manufactured, us ing t h e same formula t ion , raw materials, and pro-

cedures as preproduct ion l o t 426.

p r o d u c t i o n o r d e r f o r p o s s i b l e u s e as FSV r e load elements . T h e 354-log o r d e r

was manufactured i n 6 e x t r u s i o n l o t s , taken through t h e baking p rocess and

s t o r e d a t GLCC.

t e n s i l e s t r e n g t h t e s t i n g , and t o ORNL and BNL f o r exper imenta l purposes.

The 98 l o g s were taken from t h r e e of t h e product ion e x t r u s i o n l o t s (472,

478, and 482). A l l l o g s were g r a p h i t i z e d i n fu rnace run number 1272.

The 98 l o g s were a p o r t i o n of a 354-log

The 98 l o g s were g r a p h i t i z e d and d i s t r i b u t e d t o GA f o r

5.4.1. Sampling

The l o g s were sampled for t e n s i l e t e s t i n g by GLCC a t t h e i r Morgantown

The sampling d i a - p l a n t i n accordance w i t h a sampling p l an devised by GA.

gram is g iven i n Appendix A, Figs . A-8, A-9, and A-10. A rod 16 mm i n

5-1 7

diameter by 356 mm long w a s cored from t h e c e n t e r and a 25-mm s l a b w a s taken

from one end of each log.

shown i n Fig. A-9.

midlength c e n t e r (MLC) of each l o g as p o s s i b l e (wi th in 51 mm of t h e cen te r ;

see Fig. A-8) whi le p re se rv ing t h e logs f o r subsequent machining i n t o f u e l

element blocks. Axia l test specimens 6 .35 mm i n diameter by 23 mm long

were machined from t h e a x i a l co re , as shown i n Fig. A-9,and r a d i a l specimens

of t he same s i z e were machined from t h e end s l a b , as shown i n Fig. A-10. A

s i n g l e t e n s i l e t es t specimen (12 .8 mm i n diameter by 76.2 mm long) w a s t aken

from each c e n t e r core , as shown i n Fig. A-8, f o r measurement by GLCC.

A 102-mm c o r e w a s t aken f o r axial specimens, as

The GA axia l s t r e n g t h specimens were taken as c l o s e t o t h e

U l t i m a t e t e n s i l e s t r e n g t h w a s measured on e i g h t a x i a l specimens and

f o u r r a d i a l specimens from each l o g a t GA, and one a x i a l specimen was meas-

ured from each l o g a t GLCC.

5.4.2. Experimental Resu l t s

I n d i v i d u a l s t r e n g t h va lues f o r each l o g and t h e mean va lues grouped by

e x t r u s i o n l o t are r epor t ed i n Ref. 5-9. The average s t r e n g t h s and s t anda rd

d e v i a t i o n s f o r a x i a l specimens t e s t e d by GA and GLCC from each e x t r u s i o n

l o t are g iven i n Table 5-5. The grand mean of 12.7 MPa f o r GA d a t a com-

pares w i t h 13 .3 MPa f o r GLCC's s i n g l e specimens.

C o r r e l a t i o n between the values f o r GLCC's s i n g l e specimen and t h e GA

average va lues w a s poor (Ref. 5-9). The d i f f e r e n c e may r e f l e c t bo th t h e

s p a t i a l s e p a r a t i o n of t he sampling zones and t h e inhe ren t randomness of t h e

s i n g l e specimen measured by GLCC. S t a t i s t i c a l tests showed no s i g n i f i c a n t

d i f f e r e n c e i n mean va lues between A and B specimens ( l o c a t e d c l o s e s t t o t h e

l o g c e n t e r ) and t h e C and D specimens; t h e r e f o r e , they can be t r e a t e d as

coming from the same populat ion.

The d i f f e r e n c e s i n average s t r e n g t h (GA da t a ) between t h e t h r e e ex- t r u s i o n l o t s , as shown i n Table 5-5, were s t a t i s t i c a l l y h i g h l y s i g n i f i c a n t .

The small d i f f e r e n c e s i n s t anda rd d e v i a t i o n between t h e d i f f e r e n t e x t r u s i o n

l o t s were no t s t a t i s t i c a l l y s i g n i f i c a n t .

5-1 8

TABLE 5-5 STATISTICAL ANALYSES OF GA AND GLCC AXIAL STRENGTH DATA

No. of Specimens Tested by:

Average T e n s i l e S t r eng th and Standard Deviat ion ( m a )

GLCC

14

56

28

9 8

- S

12.3

13.6

1 1 . 1

12.7 3.0

Lot No.

472

478

482

A 1 1

.* 13.8

GA

1 1 1

4 39

2 24

7 74 I

There w a s no c o r r e l a t i o n between s t r e n g t h and t h e p o s i t i o n of t h e l o g

w i t h i n t h e g r a p h i t i z a t i o n furnace. The d i f f e r e n c e s between t h e average

s t r e n g t h s o f l o t s 4 7 2 , 4 7 8 , and 482 were accounted f o r by GLCC as d i f f e r e n c e s

i n process ing dur ing ex t rus ion .

The average r a d i a l s t r e n g t h s and s t anda rd d e v i a t i o n s f o r each e x t r u s i o n

l o t are g iven i n Table 5-6. The grand mean w a s 15.8 MPa. The d i f f e r e n c e i n

s t r e n g t h between l o t s 4 7 2 and 478 w a s n o t s t a t i s t i c a l l y s i g n i f i c a n t , b u t

l o t 482 was s i g n i f i c a n t l y weaker than t h e o t h e r two l o t s .

t h e a x i a l s t r e n g t h s , t h e d i f f e r e n c e s i n s t anda rd d e v i a t i o n s were s t a t i s -

t i c a l l y s i g n i f i c a n t , w i t h l o t 482 showing more v a r i a b i l i t y than t h e o t h e r

two l o t s .

v a r i a b i l i t y and the within-log (specimen-to-specimen) variability.

In c o n t r a s t t o

This w a s a t t r i b u t a b l e t o an i n c r e a s e i n bo th t h e log-to-log

There w a s no s t a t i s t i c a l l y s i g n i f i c a n t c o r r e l a t i o n between t h e r a d i a l

s t r e n g t h and t h e axial s t r e n g t h of t h e same l o g s ( c o r r e l a t i o n c o e f f i c i e n t

0 . 1 1 ) .

specimens a t t h e end-center p o s i t i o n compared w i t h t h e a x i a l specimens a t

t h e midlength-center p o s i t i o n are n o t unusual and have been observed i n

p r e p r o d u c t i o n l o g s (Refs. 5-1, 5-5). The d i f f e r e n c e s between t h e t h r e e l o t s

show t h a t material ex t ruded i n d i f f e r e n t l o t s can vary cons iderably i n

The h ighe r s t r e n g t h and reduced s t anda rd d e v i a t i o n of t h e r a d i a l

s t r e n g t h p r o p e r t i e s a f t e r baking impregnat ion and g r a p h i t i z a t i o n .

5-39

Av c r il g C'

S t rcng t h CLCC Extrris i o n No. o I- Lot No. Spec i m m s 'I'cistcd (Wa)

-___I- --.-___---I_

4 72 56 16.4

478 224 16.3

482 112 14.5

A 1 1 39 2 15.8

5.4.3. Appl i ca t ion of Resu l t s t o Acceptance T e s t i n g

Standard Dev i ii t ion

( m a )

1.4

1.8

2.7

2.2

The strength of ax ia l midlength-center specimens w a s both l o w e r and

more s c a t t e r e d than t h e s t r e n g t h of r a d i a l end-center specimens.

between e x t r u s i o n l o t s and v a r i a t i o n s between logs w i t h i n t h e same l o t both

c o n t r i b u t e t o t h e s c a t t e r . The log-to-log v a r i a t i o n s a p p e a r s t o be too

g r e a t t o allow q u a l i f i c a t i o n of e n t i r e l o t s . Therefore , acceptance tests

intended t o ensure minimum s t r e n g t h requirements should be based on a x i a l

midlength-center specimens and each l o g should be t e s t e d .

V a r i a t i o n s

5.4.3.1. S t a t i s t i c a l . Model. Acceptance c r i t e r i a assume t h e fol lowing sta-

t i s t i c a l model (Ref. 5 - 9 ) :

x = p + ai + B , + E i j i j J

(5-9)

where x

p is t h e grand mean s t r e n g t h , ai is t h e v a r i a t i o n sys t ema t i c t o t h e ith l o t ,

6 . is t h e v a r i a t i o n sys t ema t i c t o t h e j th l o g from t h i s l o t , and E

is an a x i a l s t r e n g t h measurement from the jth l o g i n t h e ith l o t , i j

is t h e 1 i j - random v a r i a t i o n ( i n themidlength-center sampling zone) w i t h i n t h i s log. It

w a s f u r t h e r assumed t h a t a , 6, and E are normally and independently d i s t r i b - - - 2 WL' and u r e s p e c t i v e l y .

2 U

2 l o t ' l og ' u t ed with means of zero and v a r i a n c e s of u

The l a t t e r t h r e e q u a n t i t i e s are, i n o r d e r , t h e va r i ances a t t r i b u t a b l e t o n

5-20

l o t - to - lo t v a r i a t i o n s , log-to-log v a r i a t i o n s , and within- log v a r i a t i o n s . It

is i m p l i c i t i n t h e model t h a t t h e log-to-log va r i ance i s t h e same f o r a l l

ex t rus ion l o t s and t h e within- log va r i ance is t h e same f o r a l l logs .

Values f o r t h e t h r e e components of va r i ance were c a l c u l a t e d from t h e

tes t d a t a by t h e analysis-of-var iance method. The c a l c u l a t i o n s confirmed

t h a t both lo t - to - lo t and log-to-log v a r i a t i o n s were s t a t i s t i c a l l y h igh ly 2 2

WL and 0 are shown in Table 5 - 7 ; t h e s i g n i f i c a n t . The va lues f o r u 2 a l o t ’ log’

corresponding s t anda rd d e v i a t i o n s a r e a l s o included.

The l a r g e s t c o n t r i b u t o r t o t h e spread i n t h e a x i a l s t r e n g t h measure-

ments i s t h e log-to-log v a r i a t i o n among l o g s from the same e x t r u s i o n l o t

( s e e Table 5-7), whereas the within- log va r i ance [2.67 ( m a ) ] is low enough

f o r log-by-log acceptance tests based on a few specimens p e r l o g t o b e

p r a c t i c a b l e .

2

5.4.3.2. Acceptance Criteria. The purpose of acceptance t e s t i n g i s t o

ensure t h a t material from t h e weakest l o c a t i o n (midlength c e n t e r ) of t he

l o g s meets t h e minimum s t r e n g t h requirement Smin. Because of t h e v a r i a b i l i t y

COMPONENTS

Source of Var i a t ion

Lot- to - lo t

Log-to-log

Within-log ( r e s i d u a l )

TABLE 5-7 OF VARIANCE: AXIAL STRENGTH DATA

Var i anc e Deviat ion

5-2 3

i n g r a p h i t e s t r e n g t h s , a s t a t i s t i c a l d e f i n i t i o n of minimum s t r e n g t h is

requi red . The fo l lowing two a l t e r n a t i v e d e f i n i t i o n s were considered:

90/90: A t l eas t 90% of t h e material a t t h e midlength center of t h e l o g

equa l s o r exceeds a s p e c i f i e d minimum s t r e n g t h , w i th 90%

confidence.

90/95: A t least 99% of t h e material a t t h e midlength c e n t e r of t h e l o g

equa l s o r exceeds a s p e c i f i e d minimum s t r e n g t h , w i t h 95%

confidence.

An acceptance t e s t i n g procedure which meets t h e needs can be de r ived

from t h e s t a t i s t i ca l model of Eq. 5-9, i f i t is assumed t h a t t h e p re sen t

estimate of t h e within- log variance [2.67 ( m a ) ] is exac t and w i l l remain

unchanged i n f u t u r e p r o d u c t i o n r u n s . It is assumed that n r e p l i c a t e s p e c i -

mens from t h e midlength c e n t e r of a l o g are t e s t e d and t h e i r average, x, i s

used t o estimate t h e mean l o g s t r e n g t h , p + ai + 6 . requirement S

2

-

The m i n i m u m s t r e n g t h j

w i l l b e m e t i f x meets t h e fo l lowing c r i t e r i o n : min

- 1.282

JT WL x 2 Smin + 1.282 uWL +-

where a 90/90 d e f i n i t i o n of minimum s t r e n g t h i s used, or

- 1 645 x 2 Smin + 2.326 am +

(5-loa)

(5-lob)

where a 9 9 / 9 5 , d e f i n i t i o n o f minimum s t r e n g t h i s used. The numerical f a c t o r s

i n E q . 5-10 come from t a b u l a t e d va lues f o r t h e s t anda rd normal d i s t r i b u t i o n .

5-22

Because d i f f e r e n t components i n t h e HTGR c o r e expe r i ence d i f f e r e n t

stress levels , i t is d e s i r a b l e t o d e v i s e an acceptance tes t t h a t s o r t s t h e

lrigs according t o t h e i r s t r e n g t h . Therefore , t h e fol lowing s t r e n g t h cate-

g o r i e s were considered:

Category A: minimum s t r e n g t h 10.3 MPa

Category B: minimum s t r e n g t h 8.3 MPa

Category C: minimum s t r e n g t h 5.5 MF'a

The v a l u e which must exceed f o r a log t o be a s s igned t o ca t egory A, B , o r

C can b e c a l c u l a t e d from Eq. 5-10. Values are shown i n Table 5-8 f o r f o u r

and e i g h t r e p l i c a t e tests per l o g , and f o r 90/90 and 99/95 d e f i n i t i o n s of

minimum s t r e n g t h .

The c r i t e r i a l i s t e d i n Table 5-8 were a p p l i e d t o each of t h e 98 logs .

For t h e case r e q u i r i n g f o u r r e p l i c a t e tests, t h e f o u r specimens c l o s e s t t o

t h e l o g c e n t e r ( s u b s c r i p t s A and B; see Figs. A-8 and A-9b) were used. The

a s s igned ca t egory f o r each l o g is given i n Ref. 5-9 f o r a four- o r e igh t -

specimen sampling p l an , and f o r a 90/90 o r 99/95 d e f i n i t i o n of minimum

s t r e n g t h .

5.4.3.3. Yields of Logs by Category. A summary of t h e numbers of l o g s as-

s igned t o each ca t egory under four- and eight-specimen sampling p l a n s , apply-

i ng either a 9 0 / 9 0 o r 99/95 d e f i n i t i o n of minimum s t r e n g t h , i s given i n

Table 5-9. Resu l t s are p resen ted f o r each e x t r u s i o n l o t .

Using a 90/90 d e f i n i t i o n of minimum s t r e n g t h and an eight-specimen

sampling p l an , on ly two l o g s would be r e j e c t e d as f a i l i n g t o q u a l i f y f o r

s t r e n g t h ca t egory C, and almost h a l f t h e l o g s would q u a l i f y f o r ca t egory A.

I f a 99/95 d e f i n i t i o n were used, 18 l o g s would be r e j e c t e d and about 20% of

t h e remainder would q u a l i f y f o r ca t egory A.

replacement segment of an HTGR c o r e would r e q u i r e about 25% of t h e accepted

l o g s t o q u a l i f y f o r ca t egory A and 70% t o q u a l i f y f o r A o r B. I f a 99/95

A t y p i c a l o r d e r of l o g s f o r a

5-23

No. of Tests p e r

Log

TABLE 5-8 C R I T E R I A FOR ASSIGNING LOGS TO STRENGTH

CATEWRIES A, B , OR C (AXIAL DATA)

D e f i n i t i o n of Minimum

St rength Smin

90/90 (b)

99/95(c)

90/90(b)

99/95(c)

S t rengtva) Category

A

B

C

A

B

C

A

B

C

A

B

C

Value Which Average Measured S t r eng th 2

Must Exceed

(MPa)

13.5

11.4

8.7

15.5

13.4

10.7

13.2

11.1

8.3

15.1

13.0

10.3

(a )Categor ies correspond t o t h e fol lowing minimum s t r e n g t h s :

A: 10.3 MPa B: 8.3 MFa C: 5.5 MPa

(b)At l eas t 90% of material a t midlength c e n t e r exceeds s p e c i f i e d minimum s t r e n g t h , wi th 90% confidence.

(')At least 99% of material a t midlength c e n t e r exceeds s p e c i f i e d minimum s t r e n g t h , w i th 95% confidence.

5-24

N o . of Tes ts p e r

Log

4

8

TABLE 5-9 YIELDS OF LOGS I N EACH STRENGTH

CATEGORY (BASED ON AXIAL STRENGTHS)

D e f i n i t i o n of Minimum

S t reng th

min S

90 / 90 ( a )

99/95(b)

90/90 (a)

99/95 (b)

Ext rus ion Lot

472

4 78

482

A 1 1

472

4 78

4 82

A1 1

4 72

4 78

4 82

A 1 1

4 72

4 7 8

482

A l l

A

6

27

6

39

1

12

1

14

6

29

7

42

2

14

1

1 7

No. of Logs Assigned t o S t r eng th Categor

B -

3

22

6

31

5

16

5

26

3

22

6

31

4

20

6

30 -

C

4

6

1 3

23

3

26

7

36

4

5

14

23

4

20

9

3 3

Reject

1

1

3

5

5

2

15

22

1

0

1

2

4

2

12

18

1 To t a l

14

5 6

28

98

14

56

28

98

14

5 6

28

98

14

56

28

98

(a)At l eas t 90% of material a t midlength c e n t e r exceeds s p e c i f i e d minimum s t r e n g t h , w i th 90% confidence.

(b)At l eas t 99% of material a t midlength c e n t e r exceeds s p e c i f i e d minimum s t r e n g t h , w i t h 95% confidence.

5-25

minimum s t r e n g t h d e f i n i t i o n were adopted i n place of t h e 90190 d e f i n i t i o n ,

t he y i e l d s i n t h e h ighe r c a t e g o r i e s would f n l 1 j u s t s h o r t of t hese r equ i r e -

ments, based on t h e q u a l i t y of t h e 98 l o g s considered i n t h i s experiment.

The e f f e c t on t h e y i e l d s of reducing t h e number of tests per l og from

e i g h t t o four i s small . The number of r e j e c t s would i n c r e a s e from two t o

f i v e under a 90/90 s t r e n g t h d e f i n i t i o n , and r e j e c t s would be increased from

18 t o 2 2 under a 99/95 s t r e n g t h d e f i n i t i o n . There would b e some o v e r a l l

downgrading because more b o r d e r l i n e l o g s would be moved down i n c a t e g o r y t h a n

would be moved up.

The b e t t e r q u a l i t y of e x t r u s i o n l o t 478 , i nd ica t ed by i t s h ighe r

average s t r e n g t h i n Table 5-4, i s r e f l e c t e d i n t h e y i e l d s l i s t e d i n Table5-9.

Even us ing a 99/95 d e f i n i t i o n of minimum s t r e n g t h , on ly two of t h e 56 l o g s i n

l o t 478 would be r e j e c t e d and 25% would m e e t ca tegory A requirements .

5.4.4. Conclusions

The a x i a l s t r e n g t h s (average va lue 12 .7 MPa) from t h e MLC showed con-

s i d e r a b l e l o t - t o - l o t and log-to-log v a r i a t i o n s , whi le t h e r a d i a l s t r e n g t h s

(average va lue 15.8 m a ) from t h e EC were more uniform. There were no

s t a t i s t i c a l l y s i g n i f i c a n t c o r r e l a t i o n s between a x i a l s t r e n g t h and r a d i a l

s t r e n g t h i n the same l o g , o r between s t r e n g t h and t h e p o s i t i o n of t h e l o g

i n t h e g r a p h i t i z i n g furnace .

