TOKYO (AP) — Japanese regulators have approved an unprecedented refrigeration structure to be switched on so it would form a huge underground frozen barrier around the wrecked Fukushima nuclear reactor buildings in a desperate bid to mitigate the contaminated water.

Regulators said Wednesday the structure, whose construction was completed last month, can now be activated.

Nearly 800,000 tons of water is stored at the plant destroyed in the 2011 quake and tsunami, hampering its decontamination.

The 35 billion yen ($312 million) government-funded project comes with pipes designed to freeze soil around them like giant popsicles, eventually forming a 1.5-kilometer (0.9 mile) long wall around the reactor and turbine buildings to contain radioactive water and keep out groundwater.

The structure that huge is untested.