l v M 'ECO -A".-ts

I,

Source Term Model for USNRCIterative Performance Assessment,

Phase 2

Richard Codell, USNRCTae Ahn, USNRC

John Walton, CNWRA

Nuclear Waste Technical Review BoardLas Vegas, NevadaOctober 14-15, 1992

.1 /

I .

i

i

Introduction* Temperature Model

* Waste Package Failure Model

* Liquid Radionuclide Release

° C-14 Gaseous Release

* Kinetic Effects

* Disruptive Releases

* Support for Source Term Modeling

. .. . .

Canister Temperature Model

* Semi-analytical, conduction only. . . ...

. ..

-

.

. .

. .. .

Unifor'm heat transfer properties

* Heat load can. i. l I I. , - ..

vary in time and ..space

* Mainly used tocanister failure

determine time to

. .11

0Dw

Zonation of Waste17 panels, 7 cells

_ (

= _

I

©DIMENSIONS IN FT

I .

II I~ I N

I I I . .

1.00

U)P4

HE--0.80 -

/ -4

0e4

0.60 -

0

O 40.4 ~~--q

E-H

0.20 -

0.00 -

290.00

* o-e-o--o 500 YRSo3e -e- 1000

g ^ A ^^1 500

g ~ ~~ Fo o o o 2000A A A-A - 3000

---- 96 DEGREES C

FRACTION OF CANISTERS ABOVE THEASSUMED BOILING POINT AS AFUNCTION OF TIMER CODELL 11/6/91

340.00 390.00 440.00 490.00

TEMPERATURE, DEG K540.00

Fuel Temperature vs.Canister Skin Temperature

80.0 _

70.0 -

60.0

50.0

o 40.00

" 30.0

20.0

10.0

0.0

10

0 Data

-~~ Regression0

AT = 228.197 .421443

I * . I I .. eI . . . I I

2 3 4 5 6789100

2 3 4 67891000

Time, years

Il

Other CanisterFailure Modes

Buckling- SCP design, 304L Stainless- Long cylinder- Thickness decreases by corrosion- No air gap- No stiffening

* Initial defectives.

* Disruptive scenarios- Seismic failure- Volcanism'- Drilling

Release Rate Modelsin SOTEC

1. Dissolved and Colloidala. Advective releaseb. Diffusive releasec. Kinetic effects and colloids

2. C-14 Gaseous Releasea. Metal oxideb. Cladding oxidationc. Grain and gap released. Fuel oxidation

I' ! . ,1 .I ,,,9 I I. . .

Canister Corrosion Model

* General

* Crevice

corrosion

corrosion

* Pitting

z

PITSI

INTIATE III

PPs | PITS REPASSIVATE

GROW I

t-1 t2 t3 TIME

Schematic illustration of the use of corrosion, pitting, and repassivation potential topredict the performance of a container

Dissolved RadionuclideRelease Model

6,

(6..

X~'W<r - -

Dissolved inventory

Released but undissolved inventory

I A

Liquid Diffusion Modeldamaged

Id C

rock

= 0.0

rubble-filled air gap intact rock

I , I k .~~~~l I I .I

Plutonium Releases* Pu and Am dominate dose potential,: but

* Very insoluble - Largely ignored in otherperformance assessments

* Kinetic- effects may -play an important partin releases of Pu and-other actinides

* Potential concentrations of Pu taken from databy Nitsche et al, and Wilson et al, E-5 to E-9 M

* Speciation calculations show range reasonableat 250C (not at 85CC)

(

FAST RELEASE OF RADIONUCLIDES FROM HLW FORMS

- COLLOID

o REAL COLLOIDK•'r4 '

o PSEUDO-COLLOID f .

SUPERSATURATION k (~7;.Aj

- SPECIES , covs f

- EFFECTS OF SURFACE AREA -.

- EFFECTS OF RADIATION, STRESS, PREFERENTIALDISSOLUTION AND MICROBE

w-lfvvij '

EVIDENCES FOR KINETIC EFFECTS

- MULTI-PHASE FORMATION(

- PARAGENESIS OF SECONDARY PHASES

- UNSTABLE SECONDARY PHASES WL

4.At, f , d-NA)i / )

- NONPROTECTIVE SECONDARY PHASES

- ENVIRONMENTAL CHANGES

4 ~ ~ \A Ac

Releases of C-14 from Spent Fuel

* Initial cladding oxide and crud

* Grain boundary and cladding gap

* Zircal oy oxidation

* Oxidation of fuel

I

[ I

Crd14C

CFuel Rod

/Gap . Grain Boundary

14C 14

129 12-I 1 I_ 136C 135c1Cs. 1 Cs.137C6 - 137

Cs Cs

,'TC - ,SC

I Sr mSr

UO2 Matrx Cladding

Actlnicles 14C~98%FissionProducts

Location of Radionuclides in Spent Fuel and Potential Releases of C-14'(Apted, el. al., 1989)

.~~~ , .

