The Characteristics and Subgroup Methods in Square Light Water Reactor Cell Calculations

The effect caused by the circular approximation of the geometry for cell calculations in light water reactors is studied using the continuous-energy Monte Carlo code MVP. It was found that the k_inf values were underestimated with this approximation of the geometry, especially in the case of a mixed-oxide fuel cell. To treat the square geometry, including the resonance calculation, KRAM-B was developed based on the two-dimensional neutron transport code KRAM as a deterministic cell calculation code. KRAM-B solves the neutron transport equation using a combination of the subgroup method and the characteristics method. The subgroup method is able to perform the resonance calculation faster than the ultrafine energy group calculation and predict the resonance cross section more accurately than the Dancoff factor method. It was found that the k_inf values and the effective microscopic resonance cross sections by KRAM-B agreed well with the reference MVP results.