A URANIUM CRITICAL ASSNMPLY AT LOW U235 CONCENTRATION

摘要

A critical metal assembly is described that has a cylindrical core of uranium with an average U235 concentration of 16-1/h% and a 3 inch reflector of natural uranium. The critical mass was determined to be 692 ± 4 kg of core material, from which a value for the critical mass of a bare sphere, having the same concentration, is calculated. Measurements of the prompt neutron decay constant;reactivity contributions of several materials;and radial and axial variations of fission rates of U235. U238, and Np237, as well as ratios of fission cross sections for these isotopes, are reported.