, I.I 4

Adjusted14 c Content

(Afterin Spent FuelPark, 1992)

(Ci/MTHM)

I Type Burnup U02 Zirc. Hard- TotalMwd/MTHM ll ware

BWR 35,000 0.69 0.48 0.13 1.3 l

PWR 40,000 0.73 0.22 0.26 1.21 -

Average I _ _ 0.72 0.31 0.21 1.24

.9

Model for Release -of C -14

* C-14 is in a reduced state initially in fuel

* C-14 oxidizes to carbon dioxide as -fueloxidation front passes : " -

* C-14 dioxide diffuses out throughin

same twolayers as oxygen diffuses

* C-14 released quic]ap,

kly fromand initial

grainzirc.

boundaries,oxidecladding/fuel

* Minor releases from oxidation of claddingand other metals

Time to Diffuse MostFrom Outer Cladding

C-14Oxide

t,, yrs t2 , yrsT 0 C E=19 Kcal/mol E=25 KcaUmol

350 0.00091 0.00091

300 0.0035 0.0053

250 0.017 0.043

200 0.12 0.55

150 1.3 13

100 27 690

75 169 7800

Il I , 1! -I I

Fuel Oxidation ModelAssumptions:

* No oxidation 'until canister fails

* No protection.I * Oxygen'diffus

- outer layer

of fuel. by cladding

-es through. * .e.g.

representinctwo. layers:3 grain bour idaries

- inner layer representing oxidized fuel

t. Oxide is U307 stochiometrically

* Oxygen 4

* Oxygen I

concentration zero at inner boundary

profiles in layers are at steady state

Shrinking Core Model for Fuel Oxidation

Low conversion High conversion

Oxide Layer Unoxided Fuel

Time Time

Reaction, zone

I

i II II II IIIII

I

II

IIIIII.

-1I - U

R 0 R R 0 R R 0 R

Radial position

I , I .11

C-14 Gaseous Release Model

1 ,

I ..

f : �

Parameter and Model

IdentificationVerif ication

* Grain diameter from micrographs of fuel (20

* Outer layer diameter taken as fragment size

microns)

(2mm)

* Weight gain from thermal gravametric analysisand dry bath experiments between 110 and250 degrees C (PNL)

* Activation energy and diffusion coefficientsadjusted for best fit to oxidation dataon fuel fragments in 8 temperature ranges

* Little data found on C-14 releases from fuel oxidation

I 1. 0 tO . U

I *f I oak;

.9"4

ca

eaC.,

I-

3,500

-- Time, hours

.

Ol.l -A0 - - Time, hours 1,000

-:

1.09

0

I

0012,000

0o Tme, hours 400Time, hours

U)

Q

-4

I

u)c:

5.00 Release from Engineered Barrier

20.00

15.00 -

c' TOTAL FRoo 66 TPIC T5se-U AF A l ID Al-i A If.)

xz ~~~~~~~66eda sFLIEL

10.00 - ILAjLjjln.

EPA Limit Canister Lifetime5.00 200 ± 100 years

/ (00.( AffM (,

()~~~~~~~- () 1 ) 0( I( ( ( ( ) r -r i - {},.Is\ s..i

- - - : . I

'I' I I E,% I /*J:A .

YE I \ sI/tI. (I I (()()().()

25.00

U)-

24 0.00

0

7 15.000

0W10.00

U)

. 0

W

w 5.00

°a, T- OT/L ROt1 66CH3 ( iAP ANlD G'RAIrJ

FLIELF*- LADDOI NO

tIFTRPC TN

Release from Engineered Barrier

EPA Limit- _ Canister Lifetimey ~~~~1000 ± 300 years

0.00

Af~rpa (.*e*Ai,___ Cl - -- ie-- - - -ti - I-- - - -

. . . a . . -

0.0T F -- rFT

2-000.0I 0 1 1 1 1 � -1 , , , 0 , , , r �- _ 7 .. A .

