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News Navigator: Why is Fukushima nuclear plant's treated water being released into the sea?

Piping for the "frozen soil wall" is seen at the TEPCO's Fukushima Daiichi Nuclear Power Station in Okuma, Fukushima Prefecture, in February 2021. (Mainichi/Daiki Takikawa)

The Mainichi Shimbun answers some common questions readers may have about treated water from the Fukushima Daiichi Nuclear Power Station, and why it is being released into the sea.

    Question: I heard Tokyo Electric Power Company (TEPCO) Holdings Inc. will discharge treated water from the Fukushima Daiichi plant into the ocean, is it true?

    Answer: Treated water amounts continue to increase, and TEPCO plans to build an undersea tunnel to release it 1 kilometer offshore. At present, the company stores treated water in steel tanks over 10 meters high at the plant site. Its current plan to store the water accounts for 1,016 storage tanks, but about 970 are already holding water, and all of them are expected to be full by around spring 2023.

    Q: Can we stop treated water from increasing?

    A: Unfortunately not. Contaminated water needing treatment continues to be generated, because groundwater and rainwater enter the plant's Unit 1 to 3 via cracks in their underground walls formed by the Great East Japan Earthquake and other factors.

    Nuclear fuel that melted down in the accident is called "fuel debris." When the water flowing into the reactor buildings mixes with water for cooling fuel debris, it becomes contaminated water that contains radioactive materials. About 140 cubic meters of the water is produced per day, the equivalent of 700 oil drums.

    Q: Are any measures being taken against this?

    A: Groundwater flows from the reactor buildings' western mountainous side to the eastern ocean side. As a result, groundwater is pumped from 12 wells 100 to 200 meters from the buildings' mountain side and from 46 wells around the buildings.

    Additionally, pipes have been installed in the ground surrounding the buildings. They continuously fill with a minus 30 degrees Celsius liquid to freeze the surrounding water and soil, creating a "frozen soil wall" that prevents water from flowing into the buildings. The wall costs about 1 billion yen (about $8.7 million) a year to maintain. These measures have meant that contaminated water generated in 2020 was reduced to a little over a quarter of 2014 levels.

    Q: It's not going to reach zero though, is it?

    A: TEPCO plans to reduce contaminated water amounts to no more than 100 cubic meters per day in 2025, but there is no way to reach zero. The company will continue to deal with the situation.

    (Japanese original by Takuya Yoshida, Science & Environment News Department)

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