Review of helium cooling for fusion reactor applications

Helium cooling has been successfully used for fission reactors in the U.S. and Germany in the past. Helium is an attractive coolant for fusion reactors because it is chemically and neutronically inert and can be used directly for gas turbine cycle power conversion. In addition, as was shown during ITER and other fusion power plant evaluations, it is superior from safety considerations. On the other hand, some researchers are under the impression that use of helium cooling requires high pressure, large pumping power and larger manifold sizes due its low density at atmospheric pressure. In this paper it is shown that these concerns can be eliminated through the use of heat transfer enhancement techniques to reduce the flow, pumping power and pressure requirements. A number of proven heat transfer enhancement techniques such as extended surfaces, swirl tape, roughening, porous media heat exchanger and particulate addition are reviewed. Recent experiments with some of these methods have shown that expected heat fluxes of 10 MW/m2 in fusion reactors can be removed by helium cooling at a modest pressure of 4 MPa. In this paper designs of divertor heat sinks made from copper, vanadium and tungsten with a peak heat flux of 5–10 MW/m2, cooled by helium at a pressure of 4 MPa, are presented.