Impurity activation and transfer of activation products in the liquid Li loop of fusion neutron source

In the Li loops of IFMIF-like fusion neutron sources, various types of radionuclides are generated and deposited in the Li loop components depending on conditions. This study evaluated the activation of impurity elements in liquid Li as well as the spatial distribution of these radioactive products in the Li loop under the IFMIF/EVEDA project from 2021 to 2025. The impurity concentrations of Li sampled from EVEDA Li test loop (ELTL) after the validation activities of 3850 h operation were measured. The activation of these impurity elements due to deuterons and neutrons and a back plate made of F82H were calculated. In order to estimate the spatial distributions of the activation products in the Li loop, a transfer model of the radioactive products that considered temperature, flow speed, and magnetic field conditions was developed. By employing the transfer model, the radioactivity after one year of operation in each of the Li components was obtained for the first time, and it is revealed that evaluation of the activation of impurity elements in Li is essential to consider because the activated Li impurity is not negligible as photon sources in the liquid Li, HX, and EMP.