On the improvements in neutronics analysis of the unit cell for the pebble-bed fluoride-salt-cooled high-temperature reactor

The stochastic characteristics of the randomly distributed coated-fuel particles, the thermal-neutron scattering effect of the fluoride-salt and the resonance elastic scattering effect of heavy nuclides were neglected in early neutronics studies on the Pebble-Bed Fluoride-salt-cooled High-temperature Reactor (PB-FHR). In order to assess the impact of these effects on the neutronics calculation, the stochastic effect is analyzed by applying the explicit random modeling approach and Chord Length Sampling method, the thermal-neutron scattering effect of the fluoride-salt is quantified by evaluating and processing a new thermal-neutron scattering data library, and the resonance elastic scattering effect is covered by using the Doppler Broadening Rejection Correction (DBRC) method in this work. According to the critical calculations of the PB-FHR pebble unit cells with different TRISO Packing Factor (TPF), the different stochastic modeling methods lead to a difference of kinf by tens of pcm, the thermal scattering effect of 2LiF-BeF2 results in a decreasement of kinf by 104-290 pcm and the resonance elastic scattering effect leads to a decreasement of kinf by 107-437 pcm, respectively. In addition, the thermal-neutron scattering effect and resonance elastic scattering effect can be addible, the total impact of the thermal scattering effect of 2LiF-BeF2 and the resonance elastic scattering effect of heavy nuclide leads to a decreasement of kinf by 204-747 pcm.