When fusion nuclear reactor is in operation, neutron activation causes a large number of radioisotopes. Activation calculation is a very important step in both of reactor shielding calculation and radiation safety analysis.

This study aims to develop the capability of transport-activation coupling calculation for fusion reactor based on the Monte Carlo code cosRMC.

Firstly, the built-in burnup solver "Depth" of cosRMC was employed to develop transport-activation internal coupling calculation function under fixed source mode with embedded calculation of activation related nuclide single group reaction cross-sections in neutron transport process without the transmission of neutron spectra to external activation programs. Then, the developed code was applied to the activation calculations of the first wall (FW) material steel and plasma facing component (PFC) material tungsten of the Chinese Fusion Engineering Testing Reactor (CFETR) using continuous energy cross-sections and multi group cross-sections, respectively, and calculated results were compared and verified with that of the activation program ALARA.

The comparison results of activation calculation of FW steel and PFC tungsten in CFETR show the consistency between cosRMC-based internal coupling method and ALARA program, which preliminarily verifies the correctness of the transport activation internal coupling calculation function of the developed cosRMC program.

The developed cosRMC-based internal coupling method can dynamically update neutron spectra and material information, and use continuous energy cross-sections for reaction rate calculation, obtaining reaction cross-sections related to the geometry and energy spectra of actual problems, thus accurately considering the influence of resonance zone nuclear cross-sections.