Investigation on structural integrity of graphite component during high temperature 950C continuous operation of HTTR

Sumita, Junya ; Shimazaki, Yosuke ; Shibata, Taiju 

Graphite material is used for internal structures in High Temperature Gas-cooled Reactor (HTGR). The core components and graphite core support structures are so designed as to maintain the structural integrity to keep core cooling capability. In order to confirm that the core components and graphite core support structures satisfy the design requirement, the temperatures of the reactor internals are measured during the reactor operation. Surveillance test of graphite specimens and in-service inspection (ISI) using TV camera are planned in conjunction with the refueling. This paper describes the evaluation results of the integrity of the core components and graphite core support structures during the high temperature 950C continuous operation, reactor outlet temperature of 950C for 50 days, in HTTR (High Temperature Engineering Test Reactor). The design requirements of the core components and graphite core support structure were satisfied during the high temperature 950C continuous operation. The dimensional change of graphite which directly influences the temperature of coolant was evaluated with considering the temperature profiles of fuel block. The magnitude of irradiation-induced dimensional change was about 1.2 times larger than that of isotherm for 1000C. In addition, the programs of surveillance test and ISI using TV camera were introduced.