Onagawa nuclear plant

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Onagawa nuclear plant is 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.

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].

2011.03.11 Earthquake

After the earthquake and tsunami 2011.03.11, the Onagava nuclear plant had problems, although they are reported to be small compared to the Fukushima disaster. In particular, instead of to evacuate away from the plant (as in the case of Fukushima), hundreds of residents are reported to find refuge at Onagawa [4].

It is believed, that the Onagawa nuclear plant survived the earthquake 2011.03.11 and the tsunami (and did not explode as the Fukushima nuclear plant did) just due to the professional honesty of the engineer Yanosuke Hirai. According to the Takao Yamada (Mainichi Shinbun), the Onagawa nuclear plant survived the 2011.03.11 tsunami, because long ago, Hirai had insisted to built-up the 14.8-meter-tall shield, instead of the 12 m high shield proposed in the basic project. The tsinami 2011.03.11 is estimated to be 13 meter high. [5].

2011.03.13 splash of radiation

A fire from the turbine section of the plant following the 2011 Tōhoku earthquake was reported [6]. On March 13, 2011, levels of radiation on site reached 21μSv/hour, a level at which Tohoku Electric Power Company were mandated to declare 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 [7][8][9].

The splash of the radioactivity caused the major trace at the contamination map; the article Who contaminates Japan suggests the interpretation as a result of the unauthorized release of radiation from undetermined source, located to North-East from Onagawa, perhaps at the Hamobai island. For year 2012, neither confirmation nor negation of such a concept is available.

The Japanese authorities assume the temporarily heightened values were due to radiation from the Fukushima Disaster and not from the plant itself [10], and attribute it to the Fukushima Disaster.

On March 13 20:45 UTC, the IAEA announced that radiation levels at the Onagawa plant had returned to normal background levels [10].

The three units remain in cold shutdown since the earthquake of 11 March. The April 7th aftershock damaged 2 of the 3 external power lines to the plant but cooling was maintained through the third line [11].


Some parts of the content above are copypasted from Wikipedia [12]. The Wikipedia article may be more complete than this article.


  1. Tohoku Power. http://www.tohoku-epco.co.jp/pr/onagawa/hatudensyo.html The Onagawa Plant (information).
  2. Tohoku Power. http://www.tohoku-epco.co.jp/electr/genshi/npi/onag-e.htm Onagawa Nuclear Power Station
  3. Toshiba. http://www.toshiba.co.jp/nuclearenergy/english/experiences/plant/plant.htm Nuclear List of Delivered Units
  4. http://www.reuters.com/article/2011/10/20/us-japan-nuclear-tsunami-idUSTRE79J0B420111020 Risa Maeda. Japanese nuclear plant survived tsunami, offers clues. Wed Oct 19, 2011 9:57pm EDT. When the 13-meter (40-foot) tsunami that wrecked Japan's Fukushima nuclear plant hit Onagawa to the northeast, hundreds of residents found refuge at the local nuclear plant, rather than run the other way.
  5. http://mdn.mainichi.jp/perspectives/pulse/news/20120319p2a00m0na020000c.html Takao Yamada. Onagawa nuke plant saved from tsunami by one man's strength, determination. 2012.03.19. .. personal strength and tenacity of one Yanosuke Hirai, who passed away in 1986... Hirai was apparently the only person on the entire project to push for the 14.8-meter breakwater, while many of his colleagues said that 12 meters would be sufficient and derided Hirai's proposal as excessive. Hirai's authority and drive, however, eventually prevailed, and Tohoku Electric spent the extra money to build the 14.8-meter-tall shield. Some 40 years later, on March 11, 2011, a 13-meter-high tsunami slammed into the coast at Onagawa.
  6. http://www.reuters.com/article/2011/03/11/quake-japan-nuclear-idUSLHE7E801E20110311 Chikako Mogi. Fire at Tohoku Elec Onagawa nuclear plant. March 13, 2011
  7. http://www.world-nuclear-news.org/RS-Contamination_found_on_evacuated_residents-1303114.html Contamination checks on evacuated residents. March 13, 2011. A technical emergency was declared at 12.50 today at the Onagawa nuclear power plant after radiation levels in the plant site reached 21 microSieverts per hour. At this level plant, owner Tohoku Electric Power Company is legally obligated to inform government of the fact. Within just ten minutes, however, the level had dropped to 10 microSieverts per hour.
  8. http://www.iaea.org/newscenter/news/tsunamiupdate01.html IAEA update on Japan Earthquake. March 13, 2011, 13:35 CET. Japanese authorities have also informed the IAEA that the first (i.e., lowest) state of emergency at the Onagawa nuclear power plant has been reported by Tohoku Electric Power Company. The authorities have informed the IAEA that the three reactor units at the Onagawa nuclear power plant are under control. As defined in Article 10 of Japan's Act on Special Measures Concerning Nuclear Emergency Preparedness, the alert was declared as a consequence of radioactivity readings exceeding allowed levels in the area surrounding the plant. Japanese authorities are investigating the source of radiation.
  9. http://www.washingtonpost.com/wp-dyn/content/article/2011/03/12/AR2011031205493.html?hpid=topnews Chico Harlan, Steven Mufson: Japanese nuclear plants' operator scrambles to avert meltdowns. Washington Post, March 11, 2011
  10. 10.0 10.1 http://www.mb.com.ph/articles/309172/sea-water-injected-troubled-fukushima-power-plant Sea water injected into troubled Fukushima power plant. The Manila Bulletin Newspaper Online. March 13, 2011. Meanwhile, radiation monitored at the Onagawa nuclear power plant in Miyagi Prefecture on the Pacific coast shot up on Sunday, Tohoku Electric Power Co. said, adding that it was likely caused by radioactive substances let out at the troubled Fukushima No. 1 nuclear power plant in Fukushima Prefecture. Cite error: Invalid <ref> tag; name "iaea" defined multiple times with different content
  11. http://www.csmonitor.com/World/Asia-Pacific/2011/0407/Japan-earthquake-today-Tsunami-warning-lifted-but-Fukushima-evacuated Japan earthquake today: Tsunami warning lifted, but Fukushima evacuated, Christian Science Monitor, Gavin Blair, April 7, 2011
  12. http://en.wikipedia.org/wiki/Onagawa_Nuclear_Power_Plant


Fukushima disaster, Earthquake, Tsunami, Nuclear chimney, Who contaminate Japan