The solid frozen soil wall that Tokyo Electric Power Co. is trying to create at its stricken Fukushima No. 1 nuclear power plant is falling short of expectations.
TEPCO said May 25 its attempt to freeze the soil around the crippled reactors to decrease contaminated groundwater has hit an unexpected glitch.
The utility said it has been unable to freeze the soil at about 10 percent of points it surveyed even though more than one-and-a-half months have passed since the program started.
This is due to the fact that soil temperatures have failed to drop sufficiently. In places where the temperature remains especially high, there is a possibility the soil will never freeze.
TEPCO reported the situation to the Nuclear Regulation Authority, the nation’s nuclear watchdog, saying it plans to implement additional work, such as injecting cement or other materials into the soil.
The project involved the construction of a 1,500-meter-long circular frozen soil wall around the No. 1 to No. 4 reactor buildings. The utility inserted 1,568 pipes to a depth of 30 meters and 1 meter apart. The idea was that each pipe would then freeze the soil around it once liquid of minus 30 degrees circulated inside the cylinders.
The project is aimed to stop flow of groundwater into reactor buildings, where melted nuclear fuel has accumulated in the basements, and, as a result, reduce the volume of highly contaminated water.
To date, around 34.5 billion yen ($315 million) has been spent on the project.
TEPCO started to freeze the soil in late March, with the goal of first creating an 820-meter-long portion, mainly along the side of the plant facing the sea.
According to TEPCO, the temperature of soil around pipes was lower than zero in only 88 percent of 5,800 or so sites it surveyed as of May 17. In the remaining 12 percent, temperatures were as high as 10 degrees in places.
In spots where temperatures fell short, the soil wall was riddled with holes. TEPCO plans to fill them in by injecting cement or other agents.
On the site of the plant facing a mountain, the utility has been freezing the soil in phases. Although it had planned to double the number of frozen soil sites as early as mid-May, that has not materialized.
“If the effects of the frozen soil wall fall short of what we have expected, we will hold talks with TECPO about additional steps,” said an NRA official in charge of the issue.