Multi-Assembly Analysis with an Advanced Correlated Sampling Method

Abstract

The Advanced Correlated Sampling (ACS) method, which can greatly enhance the calculation efficiency of Monte Carlo (MC) methods using a perturbation technique and a pseudo-scattering technique, is improved so as to be able to handle multi-assembly analysis. Two boundary connection methods—the neutron path connection and neutron current connection methods—are developed, and their accuracies for a 2×2 multi-assembly system are confirmed. The speedup factor against the corresponding direct MC calculation is a maximum of about 100. These boundary connection methods are also applied in pin-wise 2-D quarter core calculations as an example of a large-scale system. A newly developed perturbed neutron source iteration technique allows for very smooth source convergence. Furthermore, by incorporating the Direct Response Matrix (DRM) method as the acceleration means for the source convergence, the number of source iteration cycles is significantly shortened. The results confirm that this improved ACS method has the ability to perform pin-wise whole core calculations very accurately and efficiently.