Onagawa 2 upgrade faces further delay

Tohoku expects to spend about JPY340 billion (USD3.2 billion) on the countermeasures, which include seismic reinforcement of Onagawa 2 and construction of a 29-metre high and 800m long sea wall to protect the plant from tsunamis. The company had originally planned to complete this construction work by April 2017, but the schedule has been pushed back a number of times. The latest plan had been for the countermeasures to be in place by the end of financial year 2020 (ending March 2021).

However, Tokohu has now announced it has reviewed its upgrade works plan for Onagawa 2's operation. Based on discussions it has had with the Nuclear Regulation Authority (NRA), Tohoku has decided to expand or revise its construction works for improving the facilities at the plant. As a result, the entire plan of construction work has been delayed and is now expected to be completed in FY2022 (ending March 2023).

Tohoku applied to the 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. On 26 February this year, the NRA approved the final screening report, clearing the way for the unit to resume operation. The utility is still 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 14m above sea level, but the basement floors of unit 2 were flooded. A mission from the International Atomic Energy Agency in August 2012 concluded that 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".

Tohoku has already decided to decommission unit 1 of the plant and is considering applying to restart unit 3.