lamb - curium-244 heat source fabrication

8/4/2019 Lamb - Curium-244 Heat Source Fabrication

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DRAFT

CURIUM-244 HEAT SOURCE FABRICATION*

Contribution t oAVAILABILITY A N D COSTS O F CURIUM-244FROM POWER REACTOR FUEL WASTES

Eugene Lamb , ORNLD. G. Albertson and Paul BrownGeneral Electric

To b e presented a t

Intersociety Energy Conversion ConferencePhiladelphia, Pennsylvania

August 1973NOTICEThis report was prepared as an account of worksponsored by the United States Government. Neitherthe United States nor the United States Atomic EnergyCommission, nor any of their employees, nor any oftheir contractors, subcontractors, or their employees,makes any warranty, express or implied, or assumes anylegal liability or responsibility for the accuracy, com-pleteness or usefulness of any information, apparatus,product or process disclosed, or represents that its usewould not infringe privately owned rights. M A S T E R

*Research sponsored by the U. S. Atomic Energy Commission under contractwi th Union Carbide Corporat ion .

DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED


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DRAFTELtskwMay 2 3, 1973

Curium-244 Heat Source Fabrication

Curium Fuel Form FabricationThe selection of curium sesquioxide (2'-'tCm203) as the fuel form

for isotopic power applications was on the basis of its thermal stability,high melting point ( 2 2 6 5 C ) , low vapor pressure , compatibility withpotential encapsulant al loy s, and fabricability. Its relatively lowthermal conductivity (0.01698 W/cm.C at 1000C) can impose a limita-tion on the diameter of fabricated ^^ Cn ^O a fuel forms in order to mai n-tain the centerline temperature in a safe operating range. Because ofits inherent neutron emissions , fabrication operations involving hundredsof gram s of ^'Cn^Os must be conducted remotely in shielded cells withmanipulation of equipment and materials by master-slave manipulators.

For applications in thermoelectric generators the external tempera-ture of the zt* kCm 203 fuel will be in the range of 800-l400C, and thediameter of the fuel wil l be in the range cf 0.25 to 1.0 in. , dependingon the design of the converter system. Fabrication of densifled 2tft*Cm 203fuel pellets in this size range h a s been demonstrated using the hot -press method . A prototype source wa s assembled and operated for 22 mont hsusing 412 g of 2tfJfCm 203 emitting 956 t . The fuel consisted of 14 hot -pressed pellets, 0.531-in. diameter by 0.63- to 0.9-in. h i g h .

Developmental quantities of 2tfl*Cm have been furnished by SavannahRiver Laboratory for determination of properties and development of fabri-cation techniques at ORNL. For the large-scale applications envisionedin the late 1 970' s, the large quantities of relatively low-cost 2


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discharge fr^.s a Pressurized Hater Reactor (PWR) after 33,000 KHD/Tonneexposure i s given i n Table 1 .

/ Table 1 . Isotopic Composition o f Curium i n P W R Fueli Y'. 1 5 0 ays After Discharge With 3 3,000 KWD/T Exposure

IsotopicHaas242243244245246

Weight(%)13.670.2080.35.260.6

Half-Life(years)0.44632.

18.123 2 6 5 .4 6 5 5 .

HeatG r a n Generationof Curium16.212 . 2 8

per< w r )

Because o f t h e relatively high concentrations o f 2 < > 2C m i n t h e powerreactor fuel a t discharge, t h e heat generation rate o f t h e isotope i s afactor o f 7 . 1 higher than that o f 2t>t>Cm p e r gran o f curium. I n ordtr t omeet t h e apecification that t h e heat contribution from 2 t | 2 C a b n o w o r ethan I X o f t h e heat generated b y 2****C a t tine o f generator fueling, adecay period o f five years will b e allowed from reactor discharge t cgenerator fueling. T h e iaotopic composition o f t h e curium a t five yearsafter reactor discharge i s given i n Table 2 .

'V \ Table 2. Isotopic Composition of Curium') / Recovered From P W R W aste (33,000 M WD/T)'/j Five Yeara After Reactor DischargeIsotopic Mas s Weight Z

242 0 . 0 1 5243 0.2492 44 9 1 . 7 5245 7 . 1 6246 0 . 8 2


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T h i s n e c e s s a r y d e c a y p e r i o d c o i n c i d e s n i c e l y w i t h t h e p l a n n e ds t o r a g e o f a q u e o u s f u e l r e p r o c e s s i n g w a s t e s f o r t h r e e t o f i v e y e a r sb e f o r e c a l c i n i n g a t s o m e f a c i l i t i e s . T h e r e c o v e r y o f c u r i u m w o u l d b ep l a n n e d t o o c c u r a t a b o u t f o u r y e a r s a f t e r r e a c t o r d i s c h a r g e , a t w h i c ht i m e t h e t r o u b l e s o m e s h o r t - l i v e d h e a t p r o d u c t s o o n g t h e f i s s i o n p r o d u c t sa s w e l l m * t h e 2 < * 2C w i l l h a v e d e c a y e d t o r e a s o n a b l e v a l u e s f o r i o n - e x c h a n g ea n d s o l v e n t e x t r a c t i o n o p e r a t i o n s .

