The Onagawa Nuclear Power Plant is a nuclear power plant 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 the most modern reactor in all of Japan at the time of its construction. It was used as a prototype for the Higashidori Nuclear Power Plant. All the reactors were constructed by Toshiba.
It 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. A fire from the turbine section of the plant following the 2011 Sendai earthquake was reported by Kyodo News.
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. The company claimed this was due to radiation from the Fukushima I nuclear accidents and not from the plant itself. Source: Wikipedia