Civilian Radioactive WasteManagment system

Managment& OperalingContractor

___TRW Environmental Safety

Systems Inc.

In-Package Geochemistry

IHarlan Stockman

April 20,1999Las Vegas, NV

TRW Environmental Safety Systems Inc.B&W Services, Inc.Duke Engireerfn & Servie. hic.FluKr Dariei, Inc.Franatoe Cogema FuelsJAI Co 1

JK Research Associates. Inc.Lawrence Berkeley LaboratoyLawrence Uvermore National LaboratoryLos Alamos Nainal LabtatoryMs 0 en Cowaion

Sandta National Laboratories

Scece A Inte inal CoScience & E isering Associales, kw.Ww & StrawnWoodward-Clyde Federal ServicesC g FeWAqenq

U.S. Geogical Survey

72hw) /Xo -v

In-Package Geochemistry: Outline

(1) Purpose of Calculations(2) Review of Waste Packages (Commercial vs. DOE SNF, MD)

(3) Methods(4) Example (FFTF)(5) Needs and Work in Progress:

- Couple Geochemistry/Transport of Package and Near-Field

- Evaluate Models for Variably-Saturated WP Degradation and Flow

- Address Thermodynamic Data Needs

- More Realistic Rate Models

- Evaluate Effective Package/Near Field 02

- Cr example: Thermo data vs. f02 modeling

Cilian Radfoactive Waste WMI~ouij Pops 2 AiMd 20. 1999

Manageent SystemMR&C( or

(1) Purpose of Calculations

(a) Develop configurations/compositions for "internal" criticalitycalculations (within WP). Package degrades from water influx.

Probability of internal criticality increases if neutron absorbers are removed andftsile materials remain in package. Conservative to assume most insoluble formsof Mssile materials; e.g. PuO2 vs. Pu(OH)4.

(b) Develop configurations for external criticality (outside WP). U & Pu-bearing water leaves package and flows through drift materials andfractured tuff. Assess masses of U. Pu & absorbers deposited ex-package.

Probability of external criticality Increases if neutron absorbers remain in thepackage, and fissile materials are released. NOTconservative to assume mostinsoluble forms of fissile materials in package.

(c) Recent change in scope: provide chemistry and source term for PAtransport calculations. Add nuclides such as =Np.

Civilian Radioactive Waste ftS6ILUO Pge 3 Apd 20. 19

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(2) Codisposal Package Will Have High Glass/Fuel

Commercial Codisposal

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tainless Basket DOkeSNF CanIster (316L) & Fuel Assemblies;Basket Doped with GdPO4

Civilian Radioactive WasteManagment SystemManageMe & Ope&gCons

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(3a) Methods for In-Package Geochemistry Calculations

- Use modified (and qualified) version of E06 code, with solid-centeredflow-through (SCFT) mode. "Bathtub" has influx of J-13-likewater, mixing with water in package; outflow=inflow rate.

- Set up matrix of conditions: vary rates of J-13 flux, corrosion rate ofsteel, glass and fuel. Typically use 20 to 40 runs.

- Some runs broken into stages, with sequential exposure of packagecomponents.

- Runs produce: time-resolved pH and compositions (e.g. Cl; S04-,dissolved Fe) and volumes of aqueous phase (in and leavingpackage) and corrosion products.

Current qualified version of EQ6 has no radioactive decay; must post-decay 2 39Pu (conservative for internal criticality).

Civilian Radioactive Waste HhSun_ PagGS Api 20. 1999

Management SystemMaLage & Operating

(3b) Bathtub with SCFT (Solid-Centered Flow-Through)

- Constantly overflowing bathtub,causes continual dilution of aqueousphase-4 removal of neutron absorbers(eg. Gd, B).

-Assume Affoy 22 CRM is -4uert.

- Remnant heat and gas bubbling allowsome circulation.

- Calculation may be broken into stages,JILZ yF. \ Nl~f +; >~26Xi 'v>3 E .for greater realism or to achieve most

1 We,>z&,v,,;7<(211 extreme pH conditions.

g\M v^Z~s , Y \-\9>lJ * Calculation suite varies drip rates andcorrosion rates of steel, glass, and fuel

- 4 (-1 to 3 orders of mag. variation).