Acceptance c r i t e r i a f o r a s s ign ing l o g s t o a minimum s t r e n g t h ca tegory

can be based on a x i a l t e n s i l e tests, i f each l o g is t e s t e d . A s ta t i s t ica l

model i nco rpora t ing a separate l o t - t o - l o t var iance , log-to-log var iance , and

wi th in- log va r i ance can be adopted f o r t h i s purpose.

Acceptance c r i t e r i a which could be used f o r a s s ign ing a l o g t o s t r e n g t h

ca tegory A (minimum s t r e n g t h 10.3 m a ) , B (minimum s t r e n g t h 8.3 m a ) , o r

C (minimum s t r e n g t h 5.5 MPa) were der ived . Ca lcu la t ions were made f o r e i t h e r

four o r e i g h t r e p l i c a t e specimens p e r l o g and two a l t e r n a t i v e d e f i n i t i o n s of

5-26

/ \

minimum s t r e n g t h were considered. The f i r s t d e f i n i t i o n would r e q u i r e 90%

of the material a t t h e midlength c e n t e r of t h e l o g t o exceed the s p e c i f i e d

minimum s t r e n g t h , wi th 90% confidence (90/90); t he second would r e q u i r e 99%

of t he material t o exceed t h e s p e c i f i e d minimum, wi th 95% confidence (99/95) .

When these c r i t e r i a were appl ied t o the a x i a l test d a t a from t h e 98 l o g s ,

two l o g s would f a i l t o q u a l i f y f o r ca tegory C, whi le a lmost h a l f of t h e l o g s

would q u a l i f y f o r ca tegory A i f a 90/90 d e f i n i t i o n of minimum s t r e n g t h and

e i g h t specimens per l o g were used.

s t r e n g t h would i n c r e a s e t h e number of l o g s r e j e c t e d t o 18. Decreasing t h e

number of tests p e r l o g from e i g h t t o four would cause a s m a l l r educ t ion i n

the y i e l d s .

Use of a 99/95 d e f i n i t i o n of minimum

Using a 99/95 d e f i n i t i o n of minimum s t r e n g t h , on ly two of t h e 56 l o g s

i n the l o t o f h ighes t average s t r e n g t h (478) would be r e j e c t e d and about 25%

would q u a l i f y f o r ca tegory A .

40% f o r l o g s from t h e o t h e r two lots.

This compares wi th a r e j e c t i o n ra te of about

These resul ts provide t h e information requi red to w r i t e an acceptance

s p e c i f i c a t i o n f o r s t r e n g t h of a l o g by measuring t h e t e n s i l e s t r e n g t h on

specimens taken a t t h e MLC. The number of l o g s and specimens t e s t e d and

the confidence r equ i r ed depend on t h e confidence r equ i r ed i n des ign .

5.5. FATIGUE BEHAVIOR

The g r a p h i t e f u e l element b locks are s u b j e c t t o c y c l i c stresses from

power cyc l ing , ope ra t ing v i b r a t i o n s , and poss ib ly seismic shaking. Design

of t he components r e q u i r e s a knowledge of t h e c y c l i c f a t i g u e behavior of

g r a p h i t e under loading c y c l e s wi th d i f f e r e n t r a t i o s of minimum stress t o

maximum stress (R va lue ) . The inhe ren t s c a t t e r i n mechanical p r o p e r t i e s

o f g r a p h i t e s r e q u i r e s t h a t s u f f i c i e n t tests be made f o r s t a t i s t i c a l a n a l y s i s .

Uniaxia l f a t i g u e tests were performed on H-451 g r a p h i t e wi th R va lues rang-

ing from -1 t o 0.5 (Ref. 5-10).

5-27

5.5.1. Sampling

Specimens f o r u n i r r a d i a t e d f a t i g u e t e s t i n g of H-451 were taken i n t h e

a x i a l and r a d i a l d i r e c t i o n s a q u a r t e r of t h e way a long t h e l eng th of t h e

l o g used f o r within- log s t r e n g t h t e s t i n g ( see F ig . A-5 i n Appendix A)between

25 and 100 mm from t h e edge ( see Fig. A-11 i n Appendix A). For a given

ser ies of tests, specimens were taken from l o c a t i o n s spread uniformly over

t h e sampling zone t o prevent b i a s from l o c a l inhomogeneities i n s t r e n g t h .

C y l i n d r i c a l specimens 1 2 . 7 mm i n diameter by 25.4 mm long were used.

5.5.2. Experimental Procedure

The f i r s t t es t series cons i s t ed of 30 t o 35 c o n t r o l t e n s i l e tests of

r a d i a l and a x i a l specimens on s t anda rd f a t i g u e specimens mounted i n the

f a t i g u e machine. These tests e s t a b l i s h e d t h e mean t e n s i l e s t r e n g t h s of t h e

c o n t r o l specimens ( see Appendix B, Table B-10). Fa t igue tests w e r e run us ing

R va lues of - 1 , -0.5, 0 , and 0.5. Forty t o f i f t y specimens were included i n

each series of tests. From seven t o t e n specimens were cycled a t each of

f i v e maximum stress l e v e l s ranging from 0.6 t o 1 .0 times t h e mean t e n s i l e

s t r e n g t h . The stress l e v e l s were s e l e c t e d t o avoid an excess ive number of

run-outs beyond 100,000 cyc le s . Axial and r a d i a l specimens were measured.

5.5.3. ExDerimental R e s u l t s

A t y p i c a l S-N curve, t aken from Ref. 5-10, i n which t h e logar i thm of

t h e maximum stress S i s p l o t t e d a g a i n s t the logar i thm of t h e number of

cyc le s a t f a i l u r e N i s shown i n Appendix B, F ig . B-1, f o r a x i a l specimens

wi th an R va lue of -1. The stresses are normalized by d i v i d i n g by t h e mean

t e n s i l e s t r e n g t h . The t e n s i l e d a t a and f i r s t cyc le f a i l u r e s are p l o t t e d a t

N = 0.25, and run-outs (specimens which surv ived 100,000 cyc le s wi thout

f a i l u r e ) are shown as open c i rc les a t N = 100,000.

5-28

The S-N curves have the same form as those of many metals, except t h a t

t h e s c a t t e r band i s wider . The d a t a do n o t extend t o h igh enough va lues of

N t o confirm t h e e x i s t e n c e of an a b s o l u t e endurance l i m i t .

The usua l p r a c t i c e of ana lyz ing f a t i g u e d a t a has been t o deduce t h e N

va lue corresponding t o a p a r t i c u l a r f a i l u r e p r o b a b i l i t y from t h e d i s p e r s i o n

of l o g ( N ) va lues a t a given stress s e t t i n g , assuming a Weibull o r Gaussian

d i s t r i b u t i o n . This procedure has s e v e r a l disadvantages when app l i ed t o

g raph i t e ; i n p a r t i c u l a r , i t provides no informat ion on low f a i l u r e probabi l -

i t i e s i n the high cyc le regime. The a n a l y t i c a l problem w a s approached i n

Ref. 5-10 by i n v e r t i n g the usua l p r a c t i c e and assuming t h a t f o r a cons tan t

l i f e t he f a i l u r e stresses fo l low a s p e c i f i c d i s t r i b u t i o n (Ref. 5-11). The

fo l lowing s t a t i s t i c a l model w a s assumed (Ref. 5-10):

(5-11)

where u i s t h e peak t e n s i l e stress, S is t h e mean t e n s i l e s t r e n g t h , crand

/3 are c o n s t a n t s , and E i s a random v a r i a b l e d i s t r i b u t e d normally wi th a mean

of zero and a s t anda rd d e v i a t i o n s. Data i n Ref. 5-10 were analyzed accord-

i n g t o the model of E q . 5-11, i nc lud ing the t e n s i l e tests a t N = 0.25 bu t

exc luding t h e specimens which r a n o u t beyond lo5 cyc le s .

s t r a i g h t l i n e through t h e data and t he x / y lower t o l e rance l i m i t s (represent-

i n g t h e l i m i t s above which a t least x% of a l l obse rva t ions would f a l l , w i t h

y% confidence) were c a l c u l a t e d f o r t h e x/y combinations 90/90, 95/95, and

99/95 and are inc luded i n Appendix B, Fig. B-1. The d a t a suppor t a l i n e a r

r e l a t i o n between l o g (a ) and l o g (N) assumed i n Eq. 5-11. Resu l t s of

t h e s ta t i s t ica l ana lyses are summarized i n Table 5-10.

max

The l eas t - squa res

max

For des ign , i t i s convenient t o p l o t f a t i g u e r e s u l t s on a cons t an t

l i f e f a t i g u e diagram (Goodman diagram), which relates f a t i g u e l i f e t o t h e

fol lowing in te rdependent l oad ing cycle parameters: maximum stress, minimum

stress, stress ampli tude, and mean stress. The d a t a i n Appendix B, Fig. B-2,

provide an example of a Goodman diagram, taken from Ref. 5-10, r e l a t i n g t h e

5-29

n

Iu

I

rr, aJ

al C

T- a

m m

do .d u

(d

U

G aJ .d

k

0

.r

om

oc

c)

ol

nm

C

Ob

\o

9c

nC

Ob

b

00

00

00

00

. . . .

. . . .

Na

3N

CO

\D

bc

nC

O

dm

md

mm

ml

n

00

00

00

00

0

0

0

0

0

0

0

0.

. . . .

. .

.

ea

r-

F

Nm

%:

dz

fC

JN

-

0

00

00

00

00

. . .

. .

. .

. 0

00

00

00

0

II

II

II

II

. .

. .

. .

. .

00000000

II

II

II

II

ln

“I ln

m

00

0-

00

07

I

I

II

- 7 I m

CT w G 0 a aJ

m

a

cn n

(d

v

5-30

2 3 4 5 loading cyc le parameters f o r 50% s u r v i v a l t o 10 , 10 , 10 , and 10 c y c l e s

i n a x i a l specimens o f H-451 g r a p h i t e .

When normalized by d i v i d i n g by the mean t e n s i l e s t r e n g t h , t h e homologous

stress l i m i t s f o r r a d i a l specimens were somewhat g r e a t e r than those f o r a x i a l

specimens under s imilar condi t ions (Table 5-10).

Under r eve r sed stress c y c l i n g (R = - l ) , t h e homologous stress l i m i t s

f o r s u r v i v a l of a x i a l specimens t o lo5 cyc le s averaged 0.63 f o r 50% s u r v i v a l

and 0.48 f o r 99% s u r v i v a l (99/95 to l e rance l i m i t ) , i n good agreement wi th

L e i c h t e r and Robinson's r e s u l t s (Ref. 5-11). The homologous stress l i m i t s

f o r r a d i a l specimens averaged 0.74 f o r 50% s u r v i v a l and 0.53 f o r 99% s u r v i v a l .

5 . 5.4. Conclusions

H-451 g r a p h i t e showed c y c l i c f a t i g u e l i f e curves (S-N curves) g e n e r a l l y

resembling those o f metals, bu t wi th more s c a t t e r . For reversed stress

cyc l ing ( R = - l ) , the homologous s t ress l imits (maximum appl ied f a t i g u e

stress d iv ided by t h e t e n s i l e s t r e n g t h ) f o r 50% specimen s u r v i v a l t o 10

cyc le s averaged 0.63 i n the a x i a l d i r e c t i o n and 0.74 i n t h e r a d i a l d i r e c t i o n .

Corresponding homologous stress l i m i t s f o r 99% specimen s u r v i v a l (99/95

to l e rance l i m i t s ) were 0.48 and 0.53. The f a t i g u e l i f e and t h e homologous

stress l i m i t s increased as R increased .

5

REFERENCES

5-1. Johnson, W. R . , and G. B. Engle, "P rope r t i e s of Un i r r ad ia t ed Fuel

Element Graphi tes H-451 and TS-1240," ERDA Report GA-A13752, General

Atomic Company, January 31, 1976. Nye, J. F., Phys i ca l P r o p e r t i e s of C r y s t a l s , Oxford Un ive r s i ty P r e s s ,

London, pp. 1-8, 1967.

5-2.

5-3. Engle, G. B . , and W. R. Johnson, "P rope r t i e s of Un i r r ad ia t ed Fuel

Element Graphi tes H-451 and S0818," ERDA Report GA-A14068, General

Atomic Company, October 8, 1976.

5-31

n 5-4.

5-5.

5-6.

5-7.

5-8.

5-9.

5-10.

5-1 1.

Butland, A. T . D . , and R. J. Maddison, "The S p e c i f i c Heat of Graphite:

An Evaluat ion of Measurements," J. Nucl. Mater. 49, (1973-74).

P r i c e , R. J . , " S t a t i s t i c a l Study of the S t r eng th of Near-Isotropic

Graphi te ," ERDA Report GA-A13955, General Atomic Company, May 24, 1976.

Weibull , W . , "A S t a t i s t i c a l Theory f o r t h e S t r eng th of Materials,"

Hand. Ing. V e t . Akad., Proceedings, Royal Swedish I n s t i t u t e f o r

Engineering Research, Stockholm, N r . 151, 1939.

P r i c e , R. J . , and H. R. W. Cobb, "Applicat ion of Weibull S t a t i s t i c a l

Theory t o t h e S t r eng th of Reactor Graphi te ," Proceedings, Conference

on Continuum Aspects of Graph i t e Design (CONF-701105), USAEC Techni-

c a l Information Center , 1972, p. 547.

Brock lehur s t , J. E . , and M. I. Darby, "Concerning t h e F r a c t u r e of

Graph i t e Under D i f f e r e n t T e s t Conditions," Mater. Sc i . En&. 16, 91

(1974).

Engle, G. B . , and R. J. Price, "Strength Tes t ing of Product ion Grade

H-451 Graph i t e ; Lo t s 472, 478 and 482," ERDA Report GA-A14269, General

Atomic Company, March 1977.

P r i c e , R. J . , "Cycl ic Fa t igue of Near-Isotropic Graphi te : In f luence

of S t r e s s Cycle and Neutron I r r a d i a t i o n , " DOE Report GA-A14588,

General Atomic Company, December 1977.

L e i c h t e r , H. L . , and Robinson, E . , "Fat igue Behavior of a High-

Densi ty Graphi te and General Design C o r r e l a t i o n , " J. Am. Ceram. SOC.

3, 197 (1970).

,

n

5-32

6. IRRADIATION PROGRAM

6.1 . INTRODUCTION

The p r o p e r t i e s of H-451 g r a p h i t e dur ing i r r a d i a t i o n under HTGR condi-

t i o n s of f luence and temperature are r equ i r ed f o r des ign and s a f e t y ana lyses .

I r r a d i a t i o n behav io ra l s t u d i e s of H-451 g r a p h i t e began wi th t h e i r r a d i a -

t i o n of grade H-429 i n a series of BNWL capsu le s i n t h e ETR.

specimens were l a t e r t r a n s f e r r e d t o GA's OG capsule series and i r r a d i a t i o n

cont inued i n t h e ORR. I r r a d i a t i o n of H-451 w a s i n i t i a t e d i n t h e OG capsu le

series. Capsules OG-1, -2, and -3 w e r e i r r a d i a t e d a t 823 t o 1623 K (550' t o

135OOC) t o a peak f luence of 9 x

6-3). By ope ra t ing t h e t h r e e capsu le s i n series i t w a s p o s s i b l e t o o b t a i n

complete da ta sets over t h e f luence and temperature range of t he HTGR. The

capsu le s were i r r a d i a t e d over a per iod of approximately 5 y e a r s , and spec i -

mens from t h e GLCC development program were i n s e r t e d i n t o t h e program as they

became a v a i l a b l e . Specimens from H-451 l o t s 266, 408, and 426 were i r r a d i -

a t e d a long wi th grade H-429.

The H-429

(Refs . 6-1, 6-2, N/m (E > 29 fJ)HTGR 2

Dimensional changes and changes i n t e n s i l e s t r e n g t h , e l a s t i c modulus

and s t r a i n a t f r a c t u r e , f a t i g u e behavior , thermal expans iv i ty , thermal con-

d u c t i v i t y , and i r r a d i a t i o n c reep w e r e determined. Within-log and between-log

v a r i a t i o n s i n dimensional changes and p r o p e r t i e s were determined. Some of

t he specimens were interchanged w i t h i n t h e capsu le s on subsequent i r r a d i a t i o n s

t o provide d a t a on t h e e f f e c t on dimensional changes of i n c r e a s i n g and

dec reas ing t h e temperature du r ing i r r a d i a t i o n .

Figure 6-1 shows t h e f luences and temperatures of t h e HTGR covered by

t h e i r r a d i a t i o n d a t a . I n some i n s t a n c e s t h e i r r a d i a t i o n d a t a exceed t h e

temperature and f luence range of t h e r e a c t o r .

Capsule des ign and c o n s t r u c t i o n d e t a i l s are given i n Refs . 6-1, 6-2,

and 6-3. The i r r a d i a t i o n d a t a presented a r e e x c l u s i v e l y €or H-451 except

f o r changes i n thermal expans iv i ty and conduc t iv i ty , where d a t a from grades

6-3

ENVELOPE FOR FIRST RELOAD SEGMENT.4 YEAR FUEL, 3000 MWM REACTOR

ESTIMATED CURVE 10 \ /FOR LEA0 PLANT

8 -

6 -

4 -

2 -

0 -

/ /

/ /

I I

DIMENSIONS AN0 THERMAL EXPANSIVITY

a W + I - I 1 c u : 10

Y

N

S 8

= z

L n N

THERMAL CONDUCTIVITY 6 I

w 0 z w 3 U - I 4 z 0 a I - 2 a Y

z z o a

lo t I

4 :i 2

/' LOT266 [I TENSILE STRENGTH AND ELASTIC MODULUS

- K 673 873 1073 1273 1413 1673 "C 400 600 800 1000 1200 1400

TEMPERATURE ("C) t

F i g . 6-1. H-451 graphite irradiation data

6-2

Q

TS-1240 manufactured by Union Carbide Corporat ion and grade SO818 by AirCo

Speer D iv i s ion of A i r Reduction Corpora t ion were inc luded . These grades

w e r e a l s o manufactured f o r u se as f u e l element g r a p h i t e s i n HTGRs and are

similar t o grade H-451. The TS-1240 and SO818 specimens were i r r a d i a t e d i n

t h e same c r u c i b l e s w i t h t h e H-451 specimens.

6 . 2 . SAMPLING

Diagrams o f t h e sampling procedures f o r i r r a d i a t i o n t e s t i n g are given

i n Appendix A, F igs . A-1, A-12, and A-13 . The specimens were taken from

s l a b s which were removed from t h e same l o g s as those used f o r t h e c h a r a c t e r i -

z a t i o n s t u d i e s .

s e c t i o n of t h e l o g and from t h e same specimen popu la t ion as those used f o r

i r r a d i a t i o n .

Un i r r ad ia t ed c o n t r o l specimens were taken from t h e same

6.3. DIMENSIONAL CHANGES

Dimensional change d a t a are r epor t ed as pe rcen t s t r a i n [ ( a - l lo ) /k0 x

1001, where R is t h e p o s t i r r a d i a t i o n l e n g t h and Ro i s t h e o r i g i n a l

( u n i r r a d i a t e d ) l eng th .

