Power Density Flattening in Fusion-Fission Hybrid Reactors

The feasibility of spatial and temporal power density flattening in fusion-fission hybrid reactors was investigated by varying the concentration of ²³⁹Pu within a set of zones in the fission region and by examining two different fuel management schemes. Blanket designs with no ²³⁹Pu typically had a spatial maximum-to-average power density ratio of ∼2.5, but  this value was reduced to between 1.26 and 1.67, depending on the design and fuel management scheme selected. Unfortunately, however, significant impact occurs only with relatively high fissile concentrations, with the outer zones approaching equilibrium values. Thus, either an impractically large fissile inventory for startup or long operating histories would be required.