Impact of neutronics considerations on the selection of solid breeder and multiplier materials and configurations

Abstract

A large number of solid breeder materials have been proposed for fusion blankets. A study was performed to quantitatively compare the effect of solid breeder (SB) material choice on blanket attractiveness and to recommend priorities for focusing the solid breeder experiments. This paper summarizes the results of the extensive neutronics analysis which evaluated the achievable tritium breeding ratio (TBR) and the power multiplication factor (M) as key parameters. The study considered ten solid breeder materials (e.g., Li2O, Li2SiO3, LiAlO2), six neutron multipliers (Be, BeO, Pb, PbO, PbBi and and Zr5Pb3) and two coolants (helium and water). These breeder and multiplier materials were considered in six different design configurations which included homogenized breeder/multiplier mixtures and a separate multiplier zones. The general conclusions which can be made from the TBR results are that: (1) Be exhibits the most superior performance among neutron multiplier (M) candidates; (2) Li2O is the most attractive solid breeder candidate, showing the highest TBR for the unmultiplied, separate multiplier and homogeneous SB/M cases; (3) Li2O is the only solid breeder with a plausible chance of performing satisfactorily without a multiplier; (4) the homogeneous SB/Be cases show exceptional TBR performance and should be considered in the test program, (5) multi-region solid breeder multiplier (SB/M) cases show still excellent TBR performance; and (6) the TBR with water coolant in all cases is 5–10% higher than with helium coolant. The power multiplication results tend to vary in accordance with the TBR results and thus reinforce the above conclusions. There are two notable exceptions; the first is the case of Li7Pb2, which, although showing a high effective TBR of 1.22, exhibits a rather low M of 1.18. The other exception is that changes in 6Li enrichment affect M only slightly in all cases. The overall M is actually decreased due to the decrease of the radiative capture reaction rate in the structure material used in the blanket utilizing highly enriched lithium.