Variance reduction for global response problem based on forward Monte Carlo calculation

Monte Carlo (MC) method is extensively employed in shielding calculations with the advantages of high fidelity geometry modeling, complex radiation source description and continuous-energy cross sections. In global response problem, the detailed response estimates are required for the entire phase space. However, in deep-penetration shielding simulation, it is difficult to obtain high fidelity results due to the poor particle statistics. Accordingly, efficient global variance reduction (GVR) techniques must be applied to bias particles towards the far-source region. In this paper, the global response problems are classified into space-only response problem and space-energy response problem. To solve the two different problems, two new weight window generation algorithms are proposed for GVR based on forward MC estimates. The numerical test results show that both the global response tally and calculation efficiency have been improved. The uniform global response tally could be achieved for both space-only response problem and space-energy response problem. The proposed variance reduction techniques could be useful in MC global response calculations.