Problems of lead nuclear data in fusion blanket design

Kondo, Keitaro; Murata, Isao*; Klix, A.*; Seidel, K.*; Freiesleben, H.*

Several participants of the International Thermonuclear Experimental Reactor (ITER), such as Japan and EU, intend to introduce a Test Blanket Module (TBM) using a liquid lithium lead eutectic, which is used for the neutron multiplier and the tritium breeder. Recently a preliminary experiment in which a LiAlPb assembly was irradiated with 14 MeV neutrons was conducted at Technische Universitt Dresden. We found out that the neutron flux inside the assembly calculated with JENDL-3.3 underestimates an experimental value in the 10-16 MeV region by around 30% and that in the 0.5-5 MeV region by around 15%, while the calculated flux with JEFF-3.1 overestimates the measurement in the 5-10 MeV region by around 20%. In order to reveal a reason of the discrepancy, problems of the nuclear data libraries for lead were investigated. As a result, the following problems of the evaluated libraries were pointed out: The cross sections of the elastic scattering in JENDL-3.3 for lead isotopes are too small and cause a significant underestimation of the neutron flux above 10 MeV, which appeared in the analysis of the above experiment. Inelastic scattering data for Pb in JENDL-3.3 reproduce previous experimental double-differential cross section data most well. However, those for the other lead isotopes have some problems and cause a large underestimation of the neutron flux from 0.5 to 5 MeV. The reason of the overestimation in the energy region of 5-10 MeV with JEFF-3.1 is still unclear.