Onagawa Nuclear Power Plant

Onagawa Nuclear Power Plant
The Onagawa Nuclear Power Plant
Location of Onagawa Nuclear Power Plant in Japan
Country	Japan
Coordinates	38°24′04″N 141°29′59″E / 38.40111°N 141.49972°E / 38.40111; 141.49972Coordinates: 38°24′04″N 141°29′59″E / 38.40111°N 141.49972°E / 38.40111; 141.49972
Construction began	July 8, 1980 (1980-07-08)
Commission date	June 1, 1984 (1984-06-01)
Operator(s)	Tohoku Electric Power Company
Power generation
Units operational	1 x 524 MW 2 x 825 MW
Annual generation	5,283 GW·h
Website Japanese version, English version

The Onagawa Nuclear Power Plant (女川原子力発電所, Onagawa ( pronunciation) genshiryoku hatsudensho, Onagawa NPP) is a nuclear power plant located on a 1,730,000 m² (432 acres) site^[1] in Onagawa in the Oshika District and Ishinomaki city, Miyagi Prefecture, Japan. It is managed by the Tohoku Electric Power Company. It was the most quickly constructed nuclear power plant in the world.

The Onagawa-3 unit was used as a prototype for the Higashidori Nuclear Power Plant.

The plant conforms fully to ISO 14001, a set of international environmental management standards. The plant's waste heat water leaves 7 degrees Celsius higher than it came in and is released 10 meters under the surface of the water, in order to reduce adverse effects on the environment^[2] All the reactors were constructed by Toshiba.^[3]

According to Reuters the Onagawa nuclear power plant was the closest nuclear power plant to the March 2011 earthquake epicenter. All three reactors at the power plant successfully withstood the 2011 Tōhoku earthquake and tsunami, demonstrating the ability of a well designed nuclear facility to withstand even one of most powerful of megathrust earthquakes and tsunamis ever recorded and to shut down safely, as designed, without incident.^[4]

Following an IAEA inspection in 2012, the agency stated that "The structural elements of the NPS(nuclear power station) were remarkably undamaged given the magnitude of ground motion experienced and the duration and size of this great earthquake,” Onagawa, facing the Pacific Ocean on Japan's north-east coast, experienced very high levels of ground shaking – among the strongest of any plant affected by the earthquake – and some flooding from the tsunami that followed, but was able to shut down safely.^[5][6]

In 2013 the station operators sent an application request to restart unit 2 at Onagawa to the Japanese Nuclear Regulatory Agency.^[7]

Reactors on Site

Unit 1

Shut down manually on 25 February 2005 because it was determined that the reactor containment leaked small amounts of nitrogen. The unit was restarted once Nuclear and Industrial Safety Agency was satisfied that the countermeasures taken by the plant operator to prevent a reoccurrence were adequate.^[8]

Unit 2

• May 2006 it was confirmed that a pipe was leaking due to debris damage.
• June 7, 2006 Difficulties with pressure control prompted further inspections.
• July 7, 2006 METI and the Nuclear and Industrial Safety Agency determined that the plant's performance was not satisfactory.

Unit 3

• July 7, 2006 Due to pipe integrity concerns the reactor was shut down.
• November 25, 2006 Following repairs the reactor was restarted.

Incidents

2001

Small fire in the administrative offices. Did not affect functioning of the plant.

2005

The Onagawa Nuclear Power Plant was affected by the 2005 Miyagi earthquake and recorded vibrations above what the plant was designed for. Analysis after the event, however, found no damage to the reactor systems. Some people reported seeing smoke come from the plant after the earthquake and reported it, thinking that it indicated an accident, but the smoke was actually produced by the backup diesel generators.

