Reliable method for fission source convergence of Monte Carlo criticality calculation with Wielandt's method

Yamamoto, Toshihiro; Miyoshi, Yoshinori

A new algorithm of Monte Carlo criticality calculations for implementing Wielandt's method is developed. In this algorithm, part of fission neutrons emitted during random walk processes are tracked within the same generation, and thus a fission source distribution in the next generation spread more widely. Applying this method intensifies a neutron interaction effect even in a loosely-coupled array where conventional Monte Carlo criticality calculation methods have difficulties, and a converged fission source distribution can be obtained with fewer generations. Computing time spent for one generation, however, increases because of tracking fission neutrons within the same generation, which eventually results in an increase of total computing time up to convergence. However, since a fission source convergence is attained with fewer source iterations, a reliable determination of convergence can easily be made even in a system with a slow convergence.