Fusion-fission hybrid reactors for tritium breeding

By relieving the hybrid reactors from the requirement to breed their own tritium, it is possible to improve the performance of these hybrids. The tritium needed for fueling these reactors can be produced in reactors, such as tritium breeding hybrids, specifically designed for this purpose. The tritium breeding hybrid reactor concept considered here uses depleted uranium for neutron multiplication (very large stockpiles of depleted uranium have been and are going to be accumulated over the years) and lithium for the production of tritium. To evaluate the tritium breeding potential of such a hybrid a modified version of the bench-mark blanket model was considered. A preliminary series of calculations have been performed for blankets having a 1 cm thick niobium wall the inner radius of which is 2 meters, followed by a one meter thick breeding blanket. The breeding blanket is of a uniform composition having 6% volume fraction niobium and a variable U238-Lsub(i) volume fraction. The calculations have been performed with the ANISN code using the DLC-2 cross section library. The highest tritium breeding ratio calculated is 2.41. Perturbation calculations indicate, however, that by a proper variation of the U238-Lsub(i)sup(6) concentrations it might be possible to increase this breeding ratio to about 2.8. (B.G.)