6 .3 .1 . 873 t o 1673 K (600' t o 14OO0C)

6.3.1.1. I so thermal Dimensional Changes. I n capsu le OG-3, t h e t h i r d i n the

OG capsu le series, 219 a x i a l and 170 r a d i a l dimensional change specimens of

H-451 g r a p h i t e w e r e i r r a d i a t e d . Many of t h e s e specimens w e r e p rev ious ly

i r r a d i a t e d i n capsu le s OG-I and -2 (Refs. 6-1, 6-2); t hus , t h e t o t a l f a s t

f l u e n c e of some of t h e s e H-451 specimens exceeded t h e l i f e t i m e f l u e n c e f o r

HTGR f u e l element b locks .

Specimens were i r r a d i a t e d a t average temperatures ranging from 887 t o 1673 K (600' t o 1400'C) t o t o t a l f a s t neut ron f luences of 1.6 t o 9 . 2 x 10 25

n/m (E > 29 fJIHTGR. The d a t a are shown i n Appendix B , Fig. B - 3 through 2

6-3

B-10. The c losed symbols i n t h e f i g u r e s r e p r e s e n t i r r a d i a t i o n d a t a from

previous OG series capsu le s , whereas t h e open symbols r e p r e s e n t t h e d a t a

from capsule 0 6 3 .

Q

Radial H-451 specimens were i r r a d i a t e d t o f l u e n c e s s u f f i c i e n t t o show

turnaround i n dimensional change and, i n two specimens, a small n e t r a d i a l

expansion. The ear l ies t change i n l i n e a r dimensional change t o n e t expan-

s i o n occurred i n H-451 g r a p h i t e i r r a d i a t e d a t approximately 1273 K (lOOO°C) . Radial specimens appear t o go t o n e t expansion when exposed t o approximately

9 x N/m (E > 29 fJ)HTGR neu t ron f luence. Higher i r r a d i a t i o n tempera-

t u r e s create a g r e a t e r i n i t i a l c o n t r a c t i o n which d e l a y s crossover t o n e t

expansion u n t i l a f a s t f l uence of g r e a t e r than 9 x

2

2 N/m (E > 29 fJ)HTGR.

These d a t a and r e l a t e d e f f e c t s were inco rpora t ed i n t o t h e des ign curves

fo l lowing t h e procedures outlined i n R e f . 6-2. Isothermal s e c t i o n s through

the design s u r f a c e are shown i n Fig. 6-2.

6 . 3 . 1 . 2 .

A f t e r i r r a d i a t i o n i n capsu le O G l , two sets of f o u r a x i a l and f o u r r a d i a l

specimens were interchanged between two c r u c i b l e s f o r t h e nex t two i r r a d i a -

t i o n increments .

948 K (675OC) and 1323 K (1O5O0C), r e s p e c t i v e l y .

p re sen ted i n Fig. 6-3; i so the rma l curves are included i n t h e f i g u r e . When

t h e i r r a d i a t i o n temperature o f t h e a x i a l specimens was inc reased , t h e shr ink-

age ra te inc reased t o t h a t of specimens i r r a d i a t e d i s o t h e r m a l l y a t t h e

h i g h e r temperature.

t h e i r i r r a d i a t i o n temperature was reduced, b u t remained h i g h e r t han t h a t of

specimens i so the rma l ly i r r a d i a t e d a t t h e lower temperature t o t h e same

f luence.

correspond t o t h e lower temperature i so the rma l curve e x t r a p o l a t e d t o t h e

h i g h e r s t r a i n of t h e stepped-down specimens. The d a t a p o i n t s f o r r a d i a l

specimens are t o o c l o s e l y c l u s t e r e d t o draw f i r m conclusions, b u t t h e t r e n d s

appear similar t o those of t h e a x i a l specimens.

E f f e c t of Changing I r r a d i a t i o n Temperature on Dimensional Changes.

The mean o p e r a t i n g temperatures of t h e c r u c i b l e s w e r e

The dimensional changes are

The sh r inkage rate of axial specimens decreased when

The shape of t h e curves sugges t s t h a t t h e new sh r inkage rate may

6-4

- 2 t -3 t -4 t

I 1 I I I 1 I I I I 0 1 2 3 4 5 6 7 8 3 10

FAST NEUTRON FLUENCE N/m2) (E > 29 FJ)HTGR

(b) AXIAL 1

1225 K (952OC) \ / ' A

0

-1

I I - -2 I I I I I I I I I

0 1 2 3 4 5 6 7 8 9 10

FAST NEUTRON FLUENCE N/m2) (E > 29 FJ)HTGR

Fig. 6-2 . I r r ad ia t ion - induced dimensional change i n H-451 g r a p h i t e (design cu rves ) : (a) a x i a l d i r e c t i o n , (b) r a d i a l d i r e c t i o n

6-5

- 1

2 - $ -2 a W a z I u J

z v) z W

0

a

a '1

z -3

0

-1

AXIAL

h ISOTHERMAL e- 948 - 1323 K

-b - 1323 - 948 K (675'- 1050'C)

(1050' -675'C)

1338 K - 1068'C)

1338 K - 1068'C)

RAOIAL

2 4 6 8 10

FAST NEUTRON FLUENCE (1025 N I ~ ) (E > 29 FJ)HTGR

0711 I

Fig. 6-3. Dimensional changes i n H-451 graphite irradiated with changes i n temperature (from Ref.6-3)

6-6

6.3.1.3.

Severa l groups of H-451 specimens were made up from t h r e e d i f f e r e n t l ogs from

t h e same l o t .

included. Four o r f i v e r e p l i c a t e s w e r e used f o r each l o t and l o c a t i o n .

Between-Log and Within-Log Var i a t ions i n Dimensional Change.

I n some cases, specimens from t h e MLC and MLE i n thei l o g were

A f t e r p o s t i r r a d i a t i o n l eng th measurements, t h e d a t a were analyzed by t h e

ana lys i s -of -var iance method t o f ind whether t h e between-log and within- log

v a r i a t i o n s were s t a t i s t i c a l l y s i g n i f i c a n t .

ana lyses of va r i ance are given i n Tables 6-1 and 6-2.

n e i t h e r t h e between-log nor t h e wi th in- log v a r i a t i o n s were s i g n i f i c a n t a t

t h e 95% confidence l e v e l .

specimens were n o t s t a t i s t i c a l l y s i g n i f i c a n t f o r H-451 g raph i t e .

Summaries of t h e r e s u l t s of t h e

For H-451 g r a p h i t e ,

Di f fe rences i n shr inkage between MLC and MLE

6.3.2. 573 t o 873 K (300' t o 60OoC)

Only a few d a t a p o i n t s are a v a i l a b l e on H-451 g r a p h i t e below 827 K

(600'C) from t h e OG capsu le series. Therefore , t h e main body of d a t a f o r

low-temperature i r r a d i a t i o n dimensional changes has been taken from UKAEA

r e s u l t s (Ref. 6-4) on a nea r - i so t rop ic g r a p h i t e (code No. P I ) i r r a d i a t e d

i n t h e Dounreay F a s t Reacter (DFR) a t temperatures between 633 and 873 K

(360' and 600OC).

paper (Ref. 6-5). The UKAEA g r a p h i t e w a s manufactured wi th nea r - i so t rop ic -6

coke and had a thermal expans iv i ty a t 293 t o 393 K (20' t o 120'C) of 3 x 10

K ("C-') p a r a l l e l t o e x t r u s i o n ( a x i a l ) and 4.1 x 10 K ("C ) perpendic-

u l a r t o e x t r u s i o n ( r a d i a l ) . Therefore , i t s dimensional change behavior i s

expected t o be s i m i l a r t o t h a t o f H-451.

The UKAEA r e s u l t s were c o l l e c t e d and analyzed i n a review

-1 -6 -1 -1

The d a t a p o i n t s from Ref. 6-4 a re g iven i n Appendix B , F igs . B-11 and

B-12. The f i g u r e s a l s o inc lude Dragon d a t a on extruded nea r - i so t rop ic

g r a p h i t t s ( g r a p h i t e r e fe rence numbers 100 and 120 from Ref. 6-6). A few GA

d a t a p o i n t s on H-451 g r a p h i t e are a l s o included. Agreement between the

t h r e e sets of d a t a is good.

0 No i r r a d i a t i o n d a t a below 360' t o 400 C have been r epor t ed f o r near- iso-

t r o p i c g raph i t e s . However, r e s u l t s f o r PGA (needle-coke) g r a p h i t e i r r a d i a t e d

i n D I D O and PLUTO a t 573, 623, and 723 K (300°, 350°, and 450'C) are a v a i l a b l e

6-7

TABLE 6-1 WITHIN-LOG VARIATION I N IRRADIATION-INDUCED SHRINKAGE OF H-451 GRAPHITE, LOT 426

Or ien ta t ion Cruc ib l e Edge of

Logs

0.75

0.18

0.30

1210 (9 37)

l l lO(837)

1200 (927)

S i g n i f i c a n t a t 95% Confidence Level?

No

No

No

Mean Shrinkage (%) Fas t Is Var i a t ion

~

Axial

Rad i a l

R a d i a l

Center of Neutron

Fluence x 10-25 [N/m2 (E > 29 fJ)HTCRl

6

8

3

2.68 I 0.71

Log 6484-34 Log 6L84-41

2.01 1 0.18

S i g n i f i c a n t a t 95% Confidence Level?

2.83 1 0.36

Axial

Radial

Radia l

R a d i a l

Radial

6 1 ZlO(937)

1 910 (637)

8 11 lO(837)

3 1200 (9 27)

6 1270(997)

TABLE 6-2 BETWEEN-LOG VARIATIONS I N IRRADIATION-INDUCED SHRINKAGE OF H-451 GRAPHITE, LOT 426

2.68

1.84

2.01

2.83

2.68

Mean Shrinkage (%) Fas t 1 Temp. I Fluence x I r r a d . Neutron

0.71

0.18

0.17

0.28

0.79

Or ien ta t ion I Crucib le 1 K ('C) I [ ~ / m 2 (E > 29 ~J)HTGR] I Log 6484-33

0.79

0.16

0.20

0.36

0.82

0.69

0.14

0.19

0.36

0.79

I Is Var ia t ion

No

No

No

No

No

.o *

(Ref. 6 - 7 ) . The probable behavior o f nea r - i so t rop ic g r a p h i t e a t 573 K

( 3 0 0 C ) can be p red ic t ed from t h e P(:A d n t n by c a l c u l a t i n g t h e volumetr ic

shr inkage r a t e s a t 573 and 7 2 3 K (300" and 450 C ) and assuming t h a t t h e r a t i o

between t h e ra tes a t t h e s e two tempera tures i s t h e same f o r nea r - i so t rop ic

g r a p h i t e and PGA. This procedure was appl ied t o t h e nea r - i so t rop ic 7 2 3 K

(450°C) experimental d a t a i n F igs . B-11 and B-12. The c a l c u l a t e d 573 K

(300'C) volumetr ic sh r inkages were then converted t o l i n e a r shr inkage by

assuming t h a t t h e r a t i o of a x i a l t o r a d i a l sh r inkage is t h e same a t 573 K

(300OC) as a t 7 2 3 K (45OOC).

0

0

6 . 4 . TENSILE STRENGTH, ELASTIC MODULUS, AND STRAIN AT FRACTURE

6 . 4 . 1 . 823 t o 1623 K (550' t o 135OOC)

Approximately 500 t e n s i l e tests measured a t ambient temperature were

conducted on H-451 g r a p h i t e specimens from l o t s 2 6 6 , 4 0 8 , and 426 i r r a d i a t e d

a t several d i f f e r e n t f l uences and temperatures i n capsu le s OG-1, - 2 , and - 3 .

The pe rcen t i n c r e a s e s i n t e n s i l e s t r e n g t h and e l a s t i c modulus ( r e f e r -

enced t o u n i r r a d i a t e d c o n t r o l specimens from t h e same l o c a t i o n i n t h e same

log ) are p l o t t e d as func t ions of f a s t neut ron f luence i n Fig. B-13. For

H-451 g r a p h i t e , t h e d a t a f o r a l l o r i e n t a t i o n s , l o c a t i o n s , and l o t s f a l l i n

t h e same sca t te r bands.

The s t a t i s t i c a l sp read i n s t r e n g t h va lues i s an impor tan t parameter i n

t h e mechanical des ign o f g r a p h i t e s t r u c t u r e s . I r r a d i a t i o n causes a s i g n f i -

can t i n c r e a s e i n t h e s t anda rd dev ia t ion . However, t h e c o e f f i c i e n t o f varia-

t i o n ( s t anda rd d e v i a t i o n d iv ided by t h e mean) i s una f fec t ed by i r r a d i a t i o n .

The e s t ima ted c o e f f i c i e n t of v a r i a t i o n showed no d e f i n i t e t r e n d w i t h irra-

d i a t i o n .

Design curves p r e s e n t l y used f o r t h e i r r ad ia t ion - induced i n c r e a s e i n

e l a s t i c modulus (Ref. 6-2 ) are based on Dragon p r o j e c t d a t a (Ref. 6-6 ) f o r

change i n s o n i c e l a s t i c modulus o f a n e a r - i s o t r o p i c p i t c h coke g r a p h i t e .

The Dragon d a t a cover a wide range o f tempera tures and f luences ( see F ig .

6-9

B-14) .

Dragon curves. The design cu rves as shown i n Fig. B-13 from R e f . 6-2 w i l l

The GA d a t a on H-451 g r a p h i t e a r e i n e x c e l l e n t agreement wi th t h e

cont inue t o be used.

A design method f o r account ing f o r t h e i r r ad ia t ion - induced s t r e n g t h

increase. u t i l i z i n g all t he a v a i l a b l e d a t a i s recommended (Ref . 6 - 3 ) . The

i n c r e a s e i n s t r e n g t h S i s assumed t o be r e l a t e d t o t h e i r r ad ia t ion - induced

i n c r e a s e i n e l a s t i c modulus E as fol lows:

s/so = ,

where t h e exponent k depends on t h e g r a p h i t e grade.

0 .64 f o r a x i a l and r a d i a l specimens w a s ob ta ined from t h e c u r r e n t H-451 d a t a .

This k v a l u e i s r e f l e c t e d i n t h e design curves f o r t h e s t r e n g t h d a t a p l o t t e d

i n F ig . B - 1 3 .

An average k va lue of

6 .4 .2 . 627 t o 873 K (350' t o 600'C)

Measurements of changes i n e l a s t i c modulus (by a s o n i c method) and

s t r e n g t h ( t e n s i l e and b r i t t l e - r i n g t e s t s ) were ob ta ined on n e a r - i s o t r o p i c

g r a p h i t e i r r a d i a t e d i n t h e DFR under t h e UKAEA program (Refs. 6-4 , 6-8).

Resu l t s from R e f . 6-8 f o r material i r r a d i a t e d a t 623 t o 7 1 3 K (350' t o 44OOC)

are shown i n Appendix B , Fig. B-15. The f r a c t i o n a l i n c r e a s e i n s t r e n g t h

equa l s t h e squa re r o o t o f t h e f r a c t i o n a l i n c r e a s e i n t h e e las t ic modulus,

i n d i c a t i n g t h a t t h e s t r a i n energy t o f a i l u r e remains cons t an t .

(Ref. 6 - 4 ) show t h a t t h i s r e l a t i o n h o l d s t o about 3 x N / m

(E ' 29 fJ)HTGR (2 x

somewhat a t h ighe r f luences .

Later d a t a 2

2 N/m NDE), b u t t h e s t r e n g t h may dec rease

Dragon has r epor t ed (Ref. 6 - 6 ) changes i n t h e s o n i c e las t ic modulus of

n e a r - i s o t r o p i c g r a p h i t e s i r r a d i a t e d a t 673 and 873 K (400' and 600OC) t o

( 3 t o 4 x NDE). The f luences of 4.5 t o 6 x N / m (E > 29 fJ lHTGR

Dragon d a t a are shown i n Appendix B , Fig. B-14. The 673 K (40OOC) i n c r e a s e s

are c o n s i s t e n t w i th t h e h i g h e r f luence d a t a a l s o shown i n Fig. B-14. Design

curves f o r t h e s t a t i c e l a s t i c modulus have been de r ived from t h e Dragon d a t a

2

6-30

n

(Ref. 6 - 6 ) u s i n g a m u l t i p l e of 0 . 8 t o convert dynamic modulus t o s t a t i c

modulus ( u n i r r a d i a t e d g r a p h i t e ) and a m u l t i p l e of 0.6 t o convert f l uence

( E > 29 f.J) to f luence (NDE) (Ref. 6 - 3 ) . F o r i r r a d i a t e d g r a p h i t e , t he s o n i c

and s t a t i c e l a s t i c moduli were assumed q u a l . Curves f o r temperatures o t h e r

than 673 and 873 K (400' and 600'C) were ob ta ined by i n t e r p o l a t i o n .

c a l c u l a t e d design curves are shown i n Appendix B , Fig. B-16. For t h e low-

temperature d a t a , t h e i n c r e a s e i n s t r e n g t h w a s assumed equa l t o t h e squa re

r o o t of t h e i n c r e a s e i n modulus (Ref. 6 - 5 ) :

The

However, E q . 6-1 w a s used i n the design d a t a manual (GA-A14428; see Sec t ion

2 ) f o r t h e temperature range 6 2 3 t o 1673 K (350' t o 1400'C).

6 .4 .3 . Between-Log and Within-Log Var i a t ions i n S t r eng th Inc rease

Three groups of t e n s i l e specimens of H-451 g r a p h i t e were made up from

t h r e e d i f f e r e n t l o g s from lot 4 2 6 , and t h r e e groups contained specimens from

both t h e MLC and t h e MLE. Five o r more r e p l i c a t e specimens were used from

each l o g and l o c a t i o n . The i r r ad ia t ion - induced pe rcen t s t r e n g t h i n c r e a s e s

( r e fe renced t o c o n t r o l specimens from t h e s a m e l o g and l o c a t i o n ) were

analyzed by t h e analysis-of-var iance method. I n d i v i d u a l s t r e n g t h va lues are

given i n R e f . 6 - 3 . The r e s u l t s of t h e comparison are summarized i n Tables

6-3 and 6-4. Among one group of specimens, t h o s e from one l o g showed a

s i g n i f i c a n t l y smaller i n c r e a s e than those from t h e o t h e r two l o g s , b u t t h i s

was n o t t h e case f o r t h e o t h e r two groups ( s e e Table 6 - 3 ) .

s i g n i f i c a n t d i f f e r e n c e s i n t h e s t r e n g t h i n c r e a s e s between specimens from t h e

c e n t e r of t h e l o g and specimens from t h e edge of t h e l o g ( s e e Table 6 - 4 ) .

There were no

6-1 1

TABLE 6-3 BETWEEN-LOG VARIATIONS I N IRRADIATION-INDUCED STRENGTH INCREASE OF H-4 51 GRAPHITE,

~~

Orienta t ion

Radial

Radial

Axial

LOT 426

F a s t Neutron Mean Strength Increase (%) -25 I r r a d . Fluence x 10 Temp,

Crucible No. K ("C) [ N h 2 (E > 29 fJ>HTGF] Log 6484-33 Log 6484-34 Log 6484-41

8 1 1 l O ( 8 3 7 ) 2.01 28 32 39

6 1 210(937) 2.68 41 56 48

3 1200 (9 2 7 ) 2.83 57 35 60

Crucible No.

