Characteristic confirmation test by using HTTR and investigation of absorbing thermal load fluctuation

Honda, Yuki; Tochio, Daisuke ; Sato, Hiroyuki  ; Nakagawa, Shigeaki  ; Ono, Masato ; Fujiwara, Yusuke ; Hamamoto, Shimpei  ; Iigaki, Kazuhiko ; Takada, Shoji

The characteristic confirmation test has been demonstrating by using the High Temperature engineering Test Reactor (HTTR). The thermal load fluctuation test, which is one of marginal performance test is planned to be carried out after restarting of the HTTR. The preliminary analysis for the thermal load fluctuation test has been investigated. In the analysis, the reactor outlet temperature can continue to be stable against the reactor inlet temperature changing by thermal fluctuation. It means that HTGR have the capability of absorbing thermal fluctuation. This paper focuses on the investigation of mechanism of absorbing thermal fluctuation. With additional analysis, it is cleared that the large negative graphite moderator reactivity enhances the capability of absorbing thermal fluctuation. In addition, in the middle of the core, graphite moderator reactivity insertion trend are inverted. This trend is unique to HTGR because of large temperature difference between core inlet and outlet.