Fusion-fission hybrid studies in the United States of America

Systems and conceptual design studies have been carried out on the following three hybrid types: (1) The fission-suppressed hybrid, which maximizes fissile material produced (Pu or 233U) per unit of total nuclear power by suppressing the fission process and multiplying neutrons by (n,2n) reactions in materials like beryllium. (2) The fast-fission hybrid, which maximizes fissile material produced per unit of fusion power by maximizing fission of 238U (Pu is produced) in which twice the fissile atoms per unit of fusion power (but only a third per unit of nuclear power) are made. (3) The power hybrid, which amplifies power in the blanket for power production but does not produce fuel to sell. A series of studies led to a reference design of a fission-suppressed breeder that used liquid-lithium cooling of beryllium balls with thorium snap rings. Another series of studies considered a fission-suppressed, helium-cooled, molten-salt breeder design. Safety improvements for use in fast-fission designs were also identified. Low-burnup metal balls, which can be drained out of the blanket to passively cooled holding tanks, would be used in several of the above design concepts. Blanket designs not requiring reprocessing, called direct enrichment, were also studied. Breeding blanket designs for tokamak and tandem-mirror configurations were based on liquid-lithium, water, and helium cooling. Solid (U, Th, LiA102, Li2O) and liquid breeders (Li, LiF+ThF4) were considered. Studies indicate that as the predicted cost of the fission-suppressed fusion plant drops from twice a light-water reactor's (LWR) cost, the calculated breakeven price of uranium from the fusion breeder drops from $100/pound. A fusion plant costing 1.5 times an LWR is calculated to produce fuel at an equivalent price of $70/pound. An overall conclusion is that the deployment of fusion technology can cap the price of uranium. 18 refs, 12 figs, 4 tabs