Study on high-resolution activation analysis based on the Monte Carlo global variance reduction method

Abstract

During nuclear reactor operations, neutron activation reactions generate significant quantities of radionuclides from the structural materials, directly impacting shielding design, maintenance planning, and decommissioning strategies. This is a critical component of radiation safety analysis. As advanced nuclear reactor technology evolves, the increasing complexity of reactor geometry, material configurations, and neutron spectra complicates activation analysis. Consequently, there is a pressing need for high-resolution activation analysis of nuclear reactors. This paper presents a high-resolution activation analysis method for large-scale complex structural materials, utilizing the Monte Carlo global variance reduction particle transport technique. A fully automated coupled high-resolution activation analysis program is developed, enabling the calculation of high-resolution decay source distributions and precise evaluation of decay photon sources for extensive complex structural materials. The methodology is benchmarked against the shutdown dose rate benchmark released by the International Thermonuclear Experimental Reactor (ITER) program. Additionally, an application study of high-resolution activation analysis is conducted on a standard pressurized water reactor (PWR). The methodology demonstrated in this paper holds significant engineering value, enhancing the accuracy of activation calculations for large-scale nuclear reactor structural materials and it provides guidance for optimizing shielding design to reduce radiation exposure during operation.