The long-awaited frozen, underground wall that is expected to greatly reduce water flow in and through radioactive areas of a four-building block at the damaged Fukushima Daiichi Nuclear Generating Station was activated Wednesday, the Tokyo Electric Power Company (TEPCO) said Wednesday.
The system involves some 1,550 pipes that have been placed vertically in holes drilled 100 to 120-feet underground. Kajima Cooperation, the main contractor for the project, will pump refrigerant through the pipes to create a wall of frozen soil with the aim of greatly reducing the flow of ground water that has been a constant concern since the accident of March 2011 that resulted in meltdowns at three of he six reactors at the facility.
TEPCO said the soil would be frozen in stages that would last over a period of “months.” The company only has permission, at this point, to activate 95 percent of the barrier, leaving the remaining 5 percent un-activated while it studies the effect of the wall, which is similar to soil-freezing walls used to reduce water flow in underground tunnel construction.
“Approval has been given to activate approximately 95 percent of the wall, and approval for the remaining portions will be sought after assessment of the results of the first stage,” TEPCO said in a statement. “After completion of the first stage, the underground water inflow will be reduced to approximately 50 percent,” TEPCO said.
An estimated 400 metric tons of water has been flowing through the contaminated areas, as the plant is situated between the sea and the rising landscape behind it. Water storage and filtration efforts have been a primary focus of the past five years since the accident, but the new concern is that the frozen barrier could change water levels inside and outside of the contaminated buildings. At issue is the relative water levels – the difference between levels inside and outside the buildings – given changes could allow more groundwater to escape the area. “By leaving a (5 percent) gap in the wall, it is expected that groundwater within the perimeter will stay at a higher level than water inside the basements, thus preventing the latter's escape,” TEPCO explained.
“We understand that the biggest concern is that the contaminated water might escape from the buildings,” said Chief Decommissioning Officer Naohiro Masuda at a news conference. “We must not let that happen.”
TEPCO will seek permission to close the remaining 5 percent of the frozen barrier once it has been ascertained that water will not escape even if the wall is closed, the company said.