Hamaoka Nuclear Power Plant - Earthquake Susceptibility

Earthquake Susceptibility

Hamaoka is built directly over the subduction zone near the junction of two tectonic plates, and a major Tokai earthquake is said to be overdue. The possibility of such a shallow magnitude 8.0 earthquake in the Tokai region was pointed out by Kiyoo Mogi in 1969, 7 months before permission to construct the Hamaoka plant was sought, and by the Coordinating Committee for Earthquake Prediction (CCEP) in 1970, prior to the permission being granted on December 10, 1970. As a consequence, Professor Katsuhiko Ishibashi, a former member of a government panel on nuclear reactor safety, claimed in 2004 that Hamaoka was 'considered to be the most dangerous nuclear power plant in Japan' with the potential to create a genpatsu-shinsai (domino-effect nuclear power plant earthquake disaster). In 2007, following the 2007 Chūetsu offshore earthquake, Dr Mogi, by then chair of Japan's Coordinating Committee for Earthquake Prediction, called for the immediate closure of the plant.

On 6 May 2011, Japanese prime minister Naoto Kan asked Chubu Electric Power Company, which operates the Hamaoka plant, to halt reactors No. 4 and No. 5, and not to restart reactor No. 3 which was then offline for regular inspection. Kan said that a science ministry panel on earthquake research has projected an 87% possibility of a magnitude-8-class earthquake hitting the region within 30 years. He said that considering the unique location of the Hamaoka plant, the operator must draw up and implement mid-to-long-term plans to ensure the reactors can withstand the projected Tokai Earthquake and any triggered tsunami. Kan also said that until such plans are implemented, all the reactors should remain out of operation. Chubu Electric has decided to comply with the government request on 9 May 2011. The Yomiuri Shinbun, one of Japan's largest newspapers, criticized Kan and his request, calling it "abrupt" and noting the difficulty towards Chubu Electric's shareholders and further stated Kan "should seriously reflect on the way he made his request." Yomiuri followed up with an article that wondered how dangerous Hamaoka really was and claimed the request was "a political judgment that went beyond technological worthiness." The next day damage to the pipes inside the condenser were discovered following a leak of seawater into the reactor.

The plant has been designed to withstand an earthquake of magnitude 8.5. Sand hills of up to 15 metres (49 ft) height provide defence against a tsunami of up to 8 metres (26 ft) high, but Hamaoka currently lacks a concrete sea barrier.

On 22 July 2011 plans were unfolded to build an 18-meter-high embankment by December 2012 to prevent tsunami damage to the facility. This would protect the reactors against waves higher than the waves that occurred in the Fukushima Daiichi nuclear power plant on 11 March 2011. The barrier would also be 10 meters taller than the highest waves expected in the area in the event of 3 major earthquakes occurring at the same time. Plans were studied to build a new embankment 1.5 kilometers along the coast by the plant. Next to this a waterproof building was planned to house a backup-pump and also the wall around the reactors was extended. Overall costs of the plans: 1.3 billion dollars.