GRASS-SST: A Comprehensive, Mechanistic Model for the Prediction of Fission-gas Behavior in UO₂-base Fuels during Steady-state and Transient Conditions

Technical Report · Thu Jun 01 00:00:00 EDT 1978

DOI:https://doi.org/10.2172/6556805· OSTI ID:6556805

Rest, J. ^[1]

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1. Argonne National Laboratory (ANL), Argonne, IL (United States)

The steady-state and transient gas release and swelling subroutine (GRASS-SST) is a mechanistic computer code for predicting fission-gas behavior in UO₂-base fuels. GRASS-SST treats fission-gas release and fuel swelling on an equal basis and simultaneously treats all major mechanisms that influence fission-gas behavior. The GRASS-SST transient analysis has evolved through comparisons of code predictions with the fission-gas release and physical phenomena that occur during reactor operation and transient direct-electrical-heating (DEH) testing of irradiated light-water reactor fuel. The GRASS-SST steady-state analysis has undergone verification for end-of-life fission-gas release and intragranular bubble-size distributions. The results of GRASS-SST predictions for transient fission-gas release during DEH tests are in good agreement with experimental data. Comparisons of GRASS-SST predictions of gas release and bubble-size distributions with the results of DEH transient tests indicate that (1) coalescing bubbles do not have sufficient time to grow to equilibrium size during most transient conditions, (2) mobilities of fission-gas bubbles in UO₂ are enhanced during nonequilibrium conditions if the excess pressure in the bubble is sufficient to generate an equivalent stress greater or equal to the yield stress of the surrounding matrix, and (3) channel formation on grain surfaces and coalescence of the channels with each other and with the tunnels of gas along the grain edges can contribute to grain-boundary separation and/or the rapid, long-range interconnection of porosity. The phenomena of grain-boundary separation and/or long-range interconnection of porosity provides an important release mechanism for fission gas that has moved out of the grains of irradiated fuel.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE; USNRC
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 6556805
• Report Number(s): ANL--78-53; NUREG/CR-0202
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
220300* -- Nuclear Reactor Technology-- Fuel Elements
ACTINIDE COMPOUNDS
BUBBLES
CHALCOGENIDES
COMPUTER CODES
CRYSTAL STRUCTURE
FISSION PRODUCT RELEASE
FISSION PRODUCTS
FLUIDS
FUEL ELEMENTS
FUELS
G CODES
GASES
GRAIN BOUNDARIES
ISOTOPES
MICROSTRUCTURE
OXIDES
OXYGEN COMPOUNDS
POROSITY
RADIOACTIVE MATERIALS
REACTOR COMPONENTS
SOLID FUELS
SWELLING
TRANSIENTS
URANIUM COMPOUNDS
URANIUM DIOXIDE
URANIUM OXIDES