A Mesh-Input-Free On-The-Fly Source Convergence Indicator in Monte Carlo Power Method

A mesh-input-free on-the-fly source convergence indicator is proposed for Monte Carlo source iterations by the power method. This indicator consists of two step computations of source particle centers. In the first step, the geometric center of all source particles is computed. The spatial domain is then divided into eight subdomains by the xy, yz, and zx planes that intersect at the geometric center. In the second step, a new geometric center is computed for the source particles in each of the eight subdomains. Therefore, nine centers are obtained at each cycle of source iterations and the distances to the corresponding centers at the initial cycle are computed, yielding the nine center-distances sum (NCDS). NCDS was compared against entropy indicators defined on a fixed mesh. Visual inspection reveals that the overall trend of NCDS is as sound as the entropy indicators. The feasibility of NCDS is shown by the step-refined on-the-fly convergence diagnosis with Wilcoxon rank sum.