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Technology

The ambitious ice wall is not working at Japan's crippled nuclear plant

The devastated remains of the reactor No. 1 building at the Fukushima Daiichi nuclear plant are seen on Oct. 25.

TOKYO An underground ice wall being built around Japan's crippled Fukushima Daiichi nuclear power plant has so far been unable to fully prevent groundwater from entering buildings and mixing with contaminated water.

The plant's operator, Tokyo Electric Power Co. Holdings, began freezing soil six months ago for the project. Tepco plans to eventually encircle four reactor buildings with a 1-meter-thick, 1.5km-long barrier of frozen soil to prevent water from flowing under them.

The project has already been plagued by delays. Further setbacks could affect the entire process of decommissioning the plant.

WATER, WATER, EVERYWHERE Because the plant is located between mountains and the ocean, water from higher ground is constantly flowing beneath it and out to sea. This water is seeping into the basements of the buildings housing reactor Nos. 1 to 3, which were damaged in the March 2011 earthquake, tsunami and subsequent meltdowns. It comes in contact with molten nuclear fuel and other materials, creating a toxic brew containing cesium, strontium and other radioactive substances. With the exception of tritium, most of those substances can be filtered out.

The tainted water is being pumped out and stored in tanks on the premises. Nearly 1,000 tanks have been filled so far, and the storage system is reaching its capacity. This is a big concern, because 400 tons of newly contaminated water is being created every day.

A major focus is reducing the amount of water being tainted, as well as processing the water containing tritium.

Over 1,500 30-meter-long pipes filled with subzero coolant will be set in the ground at 1-meter intervals around the affected reactors.

The ice wall consists of 1,568 30-meter-long pipes set in the ground at 1-meter intervals. The pipes are filled with refrigerant and cooled to minus 30 C.

Tepco had planned to remove all the contaminated water from the reactor buildings by the end of 2020. With water still flowing into them, however, achieving that goal will be difficult.

NO DEEP FREEZE The utility opted for the ice wall instead of building a concrete barrier to avoid severing underground pipes and electrical wires. But the ice option is neither easy nor cheap: No one has ever tried to freeze soil over a distance of 1.5km, and the government has already spent 34.5 billion yen ($327 million) on the project.

Work to freeze certain sections of soil began in late March, far later than planned. The wall on the ocean side was completed in October. But there have been many hiccups. In some places, water is flowing so fast that it is hampering the freezing process. Meanwhile, a series of typhoons and heavy rains sharply raised underground temperatures, melting some of the ice.

These monitors, pictured here on Oct. 25, show the temperature of the ice wall. Blue indicates a subzero reading. (Nikkei exclusive photo)

Tepco and Japan's Nuclear Regulation Authority have been checking the amount of water being pumped up from a monitoring well located between the ice wall and the ocean. If the wall is working as planned, the amount of water being pumped out of the well should decline to 70 tons per day, experts say.

However, the figure has never fallen below 200 tons over the past two months. And in September, typhoon season, it occasionally exceeded 1,000 tons.

Tepco said that barring rain-related problems, the results will improve by the end of the year, though it offered no evidence to back up the claim.

Even as work on the mountain side continues, underground water is being allowed to flow normally in seven locations. That is because if the water is completely blocked, contaminated water could flow back out from under the buildings and leak outside.

The damaged No.1 reactor, back left, is seen on Oct. 25.

After confirming the effectiveness of the ice wall, Tepco then plans to finish work on the mountain side in or after 2017.

In September, the utility said it could complete the countermeasures two years ahead of schedule by increasing the number of water-purifying units. However, this assumes that the underground refrigeration system is functioning as planned.

"If dealing with the contaminated water takes too long, the entire decommissioning process may be set back," said Masashi Kamon, professor emeritus of Kyoto University.

There also are concerns about a possible delay in the government's plan to begin removing melted nuclear fuel from the plant in 2021.

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