Energy Biased Optimal Source Bias Method for Monte Carlo Criticality Calculation

The traditional fission source iterative method is adopted when the Monte Carlo code RMC is used to do the criticality calculation, that is, each source neutron is generated, stored and resampled according to the real physical process. There is a large correlation between the calculation cycles from the traditional fission source iterative method, which leads to the phenomenon of the underestimate of variance and the overall variance is not optimized. To achieve the optimal distribution in space and energy of each source neutron, and eliminate the underestimate of variance, the energy biased optimal source bias method was proposed. Based on the optimal stratified sampling method, combined with the Shannon entropy diagnosis and batch method, the method achieves the effect of global variance reduction. The method was tested by a standard PWR assembly, and the results show that the method is correct and effective.