Plans to start construction in June of frozen underground soil walls at the crippled Fukushima No.1 nuclear power plant are now askew after concerns were raised by the nation’s nuclear watchdog body.

The Nuclear Regulation Authority said plant operator Tokyo Electric Power Co. has yet to submit documents demonstrating the safety and efficacy of the project, which is unprecedented in scale.

Announced in May 2013, the frozen walls are intended to stem the flow of groundwater into the nuclear complex.

“Once the project is started, it will be difficult to turn back,” said Toyoshi Fuketa, an NRA commissioner who is screening the project planned by TEPCO and the central government. “We have to thoroughly examine every aspect of this project because it is such a drastic measure.”

TEPCO has been grappling with ways to staunch the daily flow of 400 tons of groundwater into the plant complex. The groundwater mixes with melted nuclear fuel debris and has significantly raised the volume of contaminated water that TEPCO has to deal with, in addition to tons of highly radioactive water used to cool the reactors.

The technique to build the walls of frozen soil is similar to a method used in the construction of tunnels.

A series of steel pipes that contain a liquid at minus 30 degrees spaced at 1-meter intervals will be placed around the buildings housing the four reactors, as well as the turbine buildings.

Stretching 1,500 meters, the frozen walls are expected to cut the inflow of groundwater to 130 tons from the current 400 tons a day.

TEPCO and the government plan to begin the actual freezing of soil in March 2015, with the expectation the walls could last for seven years.

The government has provided 32 billion yen ($313 million) in funding for the project.

In a test-run for building the frozen walls that was observed at the plant on May 16, the groundwater level outside the site was close to the surface of the ground, but no water was observed in holes inside the walls.

An official with Kajima Corp., which is in charge of the construction, said the trial was successful in blocking groundwater.

“We cleared a first hurdle,” the official said.

But the trial involved walls only 10 meters square, a fraction of the actual size of the massive walls that are due to be constructed.

Experts have warned that if something goes wrong with the walls, it could critically affect work to handle the contaminated water and decommissioning operations.

In March, TEPCO submitted a three-page document in its application for NRA approval of the project.

But Fuketa pointed out at a review meeting that the document fell far short of providing the necessary safety assurances to pass screening.

The NRA told the utility to provide answers to 24 items that the watchdog is concerned about, such as the possibility of land sinking, leaks of contaminated water and countermeasures in the event the frozen soil thaws.

The NRA is also demanding that TEPCO explain how the construction of the walls of frozen soil will be able to cut the volume of contaminated water.

The industry ministry, which gave the green light to the project, was baffled by the NRA’s reaction.

“We believed that we had already gained the NRA’s understanding,” a ministry official said.

But some experts are saying that TEPCO is to blame for dragging its feet and not applying until March.

“We should not relax our position as the (nuclear industry) regulator established in light of the Fukushima disaster,” said an official with the NRA secretariat.