B a s e d o n p r e v i o u s p r o c e s s i n g o f2 < t < >

C a a t S a v a n n a h R i v e r L a b o r a t o r y ,t h e s e p a r a t e d p r o d u c t w i l l b e p r e c i p i t a t e d a s c u r i u m o x a l a t e w h i c h w i l lb e c a l c i n e d t o p r e p a r e s l i g h t l y s u b s t o i c h i o m e t r i c C m O 2 a s t h e f o r a t o b es h i p p e d t o t h e f u e l f a b r i c a t i o n p l a n t . I n th e c a s e o f f u e l p r e p a r e d a sh o t - p r e s s e d p e l l e t s , t h e f o l l o w i n g s t e p s a r e i n v o l v e d i n t h e f u e l f a b r i -c a t i o n p r o c e s s :

1 . R e m o v e C m O z f r o m s h i p p i n g c a n * , a s s a y h e a t c o n t e n t , i m p u r i t i e s ,a n d m e l t i n g p o i n t .

2 . C o n v e r t t o C S 2 O 3 b y h e a t i n g a t 1 0 0 0 * C i n v a c u u m o r i n e r ta t m o s p h e r e f o r 4 h r .

3 . L o a d h o t - p r e s s d i e ( g r a p h i t e ) w i t h a s s a y e d i n c r e m e n t i n a r g o na t m o s p h e r e .

4 . V a c u u m h o t - p r e s s a t 1 4 50 * C a n d 4 0 0 0 p s i f o r 1 h r .5 . E j e c t p e l l e t s i n a r g o n a t m o s p h e r e , m e a s u r e , a n d w e i g h . '6 . O x i d i s e r e s i d u a l c a r b o n o n p e l l e t s u r f a c e b y h e a t i n g a t 1 0 0 0 * C

f o r 4 h r i n a r g o n w i t h a n o x y g e n c o n c e n t r a t i o n o f ^ 2 0 0 0 p p m ; r e d u c eo x y g e n c o n c e n t r a t i o n t o < 1 0 0 p p m a n d c o o l t o c e l l t e m p e r a t u r e .

7 . L o a d a n d w e l d i n n e r c a p s u l e ( p o s t -i m p a c t c o n t a i n m e n t s h e l l ) ,q u a l i t y c o n t r o l p r o c e d u r e s .

8 . L o a d a n d w e l d h e a t s o u r c e a s s e m b l y , q u a l i t y c o n t r o l p r o c e d u r e s .


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The design o f a vacuum h o t press used i n t h e ORNL fu el developmentprogram i s shown i n Pig. 1 a n d typical hot-pressed pelle ts a r e shown i nFig. 2 .

The resulting 2t|t*Cm2C>3 pelle ts w ill hav e a maximum density o f 1 0 . 3g / c m 3, o r 9 0 % o f theoretical density with allowance f o r t h e effect o ndensity o f 3 % chemical contaminants consisting c f light elements. T h especific power a n d power density o f hot-pressed 2l>l*Cm203 a r e given :lnTable 3 .

Table 3 . Specific Power a n d Power Densityof 2 1*Cm203 Recovered From P W R WasteTime After Reactor Specific Power* Power DensityDischa rge (years) (W/g o f C m 2 O 3 ) (W/cm 3 o f

45689

1 0*Heat contribution from 2**2Cm i s n o t included. T h e c o n -tribution o f 2t* 2Cm a t five years i s 0 .0 2 W / g o f C1B2O3.Power density calculated o n t h e basis o f 10.3 g / c m 3fuel density.

2.302.212.132.051.981.901.83

23.6822.8021.9621.1520.3619.6118.88

Fig. 1 . Vacuum H o t P r e s s .Fig. 2 . Typical Hot-Pressed Pellets .


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\Fuel forms of ^^Cn^Oa other than hot-pressed pellets may be feasible

for future application s. Other forms under consideration are as-preparedC1112O3 pow der and sint ered C1112O3 shards (prepared by cru shi ng sin ter ed Cm 203and sizing of particles) which are tamped or step-pressed into a capsule.Th e use of C1112O3 pow der loaded direc tly into a capsul e of fer s a pot ent ialsaving of 5 0% of the fabrication cost of hot-pressed pellets if a con -verter system can utilize fuel which is in the order of 5 0% of theoreticaldensit y. Experience in the fabrication of this fuel form is not availableat this tine.

