Realization of a Flat Fission Power Density in a Hybrid Blanket Over Long Operation Periods

A straightforward numerical graphical method is applied to achieve a flat fission power density (FPD) in a hybrid blanket by using a mixed fuel (ThO₂ and natural UO₂) with variable fractions of the fuel components in the radial direction. The neutronic analysis is carried out on a blanket with a hard neutron spectrum in the fissionable zone by simply omitting the moderating beryllium neutron multiplier. Mainly due to this precaution in the blanket design, the FPD could be kept quasi-constant over a relatively long plant lifetime. The peak-to-average FPD increased from 1.0704 at startup to only 1.1056 after an operation period of 24 months by a plant factor of 60% under a first-wall fusion neutron flux load of 10¹⁴ to 14 MeV·-n/cm²·s, corresponding to ∼2.25 MW/m². Consequently, a hybrid blanket of the type used in this study would not require any fuel management scheme for at least 2 yr of plant operation.