Tokyo Electric Power Co. says the refrigerated ice wall being built to slow the movement of water beneath damaged reactors at the Fukushima No. 1 nuclear plant isn’t working as expected.
Tepco said the project, which remains in its early stages, is experiencing a problem with an inner ice wall designed to contain highly radioactive water that is draining from the basements of the wrecked reactors.
“We have yet to form an ice plug because we can’t get the temperature low enough to freeze the water,” a Tepco spokesman said Tuesday.
Trenches are being dug for a huge network of pipes under the plant that will have refrigerant pumped through them. If successful, it would freeze the soil and form a physical barrier, significantly slowing the rate at which uncontaminated groundwater flows into the reactor basements and becomes contaminated.
“We are behind schedule, but have already taken additional measures, including putting in more pipes, so that we can remove contaminated water from the trench starting next month,” a spokesman said.
The coolant used in the operation is an aqueous solution of calcium chloride, which is cooled to minus 30 degrees. The ice wall employs the same technology as the trench project and involves the same contractor, Kajima Corp.
The idea of freezing a section of the ground was proposed last year. Engineers have used the technique to build tunnels near watercourses. But scientists point out it has never been used on such a large scale, or for the length of time Tepco is proposing.
Coping with the huge amount of water at the plant is proving to be a major challenge for Tepco, as it tries to clean up the mess after the worst nuclear disaster in a generation.
As well as having to collect vast quantities of water used to cool the melted down reactors, Tepco has been pumping up and storing water that drains down from inland mountains to the sea.
Full decommissioning of the plant is expected to take several decades. An exclusion zone remains in place, and experts warn that some former residential areas may have to be abandoned as settlements because of persistently high levels of radiation.