An underground ice wall built around the crippled Fukushima Daiichi nuclear power plant has so far been unable to block the flow of groundwater entering buildings and mixing with contaminated water.
okyo Electric Power Co. Holdings, the owner of the plant and known as Tepco, plans to encircle four reactor buildings with a 1.5km barrier of frozen soil to prevent underground water from flowing under them and carrying radioactive water to the ocean. Work to freeze soil began six months ago and was partially completed in October. Further delays could affect the entire process of decommissioning the power plant.
Water water everywhere
The plant is located between mountains and the ocean. Underground water constantly flows from higher ground toward the sea, passing beneath the power plant along the way. This water is flowing into the basements of the buildings housing reactor Nos. 1 to 3, which were damaged in the earthquake, tsunami and subsequent meltdowns. It comes in contact with molten nuclear fuel and other materials, resulting in water contaminated with cesium, strontium and other radioactive substances, most of which can be filtered out, except for tritium.
The tainted water is pumped out and stored in tanks on the plant’s premises. Nearly 1,000 tanks are full, and the storage system is reaching its capacity.
With 400 tons of newly contaminated water every day, a key task is addressing the twin problem of reducing the amount of water that is getting tainted and processing the water containing tritium.
The nice wall designed to freeze soil via 1,568 30-meter long pipe filled with subzero coolant set in the ground at 1-meter intervals
The ice wall was built to block the flow of water seeping into the buildings and flowing through them. The wall consists of 1,568 30-meter long pipes, set in the ground at 1-meter intervals, that are filled with refrigerant and cooled to minus 30 C. Planners envisioned a 1-meter-thick wall of frozen soil circling the plant.
Tepco had planned to remove all the contaminated water from the reactor buildings by the end of 2020, but its plans are being thwarted by water continuing to flow into them.
The utility opted for the ice wall instead of building a concrete one to avoid severing underground electric wires and pipes, but no one has ever tried to freeze soil over a distance of 1.5km, according to experts. The government has so far spent 34.5 billion yen ($331 million) on the project.
Work on freezing some sections of soil began in late March, much later than planned, and the wall on the ocean side was completed in October. However, it has already faced several difficulties. The flow of water was too fast in certain places for freezing to occur, while a series of typhoons and heavy rains sharply raised underground temperatures and melted some ice.
Japan’s Nuclear Regulation Authority and Tepco have been checking the amount of water pumped up from a monitoring well located between the ice wall and the ocean. Assuming the wall is effective, the amount of water pumped out of the well should decline. Officials expect the water being removed to decrease to 70 tons per day.
As work to freeze soil around the ice barrier has continued over the past two months, however, the smallest amount of water from the well was over 200 tons. In September, which is typhoon season, it occasionally exceeded 1,000 tons.
Tepco said the amount of water should decrease, if rainfall causes no problems, and the ice wall will show better results by the end of the year. The utility provided no evidence to back up this claim.
While work on the mountain side is also underway, underground water is allowed to stream normally at seven points because contaminated water could flow backward from under the buildings and leak outside if the water is completely blocked.
Tepco intends to confirm the effects of the ice wall on the ocean side and then complete it on the mountain said in or after 2017.
In September, the utility said it can advance by two years completion of countermeasures if it increases the number of units used for purifying contaminated water. However, this presupposes the underground refrigeration system functioning as planned.
“If dealing with the contaminated water takes too long,” said Masashi Kamon, professor emeritus at Kyoto University, “the entire decommissioning process may be set back.”
There also are concerns about a possible delay in the government’s plan to begin removing melted nuclear fuel from the plant in 2021.
Written by: DAISUKE ABE
October 21, 2016 5:00 pm JST