2011

Position of Japanese nuclear plants and spreading of tsunami

The estimated tsunami heights before making landfall, from destroyed buoy gauges. Alternatively, from a 25 March 2011 report made by the Port and Airport Research Institute (PARI), which determined tsunami height by visiting the port areas, the Fishery port of Onagawa experienced 15 m (50 ft), the highest of all surveyed areas.^[9]

The Onagawa Nuclear Power Plant was the closest nuclear power plant to the epicenter of the 11 March 2011 Tōhoku earthquake,^[10] less than half the distance of the stricken Fukushima I power plant.^[11] The town of Onagawa to the northeast of the plant was largely destroyed by the tsunami^[12] which followed the earthquake, but the plant's 14 meter (46-foot) high seawall was tall and robust enough to prevent the power plant from experiencing severe flooding. All safety systems functioned as designed, the reactors automatically shut down without damage, and no reactor damage occurred.^[13] A fire broke out in the Turbine hall,^[14][15][16] which is sited separately from the plant's reactor^[17] in a building housing the electricity-generating turbine, but was soon extinguished.^[18]

Following the tsunami two to three hundred homeless residents of the town who lost their homes to the tsunami took refuge in the Onagawa nuclear plant's gymnasium, as the reactor complex was the only safe area in the vicinity to evacuate to, with the reactor operators supplying food and blankets to the needy.^[19] At the time Reuters suggested that the Onagawa nuclear power plant may demonstrate that it is possible for nuclear facilities to withstand the greatest natural disasters, and to retain public trust.^[4] The plant was shut down following the earthquake and tsunami, in accordance with standard legally mandated procedure after such an event,^[20] but despite the IAEA finding that the plant had survived the quake remarkably undamaged,^[21] the three units remain in cold shutdown. Whereas the mishaps at Fukushima I radically changed public opinion on safety and risks, Tohoku Electric seems to have preserved much of its pre-disaster goodwill in the area of Onagawa.^[4] While the tsunami was more than 13m high at both Fukushima I and the Onagawa power plant,^[22] the largest difference between them, apart from the reactor safety systems being designed some twenty years apart, the Fukushima I seawall was built to a height of just 5.7m. Whilst the Onagawa power plant seawall was nearly 14m high and thus successfully blocked the majority of the tsunami from causing severe flood damage.^[22][23] It was this tsunami at Fukushima I that has been determined to be solely responsible for precipitating the loss of cooling and ultimately the Fukushima disaster which had a much shorter sea wall of 6 meters.^[24]

On 13 March 2011, two days after the earthquake and tsunami, levels of radiation on site reached 21μSv/hour, a level at which Tohoku Electric Power Company were mandated to declare a state of emergency, and they did so at 12:50, declaring the lowest-level such state. Within 10 minutes the level had dropped to 10μSv/hour.^[25][26][27] The Japanese authorities believe the temporarily heightened values were due to radiation from the Fukushima I nuclear accidents and not from the Onagawa plant.^[28][29] On March 13 20:45 UTC, the IAEA announced that radiation levels at the Onagawa plant had returned to normal background levels.^[28]

A 7 April 2011 aftershock damaged 2 of the 3 power lines connecting to the plant, but it did not damage any of the backup cooling systems, which remained undamaged and unneeded, including the ESWS, the ECCS and the back up diesel generators.^[30]

On 8 April 2011, a small 3.8 liter leak of radioactive water spilled from spent fuel pools holding fuel rods following an aftershock from the March 2011 Tōhoku earthquake.^[31]

Hirai Yanosuke

Hirai Yanosuke, who died in 1986, is cited as the only person on the entire power station construction project to push for the 14.8-meter breakwater. Although many of his colleagues regared 12 meters as sufficient, Hirai’s authority eventually prevailed, and Tōhoku Electric spent the extra money to build the 14.8m tsunami wall. Another of Hirai’s proposals also helped ensure the safety of the plant during the tsunami - Expecting the sea to draw back before a tsunami, he made sure the plant’s water intake cooling system pipes were designed so it could still draw water for cooling the reactors.^[22]

Reactor restart requests 2013

In 2013, the owners of the station, Tohoku Electric Power Company, sent a restart request to the Japanese Nuclear Regulatory Agency for Onagawa 2.^[7]

See also

• 2011 Japanese nuclear accidents
• List of boiling water reactors
• Lists of nuclear disasters and radioactive incidents

References

External links

• Onagawa Nuclear Power Plant site c/o Tohoku Electric Co. 東北電力・女川原子力発電所
• IAEA Alert Log