Severe storms in Japan expose fragile design of Fukushima reactor cover

A large low-pressure storm system has passed Tokyo, and is on a crash course for northern Japan and the crippled Fukushima Daiichi nuclear power plant.

NHK has learned that 3 people were killed and at least 305 people were injured due to strong winds on Tuesday.

The Meteorological Agency is urging people in northern Japan to stay indoors and watch out for gusts, high waves and lightning.

At Fukushima Daiichi, Reactor 1 was covered to prevent the diffusion of radioactive substances until mid-to-long term measures including radiation shielding are implemented.

Unit 1′s cover is designed to withstand winds up to 25 m/s.[1]  The cover is made primarily out of a Steel frame beam (40m), filmed panels for walls (approx. 20m), and filmed  panels for the roof (approx. 40m) which are assembled into large modules.

A model of the Unit 1 cover released by TEPCO in 2011

According to TEPCO, the cover could be damaged or even worse, totally displaced by winds over the designed load, which would then cause it to “spill over the building”. 1

The situation could also drastically worsen if temperature or humidity in the reactor building were to increase due to moisture in the building cover.

Steel frame beams 40m long make up the skeleton of the structure, which uses filmed panels for walls (approx. 20m), and filmed panels for the roof (approx. 40m) which were assembled into large modules. In materials handed out at a press conference in August of 2011, TEPCO outlined their design plan behind the reactor cover.

At the time TEPCO stated that a survey of the last 35 years in the nearby area had received an average maximum wind velocity of 17m/s for a period of 10 minutes.

According to NHK reports, wind speeds reached 130 kilometers per hour in a Tokyo suburb and 106 kilometers per hour in the center of the capital.[2] Winds of up to 135 kilometers per hour were observed on Sado Island in Niigata on Tuesday evening.

1 meter per second is equivalent to 3.6 kilometers per hour. Therefore the cover at Fukukshima Daiichi has a design load maximum of 90 km/hr (25 m/s), whereas known wind speeds already average over 27.75 m/s (100 m/s), and have been known to increase as high as 37.5 m/s in some coastal regions.

Bibliography

[1] (TEPCO, 2011)

[2] (News, 2012)

News, N. W. (2012, April 3rd). Storm passes Tokyo, heads for northern Japan. Retrieved from NHK: http://www3.nhk.or.jp/daily/english/20120404_01.html

TEPCO. (2011, August). Outline of the reactor building covering plan of Unit 1 at Fukushima Daiichi Nuclear Power Station. Retrieved from TEPCO: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110624e15.pdf

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