Underestimation of Statistical Uncertainty of Monte Carlo Method with Non-Analog of Fission Source Sampling

摘要

Theoretical equation on the underestimation ratio of statistical uncertainty of fission source distribution is derived using the expansion by eigenfunction and the AR model. The proposed equation well reproduce the underestimation ratio of statistical uncertainty of flux distribution obtained by GMVP and SlabMC, in which non-analog sampling for fission source is used. During the course of the present study, it was revealed that dependence of noise term on eigenmodes should be taken into account to correctly predict underestimation of statistical uncertainty when the non-analog sampling of fission source or non-analog absorption reaction is used or flux distribution is focused on. In this present summary, a simple calculation conditions (one energy group, one dimensional homogeneous slab geometry) used for verification. Thus the eigenvalues and the fission source distributions of higher modes can be analytically calculated for transport equation. Extension to more general cases would be a future task.