Development and Verification of Transport-Activation Coupling Capability in CosRMC

During the operation of nuclear reactors, many radioisotopes are generated by neutron activation. Therefore, activation calculation and analysis play a key role in reactor shielding design and shutdown maintenance. In this paper, the transport-activation coupling capability in fixed source mode was developed based on Monte Carlo particle transport code cosRMC. The transport-activation coupling capability of cosRMC has the following characteristics: the internal coupling of transport and activation was implemented through the built-in burnup solver Depth. Compared to traditional Monte Carlo-activation codes with the external coupling, internal coupling mode calculates the activation-related one group reaction cross sections of different nuclides during the neutron transport process, and the external transmission of neutron energy spectrum to activation code was unnecessary. The internal coupling mode was more efficient and flexible. By directly using continuous energy cross section to calculate one group cross sections, the pre-processing of energy spectrum related multi-group cross section was no longer required, which improves the accuracy and versatility. The transport-activation coupling capability of cosRMC was applied to a test case of iron cube model and compared with the activation code ALARA. The results of cosRMC are in good agreement with those of ALARA, which preliminarily verified the correctness of the transport-activation coupling capability of cosRMC. On this basis, the results in different conditions including constant/variable energy spectrum and continuous energy/multi-group cross section are compared and analyzed. The results showed that the reaction rates in the case of variable energy spectrum are significantly higher than those in the case of constant energy spectrum, indicating that the change of energy spectrum has a significant effect on the calculation results. The comparison between the results of continuous energy and multi-group cross section showed that for the major activation products such as 57Fe, 58Fe and 59Co, the results obtained by multi-group cross section method are all larger than those obtained by continuous energy method, indicating that different cross section libraries and treatments have important influence on activation calculation.