Liquid metal cooling issues for fusion and fission

Liquid metal application for nuclear power plants was initiated in the design of fast reactors using sodium or lead bismuth, and are very famous for sodium fast breeder reactor and lead bismuth fast reactor. In a course of development of FBR, Na and NaK were carefully compared and the former was chosen as the candidate coolant, followed by various Na cooled test reactors. PbBi fast reactor was put into practical use as a engine for nuclear ship, following research activities as a thermal reactor with PbBi coolant. In the nuclear fusion application, liquid metals of Li or LiPb will be used as a coolant and/or tritium breeder in comparison with water and helium gas. It is well known that in a nuclear reactor, materials are required to function as moderator and coolant. Though these functions are satisfied with separate materials, it is very reasonable to combine these functions to one materials, such as water or sodium, as is rearized by LWR or Na-FBR The economical success of these reactors depend on the selection of coolant material that works as neutron moderator at the same time. This design option resulted in a great reduction of the size of system and in an increase of the system efficiency. On the analogy of this history, fusion coolant might be consolidated in future to the material that works as the coolant and T breeder, such as Li or LiPb, and not in water or helium which need separate breeding material in addition to coolant. However, the MHD flow problem does not exist in nuclear power plants and the prospect for the solution of this problem will largely affect conclusions. The other example of liquid metal application, is the liquid metal target, represented by Li target for IFMIF and PbBi target for ADS. The technology required in IFMIF may be quite different, and may rather be nearer to those for inertia fusion power plant. (orig.)