Development of on-the-fly temperature-dependent cross-sections treatment in RMC code

Monte Carlo method can provide high fidelity neutronic analysis of different types of nuclear reactors, owing to its advantages of the flexible geometry modeling and the use of continuous-energy nuclear cross sections. It can also be coupled with thermal-hydraulics codes to consider feedbacks. Due to the effect of thermal motion of target nucleus known as Doppler effect, special treatments have to be used for cross sections at different temperature points. The traditional approach of pre-generated cross sections has difficulty of memory footprint when the number of temperature points is large. The target motion sampling (TMS) method was proposed and developed in Serpent code for temperature treatment based on the Woodcock tracking. In this paper, the TMS method was developed in RMC code based on the ray tracking. Moreover, Doppler-broadening rejection correction (DBRC) technique was also implemented in RMC to consider the effect of thermal motion on scattering kinematics. The pre-generated technique was proposed and applied to accelerate the calculation of TMS method. The results show that TMS method is equivalent to the exact cross-sections with DBRC, while TMS in RMC has higher efficiency in the cases of PWR and HTGR, no matter that the number of nuclides is small or large.