The magnitude 7.2 earthquake that hit the Tohoku Region1 of Japan on Tuesday 16 August caused the 3 nuclear reactors at Tohoku Electric's Onagawa Nuclear Power Plant to trip automatically.
The maximum quake was measured at 251.2 gals2 on the second floor basement of the number 2 reactor. This exceeded the design basis of 250 gals. The Nuclear Industrial and Safety Agency said that it may in fact be the first time the earthquake design basis for a nuclear reactor has been exceeded in Japan.
Tohoku Electric immediately dismissed the significance of this saying the reactors can withstand a quake of 375 gals. The reactors are designed to trip if the quake exceeds 200 gals horizontally, or 100 gals vertically. All three Onagawa reactors exceeded this limit.
Operations at the three Onagawa reactors will be suspended for some time while the effects of the earthquake on the reactors are assessed.
Meanwhile, Tokyo Electric Power Company has confirmed that water leaked from the spent fuel pools at the No. 2 and No. 6 reactors of the Fukushima I plant. It said that the water did not leak outside the facilities.
Click here to go to our commercial media page. There you will find news items about the earthquake.
Click here for an article about the Niigata earthquake last year.
1. The Tohoku Region is in the north east of Honshu, the largest island in Japan.
2. Gal is a measure of acceleration. 1 gal = 0.01 m/s2.
Philip White
International Liaison Officer
