FUKUSHIMA, Japan (Kyodo) -- The operator of the crippled Fukushima Daiichi nuclear complex began work Tuesday to extend an underground ice wall to prevent contaminated water increasing within the facilities.
The coolant-filled wall is designed to prevent groundwater from seeping into the facilities and touching melted nuclear fuel or becoming mixed with highly contaminated water inside reactor buildings.
The government has spent some 35 billion yen ($320 million) on the project. Work by Tokyo Electric Power Company Holdings Inc. to freeze the wall began in March last year.
On Tuesday, the utility opened valves to circulate coolant for the remaining section of the 1.5-kilometer-long, 30-meter-deep wall around the four reactor buildings.
TEPCO is expected to complete the wall possibly this fall by cooling the remaining portion on the west side of the buildings, a section stretching for about 7 meters.
About 400 tons of water was initially flowing inside the buildings per day but the amount has fallen to 120 to 130 tons this year, according to TEPCO. The utility aims to slash the daily inflow of groundwater to less than 100 tons with the full operation of the ice wall.
Pipes have been inserted into the ground to circulate coolant and freeze the nearby soil. Since starting the freezing work in March last year, the operator has gradually expanded the ice wall as freezing the entire wall at once could change the groundwater level, possibly causing highly radioactive water in the basements of the buildings to leak outside.
"We want to carefully freeze (the wall) by monitoring water levels both inside and outside the reactor buildings," a TEPCO official told a press conference in the city of Fukushima.