The impacts of random effect and scattering effects on the neutronics analysis of the PB-FHR

Abstract

The experimental thorium-based molten salt reactor with solid fuel will be constructed as an initial step to test and verify the technical feasibility of a large-scale thorium-based molten salt reactor in the next years. It is a type of pebble-bed fluoride-salt-cooled high-temperature reactor (PB-FHR). The pebble-bed reactors are composed of randomly distributed fuel pebbles which consist of fully randomly distributed TRistructural-ISOtropic (TRISO) coated-fuel particles. This special structure is known as the double random distribution. However, lacking of accurate modeling approach of random distribution, the regular lattice approximation was adopted in the previous Monte Carlo modeling of the 2-MW TMSR-SF0, which may introduce significant error. In order to explicitly model the random distribution of the PB-FHR, the random distribution of the TRISO coated-fuel particles within fuel pebbles are obtained by the random packing method (RPM) and the random distribution of the fuel pebbles within the reactor core are obtained by the discrete element method (DEM). In this work, regular lattice approximation approach and explicit modeling approach are applied to simulate the stochastic effect of the PB-FHR. The simulation results show that regular lattice approximation approach underestimates the keff by about 1000pcm. Besides, the thermal-neutron scattering effect of 2LiF-BeF2 and the resonance elastic scattering effect of uranium are studied in this work.