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Countermeasures for Water Leakage

Contaminated Water Leakage from the Tank in the H4 Area (follow-up)

August 26, 2013

This is follow-up information about the leakage that occurred at a tank in the H4 area of Fukushima Daiichi NPS (English information previously sent by e-mail on August 21).
Since confirming the leakage, we have been 1. Conducting prevention measures, 2. Investigating the cause, and 3. Strengthening monitoring around the area.

1.Conducting prevention measures

We are currently conducting the following prevention measures.
- We have transferred all the water from the tank in question to other tanks (completed on August 21).
- We have removed the leaked water from inside the dike and currently removing the soil, into which the leaked water had seeped, from outside the dike.
- We have strengthened patrols (from twice a day to once every three hours).

- We have also checked all tanks of the same type at the site to determine whether there has been any leakage, and found no such leakage. (However, we found two locations at H3 area tanks where a high radiation dose was measured, and are investigating the cause).

2. Investigating the cause

We are currently investigating the cause by conducting: additional monitoring of the surface of the surrounding soil, boring investigation of the soil under the tank in question, and nuclide analysis of the groundwater etc.

On August 24, we confirmed that the tank in question was the one of the three tanks that was once installed in the H1 area in around July 2011, and then moved to H4 in September 2011, since foundation subsidence of approx. 20cm had occurred during the water filling test at the part of the area where the three tanks were installed in the H1 area. The relation between this fact and the leakage is still unclear. However, we have started transferring water from the other two tanks to other tanks in the H4 area. We will continue to investigate the cause.

3. Strengthening monitoring around the area

Since the leakage was confirmed, we have been strengthening monitoring around the area.
On August 21, we found a high radiation dose of approx. 6mSv/h (total dose of both gamma and beta rays) inside the drain ditch which is connected to the H4 tank area. Additionally, all beta was detected through nuclide analysis of the water inside this ditch (please refer to the materials below). From these results, we assume that there is a possibility that the leaked water has been leaking towards the ocean. We are monitoring the seawater taken from the Unit 1 to 4 side of the South Discharge Channel (approx. 330 meters south from the exit of the drain ditch) every day, and the nuclide analysis results of Cesium-134, Cesium-137 and all beta are so far confirmed to be at non detectable or very low levels.

Today, we announced to set up a "task force for contaminated water and tanks".
Please refer to the material below for detail.