Curium Fuel Handling ProceduresThe handling of curium fuel after It is converted to C1112O3 requires

that careful attention be given to the quality of the cell atmosphere andheat removal from the powde r. Because CU2O3 can be oxidized to higher ox idesof curium in an oxygen atmosphere below 8G0* C, a dry, inert atmosphere(urually argon ) with


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due to internal heating . In gen eral , batch quantities of powder.areless than 10 g and layers of powder are less than 1/4-in. thick toprevent clumping.

Vesse ls and tools used fo/ in-cell transfers of curium oxide powderand pellets are stainless steel and are individually cooled where necessaryto provi de for heat removal from larger quantities of curium. Containersfor long-term storage are platinum-lined to preclude possible contami na-tion of the curium fuel.

Curium Fuel EncapsulationA nu mber of metals and alloys are being considered as potenti al

encapsulants for ^'Cn^C^ for space applications. These include super-alloy s (Haynes-188, Hastelloy C - 2 7 6 ) , refractory alloys (W-26% Re , T - l l l ) ,and noble metal s and alloys (Ir, F t 20% R h ) . Welding procedures aredeveloped for a particular alloy and source design using available remotevelding technology developed at ORNL for the inert gas-tungsten a rc .plasma a rc, or electron beam methods. Quality control procedures usedon completed welds include helium or 8 5 Kr leak testing and sectioningof sam ples welded under the sa me conditions and immediate in-timin g tothe fueled capsule wel d. Remote ultrasonic probe determinations of weldquality and penetration h as been utilized for 9 0Sr heat sources and can beadapted to curium sources having the necessary weldment design for thisprocedure.

Careful consideration of clearance between pell ets and the capsule wallmust be given for a feasible and economical laodlng operation. Thisclearance is usually a compromise between the desire of the fuel fabricatorto have plenty of clearance to preclude any binding of pe llets and the


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need the system designer to minimiz e gap width and temperature in crease

across the gap . In gener al, a diametral clearance of 0.020 in. for cap-sules several inches in length is worka ble.

A fabrication loading tolerance of 5 % of the nominal t hermal poweris allowed for single pellets or for small units contining less than 10pellets. This tolerance represents the estimate of ability to achievethe nominal power and does not represent the variation in the abs olutemeasur ement . In the case of assembly of multiple units or pe lle ts,lower power units can be matched against higher power units so that theoverall loading tolerance for assemblies using 10 or more small units orpellets will be 2% .

Decontaminati on of s ingly encapsulated heat sources to the usual

low surface contamination specifications required prior to assembl y intoa power generator usually represents a considerable expenditure of timeand mon ey. If the system design permi ts, a second encapsulation in aclean cell separate from the fuel loading cell greatly reduces the sur -face contamination problem.

Production-Scale Curium Source Fabrication Plant StudyA preliminary study has been made for the conversion of an existing

manipulator cell facility to provide a nominal curium source fabricationcapability of 1 0 kg of 2tft*Cm annually with the capability of expansion to20 kg annually. In this facility the source fabrication operations wouldbe done in 11 in-line cells with material transfer ports in the celldividing wa ll s. Seven of the cells would be maintained under argonatmosphere during source fabrication operation s. The nominal interior


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8dimensions of the cells are 7-ft wide by 8-ft deep by 11-ft verticalheight above the work tray.

The cost of equipment to be installed in the cells is estimatedto be $600,000 including vacuum hot presses, calorimeters, welders,NDT instrumentation, furnaces, and speciallized tools and manipula tors.For the 10 kg/year production level the cost of curium source fabri ca-tion is estimated to be $42/W , based on 10 sources requiring 1 kg of2tft>Cm each. This is a very preliminary estimate based on a single sourcedesign concept with no detailed design or specifications; theref ore, theactual cost can vary considerable from this depending on the actualsource design and specifications.

The fabrication facility would be capable of processing at greaterrates with comparatively small increases in operating cost, assuming thecomplexity of source design does not increase. For a 20-kg/year through-pu t, the source fabrication is estimated to cost $28/W .


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ORNL-DWG 65-7974R

HYDRAULIC CYLINDER

HEATING E L E M E N TP UN CH

VIEWING PORT

R COOLEDB A S E

S A M P L E

WATER-COOLED, THREADEDELECTRICAL CONDUCTORS

WATER COOLEDBELLOWS

WATE R COOLEDVACUUM JACKET

PUNCHMOLYBDENUM HE AT

REFLECTORDIE BODY

Miniature Hot Press

I*oiuus


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lamb - curium-244 heat source fabrication

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