Influence of Doppler Broadening Rejection Correction on Neutronics of PB-FHR

In epithermal energy range, the thermal motion of the target nuclides impacts the elastic scattering. The traditional constant scattering cross section approximation free gas model was adopted in Monte Carlo code to describe the scattering in epithermal energy range. Recent researches show that the bias introduced by ignoring the resonance elastic scattering increases with the temperature. The working temperature of the pebble-bed fluoride-salt-cooled high-temperature reactor (PB-FHR) is high, therefore it’s necessary to consider the resonance elastic scattering by using the Doppler broadening rejection correction (DBRC) method. In this work, the modified Monte Carlo code MCNP5 was used to analyze the pebble unit cell of PBFHR. It is found that the DBRC method results in an increase of capture reaction rate of ²³⁸U and a decrease of infinite multiplication coefficient (k_inf) by 123-1182 pcm. In addition, the absolute difference of k_inf introduced by the DBRC increases with TRISO packing factor and temperature.