TEPCO's latest plan comes after ice walls at connecting points between the turbine buildings and the trenches failed to halt about 10 percent of the flow.
The plan was reported at a meeting of the Nuclear Regulation Authority on Aug. 19, which will consider the utility's proposal in September. If it gets the green light, TEPCO will immediately begin implementation, which is expected to be complete by the end of the month.
Currently, 11,000 tons of highly radioactive water have accumulated in the trenches, which extend from the turbine buildings toward the ocean. The water flowed into the trenches after the March 11, 2011, Great East Japan Earthquake.
The government and TEPCO have been constructing “frozen soil walls” to encircle reactor buildings and turbine buildings to prevent groundwater from entering those buildings and increasing the amount of contaminated water.
The process calls for first pumping out the radioactive water in the trenches. That also requires the construction of walls at connecting points between the turbine buildings and the trenches to prevent more contaminated water from flowing into the trenches. The construction of ice walls in trenches started in late April.
In the construction, bags filled with clay and cement are amassed before being frozen with chilled pipes to create the ice barriers.
But the ice walls have failed to completely block the flow of radioactive water. From late July, TEPCO added more than 400 tons of ice and dry ice around the connecting points in an attempt to freeze the radioactive water.
Ninety percent of the radioactive water at the connecting points was successfully frozen, but the remaining 10 percent continued to flow into the trenches. TEPCO concluded that the ice walls are insufficient.
The utility said it will test the effectiveness of concrete, adhesive sodium silicate glass, iron sand and various absorption agents as an additional barrier to halt the remaining flow.
TEPCO will decide by mid-September on which materials are most effective.
During the Aug. 19 NRA meeting, Shigeaki Tsunoyama, former president of the University of Aizu in Fukushima Prefecture, asked TEPCO to consider measures other than the ice walls.
“You took the current measures without making sufficient preparations and are now facing difficulties," said Tsunoyama, who is an adviser to the Fukushima prefectural government on nuclear issues. "You should change your way of thinking.”
However, TEPCO director Takafumi Anegawa said the ice walls have been effective, despite allowing the remaining flow.
“The ice walls can block 90 percent (of the flow of radioactive water)," he said. "We want to continue efforts with this method for the time being.”