18 Juin 2013
June 18, 2013
The Nuclear Regulation Authority said June 17 that the earthquake of March 11, 2011, was tentatively not responsible for damage to key equipment used to cool a reactor in the event of an emergency at the Fukushima No. 1 nuclear power plant.
But NRA investigators said they will further examine the condition of the isolation condensers at the No. 1 reactor and produce a more definitive assessment.
The NRA expects to compile a report on the matter by the end of the year to submit to the International Atomic Energy Agency in Vienna.
The nuclear watchdog’s temporary assessment came after its on-site inspection of the No. 1 reactor building on May 30-31.
Although a Diet investigation panel suggested the possibility that the condensers were damaged by the quake before tsunami inundated the facility, an independent team appointed by the government disagreed.
The NRA investigators said leaking water that workers witnessed near the isolation condensers before the tsunami struck could have been overflowing from the spent fuel storage pool nearby, not from the condensers.
They added if the condensers had been damaged at that time, steam would have been the result, causing the area to appear misty. But the eyewitnesses said the leaks looked like spraying water from a bucket.
The isolation condensers cool steam from the reactor’s pressure vessel, condense it into water and return the cooling water into the reactor.
Installed solely in the No. 1 reactor building, the condensers were designed to function in an emergency even without a power source.
Experts concluded that a meltdown at the No. 1 reactor took place earlier than expected because the condensers barely functioned during a plant blackout, which took place after the tsunami.
The NRA said it will determine the amount of water overflow and study further the piping and the condensers themselves to reach a definitive conclusion.
But additional rounds of on-site investigations are unlikely to come easily, given the high radiation levels at the site.
Whether the condensers were already damaged by the 9.0-magnitude Great East Japan Earthquake has been a key question in the investigation of the Fukushima accident due to the implications on the adequacy of anti-quake preparedness at the Fukushima plant and other nuclear facilities.