1

8

6

QI 1 L N

I r r a d . Fas t Mean S t rength Increase (%) Is Var ia t ion

K ("C) [ N / m 2 (E > 29 fJ)HTGR] Center of Logs Edge of Logs Confidence Level?

940( 6 6 7 ) 4.6 33 4 3 No

1150(877) 4.1 31 44 No

1210(937) 2.7 50 46 N o

S i g n i f i c a n t a t 95% -25 Temp , Neutron Fluence x 10 Lot No.

4 08

408

4 26

-

Is Varia t ion S i g n i f i c a n t a t 95% Confidence Level?

No Yes

No

i

6.5. FATIGUE BEHAVIOR

6.5.1. Sampling and Procedures

The experimental procedures descr ibed f o r u n i r r a d i a t e d specimens i n

Sec t ion 5.4.2 were a l s o used t o test i r r a d i a t e d specimens. Specimens were

taken from the s a m e reg ions as those f o r i r r a d i a t e d t e n s i l e s t r e n g t h t e s t i n g .

Three groups of H-451 specimens were i r r a d i a t e d i n g r a p h i t e c r u c i b l e s i n

capsules OG-1, -2, and -3 (Refs. 6-1, 6-2, 6-3). The specimens were i r r a d i -

a t e d a t 1173 t o 1273 K (900' t o 1000°C) t o d i f f e r e n t neut ron f luence expo-

s u r e s . Ten specimens ou t of each group were t e n s i l e - t e s t e d i n t h e f a t i g u e

machine t o e s t a b l i s h t h e mean t e n s i l e s t r e n g t h . The va lues are l i s t e d i n

Appendix B y Table B-11, t oge the r wi th t h e s t r e n g t h s of u n i r r a d i a t e d companion

specimens from the same l o c a t i o n i n t h e l o g and t h e i r r a d i a t i o n cond i t ions .

A l l groups showed the expected i n c r e a s e i n s t r e n g t h a f t e r i r r a d i a t i o n . The

remainder of t h e specimens i n each group were used f o r tension-compression

f a t i g u e tests (R = - 1 ) .

l e v e l s u n t i l they f a i l e d o r reached 100,000 cyc le s wi thout f a i l u r e .

E ight specimens were cycled a t each of fou r stress

6.5.2. Experimental Resul t s and Discussion

A homologous stress S-N curve (analogous t o t h e curve f o r u n i r r a d i a t e d

specimens i n F ig . B-1) f o r a x i a l specimens of H-451 g r a p h i t e i r r a d i a t e d t o

a t 1173 K (900°C) is shown i n Appendix B, 3.0 x lo2' N / m (E > 29 fJ>HTGR

Fig . B-17. Comparison between t h e r e s u l t s i n Fig. B-17 and t h e u n i r r a d i a t e d

r e s u l t s (Fig. B-1) shows t h a t t h e homologous stress l i m i t s f o r f a t i g u e

endurance are increased by neut ron i r r a d i a t i o n . The r e s u l t s of s t a t i s t i c a l

ana lyses of t h e S-N curves f o r a l l t h e i r r a d i a t e d H-451 specimens are g iven

i n Table 6-5. The homologous stress l i m i t s f o r s u r v i v a l t o IO5 c y c l e s are

s u b s t a n t i a l l y h igher than f o r u n i r r a d i a t e d H-451 t e s t e d wi th R = -1 (Table

6-5), a t least f o r t h e axial specimens. The homologous stress 99/95 lower

t o l e r a n c e l i m i t is lower a t h ighe r f l u e n c e s as t h e r e s u l t of increased d a t a

s c a t t e r , bu t i t remains above the u n i r r a d i a t e d level . The increased s c a t t e r

may b e caused by s l i g h t warpage i n t h e h igh ly i r r a d i a t e d specimens, which

i n t e r f e r e s wi th a c c u r a t e u n i a x i a l a l ignment i n t h e test r i g .

2

6-13

TABLE 6-5 RESULTS OF STATISTICAL ANALYSIS OF FATIGUE DATA FOR H-451 GRAPHITE IRRADIATED AT

1173 t o 1263 K (900' t o 990'C) (STRESS RATIO, R = -1)

S tanda rd Dev ia t ion

s ( a )

0.046

0.044

0.056

0 Homologous S t r e s s L i m i t max/S f o r S u r v i v a l t o 105 c y c l e s ( a )

99 /95 Lower 50% P r o b a b i l i t y To le rance L i m i t

0 .93 0 .66

0.74 0.54

0.81 0.51

(a)Based on t h e model of Eq. 5-11.

O r i e n t a t i o n

rn A x i a l I 1l .b Rad i a l

Ax ia l

I n t e r c e p t of Least Sq a es

Line a 'tat

F a s t Neutron Fluence N / m 2 )

(HTGR)

3 .O

5.7

8 . 5

--

-0.010

-0.020

-0.033

Slope of Least Squares

L ine ~ ( a )

-0.004

-0.022

-0.012

I f t h e f a t i g u e stress l i m i t s are normalized by d i v i d i n g by t h e u n i r r a -

d i a t e d t e n s i l e s t r e n g t h i n s t e a d of tlie i r r a d i a t e d t e n s i l e s t r e n g t h , t h e

l i m i t s i n c r e a s e by more than a f a c t o r o f two dur ing i r r a d i a t i o n . The stress

l i m i t s f o r 50% s u r v i v a l t o 10 cyclcs and t h e 99/95 lower t o l e r a n c e l i m i t s

normalized t o t h e u n i r r a d i a t e d s t r e n g t h a r e p l o t t e d a g a i n s t neut ron f luence

i n F ig . 6-4.

5

6 . 6 . THERMAL EXPANSIVITY

6 .6 .1 . 823 t o 1623 K (550' t o 135OOC)

Thermal expans iv i ty measurements were made on H-451 g r a p h i t e ( 1 0 ~ s 266

and 426) and H-429 (Refs. 6-1, 6-2, 6-3). A l l except H-451 ( l o t 426) had

been i r r a d i a t e d i n prev ious capsules . Data on grades TS-1240 and SO818 are

inc luded ( see Sec t ion 6 . 1 ) . Measurements were made between room tempera ture

and up t o 100 K ( " C ) below t h e i r r a d i a t i o n temperature .

The a c c u m u l a t e d d a t a on n e a r - i s o t r o p i c g r a p h i t e s H-451, H-429,

TS-1240, and SO818 from capsu le s OG-1, -2 , and -3 are summarized i n Appendix

B , Tables B-12 through B-15. The f r a c t i o n a l change i n thermal e x p a n s i v i t y

is p l o t t e d as a func t ion o f f a s t neut ron f luence i n Appendix B , F igs . B-18

and B-19. A t t h e lowest i r r a d i a t i o n temperatures [865 t o 1045 K (592 ' to

772"C)I t h e thermal expans iv i ty f i rs t i n c r e a s e s by 5% t o 10% and then

s l o w l y dec reases . A t h ighe r i r r a d i a t i o n temperatures , t h e thermal expansi-

v i t y dec reases by as much as 50% of i t s p r e i r r a d i a t i o n va lue , w i th t h e

dec rease most marked a t t h e h i g h e s t i r r a d i a t i o n temperatures . Data from

a l l t h e n e a r - i s o t r o p i c g r a p h i t e s f a l l i n t o t h e same band r e g a r d l e s s o f

o r i e n t a t i o n and l o g l o c a t i o n , w i t h t h e excep t ion o f H-429, f o r which i r r a d i a -

t ion-induced changes i n thermal e x p a n s i v i t y are somewhat lower than t h e

o t h e r s .

For convenience i n des ign c a l c u l a t i o n s , t h e d a t a f o r i r r ad ia t ion - induced

f r a c t i o n a l changes i n thermal expans iv i ty , (ai - a ) / a o , of t h e H-451 and

o t h e r n e a r - i s o t r o p i c g r a p h i t e s were f i t t o t h e fo l lowing polynomial (Ref. 0

6-9) :

6-15

16 c

1 0

0 8

0 6

1 4

1 2

0 8

A A X I A L , 50" S U R V I V A L

0 0 R A D I A L , 50 S U R V I V A L 0

A X I A L . 9 9 95 LOWER TOLERANCE L I M I T

RADIAL, 99'95 LOWER TOLERANCE LIMIT 0 R A D I A L , 50 I S U R V I V A L 0 RADIAL, 93/95 LOWER TOLERANCE LIMIT

H-451 GRAPHITE IRRAOIATED AT 1173 1263K REVERSED STRESS CYCLE IR = - 1 )

FAST NEUTRON FLUENCE 11025N:m2) (E >29 fJ)HTGR

5 Fig. 6 - 4 . Fa t igue stress l i m i t s f o r s u r v i v a l of H-451 g r a p h i t e t o 10 normalized t o the u n i r r a d i a t e d t e n s i l e s t r e n g t h , v e r s u s t h e f a s t neu t ron f l u e n c e a t a n i r r a d i a t i o n temperature of 1173 t o 1263 K

c y c l e s ,

(900" to 990°C)

I

d3 -7 2 (ai - ao)/ao = (0.27830 - 4.2734 x T + 1.7815 x 10 T ) @

(6-4) -2 2 -3 @3 -2.0664 x 10 @ + 1.3601 x 10

where T is t h e i r r a d i a t i o n temperature ("C) and @ is t h e neutron f luence

(lo2' N / m 2 ( E > 29 fJ)HTcR]. Curves ca l cu la t ed from the equat ion a re

i n c l u d e d i n Appendix B , Figs. B-18 and 11-19. The s tandard d e v i a t i o n of d a t a

point-s from the des ign curves i s 0.063.

6.6.2. 623 t o 823 K (350' to 55OoC)

The thermal expans iv i ty d a t a of nea r - i so t rop ic g r a p h i t e samples i r r a d i a t e d

i n t h e DFR (Ref. 6-4) a r e reproduced i n Appendix B, Fig . B-20. No i r r a d i a -

t i o n temperature e f f e c t is apparent f o r t h e temperature range 623 t o 823 K

(350' t o 5 5 O O C . )

The r a t i o of p o s t i r r a d i a t i o n thermal expans iv i ty t o p r e i r r a d i a t i o n

expans iv i ty taken from Fig . B-20 i s t abu la t ed a s a func t ion of f a s t f l uence

i n Table 6-6.

a t temperatures between 573 and 873 K (300' and 600') are der ived from t h e

f a c t o r s i n Table 6-6.

The thermal expans iv i ty of nea r - i so t rop ic g r a p h i t e i r r a d i a t e d

6.7. THERMAL CONDUCTIVITY

6.7.1. 923 to 1623 K (650" to 1350°C)

Thermal d i f f u s i v i t y measurements were made on d i s c s of H-451 ( l o t s 266

and 426) g r a p h i t e i r r a d i a t e d a t t h r e e tempera tures [(925, 1220, and 1615 K (652", 9 4 7 " , and 1342OC)I (Ref. 6-3). The H-451 specimens from l o t 266

had been previous ly i r r a d i a t e d i n earlier OG capsu le s (Refs. 6-1, 6-2). The

measurements were made by the hea t -pulse method and t h e thermal d i f f u s i v i t y

va lue w a s converted t o t h e thermal conduc t iv i ty by mul t ip ly ing by t h e den-

s i t y and hea t capac i ty .

temperature and 1073 K (800°), except for t he specimens i r r a d i a t e d a t 925 K

Readings were taken every 100 K (OC) between ambient

(652OC), when t h e u p p e r measurement t empera tu re w a s l i m i t e d t o 773 K (500 0 C)

t o avoid t h e p o s s i b i l i t y of annea l ing .

6-1 7

TABLE 6-6 INCREASE I N THERMAL EXPANSIVITY OF NEAR-ISOTROPIC GRAPHITE

IRRADIATED BETWEEN 623 AND 823 K (350' AND 55OOC)

' Fas t Fluence [1025N/m2 ( E > 29 fJ)HTGR]

0

5

6

7

8 9

10

11

12

13

14

15

Ra t io of P o s t i r r a d i a t i o n Expans iv i ty t o P r e i r r a d i a t i o n Expans iv i ty a l a ,

1.00

1.09

1 .13

1.15

1.18

1.19

1.20

1.21

1.22

1 . 2 1

1.20

1.20

1.19

1.18

1.18

1.17

6-1 8

llie accumulated d a t a on nea r - i so t rop ic g r a p h i t e s H-451, TS-1240, and

SO818 from capsu le s OG-1, -2, and -3 are summarized i n Appendix B , Tables

B-16, B-17, and B-18. The conduc t iv i ty a t t h e i r r a d i a t i o n temperature is

p l o t t e d as a func t ion of f a s t neut ron f luence i n F ig . B-21. I r r a d i a t i o n

r a p i d l y reduces t h e thermal conduc t iv i ty t o a s a t u r a t i o n l e v e l which

i n c r e a s e s wi th i n c r e a s i n g i r r a d i a t i o n temperature . The thermal conduc t iv i ty

of a l l t h e nea r - i so t rop ic g r a p h i t e s t e s t e d f a l l s i n t o t h e same band a f t e r

i r r a d i a t i o n , even though some d i f f e r e n c e s e x i s t e d i n t h e i r p r e i r r a d i a t i o n

c o n d u c t i v i t i e s . The i r r a d i a t e d va lues are i n e x c e l l e n t agreement wi th t h e

des ign equat ions c u r r e n t l y i n u s e (Ref. 6-2).

6.7.2. 523 t o 923 K (250' t o 650'C)

The thermal conduc t iv i ty ( a t room temperature) of nea r - i so t rop ic

g r a p h i t e s i r r a d i a t e d i n t h e DFR w a s measured by the UKAEA (Ref. 6-8).

Changes i n thermal r e s i s t i v i t y f o r t h e grade (code-numbered P I , p a r a l l e l

t o e x t r u s i o n ) are given i n Ref. 6-8 and are r e p l o t t e d i n Appendix B , F ig .

B-22. Higher f luence resu l t s are conta ined i n Ref. 6-4. A few d a t a

p o i n t s a t 807 t o 923 K (435" t o 650°C) on nea r - i so t rop ic pitch-coke

g r a p h i t e s were repor ted by Dragon i n Ref. 6-6 and t h e s e p o i n t s are a l s o

included i n Fig. B-22.

The experimental d a t a on nea r - i so t rop ic g r a p h i t e s do n o t extend down t o

573 K ( 3 O O O C ) and are no t s u f f i c i e n t t o show t h e shape of t h e curve a t low

f luences . However, a cons ide rab le amount of thermal conduc t iv i ty d a t a on

PGA g r a p h i t e i r r a d i a t e d between 523 and 923 K (250' and 650'C) is a v a i l a b l e

from t h e AGR program (Refs. 6-10, 6-11). Curves taken from Ref. 6-10 showing

the f r a c t i o n a l change i n thermal r e s i s t i v i t y of PGA g r a p h i t e are included i n

Appendix B, Fig. B-22. The s o l i d carves correspond t o experimental d a t a , and

the dashed curves are e x t r a p o l a t i o n s . The d a t a p o i n t s f o r nea r - i so t rop ic

g r a p h i t e are i n good agreement wi th t h e PGA curves .

To o b t a i n va lues u s e f u l f o r des ign , t he f r a c t i o n a l changes i n thermal

r e s i s t i v i t y given by t h e smoo'th curves i n Fig. B-22 w e r e app l i ed t o t h e

measured room temperature conduc t iv i ty of H-451 g r a p h i t e , i n t e r p o l a t i n g

6-1 9

between t h e curves f o r c a l c u l a t i o n s a t in t e rmed ia t e temperatures . The con-

d u c t i v i t y a t t h e i r r a d i a t i o n temperature was c a l c u l a t e d by assuming t h a t f o r

g iven i r r a d i a t i o n cond i t ions , i r r a d i a t i o n adds t h e same increment t o t h e

thermal r e s i s t i v i t y a t a l l measurement temperatures (Ref. 6-12). The r e s u l t s

of t h e c a l c u l a t i o n s are given i n Appendix B, Table B-19.

6.7.3. E f f e c t of Change i n Temperature

Two r a d i a l specimens of H-451 g r a p h i t e which had been i r r a d i a t e d previ-

ous ly i n capsu le OG-1 a t 1623 K (135OOC) w e r e r e i r r a d i a t e d i n OG-3 a t 923 K

(65OoC), and two specimens formerly i r r a d i a t e d a t 873 K (6OOOC) were reirra-

d i a t e d a t 1613 K (1342OC). I n both cases t h e new c o n d u c t i v i t i e s were equal

t o t h e s a t u r a t i o n l e v e l f o r t h e new i r r a d i a t i o n temperature . Th i s behavior

i s c o n s i s t e n t wi th t h e c u r r e n t l y used des ign model f o r t h e conduc t iv i ty of

g r a p h i t e s u b j e c t e d to a changing i r r a d i a t i o n t e m p e r a t u r e .

6.8. IRRADIATION-INDUCED CREEP

Two programs are c u r r e n t l y under way on H-451: (1) compressive c reep

experiments a t ORNL and (2) a t e n s i l e c reep experiment a t RCN and J R C Euratom,

P e t t e n . Creep c o e f f i c i e n t s f o r des ign have been taken froi., an a n a l y s i s of

r e s t r a i n e d shr inkage experiments conducted a t RCN, Pe t t en , on H-451 g r a p h i t e

and a s i m i l i a r molded grade (AGL grade SMI-24) (Ref. 6-13). I r r a d i a t i o n

c reep i n H-451 g r a p h i t e may b e r ep resen ted by t h e equat ion:

- 24 E = 4.16 x u [ l - exp (-5 x 10 y)]exp(1.27 x 10-3T) c r

t 6.2 x u y exp(7.48 x 10-4T)

where E: is t h e t o t a l c r eep s t r a i n ( u n i t l e s s ) , cr u i s t h e app l i ed stress, MPa,

y

T i s the temperature i n K .

2 is t h e f a s t neut ron f luence , N / m (E > 29 fJ)HTGR,

n

6-20

The equa t ion a p p l i e s between 773 and 147'3 K (500" and 12OOOC) t o a f luence of

f o r t e n s i l e s t r a i n s less than 2.5% o r compressive N / m ( E > 29 fJ)HTGR 2

s t r a i n s less than 2%.

6.8.1 . Conclusions

Seve ra l i n v e s t i g a t o r s have e s t a b l i s h e d t h a t t h e form of t h e f a s t -

neutron-irradiation-induced c reep curve f o r g r a p h i t e s c o n s i s t s of a period of

t r a n s i e n t creep, which r a p i d l y s a t u r a t e s , followed by s t e a d y - s t a t e creep,

where the c reep s t r a i n i n c r e a s e s l i n e a r l y wi th f l u e n c e . The on ly p o s s i b l e

except ion appears t o b e Gray's r e s u l t s (Refs. 6-34, 6-15) f o r compressive

c reep i n i s o t r o p i c g r a p h i t e s a t 1073 K (800 C) where t h e c reep rate slowed

down a t f l u e n c e s above 6 t o 7 x sive c reep s t r a i n exceeded 2%. Another p o s s i b l e i n d i c a t i o n of reduced c reep

ra tes a t high f l u e n c e s may be i n f e r r e d from t h e LJKAEA r e s t r a i n e d sh r inkage

r e s u l t s on i s o t r o p i c g r a p h i t e s i r r a d i a t e d i n t h e DFR.

0

when t h e compres- N / m ( E > 29 fJ)HTGR 2

REFERENCES

6-1. P r i c e , R. J . , and L. A. Beavan, "F ina l Report on Graphi te I r r a d i a t i o n

T e s t OG-1," USAEC Report GA-A13089, General Atomic Company, August 1 ,

1974.

