Accuracy of Reactor Physics Parameters in Thorium-Loaded Accelerator-Driven System Experiments at Kyoto University Critical Assembly

Experiments on the thorium-loaded accelerator-driven system (ADS) were carried out at the Kyoto University Critical Assembly to reevaluate the accuracy of reactor physics parameters, including prompt neutron decay constants reaction rate distributions, subcriticality, and subcritical multiplication factor, and to reveal the dependency of these parameters on the external neutron source by varying the external neutron source of 14-MeV neutrons and spallation neutrons generated by 100-MeV protons. In preparation for thorium-loaded ADS experiments, renewed irradiation experiments are conducted with small and thin foils of thorium in the critical state to reevaluate the accuracy of the experimental analyses. In the ADS experiments, reactor physics parameters are found to be different in the same core when the external neutron source is injected separately with 14-MeV neutrons and spallation neutrons. By comparing with the calculated results, the significant impact of external neutron sources on the neutron characteristics of ADS is obtained in both the static and the kinetic experimental analyses.