Critical Experiments to Determine Amount of U-235 in Research Reactor Fuel Assemblies

Seven different critical core configurations of the IRR1 have been used to determine experimentally the reactivity changes caused by interchanging different fuel assemblies in the same core position(1'2). The data obtained with the first four critical configurations, Cores 1, 2, 3, and 4, are analyzed in this report; the other three will be analyzed and reported in a later paper. The different fuel assemblies (highly enriched MTR type fuel assemblies) interchanged in these cores varied in their burnup or loss in U-235, thus changing the core keff w i t h each interchange. The k∞ of a fuel assembly is a function of its U-235 inventory. The fuel assemblies interchange forced the control blade to alter its height in order to compensate for the change in core reactivity. The control blade reactivity worth as a function of its height was measured by period measurements so the reactivity changes due to the fuel assemblies interchange could be determined. Several different fuel assemblies in each core were measured in this manner. This experimental data can be calculated using reactor physics codes