Ōi Nuclear Power Plant

December 2005

On 22 December 2005, at 8:50am there was trouble with a power line due to strong winds and heavy snow, the reactor was shut down as a result.

July 2011

On 15 July 2011, Kansai Electric announced that two more nuclear power reactors in Fukui Prefecture would be shut down for regular inspections. The result of this decision was that 6 reactors were shut down, over half the utility's 11 reactors. The No. 4 reactor of the plant in Takahama Town will be brought to a halt for regular inspections on 21 July, and the No. 4 reactor of the plant in Oh Town, on 22 July. Regular inspections are nearly complete at two other reactors. However the plan of the Japanese government to introduce safety stress tests for the nation's nuclear plants leaves it unclear when they could be brought back on line.

On 15 July 2011, the pressure in a tank with boric-acid dropped unexpectedly. This tank injects water into the reactor in the event of an emergency. This made it impossible to inject water in a proper way into the No. 1 reactor. The reactor would be manually shut down around 9 PM on 16 July to look into the cause of the problem, although pressure returned to normal in about one hour. It was said that the trouble did not cause any leak of radioactive substances to the outside.

August 2011

In August 2011 citizens of the prefecture Shiga, at the banks of Lake Biwa, started a lawsuit at the Otsu District Court, and asked a court order to prevent the restart of seven reactors operated by Kansai Electric Power Company, in the prefecture Fukui.

December 2011

On 16 December 2011 Kansai Electric Power Company halted the No.2 reactor for a 4-month safety check.

February 2012

The results of the stress-tests of reactor no. 3 and no. 4 were approved after a meeting on 9 February 2012 of a panel of nuclear experts. The report said that the tests on the reactors were conducted appropriately and measures for earthquakes and tsunami were in place at the plant. These results would be submitted to NISA as early as 13 February 2012, after the briefing of minister Yukio Edano of Economy, Trade and Industry. But the local governments of the prefecture Fukui and the town Ōi were still very cautious about restarting the reactors, to their minds the stress tests had little priority, and they urged the central government to create new safety standards based on the lessons learned after accident at the Fukushima Daiichi nuclear power plant in March 2011.

March 2012

On 29 March 2012 the governor Keiji Yamada of Kyoto said to the Japanese Nuclear and Industrial Safety Agency that the prefecture would not accept the restart of reactor 3 and 4 at the Ōi nuclear power plant. Officials of the agency did visit Kyoto, to explain that the stress tests on the two idled reactors were approved. The governor of Shiga Yukiko Kada, who was visited later for a likewise explanation, reacted in a similar way: she asked for no hasty decisions. Although the approval of local governments was not legally required, prime minister Noda had made it clear, that the participation of the local communities would be taken into account. Mayor Yamada of Kyoto, with some 67,000 people living in areas within a radius of 30 kilometers from the Ōi power plant, added to his statement: A safety standard that reflects technical knowledge learned from the accident at Tokyo Electric's Fukushima Daiichi power plant must be presented first.

April 2012

To improve the safety at the plant an action plan was designed with a total of 91 possible measures. On 9 April 2012 of this only 54 were already implemented: the earthquake resistance of the power transmission towers was improved, satellite telephone communication was installed, seawater could be taken in to cool the systems. But an earthquake-resistant office building was not to be completed before April 2015. Until that time the assembly room close to the central control room would act as emergency-management office. Because this place offers only accommodation for some 50 people, experts had doubts about this place. Venting systems to release steam from the containment with filters to remove radioactive isotopes were planned to be built in 2015. The dam that would offer better protection against tsunamis was to be finished around March 2014.

On 13 April 2012 at a meeting of the Japanese government the stress-tests of two reactors of the Ōi nuclear plant and the safety action plan submitted by KEPCO were approved satisfactory and conform safety standards. To prevent the rise of electricity charges and an estimated power shortage of 18% in the summer of 2012 the two reactors needed to be restarted. Industry minister Yukio Edano said, that the 2 reactors were safe enough to be restarted and there was a need for their resumption.

May 2012

On 1 May 2012 Tetsuya Yamamoto, head of the nuclear crisis management team of NISA, said at a meeting at the Kyoto prefectural hall, that the Japanese government will introduce new safety standards for nuclear powerplants, but NISA might not be involved with this. The head of the Kyoto crisis team, did not accept this explanation, and said that "the government explanation is inconsistent with the demands of local people."

On 14 May 2012 Oi assembly says yes to restarting reactors. The assembly made the decision in consideration of the economic damage that a prolonged suspension could cause and conveyed its view to Oi Mayor Shinobu Tokioka later in the day. The mayor was set to make a decision on whether to approve the restarts after reflecting on the assembly's conclusion and the results of the appraisal made by Fukui's nuclear safety commission and other matters. The decision will then be conveyed to Fukui Gov. Issei Nishikawa. The assembly's decision followed an 11-1 vote in favor of restarting the reactors. One assembly member was absent due to illness.

July 2012

Reactor #3 was restarted on 1 July and reached criticality on 2 July 2012.

On 11 July 2012 Kansai Electric announced that reactor#4 was to be reactivated. The control rods would be lifted on 18 July. Criticality was to be reached the next morning. Power generation started on 21 July. The reactor could function on full output capacity on 25 July.

September 2012

The city and prefecture of Osaka requested that both units 3 and 4 be shut down, stating that the power was not needed.

October/November 2012

On 29 October 2012 Kansai Electric Power Co. announced in an interim report, that the F-6 fault running north-south between the plant’s Nos. 1-2 reactors and Nos. 3-4 reactors was found to be not active. Digging and boring surveys gave no indication of danger. According to Mitsuhisa Watanabe, tectonic geomorphology professor at Tokyo University, the fault poses security risks when the nuclear reactors continue to operate, and the seismic threat was underestimated by the authorities. An on-site inspection by the Nuclear Regulation Authority was scheduled for 2 November 2012.

March 2013

On 19 March 2013 the NRA announced that it would check the power plant on the site according to the new safety standards, before their introduction in July 2013, in order to keep the plant in operation. When no problems were found, than continued operation until September would be authorized by the NRA. After this date the reactors needed their routine maintenance. The NRA expected that the No. 3 and 4 reactors at the Oi plant would be able to clear most of the new safety standards, because countermeasures were in place. But the NRA intended to do a close examination.

June 2013

In the first weeks of June 2013 a team of inspectors, including NRA Commissioner Toyoshi Fuketa, examined the two operating reactors.

July 2013

On 3 July 2013 the NRA allowed the plant to keep the two operating reactors on line, although on 8 July new safety requirements for atomic plants would take effect. The NRA saw no serious problems at that moment. After September because of the mandatory routine checks the reactors would be taken offline. To resume operations, the reactors needed to comply with the new requirements, including the absence of active faults under the plant. Half July the outcome of the latest trench survey was expected.

September 2013

The Kansai Electric Power Company's Unit 3 at the Ohi nuclear power plant in Japan was shut down on 3 September 2013

On 14 September 2013, the day before the no. 4 Oi reactor was scheduled to close down for regular inspections, some 9000 demonstrators gathered at the Kameido Chuo Park and later marched close to JR Kinshicho Station and the Tokyo Skytree. They called for an end of Japan's dependency on nuclear power. The day after the Oi-reactor closed down, leaving Japan without any nuclear power for the third time in 40 years.

May 2014

The Fukui District finds that it will not allow the restart of the Oi no.3 and no.4 reactors.