Power has been restored to all fuel pond cooling systems at the damaged Fukushima nuclear plant in Japan, operator Tepco says.
A power cut shut down cooling systems for four spent fuel ponds at reactors 1, 3 and 4 on Monday evening, although cooling to the reactors themselves was not affected.
All cooling systems were operational by early Wednesday morning, Tepco said.
Pool temperatures remained within safe levels throughout, it added.
Cooling at the spent fuel ponds at reactors 1, 3 and 4 were all restored by 22:43 local time (14:43 GMT on Tuesday).
The cooling system at the fourth, common, pond was restored at 00:12 on Wednesday, Tokyo Electric Power Company (Tepco) said.
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The company has been criticised for its delay in announcing the incident, which began at 18:57 on Monday. It took Tepco three hours to announce that the cooling systems had been shut down.
The ponds store spent fuel from the nuclear reactors. They cool the fuel – which generates intense heat – and provide shielding from radiation. The spent fuel remains in the ponds for a year or more.
There was no immediate threat of a radiation release. But if cooling systems had not been restored, it is possible that the water in the ponds could have started to boil.
That could have led to a loss of water and eventually to the exposure of the spent fuel rods to air, releasing radiation.
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