Photo/IllutrationTanks storing contaminated water at the Fukushima No. 1 nuclear power plant (Asahi Shimbun file photo)

The industry ministry concluded that releasing diluted radioactive tritium into the sea is the most feasible option in dealing with contaminated water accumulating at the Fukushima No. 1 nuclear power plant.

The ministry’s working group said at a meeting on April 19 that separating tritium from the contaminated water is proving extremely difficult, and that four other options studied about disposal were either too time-consuming or expensive.

Releasing the water into the sea would cost 3.4 billion yen ($31 million) and take seven years and four months to complete, according to the group.

Tokyo Electric Power Co., the operator of the embattled nuclear plant, will decide on a disposal method based on the group’s findings. The utility has said it will not release treated water that still contains radioactive substances into the sea without gaining the understanding of local fishermen.

TEPCO has been struggling to ease the buildup of polluted water at the nuclear plant. Every day, tons of groundwater become contaminated with radioactive substances after entering damaged reactor buildings.

About 800,000 tons of water containing tritium are stored at the nuclear complex. This water was mostly used to cool melted nuclear fuel in the affected reactors.

TEPCO has been using a device called ALPS (advanced liquid processing system) to eliminate 62 kinds of radioactive substances, including cesium, from the water. But it cannot remove tritium.

The Ministry of Economy, Trade and Industry solicited ideas from the public on how to separate tritium from the polluted water. Six companies and one university submitted proposals.

However, experts in and out of Japan who evaluated the proposed methods concluded that none of the plans could be put into practical use in the near future.

The ministry’s working group narrowed its analysis to the five options that involved disposing of water containing tritium.

One suggestion was to inject the polluted water into deep layers of the Earth. Another proposal was to electrolyze the tritium-contaminated water and release it into the atmosphere.

The highest estimated cost in the proposals was 388.4 billion yen, with the longest period for completion reaching 13 years, according to the group’s study.

Ministry officials concluded that releasing water containing tritium into the sea after diluting it would be most reasonable in terms of both cost and time.