Automated convergence detection in Monte Carlo criticality calculations using Student's bridge statistics based on keff or Shannon entropy
A. Jinaphanh, J. Miss, Y. Richet, O. Jacquet
PHYSOR 2012, Knoxville, Tennessee, USA, April 15-20, 2012
Monte Carlo criticality calculations are based on an iterative method. It requires a converged fission source distribution before beginning tallying the effective multiplication factor (keff) or other quantities of interest. However, it is pretty difficult to locate on the run, the end of the source convergence and scores may be biased by an initial transient. This paper deals with a method that locates and suppresses the transient due to the initialization in an output series, applied here to keff and Shannon entropy. It relies on modeling stationary series by an order 1 auto regressive process and applying statistical tests based on a Student Bridge statistics. It should be noticed that the initial transient suppression only aims at obtaining stationary output series and cannot guarantee any kind of convergence. The truncation method is applied on both keff and Shannon entropy on three test cases.