Development of high temperature gas-cooled reactor fuel for extended burnup

Ueta, Shohei   ; Aihara, Jun ; Honda, Masaki*; Furihata, Noboru*; Sawa, Kazuhiro

Very High Temperature Reactor (VHTR) fuel is required to have excellent safety performance up to burnups of about 15 to 20% fissions per initial metal atom (FIMA), how are higher than the design of the Japanese HTTR fuel, 3.6% FIMA. In order to keep the integrity of TRISO fuel against the internal pressure increasing according to burnup, the SiC and the buffer layers should be designed to be thick, enough to increase the mechanical strength and to moderate the internal pressure in TRISO fuel, respectively. So far JAEA developed so-called extended burnup fuels whose target burnup was higher than those of the HTTR, and confirmed their performance by irradiation tests up to 9% FIMA. In this R&D, the new TRISO fuel designed for further extended burnup were fabricated. Indicated by the sphericity of the particle and so on, the quality of the new fuel resulted better than the past fuel for extended burnup.