Mechanistic Prediction of Fission-Gas Behavior During in-Cell Transient Heating Tests on LWR Fuel Using the GRASS-SST and FASTGRASS Computer Codes

摘要

GRASS-SST and FASTGRASS are mechanistic computer codes for predicting fission-gas behavior in UO sub 2 -base fuels during steady-state and transient conditions. FASTGRASS was developed in order to satisfy the need for a fast-running alternative to GRASS-SST. Althrough based on GRASS-SST, FASTGRASS is approximately an order of magnitude quicker in execution. 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 FASTGRASS calculational procedure is described in this paper, along with models of key physical processes included in both FASTGRASS and GRASS-SST. Predictions of fission-gas release obtained from GRASS-SST and FASTGRASS analyses are compared with experimental observations from a series of DEH tests. The major conclusions is that the computer codes should include an improved model for the evolution of the grain-edge porosity. (ERA citation 05:000987)