Experience of HTTR construction and operation; Unexpected incidents

Fujimoto, Nozomu; Tachibana, Yukio ; Saikusa, Akio* ; Shinozaki, Masayuki; Isozaki, Minoru; Iyoku, Tatsuo

From a viewpoint of heat leakage, there were two incidents during HTTR power-rise-tests. One was a temperature rise of the primary upper shielding, and the other was a temperature rise of the core support plate. Causes of the both incidents were small amount of helium flow in structures. For the temperature rise of the primary upper shielding, countermeasures to reduce the small amount of helium flow, enhancement of heat release and installation of thermal insulator were taken. For the temperature rise of the core support plate, temperature evaluations were carried out again considering the small amount of helium flow and design temperature of the core support plate was revised. By these countermeasures, the both temperatures were kept below their limits.