6-2. P r i c e , R, J. , and L. A. Beavan, "F ina l Report on Graph i t e I r r a d i a t i o n

T e s t OG-2," ERDA Report GA-A13556, General Atomic Company, December 15,

1975.

6-3. P r i c e , R. J . , and L. A. Beavan, "F ina l Report on Graph i t e I r r a d i a t i o n

T e s t OG-3," ERDA Report GA-Al4211, General A t o m i c Company, January

1977.

6-4. Kel ly , B. T . , e t a l . , "Studies of I r r a d i a t i o n Damage i n Carbons and

Graph i t e s Appropriate t o MK I1 Gas-Cooled Reactors (AGRs) and t h e

MK 111 Gas-Cooled Reactors (HTGRs)," Proceedinns, Fourth UN Int .

Conf. on Peace fu l Uses of Atomic Energy, Geneva, 1971, v. 10, IAEA,

Vienna, 1972, p. 399.

6-2 1

6-5.

6-6.

6-7.

6-8.

6-9.

Price, R. J., "Property Changes in Near Isotropic Graphites Irradiated a t 300°C to 600°C: A Literature Survey," ERDA Report GA-A13478, General Atomic Company, June 13, 1975.

Everett, M. R., et al., "Irradiation Performance and Selection of

Graphites for HTGRs," Dragon Report DP-Report-877, April 1974. . Kelly, B. T., et al., "Dimensional Changes in Polycrystalline Graphite Under Fast-Neutron Irradiation," Phil. Trans. Roy. SOC. London,

Ser. A, 260, 51 (1966). Nettley, P. T., et al., "Irradiation Experiment with Isotropic Graphite," Proceedings, Symposium on Advanced and High Temperature

Gas-Cooled Reactors, JGlich, October 21-25, 1968, IEAA, Vienna, 1969,

p. 603. Price, R. J., "Cyclic Fatigue of Near-Isotropic Graphite: Influence

of Stress Cycle and Neutron Irradiation," DOE Report GA-A14588,

General Atomic Company, December 1977. 6-10. Martin, W. H., and A. M. Price, "Determination of Dose and Tempera-

ture of Graphite Irradiation Experiments in the Dounreay Fast

Reactor," J. Nucl. Energy 2 l , 359 (1967).

6-11. Bridge, H., et al., "Effect of High-Flux Fast-Neutron Irradiation on the Physical Properties of Graphite," Carbon 2, 83 (1964).

6-12. Price, R. J., "Thermal Conductivity of Neutron Irradiated Reactor

Graphites," USAEC Report GA-A13157, General Atomic Company, October

1974.

6-13. Veringa, H. J., and R. Blackstone, "Radiation Creep in Reactor Graphites for Reactor Applications," Carbon - 14, 279 (1976).

6-14. Gray, W. J., "Constant Stress Irradiation Creep Experiments on Graphite," Proceedings of the Carbon - 72 Symposium, Baden-Baden, June 1972.

6-15. Gray, W. J., "Technical Activities Quarterly Progress Report, AEC Reactor Development and Technology Programs, Jan,-Mar., 1971,"

n

USAEC Report BNWL-1522-2, Pacific Northwest Laboratory, 1971, p. 8.1.

n

6-22

7. OXIDATION PROGRAM

Two types of water leaks are important in determining the effect of

steam oxidation on the fuel element: (1) high water concentrations, up to

1000 kPa (10 atm), which may occur in the event of a large steam leak, and

(2) low water concentrations, up to 50 Pa (500 uatm),whichcould occur dur-

ing normal operation.

above on the integrity of the fuel element graphite over the core life of

the fuel elements, it is necessary to determine ( 1 ) oxidation rates of H-451 in steam-helium mixtures as a function of H 0 and H concentration, reaction

temperature, degree of burnof f , and sample configuration, and (2) clxinges in

strength and elastic modulus due to oxidation burnof fs.

To assess the effects of water ingress as described

2 2

7.1. OXIDATION RATE OF H-451 GRAPHITE

7.1 .l. Reaction Rate Theory

Reaction rate theory for steam-graphite reactions is discussed in de-

tail in Refs. 7-1 and 7-2. The extent of the reaction of water vapor with the H-451 graphite i n an HTGR is calculated (predicted) u t i l i z i n g computer

codes OXIDE-3 (Ref. 7-3) and GOP (Ref. 7-4) with appropriate input of reac- tion rate data.

The reaction of water vapor with graphite is controlled by chemical

interactions and mass transport of the gaseous constituents within the pores

of the graphite. Low concentrations of water vapor, up to 50 Pa (500 patm)

water vapor and high concentrations, up to 1000 Pa (10 atm) are discussed.

7- 1

Controversy s t i l l e x i s t s ove r t h e mechanisms involved i n t h e r e a c t i o n of

water vapor wi th g r a p h i t e , b u t t h e r e is gene ra l agreement t h a t t h e chemical

r e a c t i o n s can b e r ep resen ted by t h e Langmuir-Hinshelwood equat ion:

R =

+ pn H2 + K3PH*0

pH20 and are K2, and K where K 1 ,

p a r t i a l p re s su res of water vapor and hydrogen, r e s p e c t i v e l y , F c o r r e c t s t h e

are r a t e c o n s t a n t s , n i s a c o n s t a n t , H2 3

b - r a t e f o r t h e e f f e c t of bu rnof f , and F c o r r e c t s t h e ra te f o r t h e e f f e c t of

c a t a l y t i c r e a c t i o n s due t o f i s s i o n product i m p u r i t i e s introduced i n t o t h e

g r a p h i t e by i r r a d i a t i o n .

q u a n t i f i e d i n H-451 g r a p h i t e ; t h e r e f o r e , c a t a l y t i c e f f e c t s cannot be considered.

C

The e f f e c t s of c a t a l y t i c i m p u r i t i e s have n o t been

The o x i d a t i o n of g r a p h i t e by water vapor c o n s i s t s of t h r e e d i s t i n c t

processes* (Refs. 7-5, 7-6, 7-7): ( 1 ) s o r p t i o n of water molecules on a c t i v e

carbon si tes, ( 2 ) chemical r e a c t i o n of t h e sorbed water t o form H and CO,

and ( 3 ) i n h i b i t i o n of water s o r p t i o n by compe t i t i ve s o r p t i o n of H molecules.

Process ( 1 ) can be expressed by

2

2

where C

r a t e c o n s t a n t s € o r t he forward and reverse r e a c t i o n s . Following process 7-2,

sorbed water reacts wi th the s o l i d phase t o form carbon monoxide and

hydrogen as expressed by

and C(H20) denote f r e e and occupied si tes and i and j are r e a c t i o n €

J 3 C(H20) -f CO + H2 + aCf

* Transport c o n s i d e r a t i o n s are neg lec t ed i n t h i s t r ea tmen t .

7- 2

(7-3)

n

where a i s an i n t e g e r having va lues from 0 t o 2 . I f a > 1 (observed i n t h e

e a r l i e r s t a g e s of ox ida t ion ) , t h e number of r e a c t i o n s i t e s i n c r e a s e s as t h e

r e a c t i o n proceeds, l ead ing t o increased r e a c t i o n rates. I f a < 1 (observed

only du r ing t h e f i n a l s t a g e s of t h e o x i d a t i o n p rocess ) , t h e g r a p h i t e becomes

less r e a c t i v e as t h e r e a c t i o n proceeds. Thus, t h e r e a c t i o n ra te i s a f f e c t e d

by burnoff ( i . e . , t h e e x t e n t of o x i d a t i o n ) .

Hydrogen molecules compete wi th water vapor molecules f o r t h e a v a i l a b l e

s i t e s (Refs. 7-5, 7-6). Thus, included i n t h e denominator of Eq. 7-1 i s a

t e r m which r e f l e c t s t h e rates of adso rp t ion of hydrogen on g r a p h i t e (process

7-3) as expressed by

2 i

J 2

These t h r e e processes form t h e b a s i s f o r t h e Langmuir-Hinshelwood equat ion:

I >

j , + j3 '~20

i1 ra te = i

1 + - 2 n + j 2 ' H ~ j , + j 3 ' ~ ~ 0

(7-5)

I f j , , t h e ra te of evapora t ion of w a t e r molecules from t h e su r face , i s neg l i -

K1 = i K = i /j and K = i , / j 3 . g i b l e , 1' 2 2 2' 3

7 .1 .2 . Experimental Procedure and Samding.

Ins tan taneous r e a c t i o n rates are measured by specimen weight- loss d e t e r -

mina t ions us ing automatic record ing microbalances (Ref. 7-1).

Specimens were taken from near t h e c e n t e r o f a l o g of preproduct ion

H-451 g r a p h i t e . The d e n s i t y of t h e specimens ranged from 1.69 t o 1.70 Mg/m . The t o t a l m e t a l l i c impuri ty conten t of t h e g r a p h i t e w a s less than 200 ppm

and i r o n ranged from < 1 t o 6 ppm.

3

7-3

K2, and K are obtained w 1 ' 3 Values of t h e cons t an t n and r a t e c o n s t a n t s K

from t h e s lopes of i so thermal p l o t s of Llic r e a c t i o n r a t e d a t a der ived from

E q . 7-1. Because a l l t h r e e ra te cons t an t s i n c r e a s e wi th burnoff , va lues of

t h e cons t an t s were co r rec t ed t o a cons t an t burnoff of 1 % .

7.1.3. Determinat ion o f React ion Rate Constants __

Values were determined f o r r e a c t i o n r a t e cons t an t s : (1) burnoff f a c t o r

Fb, ( 2 ) hydrogen exponent n, and (3) K 1 , K 2 , and K3.

t h e s e cons t an t s from experimental d a t a are given i n Refs. 7-1 and 7-2.

Recommended va lues are l i s t e d i n Table 7-1.

The de termina t ions of

7.1.3.1.

of r e l a t i v e r e a c t i o n ra te ve r sus percent bu rnof f , where the ra te d a t a are

norma l i zed to u n i t y a t 1% b u r n o f f (Ref. 7-1) .

Burnoff Fac to r Fb. The burnoff f a c t o r Fb is determined from p l o t s

TABLE 7-1

EXPERIMENTALLY DETERMINED LANGMUIR-H N HELWOOD CONSTANTS FOR H-451 GRAPHITE by

Constant

-1 -1 K sec Pa 1

-0.75 K, Pa L

-1 K3 Pa

Hydrogen exponent n

P a r t i a l P res su re Water (Pa)

Low $300

21 8 exp (-253500/RT)

1940 exp(-131900/RT)

1.02 exp(-47030/RT)

0.75

(a)Langmuir Hinshelwood equat ion:

- 1 K1 'H,O

High 2 300 s 3300

0.11 exp(-195400/RT)

8.2 x exp(119700/RT)

1.3 x lo-' exp(131400/RT)

0.75

L r a t e ( sec ' ) = 0.75

+ K3PH,0 1 + K P

2 H, L L

7-4

The i n c r e a s e i n r e a c t i o n ra te wi th burnoff is more r ap id a t lower tempera-

t u r e s . For example, a t 5% burnoff , F is 4 , 2.6, and 2.5 f o r 1093, 1173, b and 1253 K , (820°, 900°, and 980°C) r e s p e c t i v e l y .

I n t h e r e a c t o r , because of high helium p res su res , burnoff i s l a r g e l y

s u r f a c e o r i e n t e d , and t h e F t e r m is l i k e l y t o be q u i t e d i f f e r e n t from t h a t

found i n these l abora to ry experiments. b

7.1.3.2. Hydrogen Exponent n. The determined va lue of n is 0.695 f: 0.18

(Ref. 7 - l ) , and t h i s va lue is i n accord wi th n = 0.75 c u r r e n t l y used i n t h e

OXIDE-3 code (Ref. 7-3).

7.1.3.3.

from t h e s lope of t h e p l o t o f 1 / R versus l/PH o, where R i s t h e rate of

r e a c t i o n and P is the p a r t i a l p r e s s u r e of water. I t is essential t h a t

t h e p a r t i a l p r e s s u r e of hydrogen (P H,

Rate Constants KlLK2, and K3. The rate cons t an t K, i s der ived

2

H2° ) b e n e g l i g i b l e when compared wi th

L

i n o r d e r t o o b t a i n a v a l i d va lue f o r K Therefore , was e i t h e r ex- 'H20 1 '

c luded o r he ld near zero du r ing t h e experiments. 2

der ived from experiments c a r r i e d o u t under t h e s e cond i t ions are repor t ed i n

Ref. 7-2 f o r t h r e e temperatures [1093, 1173, and 1253 K (820°, 900°, and

980°C)].

disk-shaped s a m p l e s 31.8 mm i n diameter by 1.57 mm t h i c k . Previous work

(Ref. 7-1) showed samples of t h e s e dimensions t o e x h i b i t minimal mass t r ans -

p o r t c o n t r o l of t h e r e a c t i o n s .

P l o t s of 1 / R ve r sus l /PH

The p l o t s i n Ref. 7-2 summarize t h e d a t a on r e a c t i o n rates us ing

A l ea s t - squa res f i t (POLFIT) w a s used t o gene ra t e t h e s t a t i s t i c a l d a t a

r equ i r ed t o c a l c u l a t e t h e va r i ances o f s l o p e and i n t e r c e p t . An apparent

a c t i v a t i o n energy w a s c a l c u l a t e d us ing POLFIT wi th each d a t a po in t weighted

by i t s va r i ance us ing t h e methods given previous ly i n Ref. 7-1.

The r a t e cons t an t K is der ived from t h e s l o p e of a p l o t of 1 / R versus 2 t h e r e f o r e , K can be determined us ing 2 . The s l o p e i s equal t o K / K P 2 1 H 2 0 ;

known va lues of K and n. The va lue of n (see above) w a s determined t o be 1

7 -5

0.695 ? 0 . 1 8 . A s imilar va lue f o r n w a s used f o r d e r i v i n g t h e cons t an t s

used he re in . Another assumption used i n determining K2 by t h i s method i s

t h a t e r r o r s a s soc ia t ed wi th K are n e g l i g i b l e . As a precaut ion , propaga-

t i o n a l e r r o r theory w a s employed t o examine t h e c o n t r i b u t i o n s of e r r o r s i n

K t o t h e va r i ance of K

1

2 ' 1

The experimental d a t a used t o o b t a i n t h e requi red s l o p e s are given i n

Ref. 7-2.

t h e 50-Pa water vapor i s o b a r .

exponent ia l f a c t o r were es t imated from t h e Arrhenius r e l a t i o n (Ref. 7 -2 ) .

A composite of d a t a from s e v e r a l experiments w a s used t o develop

The apparent a c t i v a t i o n energy and pre-

Establ ishment of equ i l ib r ium f o r t h e compet i t ive r e a c t i o n

i s slow, p a r t i c u l a r l y a t low temperatures , and, consequently, d a t a a t

t e m p e r a t u r e s below 1 1 2 3 K (85OoC> are l i m i t e d . When a d d i t i o n a l d a t a are

c o l l e c t e d , va lues of K2 can be determined a t temperatures of i n t e r e s t down

t o about 1000 K (727OC).

The i n t e r c e p t va lues from p l o t s of 1 / R versus 1 / P = 0 w e r e used t o H2°

determine K By r ea r r ang ing t h e Langmuir-Hinshelwood equat ion , t h e i n t e r -

cep t va lue of t h e above r e l a t i o n can b e equated t o K / K However, K i s

a l s o dependent on t h e e r r o r s a s s o c i a t e d wi th K

f o r c a l c u l a t i n g K

3 '

1 3' 3 The express ion recommended 1 '

over t h e p a r t i a l p r e s s u r e s examined is given i n Ref. 7-2. 3

7 . 1 . 4 . ADvlication of Rate Cons tan ts

A p l o t of l o g ra te versus log P which compares both sets of der ived H2°

cons t an t s f o r H-451, a long wi th t h e cons t an t s p r e s e n t l y used i n t h e O X I D E

code, i s shown i n F ig . 7-1. The OXIDE code c o n s t a n t s were de r ived from a

composite of d a t a from o t h e r g r a p h i t e s (Ref. 7-l) , p r imar i ly measured a t

low water concen t r a t ions ; t h e r e f o r e , t he O X I D E code cons t an t s c l o s e l y match

t h e ti-451 c o n s t a n t s der ived h e r e i n f o r P less than 300 Pa . An a d d i t i o n a l "2O

7-6

I

"' c

v I v

I I 1 1 I I 1 I 1 I 1 I I I I ~r T = 1173 K (900OC)

pH2 = 51 Pa

/' /'

/-

I I I I t I I 1 1 I I 1 I t - 10.000 100,000 100 1000 10

P H ~ O (Pa)

Fig. 7-1. Comparison of rate c o n s t a n t s as a func t ion o f P (from Ref. 7-2)

H2°

problem wi th t h e OXIDE code lias been i ts p r e d i c t i o n s o f a near-zero-order

r e l a t i o n a t p a r t i a l p r e s s u r e s of water t h a t are too l o w ( s e e F ig . 7-1).

u s e of H-451 cons tan t s de r ived f o r h igh water vapor w i l l improve t h e re l ia-

b i l i t y of t h e OXIDE code.

t r a t i o n s i n t h e range of 1 t o 1000 kPa are p o s s i b l e , t h e high-water-level

H-451 r a t e cons t an t s should be used. For normal s t eady- s t a t e r e a c t o r opera-

t i o n , where water concen t r a t ions i n t h e range 10 t o 1000 P a are expected,

t h e low-water-level H-451 c o n s t a n t s should b e used.

The

For acc iden t cond i t ions , where mois ture concen-

7 . 2 . EFFECT OF STEAM OXlDATION ON TENSILE STRENGTH AND ELASTIC MODULUS

The f u e l element b locks are s u b j e c t t o mechanical stresses inc lud ing

compressive, due t o the weight of t h e co re components, and t e n s i l e , due t o

i r rad ia t ion- induced s t r a i n s and thermal g rad ien t e f f e c t s .

b locks may have t o wi ths tand a d d i t i o n a l s t r e s s e s r e s u l t i n g f r o m s e i s m i c

even t s . The f u e l element b locks are requ i r ed t o wi ths tand t h e s e in - se rv ice

stresses and r e t a i n t h e i r s t r u c t u r a l i n t e g r i t y . Thus, a knowledge of t h e

e f f e c t of ox ida t ion on t h c s t r e n g t h and e l a s t i c modulus is requ i r ed .

The f u e l element

7.2.1. Experimental Procedure and Sampling

The experimental work (Ref. 7-8) cons i s t ed of ox id i z ing l a r g e numbers

of small test specimens uniformly and i so the rma l ly a t 1073 and 1273 K (800'

and 1000°C) i n steam-helium mixtures , and subsequent ly measuring t h e s t r e n g t h

and e las t ic modulus o f t h e oxid ized specimens. The s t r e n g t h and e las t ic

modulus va lues o f t h e oxid ized specimens were compared wi th va lues of non-

oxid ized c o n t r o l specimens, t aken from t h e same popula t ion of specimens

used f o r ox ida t ion , t o determine changes due t o o x i d a t i o n burnof f .

I n an e f f o r t t o o b t a i n d a t a on material of h i g h e s t and lowest s t r e n g t h ,

specimens were s e l e c t e d from quar te r - length c e n t e r (QLC) and quar te r - length

edge (QLE) p o s i t i o n s of GA l o g 6 3 8 4 - 3 4 . Axial and r a d i a l specimens were

s e l e c t e d iis i nd ica t ed i n Appendix A, F igs . A-14 through A-17.

