Theoretical and Numerical Analysis of Beryllium Reflector Poisoning in High-Flux Research Reactor

Beryllium is widely used as the reflector in high flux research reactors to improve neutron economy. To investigate the accumulation characteristics and laws of neutron poisons ⁶Li and ³He during the transmutation process in the beryllium reflector—rather than merely evaluating specific test cases—this study analyzes and solves the equations of nuclide transmutation in the beryllium reflector, obtains the relevant laws of the accumulation process of each nuclide, and evaluates the negative reactivity introduced by the beryllium reflector poisoning theoretically. It is concluded that the equilibrium concentration of ⁶Li is independent of the neutron flux level, and the upper limit of ³He accumulation rate is independent of the neutron flux level. By using RMC to calculate the beryllium reflector of the Tsinghua ‌High ‌Flux ‌Reactor (THFR) and comparing with theoretical predictions, the results are in good agreement, which validates the correctness of the theoretical analysis. The relevant conclusions can save the resource consumption of long and multi-step burnup calculations, and only a few critical calculations are needed to obtain the value of the negative reactivity, thus efficiently and accurately providing important basis for the design and replacement frequency of reflector, residual reactivity design, etc. of high flux research reactors.