Top > Releases ・ Announcements > Fukushima Daiichi NPS Prompt Report > 2014 > Immediate Relase:TEPCO WORKERS DISCOVER AND HALT WATER OVERFLOW FROM TANK;NO IMPACT EXPECTED ON SEAWATER

Fukushima Daiichi NPS Prompt Report 2014


Fukushima, February 20, 2014 - Workers at the damaged Fukushima Daiichi Nuclear Power Station discovered and stopped the overflow of water from a tank storing radioactively contaminated water on Feb. 20, according to the plant’s owner, the Tokyo Electric Power Company (TEPCO).

The company said the overflow has been contained and poses no threat to public health.

The affected tank is one of many used to store water that becomes contaminated after being used to cool the three reactors damaged by the March 2011 tsunami. The overflow was discovered by TEPCO’s cooperative workers on routine patrol shortly before midnight (Japan time) on February 19, and is believed to have been caused by the overfilling of the tank. The overfilling appears to have been caused by the improper flow of water through a pipe from the processing facility to the tank. There are three valves on the pipe, of which two were improperly left open, and the other was closed but failed to function. The two valves were shut by workers at approximately 1:30 am on February 20, halting the overflow. TEPCO is continuing to investigate the reasons why the valves were open, and why the closed valve was not functioning.

Approximately 100 tons of water, which is a part of the approximately 340,000 tons stored at the site, flowed onto the ground and the area adjacent to the storage tank through a rainwater pipe attached to the tank. However, there is no pathway leading from that area to the sea, which is approximately 700 meters away, and none of the overflowed water is believed to have reached the ocean. Nevertheless, TEPCO immediately began removing the overflowed water and soil in which the water has seeped into. Checks on the other storage tanks revealed no additional overflow, and the workers were protected from radiation exposure by appropriate protective clothing.

"We are deeply embarrassed that this sort of unacceptable event would occur after the many steps we have taken to improve the management of stored water,” said Zengo Aizawa, Director and Executive Vice President of TEPCO, and General Manager of Nuclear Power and Plant Siting Division. “We will therefore conduct a thorough investigation into what occurred and determine what additional steps must be taken to prevent any similar occurrence in the future, and will further strengthen field management of stored water. It also demonstrates the need for a permanent solution to the contaminated water issue."

The overflowed water had already been treated to remove some of the radiation it picked up during the process of cooling the reactors. The water passes through a facility which removes cesium, the principal radioactive material, followed by facilities removing salt, but beta nuclides yet to be removed. Samples were also taken of the over overflowed water, and tests revealed the following levels of radioactivity:

·cesium134 :3.8×103 Bq/L

·cesium137 :9.3×103 Bq/L

·cobalt60  :1.8×103 Bq/L

·manganese54:1.3×103 Bq/L

·antimony125:4.1×104 Bq/L

·gross beta :2.3×108 Bq/L

Since this overflow was identified, no additional overflow has been detected from any of the other tanks storing water at Fukushima Daiichi NPS. Seawater monitoring is conducted day-to-day. The following is the part of the monitoring data, which indicates no effects to the outside ocean. For further monitoring results, please go to

The latest sampling results for gross beta density in the seawater taken at 5:45 am on February 20 at the south discharge channel of Fukushima Daiichi NPS has been reported as 14 Bq/L today, which indicates no significant change from 11 Bq/L, taken on February 17.

Please find detailed information at


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 35,000 employees are committed to providing safe, reliable power to its 28.8 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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