Criticality experiment of thorium reactor and analysis

In the Kyoto University criticality assembly experimental device (KUCA), the research on the nuclear characteristics of thorium reactors is one of the main objectives from the construction stage. It is because the eta value of 233U is large in the energy region of intermediate neutrons, and two of the three core are solid-moderated cores, accordingly, it is feasible to make a so-called intermediate core. The criticality experiment of a thorium reactor was not able to become a main research, but the research corresponding to the subsidy of research expense has been continued every year. It is expected to carry out the research of thorium reactors again some day. There is about 500 kg of metallic thorium in the KUCA, and by inserting it in the B stand, the change of reactivity, the distribution of neutron flux and so on were measured, and the comparative investigation with the analysis by the SRAC code was performed. Also the neutron spectra were measured by foil activation method and time of flight method. Typical fuel assemblies and the constitution of the core are shown, and the results of the experiment of bunching effect and the analysis are shown. The reactivity measurement for the materials of thorium molten salt reactors, the relation of the initial reactivity with the degree of uranium enrichment, and the analysis of the 233U fuel criticality experiment device KAMINI in India are described. (K.I.)