Used Fuel Disposition

Fuel Matrix Degradation Model

James Jerden, Kurt Frey, Bill Ebert Argonne National Laboratory ACKNOWLEDGMENT: This work is supported by the U.S. Department of Energy, Office of Nuclear Energy, Used Fuel Disposition Campaign

Used Fuel Disposition

6/7/2016 UFD Working Group Meeting 2

Used Fuel Disposition

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MPM couples cathodic and

anodic reactions

(new FY16)

Used Fuel Disposition

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MPM couples cathodic and

anodic reactions

H2 Effect: anodic protection of fuel

10-4 g/m2yr 1 g/m2yr

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Hypothetical Source Term for FMDM x 50GWd/Mt Inventory:

6/7/2016

Steel consumed

H2 effect

Steel acts as a sacrificial anode

for used fuel

Time After Canister Failure (years)

Constant temperature (40oC)

Used Fuel Disposition

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Dose Rate: Burnup, Spatial profile, Decay

Secondary Phases: U(VI) Precip. on Fuel

Diffu

sion

Te

mpe

ratu

re D

epen

denc

e

Complexation Carbonate

Process Modules In-Package→

Near Field

Surface Area

Steel Corrosion: Source of H2, Fe2+

Steel Passivation Mobile

Radionuclide Inventory

Radionuclide Mobilization

FMD Model GDSA PA Model (PFLOTRAN)

Fraction of Fuel Matrix Degraded

Solubility Limits

RN Inventory

Interactions with Bentonite

Mass/Area/Time

H2 Effect: ε-phase (NMP) Catalysis:

Radiolysis: Oxidant Rate of Production

Interface does not change: needs to be updated, optimized [FY17]

Output Interactions with Steel Corrosion Products

Input

Temperature Burnup

[H2] [O2] [CO3] [Fe] Mass of steel (?)

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FY16 Integration Accomplishments – As part of the addition of steel corrosion to FMDM we optimized the code:

• Improved math for flux calculations to improve stability and avoiding recursion • Code profiling to identify computing bottlenecks and approaches to addressing these:

sparse functions, clean up how U oxidation/reduction in bulk reactions, etc.

Fuel Matrix Degradation Model: Development and Integration

FY17 Needs – Update & optimize FMDM – PA

interface code (FMDM Fortran): • Build on successful integration runs by

GDSA in FY16

– Validation of FMDM rates – Investigate processes that could

counteract H2 effect: Br, S, others? – Communicate with canister

design/selection group - inform decisions where there is flexibility in design

Used Fuel Disposition

Discussion Slides

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Fuel Matrix Degradation Model V.3

Decoupling of fuel and steel domains allows

variable relative domain areas and leak rates to

environment

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Ideas for optimization

Use sparse functions: The overall FMDM system is very sparse (>99.5% of matrix have values of zero). Sparse matrix implementation would probably speed things up considerably – not done originally because we didn’t want to complicate building the code with the need for external libraries.

More than half of the total simulation time for a 100ka run is spent on getting the

very first time step to converge. Later time steps use the solutions from previous time steps and finish much more rapidly. Need to store FMDM step results rather than re-initializing (already done?).

Getting rid of recursion in the surface reaction function wouldn’t speed things up

too much because it doesn't branch out with multiple self-calls; it's really two completely different functions that were lumped together. The motivation for that lumping was to avoid duplicating the surface reactions in multiple places.

6/7/2016 UFD Working Group Meeting