Absolute Fission-Rate Distributions in Lithium and Hybrid Fusion Blanket Assemblies, (I)

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Abstract
Absolute fission-rate distributions in four types of spherical blanket assemblies have been measured by micro-fission chambers embodying 232Th, 238U, 237Np and 235U. The four types of assemblies were of the lithium-metal and hybrid blanket form, with and without graphite reflector, i. e. Li, Li-C, U-Li and U-Li-C, and were made up by stacking lithium, graphite and natural uranium blocks, in various combinations. The effective outer radii of the spheres composing the assemblies were, in the case of U-Li-C assembly, 3.3, 10.0, 34.1 and 55.3 cm, respectively, for the central cavity, natural uranium, lithium metal and graphite regions. Absolute measurements demand knowledge of the number of 14-MeV neutrons produced by the accelerator and the number of fissionable atoms present in the chamber wall coating. The neutron yield was estimated from the counts of an α-monitor installed on the accelerator. The fission chambers were calibrated using the same accelerator. The overall experimental errors in most cases did not reach 10%, and averaged about 7%. Most of the neutrons reflected by the graphite possessed energies below 0.3 MeV. The assemblies, when possessed of a natural uranium region, saw a two-to three-fold increase in the number of neutrons.

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