A parametric study has been performed for the blanket neutronics and economics of fusion-fission hybrid reactors. Optimum blanket designs were sought for both the electricity-producing hybrid reactor and the fissile fuel-producing hybrid reactor. Comparisons of the nuclear performances and economics between these two hybrid reactors were also conducted. A tokamak-type fusion reactor was selected as the base reactor. It was assumed that natural uranium oxide is fed to the blanket as the fertile material with lithium oxide as the tritium breeding material. In the neutronics design of the electricity-producing hybrid reactor, blanket fuel composition and arrangement were surveyed to attain high energy multiplication in the blanket. Moreover, efforts were made to suppress the blanket thermal power increase due to plutonium buildup, because it determines the frequency of blanket fuel exchange and limits the reactor load factor. On the other hand, the blanket for the fissile fuel-producing hybrid reactor was designed so that the amount of the fissile fuel bred per unit blanket thermal power is maximized. Economic analysis shows that the electricity from the symbiotic system composed of the fissile fuel-producing hybrid reactor and light water reactors costs about 30% less than that from the electricity-producing hybrid reactor. However, the large energy multiplication in the blanket of the electricity-producing hybrid reactor makes the neutron wall loading 40% lower than that of the fissile fuel-producing hybrid reactor. Therefore, the electricity-producing hybrid reactor can make its requirement for fusion technology less demanding than the other.
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