Tokyo, Jun 7 (IANS): The construction of an underground ice wall at Japan's crippled Fukushima nuclear plant, meant to stop the volume of contaminated groundwater from increasing, has entered a new phase, the operating firm said on Tuesday.

Tokyo Electric Power (TEPCO) said the first of three stages to build the wall has entered its second and final phase after getting the approval from the country's Nuclear Regulatory Authority (NRA), EFE news reported.

The wall is intended to block the flow of groundwater contained in the natural aquifer and to prevent its mixing with radioactive contaminated water by isolating the subsoil around the four reactor buildings, which were damaged by the 2011 earthquake and tsunami.

The NRA has certified that the pumping systems used to bifurcate aquifers are working properly and that the wall will not generate a hazardous back flow of groundwater.

The second phase of the first stage now covers 95 per cent of the wall around the reactors, which would reduce the volume of water entering daily into the building's basements by 50 per cent.

To build the wall, more than 1,500 pipes are inserted in the ground to a depth of about 30-35 metres around the four reactors.

The pipes will later be filled with a saline solution and the solution will be cooled to minus 30 degrees Celsius, freezing the surrounding soil and forming a frozen ground barrier around the reactor facilities.

However, the company has not set specific deadlines for completion of the project.