Comparison of neutronics performance of various TRISO fuels

Abstract

TRISO (Tristructural Isotropic) particle fuel is a type of advanced nuclear fuel developed for High-Temperature Gas-Cooled Reactors (HTGRs). Its robust containment properties make TRISO particle fuel a promising candidate for Accident-Tolerant Fuels (ATFs) for next-generation reactors. In this study, the physics model of HTTR was established with the Monte Carlo code MCNP6.2 to evaluate the neutronic properties when utilizing various TRISO form fuels in High-Temperature Test Reactor (HTTR). The fuels considered in this study include UO₂, UC, and UN embedded in the core of TRISO particles. Moreover, the UC fuel is coated with TiN (UC_TiN), while the UN fuel is coated with ZrC (UN_ZrC). These two fuel types have been recognized as having manufacturing prospects, so ascertaining the effects of these coating materials on their neutronic performance before conducting practical applications is necessary. The results indicate that the isothermal temperature coefficients of the UC and UN fuels remained negative during the experimental operation, particularly −0.022 to −0.032 lower than the UO₂_TRISO fuel in the operational temperature, −0.016 to −0.043 lower in the condition when it exceeded the temperature of operational condition, shows the safety aspect of the utilization of ATFs. The effective multiplication factor of each fuel remained nearly constant during 660 EFPD; each fuel, accounting for the initial drop, has a $\Delta k/k_{\mathrm{final}}<10\%$ indicating that the fuel replacement that occurred during the operation procedure maintained stability. Moreover, the neutron spectrum at the Beginning of Cycle (BOC) and End of Cycle (EOC) showed that the significant difference in the effective multiplication factor of UC_TRISO and UC_TiN was caused by the coating layers. The moderator-to-fuel ratio provides evidence that the difference between the fuels was caused by the fuel design instead of operational conditions, indicating that the heavy metal coating might not be suitable for HTGRs compared to TRISO coating. The spent fuel analysis is discussed to clarify fuel variations, which shows that the minor actinides of each fuel have increased about 4.2 %–27.7 % in comparison with the UO₂_TRISO, based on these neutronic mechanisms and calculation analysis, thus providing compelling evidence supporting the feasibility of applying ATFs in HTGRs.