A solution to 'long history' in the method of GVR based on weight window

Abstract Background: The 'long history' induced by the method of global variance reduction (GVR) based on weight window would reduce the efficiency of the Monte Carlo particle transport calculation with global characteristic. Purpose: To enhance the efficiency and minimize the waste of computing resource, this article proposes a solution to 'long history' based on the study of its causes. Methods: According to the event log of 'long history' in Chinese fusion engineering testing reactor (CFETR) neutron transport calculation, the cause of the 'long history' is brought up, which is in relation to particle's successively surviving in the Russian roulette games. A solution to the 'long history' by limiting particle's splitting according to the number of surviving games (weight roulette number, WRN), is came up with, which is tested in CFETR model. Results: The result shows that when the limited number is between 1 and 4, the parallel efficiency reaches 80%, with no 'long history' present and global figure of merit (pFoMG) being around 3 times of that in calculation without the limited number. Conclusion: The solution proposed prevented the 'long history' and thus greatly enhanced the efficiency of GVR. (authors)