Analysis of the Differences in Breeding Ratio and Fissile Inventory Between Heterogeneous and Homogeneous Liquid-Metal Fast Breeder Reactors

The differences in fissile inventory and breeding ratio, with respect to the differences in fertile inventory and neutron spectrum, between equivalent heterogeneous and homogeneous configurations were analyzed. To quantify the effect of spectral changes on reaction rate ratios, a calculational scheme based on properly prepared one-group cross-section sets was used. The results of the analysis show the following:

1. Most of the breeding ratio improvement that results from heterogenization is due to the higher fertile inventory of the heterogeneous configurations. Also, the higher specific fissile inventory of the heterogeneous configurations is mainly due to the higher specific fertile inventory.
2. Most of the spectral effect on the breeding ratio difference between the heterogeneous and homogeneous configurations comes from the spectral effect on the rate of parasitic neutron absorption in ²³⁹Pu.