Chubu Electric Power Company is considering a request from Japanese prime minister Naoto Kan to shut down its Hamaoka nuclear power plant on predictions of a major earthquake.
A view across the Hamaoka site
Kan made the request this morning and publicised it in a press conference. He said that analysis from earthquake experts under the Ministry of Education predicted an 87% chance of magnitude 8 earthquake in the Tokai region within 30 years and the risk of a major tsunami.
Hamaoka is the only nuclear power plant on that section of the southern coast and Kan said that for safety, and with respect to public opinion, he is requesting it be shut down and prepared for the potential Tokai event. He wants the establishment of a sufficient embankment to protect against tsunami.
The Nuclear and Industrial Safety Agency (NISA) later issued a request to ensure effective protection measures are in place with a suspension of operation in the meantime. Chubu will have to have install additional air-cooled emergency diesel generators and stock spare parts for seawater pumps that run the residual heat removal system. Carrying out this work and satisfying NISA of the plant's fitness to restart could take many months.
A statement from Chubu simply noted its receipt and consideration of the government request.
The Japan Meteorological Agency has a special program to monitor seismic activity that could be a precursor of a long-awaited quake in the Tokai region. It has a three level warning system should anomalies begin to appear, but currently sees 'no anomalous activity.'
There is no legal precedent in Japan for a politician to order the closure of a nuclear power plant that is in line with NISA's independently set regulations, or for him to influence NISA into ordering a suspension of operation. Another consideration for government and the electric company is the effect on people that a sudden drop in power supply could have, particularly with seasonal demand increases.
Hamaoka nuclear power plant consists of five boiling water reactors. The first two are now permanently shut down after Chubu decided it would not be economic to upgrade their seismic safety when regulations were revised after the earthquake of July 2007.
Remaining units 3, 4 and 5 were built in 1987, 1993 and 2005 respectively while a seventh is planned to replace the two shut down ones. Unit 3 is now undergoing periodic inspection, while units 4 and 5 are operating.
All affected Japanese reactors shut down safely during the earthquake of 11 March, but the subsequent tsunami disabled cooling and back-up power at at Fukushima Daiichi. Thousands of people were evacuated while three reactors went on to suffer partial core melts and used fuel ponds got into trouble. Although nobody has been hurt by radiation, there was a significant release and the site is still months away from full stabilisation.
Researched and written
by World Nuclear News