Robust Statistical Error Estimation of Local Power Tallies in Monte Carlo Calculation of Light Water Reactor

The overlapping batch means method (OBM) has been investigated for robust statistical error estimation of local power tallies in Monte Carlo (MC) reactor core calculation. Originally, a nonoverlapping version was introduced in MC criticality calculation by Gelbard and Prael. However, the issue of batch size optimization was thought of as a lack of robustness. In this work, OBM with asymptotic bias correction was implemented with the batch size of the square root of the number of generations and compared with the orthonormally weighted standardized time series method (OWSTS). Numerical tests were conducted for various positions of the core of a pressurized water reactor. Results obtained indicate that neither OBM nor OWSTS consistently outperforms the other in terms of an overall performance measure incorporating bias and stability. Therefore, OBM with asymptotic bias correction can be an option to statistical error estimation in production MC criticality codes since OWSTS lacks an automated process to determine the number of weighting functions and can output the estimate only at the final generation. It is also shown that OBM with asymptotic bias correction performs equally regardless of the batch size.