Reactor Physics Research Activities Related to the Very High Temperature Reactor in Japan

Reactor physics research activities in Japan that are related to the very high temperature reactor (VHTR) for multipurpose use are briefly summarized. Emphasis is placed on critical experiments. Neutronic core design accuracy required for the experimental VHTR is made clear, and nuclear data compilation and neutronic calculation code development are described. For experimental work, after a review of the results of all reactor physics experiments performed on the Semi-Homogeneous Experiment at the Japan Atomic Energy Research Institute, its reconstruction program to the VHTR critical assembly is presented. The aim of this program is to perform a detailed mockup experiment of the experimental VHTR loaded with low-enriched uranium-coated particle fuels. Finally, improvement of the neutronic calculation accuracy attained through comparison between calculation and experiment is illustrated, and some future problems are pointed out.