Onagawa 2 restart delayed by 'several months'

Tohoku said that work to fireproof electric cables at the unit is taking longer than planned.

"Regarding fire protection work, since late August last year, we have been carrying out work mainly on wrapping electrical conduits with fireproof materials, but the work area is narrow due to equipment and scaffolding installed for other safety work," it said in a statement. "There were many problems, so we proceeded with the construction while changing the route of the conduit according to the site situation.

"Recently, it has been confirmed that the amount of construction work has increased due to confirmation work for changing the route of electrical conduits and completing fire protection measures work, and as a result, the construction period for fire protection measures work is expected to be delayed, so safety measures work will be carried out. We are currently re-examining the completion date."

Tohoku said it currently anticipates a delay of several months regarding the completion date of the safety measures.

The company applied to the Nuclear Regulation Authority (NRA) in December 2013 for a safety assessment of Onagawa 2 - a 796 MWe boiling water reactor (BWR) - to verify countermeasures applied at the plant meet new safety standards. In late November 2019, the NRA approved a draft screening document that concluded the upgraded plant will meet revised safety standards, introduced in January 2013. In February 2020, the NRA approved the final screening report, clearing the way for the unit to resume operation. Tohoku is required to complete the countermeasure upgrades and obtain the approval of local authorities before it will be able to restart Onagawa 2.

The Onagawa plant was the closest nuclear power plant to the epicentre of the earthquake and tsunami of 11 March 2011, but sustained far less damage than expected. The earthquake knocked out four of the plant's five external power lines, but the remaining line provided sufficient power for its three BWRs to be brought to cold shutdown. Onagawa 1 briefly suffered a fire in the non-nuclear turbine building. The plant was largely unaffected by the tsunami as it sits on an elevated embankment more than 14 metres above sea level, but the basement floors of unit 2 were flooded.