Study on neutronics design of accelerator driven subcritical reactor as future neutron source, part 2: kinetic characteristics

In this paper, kinetic behavior of the accelerator driven subcritical reactor (ADSR) is investigated through the neutronics calculation in relation with a future plan of neutron source in Kyoto University Research Reactor Institute (KURRI). This neutron source is a hybrid system of the spallation neutron source and the subcritical reactor where the generated neutrons by spallation reactions are multiplied in the subcritical reactor. Kinetic behavior is important in the neutron source for research purpose since the pulse operation of accelerator can provide pulsed neutrons. Kinetic characteristic of this neutron source is examined by using the MCNPX code with taking advantage of the time-dependent tally capability. High-energy protons (500 MeV) are assumed to be injection particles, meanwhile 14 MeV neutrons are also considered to make a comparison. From the calculation results, time-dependent behavior of neutron flux in the ADSR was revealed. The results will provide basis for further investigation on the thermal-hydraulics and mechanical stress analysis of the ADSR. The calculated results also indicate that the kinetic behavior of neutron source is almost similar regardless of either 500 MeV protons or 14 MeV neutrons injection. Therefore, the basic experiments of ADSR can be carried out using the Kyoto University Critical Assembly (KUCA), where there is only the 14 MeV neutron source. The experimental data obtained in KUCA will be useful for verification of nuclear design method of the ADSR. However, to confirm the detailed neutronics characteristics of ADSR experimentally, a high-energy proton accelerator will be highly desirable.