Effect of isotope enrichment on performance of lead-lithium blanket of inertial fusion reactor

Simulation studies on neutron transport and material activation for lead-lithium (Pb-17Li) blanket of the inertial fusion reactor "KOYO-FAST" were performed with the PHITS code and the EASY 2005 code. Tritium breeding ratio (TBR) and productions of harmful radioactive isotopes ²¹⁰Po and ²⁰³Hg in the blanket are made clear. The blanket performances improved by enrichment of stable isotope (⁶Li, ²⁰⁴Pb, ²⁰⁶Pb or ²⁰⁷Pb) are also made clear. The TBR is 1.28 for the blanket with a natural Pb-17Li alloy. The large TBR is allowed because of large blanket space in the reactor chamber. The TBR reaches 1.64 when ⁶Li is enriched to 90%. In this case, intermediate and thermal neutrons, that are necessary to produce ²¹⁰Po and ²⁰³Hg, are preferentially captured by the ⁶Li (n, α) T reaction. Then, the productions of ²¹⁰Po and ²⁰³Hg are mitigated. The enrichment of ²⁰⁴Pb leads to a small TBR, because neutrons are captured by ²⁰⁴Pb due to its large cross section for (n. γ) reaction. The TBR of ²⁰⁶Pb or ²⁰⁷Pb enriched Pb-17Li is more or less the same with that of the natural Pb-17Li. In these cases, the productions of ²¹⁰Po and ²⁰³Hg are slightly mitigated because of the removal of ²⁰⁸Pb and ²⁰⁴Pb from the blanket.