A High-Gain Fusion-Fission Reactor for Producing Uranium-233

The neutronics of several fusion-fission hybrid reactors were studied to develop a design capable of producing ²³³U while maintaining a self-sufficiency in tritium. High breeding rates are achieved by using an equilibrium concentration of ²³⁸U and ²³⁹Pu instead of thorium in a converter region to produce a significantly greater multiplication of the 14-MeV source neutrons. The final blanket design has an 18-cm neutron converter that consists of 0.5-in-diam pins of 92% ²³⁸U/8% ²³⁹Pu with a 0.7-in. pitch. The 40-cm breeding region consists of 0.5-in.-diam pins of ThC with 0.6-in. pitch; the overall blanket thickness is 102 cm. The tritium and fissile breeding ratios are 1.052 and 1.880, respectively, and there are 3.537 ²³³U nuclei produced per fusion neutron. An analysis of the performance of the blanket over a 2-yr period was carried out, including the buildup and depletion of fissionable nuclides and fission products. The final design requires an inventory of ∼30 000 kg of ²³⁹Pu, which must be produced for the design to be viable. A preliminary static and time-dependent study was done for a startup cycle to serve this purpose.