Research on irradiation-Thermo-mechanical coupled analysis for HTGR fuels

Predicting the thermo-mechanical response of TRISO particle fuel is important for fuel performance assessment in high-temperature gas-cooled reactors. This study developed CoaPAC (COated fuel Performance Analysis Code), a spherical TRISO fuel performance code that couples implicit heat transfer, fission gas and CO release, viscoelastic coating mechanics, gap evolution, and pressure-vessel (PV)-type failure models. First, CoaPAC was benchmarked against the IAEA CRP-6 mechanical test case, and its results were compared with published results from other fuel performance codes for the HFR P4, HFR-EU1, and NPR-1 irradiation conditions. The results show that CoaPAC reproduces the principal evolution trends of key thermo-mechanical variables, and the comparisons support the consistency of the basic physical modules and their coupled implementation. CoaPAC was then applied to a complex full-life-cycle scenario involving irradiation, storage, and accident heating. The results demonstrate that, under a continuous and complex operating history, CoaPAC can reasonably describe the coupled responses of TRISO particles, including heat transfer, gas composition, coating stress, and failure behavior at different stages. Therefore, the verification and comparison analyses conducted in this study support the accuracy and reliability of the code, demonstrate the reasonableness of its thermo-mechanical model implementation and its capability to handle complex conditions, and further clarify priorities for future code development.