The implications of impurities on shutdown dose rates in the burning plasma experimental tokamak

With the growing demand for nuclear fusion energy, understanding radiation safety implications in experimental tokamaks becomes critical. Structural material impurities like cobalt (Co) significantly impact shutdown dose rates (SDDR) through long-lived radionuclides such as ⁶⁰Co, affecting maintenance feasibility and waste management. Current assessments using contact dose rates (CDR) often overlook complex geometrical effects, potentially underestimating radiation risks. This study employs a comprehensive approach integrating 3D Monte Carlo neutron transport, FISPACT-II activation analysis, and the NATF toolkit to evaluate impurity impacts in a burning plasma experimental tokamak. The results reveal that SDDR exhibits strong linear correlations with Co content (p < 0.01) inside tokamak, and statistically significant linear correlations (p < 0.05) for locations outside the tokamak. Geometric effects cause up to 6.5-fold differences between SDDR and CDR. The work demonstrates that maintaining Co below 0.05 wt. % enables remote handling compliance while highlighting the necessity of localized shielding for maintenance optimization. This research provides the full-device SDDR mapping with geometric considerations for the Chinese-designed tokamak, offering crucial insights for material specification and radiation protection strategies in fusion reactors.