- Base caseJt 2 -0.2 atm

.,- Sensitivity studies to judge effects ofniecti~e-nicli lower oxygen potential, CO2, "J-13"

te- ~~~~~~~~~~~~~composition, gjass composition, theruuodata, Fe-oxides...

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Clvilian Radioactive Waste Pag6 Ap 2 1999

Management SystemManagemen & opertingContor

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(4c) 2nd Stage, Major Minerals Stabilize by 5000 Years

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(4d) 2nd Stage, Pu Speciation (GdPO4 Basket)

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(4e) All FFTF Scenarios: "Average" Aqueous Pu?

1E-1 I - :al l I Pu1E{12 _---0fal 112 Pu1E.03 & _-__211 __u

1E-04 -____ __ -_ _ ---- abc r22 Pu_ E5 --- Oa2211 PUoIE-06 748- F I- -- t '- - - _*f2 Pu

!E-08 -f g 1021 PulE-S i- - - - fWg2O2 PuIE-10 __ J~is 2Wg2022 Pu

tE 12 J_ _ _ __ - _ - ____ ...2022 PuIE-13 ( - ! | {sOa 2 Pu

IE+1 IE+2 1E+3 1E+4 IE+5 1E+6 fsOS2022Pufs2_2022 Pu

Tune (years)

Aqueous Pu for FFrF DOE SNF models. Log10(fCO2) - -2.5. High Pu occurs mainly when glasscanister degrades rapidly with fuel exposed. Dip rates vary 0.0015 to 0.l5m3/year, SS from 0.1 to Ipiyear, glass and fuel rates vary by -2.5 orders. Imm owfi ra fr BBA8OOO-1717-I7014- REV 0w. co (r fieIz~SfW: SS~cel rate (I=low. 2=high); G=Olass rate (O1i rece, Iu~w. 2=iig); FFul rae(1=ow 2=lii-; Wdrp rae(Iu.OO15. 20.015, 3=.15).

ivlian Radioactive Waste' H p II , lgManagement SystemManagenelSOpemlingc MA.

(5a) Couple Geochemistry of Package and Near-Field

Feed outputs of in-package calculations into near-field transport and chemistry.

Approaches:-New EQ3/6: flow-through with variable saturation; passes output solutioncomposition from one run to next. Each EQ6 "cell" sees a time-varying outputfrom previous. Transmutes and tracks daughters (e.g. =Pu -> =U).

-GRIM code from Sandia - couples outputs/inputs from series of EQ3/6 runs,decays and sorbs between cells if desired, does all bookkeeping for DTN.

-PHREEOC v2 under qualification at M&O -dual porosity, solid solutions,dispersion (also has reactions, decay, sorption, 1 D advective transport). Aidsqualification of other codes; may be necessary for fractured material. EQ6DB will be ported to PHREEQC:

-LaGrangian version of EQ316 under development at LLNL - like adaptivelygridded" version of PHREEQC, stronger ties to current EQ6 models.

Need consistency in Pu solubility control.

Cvwian Radioactive Waste WSUa_" Pag. 12 Apri 2D 1999

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(5b) Model "Drip-Through" Package (Variable Saturation)

Consider possibility that no significant stagnant pools form inpackage; water drips through from inlet to outlet, intermittentlycontacting package components.Consistency with VA/other M&O models?

Patch corrosion model=> low probability of breaches = eitherpartial bathtub or no water in package at all to -n-104 years.Need to iterate: PA must calculate probability of bottombreach based on calculations of in-package chemistry.

Will drips that run over package components reach saturation beforehitting a stagnant pool (or leaving package)?If any stagnant pools are present, will their effects overshadow drip-through?

Cvilin Raioactive Waste Io~a*u Paw 13 At20.19W

Mna SystemManaen &Opoiab

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(5c) Address Thermodynamic Needs

Examples of Specific Needs:

PuO2.nH20, Np solids, Th& Pu phosphate complexes, Crcompounds, U solid phosphate data, standardization on NEAactinide data.

Temperature issues:

Most data for 25C only; desirable to extrapolate to ~60C; in VApackages may not cool below 50C for -30,000 years. With newthermal loading, this may be less of a issue.

Qualification:Need consistent databases across M&O. Most data additions &corrections performed for previous studies; must document via3-15 or 3.12 process.

