Characteristic measurements of silicide fuel core in JRR-3M

The JRR-3M (Japan research reactor no.3), a light water moderated and cooled pool-type research reactor with maximum thermal power of 20MW using low enriched uranium fuels, attained first critically on March 22, 1990, and has been operated for beam experiments, irradiation test of reactor fuels and materials, production of radioisotopes, and so on. The fuel conversion of the JRR-3M was projected from the aluminide (UAlx-Al) fuels to the silicide (U3Si2-Al) fuels in order to reduce the number of spent fuel generated a year. For the purpose of controlling increased excess reactivity due to an increase of uranium loading, the silicide fuel elements install the cadmium wires covered by the aluminum alloy as the burnable poison. The characteristic measurements of the silicide fuel core were started on September 6, 1999. The minimum critical core, the excess reactivity, reactivity worth of control rods, moderator temperature coefficient of reactivity, heavy water dump effect, etc. were main measurements of the fuel conversion. As the result, the minimum critical core was achieved with 15 standard fuel elements, the excess reactivity was measured to 14.1%Δk/k, shut down margin was measured to 19.3%Δk/k, heavy water dump effect was measured to 1.55%Δk/k. Beside, the characteristic measurements correspond approximately with results of the neutronics design calculations and the aluminide fuel core. (orig.)