-0 00.0'ri MNEi,,(;(()I(.()-'2 EAIS

(2 C - v.4 Cev%- , ~ t P A .- A-

- _ d--.- - r CI-

- "A ,.- c L

r1~f t -

_.j ( ) (00 . ( ) I ( () () (). )

n.2 C(t'i J S. (2 OL 0) Vt. " t

- -7' T- c wVIIA I -lf

02 t)6M.-k

1- -M" - , 1f'. - I .r .. c "I. *wh - . _ *r-

Transient Oxidation Effects

0.20

0.15

> 0.10

0.05

C)OO 0° , 0 0 5 10 15

hours

Not included in fuel oxidation model

Increase in Surface Area

(liquid and Gas Models)

- STORED ENERGY

EY ( AV) 2

2 ( 1 - 2 v) 3 V

E : YOUNG'S MODULUSv : POISSON'S RATIOAV : VOLUME CHANGEV : VOLUME

- CONVERSION TO FRACTURE ENERGY

I I I I, ? 1 .. I

Disruptive Releases

e Intrusive Volcanism-Dike 1000 - 4000 m long, 1-10 m wide

* Extrusive Volcanism- Cindercone, 25 - 100- m radius

* Drilling intercepts repository- Brings up contents of waste package- Brings up contaminated rock

:

COMPARISON OF INVENTORY TO CURRENT EPA10,000-YEAR CUMULATIVE RELEASE LIMIT AT

ACCESSIBLE ENVIRONMENT AND NRC 10CFR60.113MAXIMUM RELEASE RATES FROM THE ENGINEERED

BARRIER SYSTEM*

GASEOUSRADIONUCLIDES

INVENTORY AT1,000 YEARS (Ci)

EPA 10,000-YEARCUMULATIVE

RELEASE LIMIT, Ci(ANNUAL AVG. CI/YR)

NRC POST-CONTAINMENT

PERIODRELEASE LIMIT

F ROM EBS (Ci/YR)

"4C 62,000 6,200 (0.62) (3)

(..3 /)

**1.07

1"2 1,950 6,200 (0.62) *1.07

SEI-VOLATILERADIONUCLIDES

25,050

806,000"Tc

62,000 (6.2)

620,000 (6.2)

62,000 (6.2)

(1.1)

(.31)

"*1.07

8.06

e'1.0721,390

"BASED ON 62.000 MTIHM SPENT FUEL*NUCUDES FOR WHCH TNE MAXIMUM RELEASE RATE IS GREATER THANI X 104 PER YEAR IHVENTORY BECAUSE OF THEIR SUMALL INVENTORIES HUPS 12SNW TR" 2527 91

. .

It I 14 -I . I4

VAPOR PRESSURES

SPEC=E,.. VAPOR PRESSURE (ATMOSPHERES)

CO2-

1 00°C. * I . .

4 , .2C

2100°

> 12,000

12 6 x 10-2 3.7

Tc 2 07

9.1 x104

1.2 x 104

5.4 x 10-2

3.7 x 10-2

(FROM LANGE'S HANDBOOK OF CHEMISTRY, 13TH EDITION, 1985)

. An..pt.-/ NRGIVKSP. 125 NWTRB6 22-91

Biggest Information Needsfor Source term

* Integrity of canisters?

* How does water get into canisters?- drying of rock- saturation and rewetting- flow rate back to canisters

* How does water interact with fuel?

* Does cladding offer protection?

* Are kinetic effects important? Will colloidsform as fuel disintegrates, and are theyimportant for transport of randionuclides?

I * I I. I I~~~~~~*i b' * k ,- & W. .. I ..S

.% J , -

Conclusions

NRC SOTEC model includes:

* Waste package-- ~ ~ rz

failure

* Release of liquid- Colloids treated

(dissolved)by empiric

radionuclidesal data -

* Gaseous releases of C-14

Other analyses and codes -for:* Other gaseous nuclides* volcanic intrusions* drilling

I.

Work at NRC and CNWRAin Support of Source Term

* EPSPAC - Detailed Source TermModel

* Natural Analogs- Alligator Rivers- Pena Blanca- Santorini-- Cigar Lakes- Oklo

* Kinetic Effects of Fuel Dissolution

* Thermodynamic Properties of Actinidesin High-Temperature Aqueous Solutions

* Metallic Phases in Spent Fuel