Correlation diagnosis method for heterogeneous Monte Carlo eigenvalue simulations based on a diffusion approximation

摘要

This paper presents a predictive model of the correlation level present in tally regions of any mesh size without requiring extensive high accuracy discrete tallies. This model provides a quick indication of the accuracy of the variance estimated from uncorrelated statistics. The prediction is developed from the generalization of the Multitype Branching Processes (MBP) model to a continuous space and solving correlation coefficients (and thus variance correction factors) exactly in an equivalent homogeneous problem. The real heterogeneous problem is homogenized in a way that preserves neutron migration area. Correlation coefficients and the asymptotic variance underestimation ratio of the homogenized problem provide a rough estimate of the correlations observed in the real heterogeneous problem for a given tally region size. (C) 2019 Elsevier Ltd. All rights reserved.