Engineers have discovered that 1,300 liters of water leaked from a cooling system intended to stabilize the temperature of the spent fuel at the Reactor Unit 5, which was offline but loaded with fuel rods when the plant was damaged by the earthquake and tsunami in March 2011.

The source of the leak was a 3 mm-diameter hole near a flow valve, a statement published by the Japanese energy giant on Sunday asserts. However it is unclear from company data if the location of the opening has been discovered, or whether it was calculated with flow measurements.

If no new cold water is pumped in at such rate it will reach the dangerous threshold of 65C by the midpoint of the month in roughly 9 days.

Such temperatures, which have not been routinely seen at the plant since the failing of the cooling system in the immediate aftermath, would increase the possibility of dangerous reactions and further radiation leaks in the plant.