Measurements of reaction rate distribution in the core with collimator

Experiments on the base of accelerator driving subcritical reactor (ADSR) with FFAG (Fixed Field Alternating Gradient) accelerator in Kyoto University Critical Assembly (KUCA) are scheduled in 2005 fiscal year. However, it is necessary to examine the influence of the high energy neutron on the core generated by the nuclear spallation reaction as an external source in a basic experiment with FFAG accelerator. Putting the device of one collimator from the target, the high energy neutron is irradiated directly to the fuel body as the preparation stage. The reaction rate distribution in the fuel body was measured by using Indium wires in the experiment. It is understood that the reaction rate distribution in the fuel body area is compared and doubles without the collimator because the neutron generated from the target reaches the fuel body without being decelerated by void passage and because deflecting neutron and low energy neutron are absorbed. Moreover, about 60% reaction rate has decreased by closing the void passage at the center of the collimator with polyethylene in the fuel body area. (T.Tanaka)