The tandem mirror hybrid reactor

Abstract

A tandem-mirror fusion reactor was designed to produce fissile fuel for conventional fission-power reactors. The tandem-mirror concept lends itself to the development of an excellent hybrid reactor because of its cylindrical geometry and steady-state nature. Different coolant technology, fuel cycles, and physics operating modes were considered. The four technologies distinguished by coolant type are: (1) gas, either helium or steam, (2) water, (3) liquid metal, and (4) molten salt. Four physics operating modes were considered: (1) the two-component, (2) Kelley, (3) thermal and (4) thermal barrier. The thermal-barrier mode was finally chosen because of its simultaneous high Q and low beam, and magnet technologies gave superior performance. The design described, however, uses the Q ∼ 2 thermal mode because the thermal barrier concept was invented toward the end of the study. The neutral-beam injectors are of the negative-ion type operated at 400 keV. The magnet technology under consideration is based on Nb 3Sn conductor operated at 12–15 T. The plasma exhaust is converted at 50% efficiency to electricity in a one-stage, direct-energy converter. We set the size of the commercial plant at 4000 MW nuclear and placed primary emphasis on 233U production. We dropped water as a coolant option because of poor breeding resulting from neutron moderation. Liquid metal was dropped because of its safety-related fire-hazard and MHD-design problems, which resulted in some drop in breeding. After a more thorough study of molten salt and helium, we judged the molten salt case we studied to require too much development with too great a risk of not finding solutions to problems such as fabrication of molybdenum structures. The helium-cooled, Th-metal blanket performed well and resulted in a fuel cost of $ 70/g 233U (compared to $ 80/g for molten salt) and had a support ratio of 9, which is not as high as the fission-suppressed molten-salt case of 20 but is still a large number. The general class of fission suppressed blankets of which molten salt is only one example was judged to be well worth further study. The electric power capacity of 233U-fueled, light-water fission reactors that can be supported by the hybrid of the same nuclear power is 11 000 MWe for the gas-cooled case and 28 000 MWe for the molten salt case at an add-on cost of electricity of 24% for He and 14% for molten salt to account for the hybrid part of the system.