Fukushima Daiichi NPS Prompt Report 2013

TOKYO-A progress report on the investigation into lingering questions about the causes of the Fukushima nuclear disaster has yielded valuable information that will help add safety measures to the world's nuclear power plants, according to the utility that owns the Fukushima Daiichi facility.

The report, released on December 13 by Tokyo Electric Power Company (TEPCO), is the first progress report on TEPCO's continuing investigation into the causes of the crippling of three of the facility's reactor units after the Great East Japan Earthquake and subsequent tsunami of March 2011. (A fourth unit, also damaged but not in use at the time of the earthquake and tsunami, and from whose storage pool fuel is currently being removed, is not addressed in this report.)

"I welcome this report, as well as the continuing study and analysis of the Fukushima Daiichi accident," said TEPCO President Naomi Hirose. "This report's findings have verified the appropriateness and effectiveness of the safety measures we are implementing at our Kashiwazaki-Kariwa Nuclear Power Station." TEPCO is currently seeking regulatory approval to restart Kashiwazaki-Kariwa, the world's largest nuclear generating facility and a key component the company's, and Japan's, recovery.

Facility Withstood Earthquake

Of particular note is the report's finding that the accident at Unit 1 was, in fact, caused by the impacts of the tsunami. The Fukushima Nuclear Accident Independent Investigation Commission of Japan's Diet (Parliament) had raised the possibility that it may have been the result of a loss of coolant from pipe failure associated with the earthquake, not the subsequent tsunami and loss of emergency power. If so, that would have contradicted the prevailing understanding that the facility had weathered the 9.0 magnitude earthquake well, an important consideration for future designs incorporating seismic safety principles.

But, the report says, Unit 1 did in fact survive the earthquake intact. Data recorded by wave meter records and other instruments, along with photographic sequences of the incoming tsunami along with other data, make it clear that the loss of emergency diesel generator power caused by the tsunami, and the resulting failure of the cooling systems, caused the accident.

The report was less conclusive on why water injected into Unit 1 to 3 reactors from fire trucks in the immediate aftermath of the tsunami and failure of the cooling systems was insufficient to cool the reactor core and prevent a meltdown. It is possible, the report says, that the water found its way into other systems and failed to reach the core, but investigation into the actual amount of water injected into the unit and its impact on the progress of the accident will be a focus of continued study.

Other Findings

The over 300-page report makes numerous technical findings both about the causes of the accident and the sequence of events, somewhat different for each of the three units, that led to their failure. It also reports on the current status of the three units, including ongoing efforts to determine the locations where water currently being used to cool the molten cores may be leaking from their primary containment vessels.

The report may be found at
http://www.tepco.co.jp/en/press/corp-com/release/2013/1233101_5130.html