Mitigation of the Temperature Margin Reduction due to the Nuclear Radiation on the ITER TF Coils

In the International Thermonuclear Experimental Reactor (ITER), the nuclear radiation escaping from the vacuum vessel reaches the superconducting Toroidal Field (TF) magnets, contributing to the reduction of the temperature margin ΔTmar, i.e., of the difference between the current sharing temperature and the operating temperature. The TF magnets are designed to operate at a minimum ΔTmar of 0.7 K. However, recent design activity on in-vessel components, e.g. the blanket and the in-vessel coils for plasma stability, suggests a potential enhancement of the nuclear heat load on the TF coils. A detailed re-assessment of ΔTmar in the TF magnets during plasma operation is thus required, together with the study of possible strategies to mitigate the corresponding margin reduction. The extensively validated Cryogenic Circuit Conductor and Coil (4C) code, developed for the thermal-hydraulic analysis of transients in superconducting magnets, including their cooling circuit, is used here for the simulation of the standard ITER operating scenario. Among the different possible mitigation strategies, we consider the variation of the cooling He mass flow rate, both in the winding and, separately, in the casing, and its effectiveness in terms of ΔTmar is assessed.