Safety upgrades at unit 2 of Japan's Onagawa NPP in Miyagi Prefecture will not be completed in February as planned, Tohoku Electric Power Company announced. The target had been to restart commercial operation in May. Tohoku said it expects a delay of several months for completion date of the safety measures.

"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.”

It added that the amount of construction work had increased due to confirmation of the need to change the route of electrical conduits and complete fire protection measures. “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."

The Onagawa NPP was the closest to the epicentre of the earthquake and tsunami of 11 March 2011, but sustained relatively little damage. Although the earthquake destroyed four of the plant's five external power lines, but the remaining line was able to power its three boiling water reactors (BWRs) enabling them to be brought to cold shutdown. Unit 1 suffered a small fire in the turbine building. The plant is built on an elevated embankment more than 14 metres above sea level, which provided protection from the Tsunami, although but the basement floors of unit 2 were flooded.

Toholu Electric applied to the Nuclear Regulation Authority (NRA) in December 2013 for a safety assessment of the 796 MWe unit 2 to ensure countermeasures met new safety standards introduced in January 2013. NRA in 2019 approved a draft screening document that concluded the upgraded plant will meet revised safety standards and approved the final screening report in early 2020.

The Japanese government is seeking to increase the use of nuclear to reduce the use of fossil fuels, increase energy security and cut emissions. Before the March 2011 accident at the Fukushima Daiichi NPP, Japan had 54 reactors in operation providing around 30% of its electricity. However, within 14 months of the accident, all the plants were closed pending regulatory change in line with more stringent safety checks and regulations. Subsequently a number of nuclear units were closed permanently. To date, 12 of the remaining 33 operable reactors have cleared inspections confirming they meet the new regulatory safety standards and have resumed operation. Another 17 have applied to restart. The restarted plants are Sendai 1&2, Genkai 3&4, Ikata 3, Mihama 3, Ohi 3&4 and Takahama 1-4

Onagawa NPP was unaffected by the recent magnitude 7.6 earthquake, which has killed more than 200 people in the Hokuriku region. Hokuriku Electric Power reported a small oil leak from transformers at its Shika NPP, which was nearest to the epicentre. The two Shika reactors have been shut since the Fukushima accident. As well as the oil leak, Hokuriku Electric reported temporary power outages, and water spill-over from used nuclear fuel pools in the wake of the earthquake. A tsunami reached the facility some 90 minutes after the quake but the waves did not cause safety problems as the plant is built about 11 metres above sea level and has a four-metre high seawall.

NRA has now asked for further investigation even though initial assessments showed the Shika’s cooling systems and ability to contain radiation remained intact. NRA officials said Hokuriku should consider a possibility of fresh damage to transformers and other key equipment as aftershocks continue. NRA chairman Shinsuke Yamanaka urged Hokuriku to thoroughly investigate the cause of the transformer damage and report its findings. Hokuriku still hopes to restart unit 2 by 2026.

Image: Onagawa nuclear power plant