7- 8

Groups o f s a m p l e s were randomized and a l l o c a t e d fo r ox ida t ion according

t o Appendix B , Table B-19.

Af t e r ox ida t ion , approximately 0.6 mm was removed from each end o f each

oxid ized specimen and each specimen c u t i n h a l f t o provide two specimens

6.34 mm i n diameter by approximately 2.3 mm i n l eng th .

Oxidat ion specimens were 634 mm i n l eng th .

The appa ra tus used f o r t h e ox ida t ion measurements i s descr ibed i n

Ref 7-8.

t aneous ly i n each experiment.

hydrogen, and t h e ba lance helium was used f o r ox id i z ing t h e specimens.

Seve ra l o f t h e c y l i n d r i c a l g r a p h i t e specimens were oxidized simul-

A gas mixture composed of 3% water vapor , 5%

To determine the e x t e n t of ox ida t ion , t h e o x i d a t i o n process w a s i n t e r -

r u p t e d p e r i o d i c a l l y and t h e samples were cooled and weighed t o 20.1 mg. The

percent burnoff w a s c a l c u l a t e d from changes i n specimen weight .

I t w a s a n t i c i p a t e d t h a t use of small-diameter samples i n a hydrogen-

r i c h gas mixture would ensure r e l a t i v e l y uniform o x i d a t i o n throughout t h e

bulk of t h e samples.

de te rmining r a d i a l d e n s i t y p r o f i l e s on a number of nonoxidized and oxid ized

Uniformity of ox ida t ion burnoff w a s confirmed by

specimens. Techniques f o r measuring t e n s i l e s t r e n g t h and e las t ic modulus

are r epor t ed i n Ref. 7-9.

7 . 2 . 2 . Experimental Resul t s

Complete d a t a sets of u l t i m a t e t e n s i l e s t r e n g t h , e l a s t i c modulus, and

s t r a i n a t f r a c t u r e are t abu la t ed i n Ref. 7-8.

7 . 2 . 2 . 1 . Oxidation-Induced Bulk Dens i ty P r o f i l e s . Bulk d e n s i t y p r o f i l e s

fo r nonoxidized c o n t r o l specimens of H-451 and f o r t h r e e oxid ized specimens

a r c givcw i n K c T . 7-8. There is l a r g e s c a t t e r i n t h e d a t a , which is due t o

cbxpcrinicwtal d i f f i cu l ties and the heterogeneous na tu re of t h e g r a p h i t e .

T l i c oxid;i t ion p r o f i l e s a r c uniform for a l l specimens oxid ized a t 1073 K

o r 1273 K (800" or 1000°C). I t was a n t i c i p a t e d t h a t some p r e f e r e n t i a l oxi-

d a t i o n on thc o u t e r s u r f a c e of t h e specimens would occur a t 1273 K (1000°C);

7-9

t h a t is , t h e f i n a l dens i ty p r o f i l e a long t h e r a d i u s a f t e r ox ida t ion should Q i nc rease from t h e o u t e r edge toward t h e c e n t e r . In most cases , ox ida t ion

a t 1273 K (lOOO°C) produced uniform p r o f i l e s . I t is concluded from t h e bulk

dens i ty p r o f i l e d a t a t h a t a l l UTS specimens were oxid ized uniformly ac ross

t h e r a d i u s .

7 . 2 . 2 . 2 . U l t i m a t e Tens i l e S t r e n g t h , E l a s t i c Modulus, and S t r a i n a t F rac tu re .

The UTS and e l a s t i c modulus va lues f o r nonoxidized c o n t r o l material were

h ighes t i n t h e a x i a l d i r e c t i o n and inc reased from t h e center t o t h e edge of

the log . The u l t i m a t e t e n s i l e s t r e n g t h s and e l a s t i c modulus were i n agree-

ment wi th o t h e r d a t a obta ined on t h e same l o g and o t h e r l o g s of H-451

g r a p h i t e (Ref. 7-9).

S t a t i s t i c a l ana lyses were performed on the d a t a t o (1) determine

w h e t h e r the d i s t r i b u t i o n of UTS w a s Gaussian (us ing the chi-square analysis)

(Refs. 7-10, 7-11) , (2) compare popula t ion mean va lues of s t r e n g t h and

e l a s t i c modulus f o r c o n t r o l and ox id ized specimens [us ing a comparison of

popula t ion means (CPM) tes t ] (Ref. 7-12), and (3 ) determine the maximum,

minimum, and most probable (mean) rates of proper ty change wi th burnoff a t

95% confidence (us ing t h e CONFTD computer code, de r ived from a technique

given i n Ref. 7-12).

The UTS d a t a followed a Gaussian d i s t r i b u t i o n . Confirmation of a

Gaussian d i s t r i b u t i o n is important s i n c e both the CPM test and t h e CONFID

computer code assume Gaussian d i s t r i b u t i o n s ,

The r e s u l t s of t h e CPM and CONFID ana lyses are given i n Tables 7-2 and

7-3, r e s p e c t i v e l y . The rates of changes i n UTS and E from t h e CONFID calcu-

l a t i o n s arc’ presented g r a p h i c a l l y in Ref. 7-8, where t h e most probable r a t e

changes arc shown as l i n e a r r e g r e s s i o n l i n e s . A comparison of nonoxidized

and oxid ized UTS va lues showed t h a t s t r e n g t h decreased wi th ox ida t ion . The

populat ion means of t h e c o n t r o l and ox id ized specimens were compared (see

Table 7-2, column 7 ) . No s i g n i f i c a n t reduct ion i n UTS o r modulus ( a t 95%

confidence) w a s observed i n a x i a l specimens oxid ized up t o 2% and 1% burn-

o f f , r e s p e c t i v e l y .

7-10

Lr, 0

w

w

0

c O

N

!2 m h

r3 v

l.

h

m

q-

3.-

.

. e .

I.

'1

?".,?

?".

'9 I

I I

1 .

I I

-0

0-

0-

0

0

I I

I I

O

I1

00

0 -

IO

0

9

I?

0

r. 7

0

m

9

0

m

U

0

0

ro

- I ro

0

m.

0

(?

c

I m

0

s

0

m c

I r. 9

-

n

m

I- I W

m

In

0

I? I?

0

In

N

0

0

0

I 7

-J. m

m

U I

N

c

0

0

m

n

0

.? 0

m

m

U I

U

I?

9

r. I

W

m

0

m

N I

9 7

N

In I

m

m

7-1 1

TABLE 7-3 REDUCTION I N ULTIMATE T E N S I L E STRENGTH AND E L A S T I C MODULUS

Burnof f Temp 9

K ("C)

CA

CA

CA

EA

CR

ER

CR

ER

X Reduction/l% Burnoff

Burnof f Maximum Mean Minimum Range (2.3% (Most (2.3%

% P r o b a b i l i t y ) P robab le ) P r o b a b i l i t y )

CA

CA

CA

EA

ER

, 0.0

0 .o 1.70

3.74

4.32

3.23

3.18

3.72

1073 (800)

1273 (1000)

1273 (1000)

1273 (1000)

1073 (800)

1073 (800)

1273 (1000)

1273 (1000)

1073 (800)

1273 (1000)

1273 (1000)

1273 (1000)

1273 (1000)

0- 2

0-2

0-8

0-6

0-10

0-1 4

0-20

0-8

Elas t ic

0- 2

0-2

0-8

0-5

0-6

(a ) CA: c e n t e r ax ia l specimens.

EA: edge axial specimens.

CR: c e n t e r r a d i a l specimens.

11.17

7.32

3.85

6.48

6.06

5.14

3.92

5.93

Mod ul us

14.04

11.56

4.88

9.53

9.31

5.60

1.73

2.82

5.14

5.32

4.60

3.59

4.79

10.46 1 0.01

3.71

3.26

6.10

7.83

0.0

1.45

1 .96

6.11

n

ER: edge r a d i a l specimens.

7-1 2

The e f f e c t of ox ida t ion on UTS f o r a x i a l edge and c e n t e r specimens

oxid ized a t 1073 K (800°C) is shown i n Fig. 7-2. The d a t a i n Fig. 7-2

i n d i c a t e no dec rease i n s t r e n g t h occurred i n t h e c e n t e r specimens up t o 2%

burnoff , whereas a s l i g h t decrease w a s observed i n t h e edge specimens. The

UTS r educ t ion rates f o r o x i d a t i o n a t 1273 K (1000°C) are shown i n F ig . 7-3.

Again, t h e edge specimens l o s t s t r e n g t h a t a h ighe r rate than t h e c e n t e r

specimens.

shown i n F ig . 7-4.

2% a t e i t h e r 1073 o r 1273 K (800" o r 1000°C).

The combined d a t a f o r a x i a l c e n t e r samples a t low burnoff are

No s t r e n g t h r educ t ion w a s observed f o r bu rnof f s up t o

The UTS d a t a f o r r a d i a l edge and c e n t e r specimens are presented i n

F igs . 7-5 and 7-6 f o r ox ida t ion a t 1073 and 1273 K (800' and 1000°C),

r e s p e c t i v e l y . The r a d i a l specimens l o s t s t r e n g t h a t a f a s t e r rate than

a x i a l specimens, and i n both cases edge specimens l o s t s t r e n g t h a t a f a s t e r

ra te than c e n t e r specimens.

The e f f e c t of o x i d a t i o n on e l a s t i c modulus of a x i a l c e n t e r specimens

a t 1073 and 1273 K (800" and 1000°C) i s given i n Fig. 7-7. N o e f f e c t o f

burnoff up t o 12 w a s observed, b u t above 12 t h e r educ t ion of t h e e las t ic

modulus was s i g n i f i c a n t . Changes i n modulus o f a x i a l c e n t e r and edge

specimens may be compared i n Fig. 7-8.

i s reduced a t a h i g h e r ra te than t h a t o f c e n t e r specimens. F igure 7-9 i s a

p l o t of e l a s t i c modulus ve r sus burnoff f o r r a d i a l specimens oxid ized a t

1273 K (100O'C).

The modulus o f t h e edge specimens

The t r e n d s f o r UTS and e l a s t i c modulus are summarized i n Table 7-3 by

comparing t h e r e l a t i v e r educ t ion i n each proper ty a t 1% burnoff .

i n Table 7-3 were obta ined from CONFID, which can be used t o c a l c u l a t e , a t

95% confidence, t h e most probable (50% p r o b a b i l i t y ) o r mean dec rease i n

proper ty and t h e maximum and minimum (2.3% p r o b a b i l i t y ) dec rease i n proper ty .

Reductions i n s t r e n g t h and e l a s t i c modulus were g r e a t e r when t h e specimens

w e r e ox id ized a t 1073 K (800°C) compared t o 1273 K (lOOO°C), and changes

were g r e a t e r f o r edge specimens than f o r c e n t e r specimens.

w a s p a r t i c u l a r l y s i g n i f i c a n t i n modulus d a t a where t h e average dec rease i n

edge specimens a t 1273 K (1000°C) was twice t h a t of center specimens.

The r e s u l t s

Th i s phenomenon

7-13

0 0

Fig. 7-2. Tensile strength versus burnoff for H-451 graphite (log 6484-34 , quarter-length axial edge and center specimens) oxidized at 1073 K (8OOOC)

7-3 4

20 68 130001

11.24 (25001

- - - z 0" I

I- 13.79 2 (2000)

I

I

W

W

I- v)

W

v) z W !-

2

10.34 ( 1500)

6.89 (1000)

\ 0

1 1 10 20

BUANOFF (96)

Fig. 7-3. T e n s i l e s t r e n g t h ve r sus burnoff f o r H-451 g r a p h i t e ( l o g 6 4 8 4 - 3 4 , quar t e r - l eng th axial specimens) ox id ized a t 1273 K (lOOO°C)

7-35

17.93 (26001

f 16.55 (24001

0 0 0

0 0 0 0

15.17 (22001

13.79 (2000)

i 2 I &

11.03 (16001

z w a

w 9.65 z

(1400) z u1 I-

( 1 200) a'27 t

I

(1000)

6'89 I I

U

0 0

0 OXIDIZED AT 1073 K (8OOoC) 0 OXIDIZED AT 1273 K (looO°C) A NONOXIDIZED CONTROLS 0

0 0

0 Q

0

' e

I -1 . - .-_I --- . L - - l - L I 1 I 0 4 O G 0 8 10 1 2 1 4 1 6 1.8 0 2

EURNOFF l"/)

Fig. 7 - 4 . Tensile strength versus burnoff for H-451 graphi te ( l o g 6484-34 , quarter-length axial center specimens)

7-36

20.68 (3000

17.24 (25001

- 13.79 - (2000)

2 E a I I- o z W

I

a

d L;;

E 10.34

W

v) z

( 1500)

6.89 ( 1000)

3.45

5 10 15 20 (500)

BURNOFF (%)

Fig. 7-5. Tensile strength versus burnoff for H-451 graphite (log 6484-34, quarter-length radial specimens) oxidized at 1073 K (800OC)

7-1 7

a

0

1.38 I I "

BUR N O F F W')

Fig . 7-6 . T e n s i l e s t r e n g t h v e r s u s burnoff f o r H-451 g r a p h i t e ( l o g 6484-34 , quar t e r - l eng th r a d i a l specimens) ox id ized a t 1273 K ( l O O O ° C )

7-3 8

c

U I

11 (1.6)

- W-

I E! 9.7 'I (1.4) 2 2 * 8.3 3 (1.2)

sc

a Y

3 0 0 E

I- 0 6.9 * (1.0) 4 w

5.5 (0.8)

4.1

0 0 0 0

0 OXIDIZED AT 1073 K (8OOOC)

A NONOXIDIZED CONTROLS OXIDIZED AT 1273 K (lOOO°C)

0 0

0 0 0

1273 K (1 ooooc) 1 -

0

8 0

I I I I I I 1 (0.6) 1 2 3 4 5 6 7 a

BURNOFF (%)

Fig. 7-7. Elast ic modulus v e r s u s burnoff f o r H-451 g r a p h i t e ( l o g 6 4 8 4 - 3 4 , quar t e r - l eng th a x i a l c e n t e r specimens)

0 E D G E OF LOG

@ CENTER OF LOG 11.0 (1.6)

9.7 (1.4)

8.3 (1 .a

6.9 (1 .O)

5.5 (0.8)

I 1 1

1 1 1 1 1 1 1 1 1 4 5 6 7 a 9

4.1 I (0.6) 1 2 3

BURNOFF (%)

Fig. 7-8 . Elastic modulus versus burnoff for H-451 graphite (log 6484-34 , quarter-length axial specimens) oxidized at 1273 K (lOOO°C)

0

7-2 1

n Changes i n s t r a i n a t f r a c t u r e were measured on nonoxidized c o n t r o l

specimens and on specimens oxid ized t o b u r n o f f s u p to 12X.

anonin lous , showing no changes i n a x i a l cc%ntcr spcbcimens a t 4.3% burnof l ,

about 50X reducl ion i n r a d i a l c e n t e r specimens a t 2.82 t o 9.3X burnof f s ,

and about 40% r educ t ion i n r a d i a l edge specimens a t 5.5% t o 12% burnof f s .

No f i r m conclusions can be drawn from t h e s e d a t a .

The d a t a were

7.2.2.3. Conclusions. The t e n s i l e s t r e n g t h of H-451 g r a p h i t e decreased by

r

an average of 3.6% i n c e n t e r a x i a l specimens when oxid ized t o burnoffs up t o

2.0% a t e i t h e r 1073 K o r 1273 K (800" o r lOOO"C), and no s i g n i f i c a n t reduc-

t i o n i n e l a s t i c modulus i n t h e s e same specimens w a s observed when oxid ized

t o bu rnof f s of up t o 2.0% a t 1273 K (1000°C).

t e n s i l e s t r e n g t h and e l a s t i c modulus f o r c e n t e r axial specimens w a s g r e a t e r

a t 1073 K (800OC) than a t 1273 K (1000°C) and, i n gene ra l , t h e r educ t ion

was h ighe r i n r a d i a l specimens than i n a x i a l specimens.

The rate of r educ t ion of

I n gene ra l , t h e r educ t ion rate of e l a s t i c modulus w i t h burnoff w a s

g r e a t e r than t h a t of t e n s i l e s t r e n g t h .

s t r e n g t h and e l a s t i c modulus f o r a x i a l specimens oxid ized a t 1273 K (lOOO°C)

The r a t e o f r educ t ion of t e n s i l e

w a s g r e a t e r a t t h e edge than a t t h e c e n t e r of a log .

REFERENCES

7-1.

7-2.

7-3.

7-4.

"Quar te r ly Progress Report f o r the Per iod Ending August 31, 1976,

HTGR Fue l s and Core Development Program," ERDA Report GA-A14046,

General Atomic Company, September 29, 1976.

"Quar te r ly Progress Report f o r t h e Per iod Ending May 31, 1977, HTGR

Fue l s and Core Development Program," ERDA Report GA-A74418, General

Atomic Company, June 1977.

Peroomian, M. B . , A. W. Barsell, and J. C. Saeger , "OXIDE-3: A

Computer Code f o r Analys is of HTGR Steam o r A i r I ng res s Accidents ,"

General Atomic Report GA-A12493, January 15, 1972.

Giberson, R. C . , and G. L. Tingey, "React ions of Gaseous Impur i t i e s

i n a High Temperature Gas Cooled Reactor ," USAEC Report BNWL-974,

1968.

7-22

u 7-5.

7-6.

7-7.

7-8.

7-9.

J o h n s t o n e , H. F. , C. Y. IChen, and D. S. S c o t t , " K i n e t i c s of t h e

S t e a m Carbon Reac t ion i n Porous G r a p h i t e Tubes," Ind . Eng. Chem. 4 4 , 1568 (1952).

Walker, P. L., Jr . , F. Riisinko, Jr., and L. G. A u s t i n , "Gas R e a c t i o n s

of Carbon," Advanced C a t a l y s i s 11, 149 (1959) .

Ergun, S. , and M. Menken!, "Reac t ions of Carbon w i t h C 0 2 and Steam,"

i n Chemistry and P h y s i c s of Carbons, v. 1 , P. L. Walker, Jr. ( e d . ) ,

Marcel Dekker, New York, 1965, p. 229.

Velasquez , C . , e t a l . , "The E f f e c t of S team O x i d a t i o n on S t r e n g t h

and E l a s t i c Modulus of G r a p h i t e H-451," DOE Repor t GA-A14657, Genera l

Atomic Company, December 1977.

Johnson, W. R . , and G. B. Engle , " P r o p e r t i e s of U n i r r a d i a t e d F u e l

Element G r a p h i t e s H-451 and TS-1240," ERDA Repor t GA-A13752,

Genera l Atomic Company, J a n u a r y 31, 1976.

7-10. Bevington , P. R . , Data Reduct ion and E r r o r A n a l y s i s f o r t h e P h y s i c a l

S c i e n c e s , M c G r a w - H i l l , N e w York, 1969, pp. 84 and 314.

7-11. Johnson, N. L., and F. C. Leone, S t a t i s t i c s and Exper imen ta l Des ign ,

v. 1 , John Wiley and Sons, New York, 1964, p. 224.