Civilian Radioactive Waste i-p 14 APm 20 199

Management system

Cut~ Oerf

(5d) Example: Th and Pb Solubility in Glass Waste Models"Okd' = EQ3J6 coi database (cwirent). From SAND95-2730

Phosphate-beaing glass, no matrix, PC02=1035 Femald glass, O.P.Cement matrixI g .1l~I I .... * I ..le-2

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expenments)

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(5e) Moire Realistic Rate Models

Useful addition to EQ6: Composition dependence for "specialreactants" - rate laws with no saturation check, but pH dependence.

Glass rates probably very "conservative"; assume all cracks availableas surface area. May greatly overestimate overall dissolution rate?

Importance: glass dissolution in DOE SNF can create conditionsthat dissolve all U and Pu.

Develop effective rates for intermittently wet solids in "drip through"model, ffthe drip-through condition is shown to. have significant effect

on source term.

Do complicated rate laws (e.g. TST for dissolution and precipitation) add

useful realism? (Answer probably not, at current levels of uncertainty.)

Civili RadioacUve Wasteantent SystmMangemnt&OPfWat9

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Paw le A0#20. *999

(5f) Worth it to Add TST Rate Laws?From SAN95-2730

No matrix, C02, Qtz TST ppnle+O

-0a) le-1ECWo 1 e-20(n(0co

1le-3

(0

0E le-4=n

Transition State Theory Rate Law forGlass Dissolution:

Rate (in moleslsec) =

S k. (alNj + a V2 ) . ( - (QIK~a)ll

a = H+ activity; N- -1; N 2- 0.4.

K = quasi-solubility product forhypothetical SiO2-rich surface layer.

Model calculation: glass marbles -I cmdiameter, with 0.04 cm diameter quartzsand in interstices, water-saturated,sand/glass 1/300 by weight; ppn lawderived from TST dissolution law.(New EQ6 mode to model glass dissolution describedin SAND95-2730.)

I e-5

0 10 100

Ume (yews)1000 10000

Civilin Radioacve Wastenent System

Mam& Opera

Page 17 AvI20 .ig

(5g) Evaluate Effective Package fO2�1

Stagnant zones may control to lower f02 (at later times, after radiolysis effectslessen). Surface waters (e.g. streams) and aerated ground waters have redoxcouples that suggest effective 2 << 0.2 atm.Importance:

(1) pH control from chromium oxidation:

Cr+ H 2 0+1.502 = CrO + 2HIn Pu-ceramic WP calculations, dropping f02 to 10-10 reduces Gd loss(from GdOHC03) from >50% to <1% (by preventing low pH extremes).(2) At lower oxidation states, actinides can be much less soluble; e.g.Pu(V) carbonate complexes much less stable than Pu(Vl).

Methods:Sensitivity studies determine minimum f02 for significant impact.Detailed models of oxygen diffusion and consumption within package.

IIII

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Civlan Railoaclve WasteManagement systemMa mont&OpemtingCo!rack

Pang 18 Api 20.4 1g9

(5h) Joes it Help to Add Cr Thermo Data for Cr SolubilityControl at 0.2 atm fO2?

Added to date:New BaCO3 / Ba complex data (affects Cr concentration by stabilizing BaCrO4) inglass systems. Very limited effect.

KFe3(CrO4 ) 2(OH)6 and KFe(CrO 4) 2:2H2 0, Fe3(OH)7CrO4 FeOHCrO4 , FeCro4+ (solidsundersaturated in most runs; no effect, only significant under acid conditions, andwhen Fe activity is kept high, as before Fe(OH)3 ripens to FeOOH).

NiCrO4(Ni(OH) 2) 3 and NiCrO4(aq) (undersatutrated in all runs; no effect).

(FeCr)(OHl) 3 solid solutions: very low Cr activity coeffcients at low Cr content(-0.001). However, only significant when precipitation of FeOOH is suppressed, andFe(OH)3 is orders of magnitude more soluble.

(FeCr)OOH (Cr-Goethite solid solution -- up to 11 % Cr substitutes, but no publishedthermodynamic data exist -- contact Alex Navrotsky?).

CrO4= substitution for S04= (Can infer thermo data, but the substitution is significantonly when abundant, insoluble sulfates exist -- e.g. BaSO4 ).

Civilian Radioactive Waste "'S- Pas AP- 20.199

Uanag!Mat SystemIanagement & Operatng

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