Since July, Tepco has injected more than 400 tons of ice and dry ice to freeze radioactive water in a section that connects the tunnel, used to run cables, with the turbine building of reactor 2, one of three reactors that suffered core meltdowns in March 2011.
By freezing the water, Tepco had hoped to create a wall of ice to block the flow of water between the turbine building and the tunnel. The process would have made it easier to pump out highly radioactive water from the tunnel.
But the temperature inside the section did not fall low enough despite the use of large amounts of coolants, officials said at a meeting with the Nuclear Regulation Authority, acknowledging that the strategy did not work.
Tepco now plans to use filler, from mid-September at the earliest, to slow the flow of water in the unfrozen part of the section. The move is expected to facilitate the freezing of the remaining section.
At Tuesday’s meeting, NRA members and experts questioned or even expressed doubt about the effectiveness of the measure. Tepco said it will continue using ice to cool the section.
The underground tunnel is estimated to hold 5,000 to 6,000 tons of highly radioactive water that originated in the reactor 2 turbine building. Experts believe some of the water is leaking into the ground.