7-12. Bevington , P. R., op. c i t . , p . 104. -

7-23

8. ACKNOWLEDGMENTS

The author gratfully acknowledges the contributions of R. J. Price, L. A. Beavan, and R. D. Burnette in helping to summarize the data and

in commenting on the manuscript.

c

8- 1

APPENDIX A

SAMPLING DIAGRAMS

A- 3

EDE 432 ....,

DISCARD TOP 25.4 mr

I BE///I 152mm I\\ BE

END /I 152mm I\ SLAB 1 I n

L'- It / I 152,mm

SLAB 4 '+ SLAB 5

D ISCAR fl

Fig. A-1. Sampling diagram of H-451 for within-log property measurements: slabs and sections

A- 3

A-4

.. l-l =I a) 6 h

4J Lc

3 b a 0

$4 a

.-I

.

..

4-5

h

u Ll

h, a

0

k a

M

TO RADIAL (RADIAL DIRECTION) I

I I I DIRECTION

1. I 3 (AXIAL) 3 (AXIAL)

2 (RADIAL)

J 1 (CHORD)

J 1 . 1 (RADIAL) I

I PERPENDICULAR I TO RADIAL I DIRECTION I I

EE POSITION - 2 (RADIAL)

MLE POSITION - 2 (RADIAL)

Fig . A - 4 . O r i e n t a t i o n of or thogonal axes for d e f i n i t i o n of Poisson ' s r a t i o d a t a i n Table B-4

A-6

SLAB 2 FATIGUE SPEC I M ENS

SLAB 3

t ' SLAB4

t SLAB 5

SLAB 6

ALL DIMENSIONS IN mm

25.4

Fig. A-5. Locations of slabs (shaded) f o r s t a t i s t i c a l strength tes t ing H-451 graphite ((log 5651-90)

A- 7

rn

RADIAL SPECIMENS RADIAL SPECIMENS

216 rnrn-

Fig. A-6. Coring plan for center zone of A and B sections of slabs (see Fig. A-5)

A-a

b-4 25.4 mm

Fig. A-7. Coring plan f o r edge zone of A and B sections of s l a b s (see F i g . A-5)

SLAB E 25 mm THICK

THIS CORE HAS BEEN ENLARGED TO SHOW DETAIL

16 mm DIAMETER ON ROO c 356 mm DEEP

R O D C

-432 mm DIAMETER-

:ORE TAKEN :OR GLCC rENSlLE TEST iPE C IM E N

mm

--CORE TAKEN FOR GA TENSILE TEST SPECIMENS

F i g . A-8. Sampling diagram of H-451 logs for t ens i l e strength

A-10

n

u

0

0

(r

z

w

0

w

v)

E n

0

0

(1

E

00 “1

E

Y I

I- z

0

a, a

rn d

(d

.rl

3 .. n m

a, al rn

a, k 0

c)

2 (d

rn M

0

rl

rn U

F

& W 0

E

(d k

M

m

0 0

WJ

m P) a) m U

rl a

E

(d

cn M

.I+ Frr

0

N

R

A-1 2

n

RADIAL SPECIMENS

RADIAL SPECIMENS

F i g . A-12. Sampling diagram f o r i r r a d i a t i o n specimens: c e n t e r zone, from s l a b 3 (see F i g . A-1)

.(> '

.

A-15

n

/

933.6 rnm

196.9 mrn

%

/

/’

\ 7’

\ 7

165.1 mrn \

Y

<--;a /

- 0x1 OAT1 0 N SPECIMENS

POSITION QUARTE R-LEN GTH

Fig. A-14. Sampling plan of graphite log showing slab designated for oxidation tests

U

7

h M

d

Frc

w

P

fd rl

m

(d

1cc 0

7.9-mm COR E 63.5 mm DEEP

7.9-mm COR E 63.5 mm DEEP

196.9 mm

Fig. A-16. Sampling diagram of H-451 graphite: center sect ion of s lab from Fig. A-15

A-1 8

n

E

E

3

P

2 I

A-1 9

APPENDIX B

EXPERIMENTAL RESULTS

B- 3

h

rp

7 7. 0

.j

I U

m U

UJ

c

U

U

m

.3

\o

2 E

J

J s

..4

B- 3

TABLE E-2 ULTINATE TENSILE STRENGTH: H-451. LOT 426

MLE

14.04 (2.5) (191

13.69 (2.9) [ l a ]

14.13 (1.6) [20]

13.75 (1.7) [ 2 0 ]

13.91 (2 .2 ) [77]

Log No.

EC

15.87 (2.4) 1201

12.31 (3.0) [201

15.38 (0.8) [ la]

12.33 (2 .0) 1201

13.94 (2 .6 ) (781

GA

td

.b I 6484-33

6484-34

6484-40

6484-41

Mean, lot 426

- GLCC

92

198

155

184

-

-

~ ~~~~ - ~~

Mean Strength (Wa) (S tanda rd Deviat ion, MPa) [No. of Repl i ca t e s ]

Ax ia l 1 Radia l

MLC

14.54 (1.5) [I91

14.18 (0.8) [20]

12.99 (1.6) [20]

12.93 (1.2) [20]

13.65 (1.6) 1791

ULE

20.16 (2.3) [151

19.42 (1.8) [20]

18.04 (1.1) [19]

18.66 (1.6) [19]

19.01 (1.9) [731

EC

18.44 (1.3) [20]

14.10 (0.9) [20]

16.67 (1.0) (201

11.86 (0.8) (201

15.26 (2.7) 1801

EE

20.14 (1.6) [I91

18.62 (1.9) [201

16.83 (1.1) 1191

16.53 (1.4) (201

18.01 ( 2 . 1 ) I781

t

- MLC

10.44 (1.5) [201

10.38 (2.1) 1181

11.72 (1.4) [201

10.44 (2.9) [20 ]

10.75 (7.1) [781

EE

17.47 (1.2) [20]

14.74 (2.4) [191

15.14 (1.0) (201

13.43 (1.9) 1191

15.22 (2.2) [78]

=c

EC

Log No.

EE MLC

l o t 426

MLC

8.13 (0.21) [SI

8 . 2 0 (0.14) [8 ]

7.86 (0.21) [8 ]

7.58 ( 0 . 2 4 ) [8]

7.93 (0 .28 ) [32]

TABLE B-3 ELASTIC MODULUS IN TENSION: H-451, LOT 426

Mean Modulus (GPa) (Standard Deviation, GPa) [No. of Replicates]

MLE

9.03 (0.28) [81

9.03 (0.21) [81

8.67 (0.21) [8 ]

8.62 (0.21) [8]

8.82 (0 .28 ) [321

Axial I

8.41 (0.21) [81

8.13 (0.21) [81

8.55 (0.07) 181

7.31 (0.21) [81

8.13 (0.21) [321

9.03 (0.21) [a]

8.76 (0.55) [E]

8.96 (0.76) [a ]

8.00 (0.48) [8]

8.69 (0.62) [32]

7.24 (0.41) [8]

7.72 (0.76) [81

7.31 (0.21) (81

7.17 (0.28) 181

7.38 (0.48) [32]

i . 7 9 (0.21) [E] 7.65 (0.21) [8]

7 . 3 1 t O . - 8 ) [8 ] 7.58 ( 0 . 2 8 ) [8]

7 . + 5 ( 0 . 2 1 ) [8 ] 7.51 ( 0 . 3 5 ) [81

6.81 (0.21) [E] 7.03 (0.35) 191

7.38 (0 . i8 ) [321 7.45 (0.41)[33]

6.76 (0.21) [81

6.83 (0.34) [a]

7.03 (0 .14 ) (81

6.89 (0.14) [51

6.89 (0.28) 1291

Radial

MLE I EC I EE

Log No.

GA

5651-63

5651-63

5651-63

Mean Mean

W 5651-63 a\

. I

5651-28

5651-63

Mean

5651-28

5651-63

Mean Mean

565 1-63

- LCC

!2

-

!2

!2

!2

8

!2

I8

22

22

-

Location of

,pacirnen i n Log

?ILC

XLC

X I C

MLC

MLC

MLC

MLE

MLE

EE

K r e c t i o n f Applied S t r e s s

Radia l

Radia l

Radia l

Axia l

Axia l

Axia l

Axial

Axial

Axial

( a )Pe rpend icu la r t o r a d i a l d i r e c t i o n .

.Q -

D i r e c t i o n O f

T ransve r se S t r a i n

Axia l Radia l

Axia l Radia l

Axia l Rad ia l

Axia l Rad ia l

Radia l

Radia l

Radia l

Radia l

Radial Chord (a)

Radia l Chord (a)

Radia l Chord (a)

Radia l Chord (a)

TABLE 8-4 POISSON'S RATIO: H-451. LOT 266

Poisson ' s Ratio (Standard Devia t ion) [No. of Measurements]

'13 = '23

0.120 (0.001) [31

0.096 (0.019) [ lo]

0.112 (0.002) (641

0.110 (0.009) [771

- '12 = '21 -

0.137 (0.001) [3]

0.104 (0.011) [ l o ]

0.107 (0.006) 1641

0.108 (0.008) [771

'31 * '32

1.125 (0.009) [61

1.130 (0.019) [2&1

1.125 (0.008) [481

1.127 (0.013) [ i81

"32

).I23 (0.009) [ I 2 1

0.121 (0.003) [641

0 . 1 2 1 (0.005) [76]

0.110 (0.010) [40]

I^.

0.113 (0.007) [ I21

0.114 (0.006) 16L1

0.114 (0.006) [761

0.1 17 (0.006) [ 4 0 ]

TABLE B-5 FLEXURAL STRENGTH: H-451, LOT 426

17.1 ( 4 . 2 ) [ZO]

17.7 (1.4) [ZO]

17.4 (3.1) [40]

Log N o .

22.2 (1.2) [20] 21.7 (1.7) I201 22.5 (1.0) [20]

21.1 (1.3) 1201 18.4 (1.1) [201 19.6 (1.7) (201

21.7 (1.4) [40] 20.0 (2.2) [A01 2 1 . 1 (2.0) [A01

6484-40 I 155

lot 426 I

Mean Strength (MPa)(Standard De\

Axial

ation, Wa) [No. of Replicates]

Radial

TABLE B-6 ULTIMATE COMPRESSIVE STRENGTH AND ELASTIC MODULUS IN COMPRESSION: H-451, LOT 478

- v - I

GA GLCC MLC MLE EC EE I I Loe No. I Axial

MLC MLE EC EE

I Radial

49.4

52.2

53.1

51.6

3.1

55.9

57.8

56.1

56.6

2.2

7194-49

7194-52

7194-87

a L o t mean I 03 Standard deviation

58.9

58.9

60.5

59.4

1.9

7194-49

7194-52

7 1 9 4-87

Lot mean

Standard deviation

49.2

50.0

53.6

50.9

3.1

15

72

35

15

72

35

Ultimate Compressive St

50.3

51.8

53.7

51.9

2.7

Elastic

6.0

6 .4

6.6

6 . 3

0.8

Modulu

6.8

6.7

7 .3

6.9

0.5

xength (MPa)

55.2

58.3

62.9

58.8

5.0

52.4

48.3

48.2

49.6

2.7

in Compression (GPa)

6.2

6.0

6.9

6.4

0 .7

6.9

6.8

7.7

7.1

0.8

5.2

4.7

5 .O 5.0

0.5

54.6

54.5

50.3

53.1

3.0

5.4

5.2

5.4

5 .3

0.3

5 .4 1 5.7

5.4 I 5.5

0.45

TABLE 8-7 T H E W EXPANSIVITY: H-451. LOT 426

Ec EE

4.00 (0.18) 181 3.88 (0.09) [81

4.31 (0 .08) [E] 4.13 (0.12) [E]

3.90 (0.13) [E] 3.89 (0.09) [E]

4.07 (0.22) [24] 3.97 (0.15) 1241

I Mean Thermal Expans iv i ty x l o6 K-l ("C-') [Standard Dev ia t ion x lo6 K-' ("C-')I [No. of R e p l i c a t e s ]

ULC

4 .51 (0.29) [81

4.63 (0 .20 ) [8]

4.42 (0.18) [E]

4.52 (0.23) [241

Log No. I Axial I

92

198

184

GA

4.08 (0.14) [El 3.86 (0.20) [8]

4.10 (0.10) [8] 3.92 (0.19) I81

3.92 (0.07) [81 3.90 (0.09) [81

4.03 (0.13) [24] 3.89 (0.16) [241

6484-33 W I 6484-34 u)

6484-4 1

Mean, l o t 426

4.65 (0.13) [8]

4.66 (0.25) [E]

4.50 (0.18) [8]

4.60 (0.20) [24]

I

mcc ULC I MLE

< . i o ( 0 . 1 ~ ) [8] 4 . 7 0 (0 .21 ) [8]

4.55 ( 0 . 2 7 ) [e] 4.59 (0.10) [ E l (1.43 (0.16) (81 4.59 (0.18) [81

4.56 (0 .22) [241 4.63 (0.17) (241

Rad ia l

MLE I EC I EE

.

GA GLCC

64 84-33 92 -34 198 -4 1 184

TABLE B-8 ANISOTROPY FACTOR: H-451, LOT 426

MLC MLE EC EE

1.12 1.18 1 .I2 1.17

T-- Log No.

a (radial) (a) Mean Anisotropy Factor,

( a ) ~ e a n of three logs.

B-10

% '

$73 K (200°C) (a)

120 (27) [81

115 (6) 181

125 (14) [71

112 (7) [71

122 (21) [15]

114 (6) 1151

* c .

673 K (400°C)(a:

92 (7) [81

88 (6) [81

92 (4) [71

88 (4) [71

92 (6) [151

88 (5) 11.51

Log No.

Orientation

Axial

Radial

GA

Mean Tensile Strength (+Standard Deviation)

(ma)

18.9 2 1.8

13.9 + 2.3

6484-34

6484-34

6484-4 1

64 84-4 1

Mean, Lot 426

W I

GLCC

198

198

184

184

Orientation

Axi a1

Radial

Axial

Radial

Axial

Radial

TABLE B-9 THERMAL CONDUCTIVITY: H-451, LOT 426, MLC

Mean Thermal Conductivity, W/m*K (Standard Deviation, W/m*K) [Number of Replicates]

295 K (22°C) (a) ~~

136 (17) [81

129 (10) 181

147 (17) [71

139 (13) [71

141 (18) 151

134 (13) 1151

' (a)Temperature of meas

TABLE B-10 MEAN TENSILE STRENGTH OF UNIRRADIATED H-451 GRAPHITE

SPECIMENSUSED IN FATIGUE STUDY

1073 K (800"Cfa)

TABLE B-11 IRRADIATION CONDITIONS AND MEAN TENSILE STRENGTH OF IRRADIATED H-451 GRAPHITE

USED I N FATIGUE STUDY (ALL SPECIMENS MLC LOCATION)

O r i e n t a t i o n

I Axial W

tQ &a

Radial

Axial

1 I I 1 Mean T e n s i l e MeanTens i l eS t r eng th

F a s t Neutron S t r eng th of Un i r r ad ia t ed Fluence N / m ) I r r a d i a t i o n Temperature (+-Standard Companions

Deviat ion) ( 2 Standa rdDev ia t ion ) (E > 29 fJIHTGR K O C ( m a ) (Wa)

3 .O 1173 900 14.5 2 2.1 10.8 2 0.9

5.7 1223-1 263 950-990 22.4 ?r 2.6 11.5 t 1.7

20.2 2 1.9 10.8 t 0.9 8.5 1 1 73-1 243 900-970

. ,

TABLE B-12 SUMMARY OF IRRADIATION-INDUCED CHANGES IN THERMAL EXPANSIVITY OF H-451 GRAPHITE

IRRADIATED IN CAPSULES OG-1. O G - 2 . AND OG-3

B-3 3

TABLE B-13 SUMMARY OF IRRADIATION-INDUCED CHANGES IN THERMAL EXPANSIVITY OF

H-429 GRAPHITE IRRADIATED IN CAPSULES OG-1, OG2, and 0 6 3

GA Log No.

4 9 74-04A

Orientat ion

Axial

Radial

Mean Irradiation Temperature

K

1165

1180

1170

1435

1460

1480

1705

1675

1165

1145

1170

1435

1460

1480

1705

1675

O C

89 2

907

89 7

1162

1187

1207

1432

1402

__ .

892

872

89 7

1162

1187

1207

1432

1402

3.0

5.2

7.2

5.6

8.6

11.4

6.6

8.8

3 .O 5 - 6

7.2

5.6

8.6

11.4

6.6

8.8

Q .

Average Percent Change in

CTE 295-773 K (22°-5000C)

-8

-4

-21

-1 3

-28

-4 1 -22

-30

+2

+1

-1 9

-9

-29

-39

-1 7

-27

GA Log No.

5651 -73

m I U

cn

TABLE B-14 SUMMARY OF IRRADIATION-INDUCED CHANGES I N THERMAL EXPANSIVITY OF

TS-1240 GRAPHITE IRRADIATED I N CAPSULES 06-2 AND 0 6 3

O r i e n t a t i o n

Axial

Radial

Location i n Log

Midlength- cen te r

Midleng th- edge

Midlengt h- cen te r

md leng th - edge

Mean I r r a d i a t i o n Temperature

K

895 1040 1195 1250 1380 1415

880

865 1080 1195 1200 1475 1500

8 80

O C

622 767 922 977

1107 1142

607

592 807 92 2 927

1202 1227

607

--

Fluence

(E > 29 fJIHTGR (x ~ / m ~ j

1 .2 1 .7 2.5 4.9 2.9 5 . 9

2.3

1 .2 1.7 2.5 4.9 2.9 5.9

2.3

Average Pe rcen t Change i n CTE

295-773 K (22°C-5000C)

+7 +2 -1 -36 +1 -33

+6

-1 -4 -4 -20 -11 -4 7

+4

Lot

-25 Mean I r r a d i a t i o n Fluence x 10 2

(N/m ) Tempera tu re

GA Locat ion Log No. O r i e n t a t i o n i n Log K O C (E > 29 fJIHTGR

6484- 22 Axial Midlength 1040 767 I 2.4 c e n t e r 1655 1382 2.9

Radial Midlength 101 0 737 2.4 center 1655 1382 2.9

4B

Average P e r c e n t Change i n CTE 395-773 K (2Z0-5OO0C)

+3 -1 2

+7 -1 1

td I

Q\ Y

.

875 890 900

1195 1205 1210 1625 1625 1620

t c 2

602 617 627 922 932 937

1352 1352 1347

TABLE B-16 SUMMARY OF IRRADIATION-INDUCED CHANGES IN T H E W CONDUCTIVITY OF H-451 GRAPHITE IRRADIATED I N

CAPSULES OG-1, OG-2, AND 0 6 3 (ALL SPECIMENS FROM MLC OF PARENT LOG)

~~

GLCC Lot No.

266

266

426

GA Log No.

