Ohi 3 reaches critical milestone in restart

Unit 3 of the Ohi nuclear power plant in Japan's Fukui Prefecture reached criticality this morning, operator Kansai Electric Power Company announced. The reactor - the sixth to be restarted after clearing the country's revised safety regulations - is expected to resume commercial operation early next month.

Unit 3 of the Ohi nuclear power plant in Japan's Fukui Prefecture reached criticality this morning, operator Kansai Electric Power Company announced. The reactor - the sixth to be restarted after clearing the country's revised safety regulations - is expected to resume commercial operation early next month.

Ohi units 3 and 4 (Image: Kansai)

Following the shutdown of all of Japan's reactors after the March 2011 accident at the Fukushima Daiichi plant, Ohi 3 and 4 were given permission to resume operation in August 2012. However, the two 1180 MWe pressurised water reactors (PWRs) were taken offline again for Nuclear Regulation Authority (NRA) inspections in September 2013.

The NRA announced in May 2017 that the two units meet safety standards introduced in July 2013. The NRA approved Kansai's plan for strengthening the units in August last year. The regulator subsequently conducted pre-operation inspections of the units to confirm that the safety countermeasure equipment complies with the approved construction plan at the plant. The governor of Fukui Prefecture approved the restart of Ohi units 3 and 4 in November.

Kansai began loading the 193 fuel assemblies into the core of unit 3 on 9 February, completing the process on 13 February. The reactor was restarted at 5.00pm yesterday. Kansai said Ohi 3 attained criticality - a sustained chain reaction - at 3.00am today.

On 13 March, Kansai said: "After reaching criticality, the plant will start power control operation on 16 March 2018 as the final stage of the periodic outage inspection following various types of tests." It added, "In early April, the plant will restart full-scale operation after the completion of the comprehensive inspection performed by the Nuclear Regulation Authority."

Kansai earlier said it expects to refuel Ohi 4 in mid-April, restart it around mid-May, with commercial operation expected to resume in early June.

In December, Kansai said it will not seek permission to restart Ohi units 1 and 2, which have been offline since July 2011 and December 2011, respectively. The company announced on 1 March that it had applied to Japan's Ministry of Economy, Trade and Industry for approval to decommission the two 1175 MWe PWRs, which are approaching 40 years old.

Ohi 3 is the sixth of Japan's 42 operable reactors which have so far cleared inspections confirming they meet the new regulatory safety standards and have resumed operation. The others are: Kyushu's Sendai units 1 and 2; Shikoku's Ikata unit 3; and Kansai's Takahama units 3 and 4. Another 18 reactors have applied to restart.

Kyushu Electric Power Company expects to restart both units 3 and 4 at its Genkai nuclear power plant in Saga prefecture later this year.

Nuclear energy is expected to account for 20-22% of Japan's power generation in 2030, with a similar portion coming from renewable sources. The remainder of the country's power generation will be met by coal (26%), LNG (27%) and oil (3%), according to Japan's latest energy policy. That policy supports "utilizing nuclear power generation whose safety is confirmed".

Researched and written
by World Nuclear News