Tokyo Electric Power Co. admitted failure Friday in its bid to halt the flow of toxic water into underground tunnels alongside the ocean at the Fukushima No. 1 plant and said that it will try using a specially developed cement instead.

Some 11,000 tons of highly radioactive water have accumulated in the tunnels, trenches dug to house pipes and cables that are connected to the reactor 2 and 3 turbine buildings of the wrecked facility, according to Tepco.

There are fears that this toxic buildup, which is being caused by the jury-rigged cooling system and groundwater seepage in the reactor basements, could pour into the Pacific, which is already being polluted by other radioactive leaks. Groundwater is entering the complex at 400 tons a day.

Extracting the toxic water is a critical step in Tepco’s plan to build a huge underground ice wall around the four destroyed reactors to keep groundwater out.

Initially, Tepco sought to freeze the water in a section of tunnel connected to the No. 2 reactor building. This was intended to stop the inflow and allow the accumulated water to be pumped out. The utility said it took additional measures that also failed.

On Friday, Tepco proposed a new technique for the tunnels: injection of a cement filler especially developed for the task while pumping out as much of the accumulated water as possible.

Under the new method, however, it would be difficult to drain all of this water and some of it would be left behind, endangering plant workers, Tepco acknowledged.

Nevertheless, a Nuclear Regulation Authority panel of experts green-lighted the new strategy at a recent meeting. Some of the experts argued that Tepco should stick to the original plan and draw out all of the water. Others said giving up on it may hamper the construction of the ice wall.