Study of a heat exchanger for heat removal in the ARC fusion reactor

ARC ("Affordable, Robust and Compact reactor") is a conceptual design of a nuclear fusion reactor developed by the "Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center". ARC is a tokamak with a power of 200–250 MWe, which uses molten salts of fluorine, lithium and beryllium (FLiBe) as coolant. Once built, it will aim to reduce the costs, the complexity and the size of nuclear fusion plants. In the present study will be proposed a possible design of a heat exchanger to be implemented in the ARC design for the heat transfer from the FLiBe to a secondary fluid used within a Brayton cycle for electricity generation. The technology chosen are multiple heat pipes which use sodium as fluid. From the numerical analyzes, carried out with the Comsol Multiphysics software, it was found that a single heat pipe is able to exchange a thermal power of approximately 4.2 kW with air as secondary fluid. This value can be increased by applying some modifications with respect to the original design: using helium at 25 bar instead of air, applying radial fins to improve the heat exchange and increasing the thickness of the porous matrix, the thermal power exchanged within a single heat pipe reaches about 8.8 kW.