Coolant has been found leaking at four locations from pipes in the underground wall of frozen soil surrounding reactor buildings at Japan's Fukushima Daiichi nuclear power station.
Tokyo Electric Power Co (Tepco) confirmed that some 20 cubic meters of the coolant had leaked from the pipes.
It said the coolant liquid contains calcium chloride, commonly used as a snow-melting agent, but that it is not an environmental contaminant.
Tepco noticed the leak problem in late 2019 when the volume in a coolant tank dropped abnormally.
Workers examined the ice wall piping and found leaks in the joints in the pipes between the unit 2 and unit 3 reactor buildings.
The company is poised to investigate the cause of the leaks and replace the problematic parts.
Tepco ordered the construction of the ice wall in May 2013. The 1.5km long wall operates by circulating a coolant with a temperature of minus 30 degrees Celsius through 1568 pipes that extend to a depth of 30m below the surface.
The soil around the pipes freezes to stop groundwater from flowing into the reactor buildings where it becomes contaminated. The ice wall started operation in March 2016.
Photo: Schematic of the ice wall at Fukushima Daiichi (Credit: Tepco)