Convergence characteristics and Wielandt acceleration of the time source method for Monte Carlo alpha eigenvalue calculations

Abstract

This paper discusses the source convergence of Monte Carlo calculations for α-eigenvalues. Compared with the conventional “k–α method”, the “time-source method” has a strong neutronic coupling even in a system where the fission sources are loosely coupled. The dominance ratio of the time source is smaller than that of the k–α method. The time-source method has a drawback in that it requires a much longer computation time. Furthermore, the time-source method cannot be applied to critical or supercritical systems owing to the long fission chain. A new technique is developed to overcome these drawbacks by introducing the Wielandt method for increasing the dominance ratio. This technique, which uses the Wielandt method in an opposite manner, reduces the computation time and expands the availability in a supercritical system. Because the source convergence of the time-source method is inherently stable, the new method causes a limited adverse effect on the source convergence.