Fukushima Daiichi NPS Prompt Report 2015

Improvements are designed to protect nearby ocean waters from runoff

FUKUSHIMA, August 18 TEPCO is taking additional steps at Fukushima Daiichi Nuclear Power Station to protect the ocean from stormwater runoff during heavy rains.

Today, TEPCO has been physically reconfiguring Drainage K, essentially replacing it with a covered drainage channel parallel to Drainage C that will lead to the protected port area. Work on the new Drainage K began in May 2015 and is expected to be completed by the end of FY2015.

Earlier this year, when it was discovered that Drainage K showed intermittent spikes in radiation after periods of heavy rain, eight pumps were installed to temporarily divert water from Drainage K to Drainage C, keeping the water within the port area. As currently configured, Drainage K runs into the sea and Drainage C runs into the port area, where there are multiple precautionary measures designed to keep the contamination from reaching the open sea.

TEPCO had explored the potential for increasing the temporary pumping capacity in case of heavy rainfall, but the holding space from which the water is pumped is too small to accommodate additional pumps. As weather records indicate rains heavy enough to exceed the pumping capacity occur a few times a year, sometimes in connection with typhoons, there were a few times that rainwater overflowed from Drainage K.

On July 16, TEPCO discovered that during exceptionally heavy rainfall, the flow in Drainage K exceeded the capacity of the pumps, and some water overflowed into the sea. Although the water around the opening of Drainage K showed a temporary increase in radioactivity, levels dropped back the following day:

 -July 16: Cs-134 160Bq/L, Cs-137 670Bq/L, Gross β 1,100Bq/L
 -July 17: Cs-134 2.4Bq/L, Cs-137 20Bq/L, Grossβ 39Bq/L

*Concentration Limit Specified by the Rule for the Installation, Operation, etc. of Commercial NPS: Cs-134 60Bq/L, Cs-137 90Bq/L
*WHO Guidelines for drinking-water quality: Cs-134 10Bq/L, Cs-137 10Bq/L

Continual monitoring of water around the port entrance showed no significant increases in radioactivity.

Moreover, on August 17, TEPCO discovered from previously installed camera that during heavy rainfall, the rainwater in Drainage K overflowed to the sea for approximately 4 minutes. Recorded video is available from the following URL and TEPCO will continue to monitor the surrounding ocean at Fukushima Daiichi but expects that since the overflow was very limited, there is no significant impact to the sea.

http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=e97v94qt&catid=61699

Long-term improvement

TEPCO has been constructing a long-term solution. To provide a permanent solution, reconfiguring the Drainage K is essential in order to protect the ocean by replacing it with a covered drainage channel parallel to Drainage C that will lead to the protected port area. The work is expected to be completed by the end of FY2015.

For more detailed information, including drawings of the current and future drainage systems, go to URL http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2015/images/handouts_150716_01-e.pdf

About TEPCO

Tokyo Electric Power Company, Inc. (TEPCO) is Japan's largest power company, supplying energy to the greater Kanto area, including Japan's two most populous cities, Tokyo and Yokohama. Its 34,000 employees are committed to providing safe, reliable power to its 29.0 million customers, diversifying energy resources to ensure sustainability, and contributing to economic growth while fully meeting its responsibilities after the Fukushima Daiichi accident.
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