5651-28

565 1-28

64 84- 34

Orientation

Axial

Radial

Axial

Radia

Me an Irradiation Temperature K OC

875 890 900

1195 1205 1210 1625 1625 1620

602 61 7 627 922 9 32 937

1352 1352 1347

-- 925 652

1615 1342 1220 I 947

--

-25 Fluence x 10 2

(N/m (E > 29 fJIHTGR

0 2.0 3.7 5.5 2 .8 5 . 3 7.7 3.2 6.1 9 .o

0 2 .o 3.7 5.5 2 .8 5 .3 7.7 3.2 6 .1 9.0

0 1 . 8 2.4 2.9 0 1 . 8 2.4 2.9

Mean Thermal Conductivity (W/m.K) f Standard Deviation

At 293 K (2OoC)

145.2 2 1 . 3 34.7 2 1.4 30.1 2 0.9 29.6 2 1.4 48.8 2 1 .8 41.3 2 8.4 43.6 2 6 .8 79.8 f 4.2 80.9 2 4.0 68.9 2 9.2

123.0 2 7.1 32.0 2 1.9 27.8 2 3.1 25.9 2 0 . 8 42.9 f 3.3 34.2 f 4.3 31.2 f 5.1 83.5 5 7.2 65.7 f 8.2 56.2 2 2.8

136.0 f 17.2 34.0 f 3.0 60 .8 4 5.1 82.4 f 1.1

128.9 2 10.0 29.6 2 4.1 58.9 2 3.1 72.4 f 1 . 3

At Irradiation Temperature

-- 33 .3 f 2.7 32.5 f 4.3 31 .5 2 4.4 40.0 2 1.7 39.8 f 3.0 34.1 2 5 .9 41.1 2 1.2 40.7 f 0.6 34.5 2 3.8

-- 33.3 2 2.7 29.5 f 3.2 28.0 f 4 . 7 36.1 2 2.8 29.5 2 2.0 30.7 2 6.1 39.3 f 3.4 36.4 2 2.0 33.1 f 4.4

-- 32.0 f 6.6 39.0 2 6 .7 32.5 f 6.3

29.8 f 6.7 35.4 f 6.4 31.9 f 6 . 3

--

TABLE B-17 SUMMARY O F IRRADIATION-INDUCED CHANGES I N THERMAL CONDUCTIVLTY O F TS-1240 GRAPHITE

IRRADIATED I N CAPSULES OG-2 AND O G 3 (ALL SPECIMENS FROM MLC O F PARENT LOG)

910 915

1220 1220 1620 1615

ucc L o t N o .

637 642 947 947

1347 1342

1

910 915

1220 1220 1620 1615

m I

00 U

637 642 947 947

1347 1342

GA Log N o .

5151-73

5651-73

O r i e n t a t i o n ~~

A x i a1

R a d i a1

M e a n I r r a d i a t i o n T e m p e r a t u r e

K OC

-25 Fluence x 10

0 1.7 3.5 2.5 4.9 2.9 5.8

0 1.7 3.5 2.5 4.9 2.9 5.8

M e a n T h e r m a l C o n d u c t i v i t y (W/m.K) 2 Standard D e v i a t i o n

A t I r r ad i a t i o n 293 K (22°C) T e m p e ra t u r e

97.9 2 8.4 30.5 f 1.2 26.5 f 0.9 45.5 f 3.7 51.5 f 2.1 68.8 t 3.4 66.0 f 7.9

103.3 f 4.2 28.5 f 2.8 27.5 f 0.8 37.0 f 2.2 50.1 t 1.4 64.5 f 5.5 65.4 2 2.8

-- 34.1 f 1.7 27.9 2 5.0 38.2 f 2.4 36.5 f 4.0 37.2 f 1.5 37.5 f 4.6

-- 32.6 f 0.3 25.1 f 3.4 29.9 f 1.7 37.6 2 4.7 33.5 f 1.2 37.0 t 3.5

C '

(N/U12) (E > 29 fJIHTcR

0 1.8 2.4 2.9

I ',

At 293 K (22OC)

135.1 f. 5.0 28.6 ?I 0 .8 50.5 2 0 . 8 64.5 f. 4.9

TABLE B-18 SUMMARY OF IRRADIATION-INDUCED CHANGES IN THERMAL CONDUCTIVITY OF SO81 8 GRAPHITE

IRRADIATED IN CAPSULE OG-3 (ALL SPECIMENS FROM MLC OF PARENT LOG)

4-B

4-B

AirCo

6 4 84-2 2

6484-22 925

1220 1615

Orientation

Axial

6 5 2 947

1342

Radial

Mean Irradiation Tem erature -7F-p-

---I--- -- 925 6 5 2

1615 1342 1220 1 947

I * c

I Mean Thermal Conductivity

(W/m-K) f: Standard Deviation -25 I Fluence x 10

0 1.8 2.4 2.9

125.9 f. 5.0 28.4 2 0 . 8 43.7 f: 4.2 65.8 f: 2.3

At Irradiation Temperature

-- 26.7 f. 4.6 36.7 2 4 .2 34.3 2 4 . 4

-- 27.0 2 5.0 32.3 2 4 .3 33.0 f. 4 .2

- T e m p e r a t u r e

K ("C)

573 (300)

-

w I h) 0

1673 (400)

TABLE B-19 CALCULATED THERMAL CONDUCTIVITY AT IRRADIATION TEMPERATURE OF NEAR-ISOTROPIC G U P H I T E

IRRADIATED BETWEEN 573 AND 873 K (300' AND 600°C)

Fast Neutron Fluence, (N/m2 x (E ' 29 fJ)HTGR

0.9 1.8 2.7 3.6 4.5 8.9 13.4

0.9 1.8 2.7 3.6 4.5 8.9 13.4

T h e r m a l C o n d u c t i v i t y (W/m-K)

R a d i a l

11.7

9.2 7.9 7.1 6.7 5.9

5.9

19.7 14.6 13.0 11.7 10.9 9.6 8.8

A x i a l

13.4 10.5

9.2 8.4 7.9 7.1

6.7

23.0 17.2 15.1 13.8 12.6 11.3 10.5

T e m p e ] K

773

873

. t u r e DC

500

600

-

Fast Neutron Fluence, (N/m2 x (E ' 29 fJ)HTGR

0.9 1.8 2.7 3.6

4.5 8.9 13.4

0.9 1.8

2.7 3.6 4.5 8.9 13.4

T h e r m a l C o n d u c t i v i t y (W/m.K)

R a d i a l ~

28.9 20.9 18.4

16.7 15.1 13.0 11.7

3 2 . 2

2L.3 20.5 18.0

16.7 - 15.5 13.8

A x i a l

0.080 0.058 0.052 0.046 0.042 15.1

0 . 0 3 3

37.2 18 .O

23.8 20.9 19.7 18.0

16.3

i

mc

W

P-

c

Uf

NC

7

-

a 0 T

Li

t

4. 0 E 1 c e L 4 a

c

2 - I

Ji

C

40

4

.r( . m

u0

I u

z

ma

l o

m

B-2 1

(edW) x

vw

~

'SS3YlS 311SN31 lV

3d

0

1,

a

- S/xvWo 'H

19N3tllS

311SN31 NV3W

AB 0301h10 SS

3YlS

311SN31 lV

3d

B-22

n

0

I FQ M

d

k

..

n

, . . . . , . .

. . . . . . . -..

.I .

, ,

C '

I I I I 1 I I I I '

t

" c

MINIMUM STRESS, (JMIN (MPa)

td I h) w

MINIMUM STRESS 'MIN MEAN TENSILE STRENGTH -s

Fig. B-2. Constant life fatigue diagram (Goodman diagram) for H-451 graphite: axial direction (from Ref. 5-10)

W (1 2 a

m -1 t a .+ 0

5 -2

h) z VJ z w E Q -3

-4

0 IRRADIATION TEMP 875 K - 975 K 0 IRRADIATION TEMP 1075 K - 1175 K

1 I I I I I I 1 I

Fig. B-3. Dimensional change in H-451 graphite: axial direction; irradiation temperatures 875 K to 975 K and 1075 K to 1175 K (602' to 702OC and 802' to 902OC) (from Ref. 6-3)

sz-a

N

W

z

c

-4

0

z

n

7 c

rn z

c)

m

rn =a

6

-V

I

0

2

N

VI .

1

3,

VL

n

rn

M

i2 - I -4

D

50

U

OIM

ENSI

ONA

L CH

ANG

E AU

/P (5

6)

0

I 4

I N

I b

w

00

-4

-4

rnrn

55

w

-

UN

m

u

%V

I

!*

G

0 N

LD

m

-

I

Y

’E

-0

7

v)

N

$!

-O

D

-- E

a

I- I

2

--

z A

w - N

E

-L

oN

0

.

2

v)

- W

0 2

W a

A U 2

-eo

a

l- a W

2

-m

-N

q.?

I I I I I I I I I I I I I I I I I

Y

v)

r- 2 I

Y

LD

I- C

C

n

c 2

I- 0

E

5 0 9

a

E

c

N

c)

c

I I

I

(96) bDV

39NVH

3 lVNO

ISN3W

IO

c

0

d I

n

B-26

i c ' ,

B

1625 K

- (1352' 0 IRRADIATION TEMP 1475 K - 1575 K 0 IRRADlATlON TEMP 1575 K - 1675 K

B

0

I I I I 1 I I I I 1 2 3 4 5

NEUTRON FLUENCE (lo25 N/rn2) (E > 29 fJ)HTGR

Fig. B-6. Dimensional change in H-451 graphite: axial direction; irradiation temperatures 1475 K to 1575 K and 1575 K to 1675 K (1202O to 1302OC and 1302" to 1402OC) (from Ref. 6-3)

e 1525 K (1 252OC)

0 IRRADIATION TEMP 0 IRRADIATION TEMP

875 K - 975 K 1475 K - 1575 K

I I I I I I I I I 1 8 9 10

Fig. B-7. Dimensional change in H-451 graphite: radial direction; irradiation temperatures 875 K to 975 K and 1475 K to 1575 K (602' to 702OC and 1202' to 1302OC) (from Ref. 6-3)

!

C ' , c 1

1

0

.o 0- - 1

5

2

9

1 w W L

0 -2

0

2_

a

VI 2 w

-3

-4

0 IRRADIATION TEMP 975 K - 1075 K 0 IRRADIATION TEMP 1275 K - 1375 K

I I I I I I 1 I I

NEUTRON FLUENCE (1025 N/rn2) (E > 29 fJ)HTcR

Fig. B-8. Dimensional change in H-451 graphite: radial direction; irradiation temperatures 975 K to 1075 K and 1275 K to 1375 K (702' to 802OC and 1002' to 1102OC) (from Ref. 6-3)

I I I I ”? I I I I I I 1 I I I I I I

V

0 N

UI

m

Y

u)

N

N

- c

N

m

c

0

c

I

(%I AhV

39NVH

3 lVNOISN3UUIO

!? m

m

b

a a

I- I

=!

A

w E

Wm

N

- N . z

-z 0 - W

0

z

w 3

-I U

bZ

0

a

!- 3

W z

m

N

c

n

B- 30

...

I I I I I I I I .

I

I I I I I Y

Y

mm

w

w

=!e

I

I

YY

00

I c

0

c

N

0

I

(%) rlD

V 39N

VH

3 lVNO

ISN3H

llO

0

U

M UN

a

0

km

d--

a -0

r

lc

cdcd d

av

Cd

O

kN

0

m

a0

&

U

.. c d

o

u

B-31

n

0

- 1

-2

-3 s - w U z I u a

-1 -4 a 0

z

z v) z w

0

0

-- 1

-2

- 3

RADIAL

0 5 10 15 20 25 30 35 40

Fig. B-11. Dimensional changes in near-isotropic graphite irradiated at 6 3 3 K t o 7 7 3 K (360' to 5OOOC) (data from Refs. 6-4 and 6 - 6 )

..

u-32

0

-1

-2

- -3 ae - w c3 2

I 0

a

A -4 a 0 v , '

5

z

z w

0

0

-1

-2

-3

7 SOURCE I RRADlATlON OF DATA TEMPERATURE

K UKAEA I 773-823 500-550 UKAEA 823-873 550-600 DRAGON 1873 600

I I I I I I I

GA 798-868 525-595

AXIAL

RADIAL

5 10 15 20 25 30 35 40

FAST NEUTRON FLUENCE N / d ) (E >29 fJ)HTcR

Fig. B-12. Dimensional changes in near-isotropic graphite irradiated at 773 K to 873 K (500' to 600OC) (data from Refs. 6-4 and 6-6)

B-33

200

100

TENSILE STRENGTH

TI R R = 860- 940 K (587'- 667'C)

DESIGN VE

0

I I 1 I J

TIRR' 1600-1630 K 200

(1327'-1357'C)

loo t ~ 0 DESIGN CURVE

0 2 4 6 8 10

H-451 YOUNG'S MOOULUS

TI R R = 860-940 K 200 *

(587'-667'C)

u t; I! w

W v)

w re 0

a

z

TlRR= 1110-1250 K

T (8370-977'C)

200 c d

200

100

0

TlRR = 1600-1630 K (1327'-1357'C)

T

0 2 4 6 8 10

FAST NEUTRON FLUENCE N h 2 ) (E>29 fJ)HTGR

Fig. B-13. Changes in tensile strength and elastic modulus of H-451 graphite as a function of fast neutron fluences. denote 2 one standard deviation (from Ref. 6-3)

Error bars

.

Q B-34

W I

W cn

C '

+loo . +80 ae

l w +60

3 -20

-40 0

1173 K 673 K CLIrrn,.nn\ m

1673 K % (14OO0C)

A R

0 e 673 K (400OC)

-1 A A 1473 K (12OOOC)

1673 K (14OO0C)

0 1 .o 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0

FAST NEUTRON FLUENCE N h 2 ) (E>29 fJ)HTcR

Fig . B-14. F r a c t i o n a l changes i n sonic e l a s t i c modulus of ex t ruded nea r - i so t rop ic p i t c h coke g r a p h i t e (Dragon code No. 100) (from Ref. 5-7)

FRAC

TIO

NAL

CHAN

GE

IN E

LAST

IC

MO

DULU

S (E

/E,)

AND

STRE

NGTH

(S/S,)

m

I w

m

c

300

200

a

/ /'

I I I I I I 6 8 10 12 0 2 4

FAST NEUTRON FLUENCE N/m2) (E >29 fJ)HTGR

Fig. B-16. Calculated percent increases i n s t a t i c e l a s t i c modulus of near- isotropic graphites ( so l id parts of curves correspond t o data i n Refs. 6-6 and 6-8; broken parts are extrapolated)

B-37

1 4

1 2 I ?

X a -

0.4 t

- - - 0

0

0 0 0

0 90'90 e-3 0

95'95

99/95 -- LOWER TOLERANCE LIMITS

H-451 GRAPHITE AXIAL ORIENTATION MIDLENGTH CENTER LOCATION IRRADIATE0 AT 1173 K (900°C) TO 3.8 x 1025 ~ i m 2 (EFFGO) [3.0 x N/m2 (E >29fJ)HTGRI

1 I I 1 1 I I I l l I I I l l 1 1 I l l I I I l l I 1 1 1 1 IO 100 1000 10.000 101 0

NUMBER OF CYCLESTO FAILURE

Fig. B-17. Fa t igue test d a t a i r r a d i a t e d t o 3.0 x N/m2 (E > 29 fJ)HTGR a t 1173 K (900OC). Log-log p l o t of normalized peak stress ve r sus number of cyc les t o f a i l u r e , w i t h stress r a t i o , R = -1. Lower x /y t o l e r a n c e l i m i t s r e p r e s e n t the ltmtts above wWch x% of a l l d a t a would f a l l , w i th y% confidence; a x i a l specimens; open c i r c l e s r ep resen t run-outs (from R e f . 5-10).

OESIGN CURVE 0

u 0 0 In

0

cv 0

c! Y m

I In

cv

r-

m -40 L

t TlRR = 865 - 1045 K

(592' - 772'C)

0

SYMBOL 0 0

0 8 + A v

0

X

GRADE H-451 H-451 H-451 H-451 H-451 H-451 H-429 H-429 TS-1240 TS-1240 TS-1240 TS-1240 SO818 SO818

LOT 266 266 266 266 426 426

-

-- _ _ -_ _- - -. - .. 4B 40 -

923 K (65OOCl

MLC

MLC

MLE

MLC

2 20 E w I + W W a

a 5

a

E o >

w W z I

I- z w u ce w

-20

n

-40

-60

TiRR 1080 - 1205 K (807' - 932OC)

I I I I

0 2 4 6 8 10

FAST NEUTRON FLUENCE N/m2 (E>29 fJ)HTGR

Fig. B-18. Percent change in thermal expansivity 1295 K to 773 K (22" to 500°C)] of near-isotropic graphites as a function of fast neutron fluence: irradiation temperature 865 K to 1205 K (592' to 932OC) (from Ref. 6-3)

B-39

2o t 0

-20

-40

SYMBOL

e 0

.8 + X A A V

0

I I ORIEN- I L O C A - - ~

H --45 1 H -45 1

H--451 H - 4 2 9 H -429

H -45 1

TS-1240 TS-1240 TSS1240 TS- 1240 50818 SO818

A X R A D A X R A D A X R A D A X R A D A X R A D A X R A D

MLE MLE MLC MLC MLC MLC MLC MLC MLE MLE MLC MLC

r T ~ R R = 1250 - 1380 K (977' - 1107OC) -CURVE

1323 (1050°C) I

-60 I I I I I I 20

0

-20

$ -40 DESIGN CURVE 1523 K (125OOC)

+ DESIGN

I I I I I

0 2 4 6 8 10 12 -

FAST NEUTRON FLUENCE N/m2) (E>29 fJ)HTGR

Fig. B-19. Percent change in thermal expansivity [295 K to 773 K (22' to 500°C)] of near isotropic graphites as a function of fast neutron fluence: irradiation temperature 1250 K to 1705 K (592' to 932'C) (from Ref. 6-3)

B-40

c

0 623 K (35OOC) A 625-773 K (35O0-5OO0C) 0 773-823 K (50Oo-55O0C)

1 -

I I I I

5 C 4

3

2 TEMPERATURE

Fig. B-20. Change i n thermal expansivity of near-isotropic graphite irradiated at 350" t o 55OoC (data from Ref. 6-4 )

B-4 1

AXIAL RADIAL

0 H-451 GRAPHITE, LOT 266

A H-451 GRAPHITE, LOT 426

0 TS-1240 GRAPHITE

0 H-451 GRAPHITE, LOT 266

A H-451 GRAPHITE, LOT 426

0 TS-1240 GRAPHITE

O S 0 8 1 8 GRAPHITE 0 SO818 GRAPHITE

100

50

0

T I R R = 1 1 9 5 - 1 2 2 0 K (922' - 967'C)

I TlRR = 1615 - 1625 K

(1342' - 1352'C)

50 c

TIRR= 1195- 1220 K (922' - 967'C)

TlRR = 1615 - 1625 K (1342' - 1352'C)

X Y

" 0 5 10 0 5 10 a -

F A S T N E U T R O N F L U E N C E N/m2) (E>29 fJ )HTcR

Fig. B-21. Thermal conductivity at the irradiation temperature for H-451 and other near-isotropic graphite8 as a function of fast neutron fluence (from Ref. 6-3)

B-42

20

7 I

c

10

5

/ O 623 K (35OoC) /------------ / -4-

0 0-

0' 0 0 -// 0 0

O O

0

8

SYMBOL

0

S O U R C E T E M P E R A T U R E OF D A T A

U KAEA 643-713 K (37Oo-44O0C) DRAGON 708-723 K (435O-45OoC) UKAEA 723-743 K (45Oo-47O0C) UKAEA 823 K ( - 550OC) DRAGON 895-921 K (622O-648OC)

5 10 15 20 25 30 35 40 0

FAST NEUTRON FLUENCE N/m2) (E >29 fJ)HTGR

6 Fig. B-22. Irradiation-induced changes in thermal resistivity of near- isotropic graphite (data points from Refs. 6-6 and 6-8; curves from Ref. 6-10)

B-43

GENERAL ATOMIC COMPANY P. 0. BOX 81608

SAN DIEGO, C A L I F O R N I A 92138