Optimization of TRISO fuel particle for thorium-based pebble bed fluoride salt-cooled high-temperature reactor

[Background] Thorium-based pebble bed fluoride salt-cooled high-temperature reactor (PB-TFHR) is one of the reactor types in the fourth generation reactors. It uses pebble fuel design filled with TRISO (TRi-structural ISOtropic) coated fuel particles dispersed in a graphite matrix and has good neutronic and safety performances. [Purpose] This study aims at the radius of kernel, thickness and density of coating layers of TRISO in PB-TFHR for neutron properties, the production of fission gas with krypton, xenon and iodine, and failure rate of coated fuel particles. It can provide a design reference for the reactor physics of FHR. [Methods] The Standardized Computer Analyses for Licensing Evaluation (SCALE) 6.1 program and the corresponding submodules such as burnup and cross section processing were used to calculate the critical and burnup for the PB-TFHR and the PANAMA model was used to calculate the failure rate of TRISO coated fuel particles. [Results] The results show that when the thickness and density of coating layers are maintained unchanged, a larger radius of kernel (≥ 0.01 cm) is required to meet the requirement that the reactor is under-moderated while the temperature feedback of core is always negative. When the thickness and density of the coating layers keep constant, at the same burnup, the smaller the radius of kernel is, the less fission gas is produced and the smaller the failure rate is. When the density of coating layers is not changed, variations of the thickness of the porous carbon buffer and the inner pyrolytic carbon layer have a great influence on the k_eff whilst keeping the thickness of the coating layers unchanged, only changing the density of the coating layers does not affect the k_eff obviously. [Conclusion] The analysis of this study give the optimal structure of TRISO coated fuel particle and provide some reference for the physical design. (authors)