An underground ice wall designed to curb the buildup of radioactive water at the Fukushima Daiichi plant will see near completion on Friday. But it’s not yet clear when it can be put into service as the nuclear regulator has not yet given a green light to its use.

The barrier will almost be finished Friday. Only the last procedure, which involves filling underground pipes with coolant, remains.

The wall made of frozen soil stretches about 1.5 kilometers around 4 reactor buildings.

Tokyo Electric Power Company aims to cut the amount of groundwater that seeps into the buildings and then becomes contaminated. The utility expects the barrier to reduce the inflow to 10 tons a day. That’s less than one tenth the current level.

The project to build the wall began in June 2014 at a cost of about 290 million dollars from the national coffers. The plan is to start operation by the end of March.

But the Nuclear Regulation Authority has not given its approval. It fears radioactive water could leak from the reactor buildings if the wall makes the level of groundwater lower than that of contaminated water.

TEPCO says it will closely monitor groundwater levels and inject water if the levels fall too far.

But the regulator insists changes in groundwater levels could cause unintended consequences.