A governmental investigative panel on the 2011 Fukushima nuclear disaster has pointed out that the absence of preparatory steps for tsunami and severe accidents on the part of plant operator Tokyo Electric Power Co. (TEPCO) was one of the main reasons for the disaster.
But Masao Yoshida, chief of the Fukushima No. 1 Nuclear Power Plant at the time of the nuclear accident, stressed in subsequent testimony that he could not predict such a huge earthquake and tsunami. Despite this, he acknowledged that he was overconfident in measures against a severe accident and did not properly grasp the conditions of emergency facilities.
In 2008, Yoshida was in charge of overseeing nuclear power plant construction as head of TEPCO head office's nuclear power facilities management division and drew up a projection of deadly tsunami as high as 15.7 meters, according to the panel's report. But he failed to implement tsunami measures such as building a levee along the Fukushima power plant, saying the projection was prepared based on a worst-case scenario.
When questioned by the investigative panel, his testimony shows, Yoshida challenged critics, wondering if any Japanese seismologists and tsunami experts had forecast a magnitude-9 earthquake. He also challenged critics for blaming him for failing to take a giant tsunami into consideration. ''This time, 23,000 people (in reality, about 16,000 people) died. Who killed them? It's strange to shift the blame only here (the Fukushima plant),'' he testified.
When asked why he did not imagine the malfunctioning of multiple nuclear reactors, Yoshida referred to the Kashiwazaki-Kariwa Nuclear Power Plant, also operated by TEPCO, which was damaged by the Niigata Chuetsu Offshore Earthquake in 2007. He said that although the actual quake far surpassed the designated safety limits of equipment at the power plant, the facility suffered little damage. He said that that experience convinced him that Japanese nuclear power designs were strong enough to withstand natural disasters and made him overconfident.
Yoshida was also asked about why he did not notice the halting of an isolation condenser (IC) capable of cooling a reactor for an extended period without an electrical source at the Fukushima plant's No. 1 reactor which experienced a meltdown and hydrogen explosion. He responded that duty personnel had long thought the system was intact. He said he should have checked repeatedly if the IC was OK, adding he was deeply sorry for the lapse.