A Safety evaluation of HTTR core graphite structures against the Great East Japan Earthquake

Iigaki, Kazuhiko ; Ono, Masato ; Shimazaki, Yosuke ; Tochio, Daisuke ; Shimizu, Atsushi ; Inoi, Hiroyuki; Takada, Shoji; Sawa, Kazuhiro

On March 11th, 2011, the Great East Japan Earthquake which is one of the largest earthquakes in Japan occurred and the maximum acceleration in observed seismic wave in the HTTR exceeded the design value in a part of input seismic motions. Therefore, a visual inspection, a seismic analysis and a performance confirmation test of facilities were carried out in order to confirm the integrity of facility after the earthquake. The seismic analysis was carried out for the reactor core structures by using the response magnification factor method. As the results of the evaluation, the generated stress in the graphite blocks in the reactor core at the earthquake were well below the allowable values of safety criteria, and thus the structural integrity of the reactor core was confirmed. The integrity of reactor core was also supported by the visual inspections of facilities and the operation without reactor power in cold conditions of HTTR.