World Nuclear Association Blog

Onagawa: The NPP that withstood the tsunami

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A fascinating brochure has been published outlining the story of the Onagawa nuclear power plant and how it withstood the earthquake and tsunami of March 11, 2011. It is available here.

The report reviews the differences between what happened at Fukushima Daiichi, Fukushima Daini and Onagawa. 

Onagawa faced a stronger earthquake and tsunami of similar height to Fukushima Daiichi, at around 13m. The earthquake disrupted external power supplies, but with a combination of one remaining external power line and six of the eight diesel generators the plants shut down and cooling systems started as planned - in fact Unit 2 was in the process of starting up as the earthquake struck and reached cold shutdown a few minutes later.     

When the tsunami struck the damage caused to Onagawa was much less severe than at Fukushima Daiichi and Daini, because the Onagawa plant had been built at a height of 14.8m, higher than the tsunami waves. There was some disruption to unit 2 cooling, but all reactors achieved cold shutdown as planned.

The preparedness and efforts of staff at Onagawa were recognised when they were presented with a WANO (World Association of Nuclear Excellence) Award for Nuclear Excellence.

 Onagawa WANO 
Onagawa staff whose combined efforts earned them a WANO Nuclear Excellence Award 

Perhaps even more remarkable is how the Onagawa nuclear plant became a place of refuge for people from the area surrounding the plant, where many had died, and even more had been made homeless.

On March 11, 1,500 people working at the site were stranded, without any reports how their friends and family outside the plant had fared. From the devastated surrounding area 50 people sought shelter at the plant. Eventually the site would become a refuge for 364 people from the local community.

 Onagawa Refugees  

Local refugees offered shelter in Onagawa gymnasium

The article shows how robust nuclear power plants are when back up power supplies and flood defences are properly in place. Since the accident at Fukushima 'stress tests' have been carried out at reactors around the world to ensure that plants are sufficiently prepared. Even at Onagawa defences have been strengthened even more.