THE DEVELOPMENT OF FISSION PRODUCT DIFFUSION/RELEASE MODEL FOR FAILED TRISO PARTICLES

TRISO coated fuel particle has been adopted in the design of various reactors and Accident Tolerant Fuel (ATF) due to its excellent accident tolerant performance under high temperatures and other severe conditions. Accurately estimating fission product release from TRISO-coated fuel particles is indispensable to calculate the mechanistic source term. In most models, a bare kernel is substituted conservatively for failed particle. Thus, a theoretical method was proposed to describe the transport of fission products in intact and failed fuel particles. In this paper, to analyze the diffusion and release characteristics of intact TRISO-coated fuel particles' fission products, the fission products diffusion model of TRISO-coated fuel particles with thermal-mechanical coupling was established based on the COMSOL Multiphysics software and verified by the IAEA CRP-6 benchmark. The results indicate that the predictions by the developed fission product transport model is reasonable. Moreover, to analyze fission product release for failed partials, a conceptual theoretical method was proposed. The adsorption and desorption constraint model for fission products at the gas-solid interface and the gas phase diffusion model were added to the original model to analyze. Subsequently, predictions comparison for fission products' fractional release in failed particles between the proposed method and the Settings adopted in BISON were completed. The result suggests that the gas-phase diffusion model is feasible and seems favorable to simulate the diffusion of fission products in the failed coating layers.