Earthquake hit plant set for restart

18 January 2006

Unit 2 of Japan’s Onagawa nuclear plant in Miyagi prefecture is expected to restart operations by the end of the month after all three units at the facility shut down last August following a major earthquake.

Concerns that the magnitude 7.2 quake may have damaged the structural integrity at the plant surfaced after seismometer readings showed the shock had exceeded acceptable design levels.

However, while the quake damage did not affect safety at the reactors, authorities expressed concern that a magnitude 7.6 quake is set to hit the region within the next 30 years.

During three months of investigations, plant owners Tohoku Electric re-examined earthquake standards for Onagawa's nuclear reactors, finding that unit 2 could withstand the predicted magnitude 7.6 quake without affecting safety.

Furthermore, analysis of the potential impact arising from a magnitude 8.2 quake and a magnitude of 7.2 quake with an epicentre directly beneath the station found that unit 2 reactor's equipment and pipe system would be damaged, but that safety mechanisms would remain operational.

Following a review by the Nuclear and Industrial Safety Agency (NISA) the governor of Miyagi prefecture has endorsed the safety report, effectively giving the green light for operations at unit 2. Units 1 and 3 are expected to restart following a similar series of safety analyses.

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