Generation of few-group constants by Monte Carlo code cosRMC

Driven by the huge advantage of Monte Carlo method, the application of assembly homogenization by continuous-energy Monte Carlo method draws more and more attention. This paper presents the theory and the verification results of few-group constants generation for a conventional two-step procedure by Monte Carlo code cosRMC. Currently in cosRMC, 69 WIMS fine group constants are tallied and then B1/P1 equations are solved to compute few-group constants with leakage correction. And diffusion coefficient can be obtained by the B1/P1 leakage term. In addition, diffusion coefficient calculation based on classic out-scatter approximation and in-scatter approximation using the B1/P1 current spectrum are included in cosRMC as well. For verification, the simulation results performed by the nodal diffusion code SIMULATES using group constants generated by cosRMC have been compared to cosRMC Monte Carlo solution. The k(inf)/k(eff)/power distribution (radial & axial) obtained by two schemes cosRMC-SIMULATE5 and cosRMC shows good agreement with each other regarding to single assembly/full core level benchmark. These positive outcomes indicate that the few-group constants generated by cosRMC are highly accurate.