Thermal-hydraulic modeling of a novel HTS CICC for nuclear fusion applications

A thermal-hydraulic model has been developed for the novel cable-in-conduit conductor (CICC) recently proposed by ENEA, which foresees the use of 2nd Generation REBCO-based Coated Conductor tapes stacked into twisted grooves slotted into an Al core. A central hole in the Al core provides a low hydraulic impedance channel for the coolant, while direct cooling of the tape stacks is achieved through small channels at the bottom of the grooves and other small passages around the stack. The coolant could be either supercritical helium (SHe), for high-field/high-current applications, as in fusion magnets, or liquid nitrogen (LN2), for self-field/lower current requirements. The issues of the thermal-hydraulic performance and optimization of such a CICC are addressed for the first time in this paper. The 4C code is used to develop an adequate model for this complex 3D problem, taking advantage of the 1D nature of the coolant flow. The model, first calibrated and then validated using the results of thermal-hydraulic tests performed in cryogenic conditions at CRPP, is used to evaluate the flow repartition among the different cooling paths in the CICC for SHe at 4.5 K and for LN2 at 77 K. The model is finally used to perform parametric analyses, varying, e.g., the central hole diameter, as well as the size of the grooves at the bottom of the tapes, within the limits imposed by structural constraints, and to assess the cooling capability of the cable.