Chubu Electric Power Company has agreed to comply with a request from Japan's prime minister that it shuts down its Hamaoka nuclear power plant until its tsunami defences are strengthened. However, the company says that the plant is already adequately protected against tsunamis.
|Hamaoka (Image: Chubu)
Prime minister Naoto Kan asked Chubu on 6 May to shut down units 4 and 5, and not to restart unit 3 of its Hamaoka plant in Shizuoka prefecture, which is currently offline for regular inspections. Units 1 and 2 have already been permanently shut down. He said that analysis from earthquake experts under the Ministry of Education predicted an 87% chance of a 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 was requesting it be shut down and prepared for the potential Tokai event. He wants the establishment of a sufficient embankment to protect the plant against a large 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 announced today that its board of directors has decided to comply with the prime minister's request that the Hamaoka plant is shut down. The company noted, however, that the loss of some 3473 MWe of generating capacity would be a heavy burden for both the company and local residents. Chubu said that it would set up a task force to determine measures to compensate for this lost capacity.
According to Chubu, a study of the literature about historic tsunamis that have impacted the area in which the Hamaoka plant is located suggests that the tsunami with the greatest impact followed the massive Ansei-Tokai earthquake in 1854. Using numerical simulation analysis, a study was conducted on the maximum water level for tsunamis in the site vicinity, with the results showing that tsunami height in the area, even accounting for high tide, was up to 6 metres above sea level. In comparison, the Hamaoka site sits some six to eight metres above sea level, and thus above the tsunami height, indicating the site is safe from tsunamis. Furthermore, the Hamaoka plant is protected from the sea by sand dunes between 10 and 15 metres in height and about 60 to 80 metres wide. In addition, doors to reactor buildings, which house facilities critical to safety, are built to be waterproof, Chubu noted.
|Hamaoka safe from tsunamis (Image: Chubu)
Under the request issued by NISA, Chubu will have to 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 is likely to take many months.
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.
Researched and written
by World Nuclear News