An ice wall intended to halt the flow of groundwater at Japan’s Fukushima Daiichi Power plant operated by Tokyo Electric (TEPCO) (9501.T) may have partially melted, broadcaster NHK reported on Friday.

TEPCO plans to reinforce the wall as early as at the start of December and is considering further countermeasures, NHK said.

The ice wall was built to prevent the contamination of groundwater at the wrecked nuclear power plant, part of a costly and troubled effort to secure the site following the 2011 earthquake and tsunami.

TEPCO did not immediately confirm details of the report.

Reuters