Tohoku seeks Onagawa 2 restart

30 December 2013

Tohoku Electric Power Company has requested a safety review by Japan's nuclear regulator of unit 2 at its Onagawa plant, prior to its restart. The Onagawa plant sustained far less damage from the March 2011 earthquake and tsunami than expected.

Onagawa NPP 400 (NRA)
The Onagawa plant (Image: NRA)

The company applied to the Nuclear Regulation Authority (NRA) on 27 December for a safety assessment of Onagawa 2. The assessment will verify whether measures taken at the plant meet new safety standards. The previous day, Tohoku presented a proposal to Miyagi Prefecture, Onagawa town and Ishinomaki City to hold preliminary talks about ensuring the safety of the Onagawa plant.

The plant is on Japan's northeastern coast and was the closest plant to the epicentre of the massive earthquake and tsunami of 11 March 2011. Although the earthquake knocked out four of the five external power lines, the remaining line provided sufficient power for the plant's three boiling water reactors (BWRs) to be brought to cold shutdown. Onagawa 1 briefly suffered a fire in the non-nuclear turbine building.

A mission from the International Atomic Energy Agency (IAEA) in August 2012 concluded, "The structural elements of the nuclear power station were remarkably undamaged given the magnitude of ground motion experienced and the duration and size of this great earthquake." The plant was largely unaffected by the tsunami as it sits on an elevated embankment more than 14 metres above sea level.

"Some minor damage resulted due to the quake, but we have confirmed the soundness through on-site checks. Having our safety improvement measures checked will also bring a sense of reassurance to the local people," Tohoku executive vice president Shigeru Inoue was cited as saying by the Kyodo news agency.

Onagawa 2 is the fourth Japanese BWR to request safety checks prior to restart. The NRA has ordered all BWRs to be fitted with filtered venting systems, which help reduce pressures in the reactor containment during emergency situations leading to reactor core damage and the partial or total loss of safety systems.

The unit becomes the sixteenth Japanese reactor to begin procedures for its restart. Tohoku plans to apply later for safety assessments of Onagawa units 1 and 3.

Researched and written
by World Nuclear News