Development plan of high burnup fuel for high temperature gas-cooled reactors in future

Plan and status of research and development (R and D) were described on coated fuel particle (CFP) and fuel compacts for the core of small-sized high-temperature gas-cooled reactor (HTGR) HTR50S at second step of phase I (second core of HTR50S). Specifications of existing CFPs for high burnup (HTR50S2-type-CFPs) were adopted as specifications of CFPs, to reduce R and D. HTR50S2-type-CFPs were fabricated based on technology developed in High Temperature Engineering Test Reactor (HTTR) project. The first irradiation test of HTR50S2-type-CFPs is now being carried out. In addition, R and D for fuel compact with high packing fraction is planned, because volume fraction of UO₂ kernel to whole of HTR50S2-type-CFP is rather smaller than that of the HTTR-type-CFP.We would aim to complete the proof of nuclear/thermal design of second core of HTR50S on integrity of fuel, feeding back results of R and Ds and nuclear/thermal design to each other. In addition, we describe outline of R and D plans for core of HTR50S in phase II and practical HTGR in Japan in future, naturally safe HTGR. (author)