The much-hyped ice wall at the crippled Fukushima No. 1 nuclear power plant has failed to stop groundwater from flowing in and mixing with highly radioactive water inside the wrecked reactor buildings, operator Tokyo Electric Power Co. Holdings Inc. has admitted.

Tepco officials also said at a meeting of the Nuclear Regulation Authority in Tokyo that it is not the utility’s ultimate goal to shut out groundwater with the ice wall, which has been built around the four damaged reactor buildings at the plant.

Tuesday’s announcement was apparently the first time the utility publicly said it is technically incapable of blocking off groundwater with the frozen wall.

Five years after the March 2011 quake and tsunami triggered the nuclear crisis, Tepco continues to be plagued by radiation-tainted groundwater, mostly rainwater that is mixing with contaminated water in the basement of the damaged reactor buildings.

In response, Tepco has completed most of the 1.5-km-long sunken wall of frozen soil around the stricken reactors to keep groundwater out. It has also built “subdrain” wells around the buildings to pump up the tainted groundwater for treatment and ultimate discharge into the Pacific.

While the completed sections of the ice wall began operating in March, it has not made a visible impact in reducing the amount of groundwater inflows. According to Tepco, the amount of groundwater pumped up from wells near the ocean – the last defense before flowing into the sea – averaged 321 tons per day in June, just 31 tons less than the daily average in May.

Asked whether Tepco plans to eventually block rainwater from seeping through the ice wall, a Tepco official said it is not technically feasible “to keep out the groundwater 100 percent,” according to a video of the meeting released Tuesday by the NRA.

“We are aiming to control the amount of water going into the reactor buildings, with the ice wall and subdrains,” said Tomohiko Isogai, an official in charge of dismantling the plant.

Kiyoshi Takasaka, a nuclear expert at the Fukushima Prefectural Government, said it was the first time he had heard such a comment from Tepco, pressing the firm on whether it marked a “change of policy.”

A Tepco official denied this, saying that while it wants to “close off the wall as much as possible,” its ultimate goal has been to “curtail” groundwater inflow, not halt it.

Also at the meeting, NRA acting head Toyoshi Fuketa demanded that Tepco move quickly to reduce the amount of highly radioactive water inside the reactor buildings, saying such water presents the risk of escaping in the event of another monster tsunami. Some 60,000 tons of highly tainted water remain in the leaking basements of reactor buildings 1, 2, 3 and 4.

“We want the amount of (radioactive water) inside the buildings to be reduced as much as possible,” he said.