The study of irradiation-induced failure behavior for the TRISO-coated fuel particle in HTGR

Tristructural-isotropic (TRISO) coated fuel particles are a key component in the high-temperature gas-cooled reactor (HTGR) fuel element concept, and their integrity is of utmost importance for the nuclear reactor safety. Many fuel performance models regarding the analysis of the particle stresses and failure fractions have been developed in the past by various countries. However, a significant gap presently remains in how the changing coating layer properties affect the particle stresses and failures under irradiation. The development of a first comprehensive stress and failure fraction calculation model in China has been initiated by the Institute of Nuclear and New Energy Technology at Tsinghua University. Analytical solution calculations and a Monte Carlo approach were employed to evaluate and predict the tangential and radial stresses as well as the failure fraction under normal or extreme conditions for TRISO fuel particles. The statistical effects from the particle geometry during the manufacturing process on the stresses of IPyC/SiC/OPyC layers were investigated. The role of SiC restraint on PyC in the stress calculation model was determined as well as the contributions to varying stresses from the simultaneous changes of the PyC density and anisotropy under irradiation. The Monte Carlo approach was used to calculate the failure fraction of TRISO-coated particles induced by modified particle stresses, indicating that the particles were less likely to fail compared to the base case using nominal data. Sufficient validity and reliability for the use of the present stress and failure fraction model was demonstrated when verified with other modeling results and validated against experimental data. Successful methods were presented to analyze and predict failure behavior for TRISO particles in China extending to higher irradiation temperature and burnup. (C) 2019 Published by Elsevier B.V.