Real variance analysis of unbiased ratio estimator in Monte Carlo k-eigenvalue calculation

Abstract

In this paper, the unbiased ratio estimator has been applied to keff estimation in a continuous-energy Monte Carlo analysis of a quarter core SMR loaded with vacuum and albedo (a = 0.8) boundary conditions. It is confirmed that the bias-to-real variance ratio slightly decreases as the neutron leakage increases in the reactor. However, the URE is able to successfully correct the bias, which was still noticeable with small particle histories. In addition, it was demonstrated that the URE is effective over the practical range of weight cut-off threshold for the Russian roulette.