Uranium-238 to uranium-235 fission-ratio distribution in spherical lithium-- metal assemblies with and without a graphite reflector

Spherical lithium-metal assemblies with and without a graphite reflector were prepared by stacking lithium and graphite blocks to investigate the neutronics in the fusion reactor blanket. The ratio of $sup 238$U-to-$sup 235$U fission rates was measured by micro-fission chambers. The fission ratio was calculated by the one-dimensional transport code ANISN with the P$sub 5$-S$sub 8$ approximation using a 42--group neutron cross-section set. The fission ratios measured in the lithium-metal assembly without a graphite reflector agree well with the calculated ones. In the assembly with a graphite reflector, however, there is a large discrepancy between experiment and calculation. (auth)