The operator of Japan's tsunami-crippled Fukushima nuclear plant said Tuesday power for cooling systems at three spent fuel pools was still out more than 14 hours after it failed.
The power outage occurred at 6:57 pm Monday (0957 GMT), Tokyo Electric Power Co., (TEPCO) said, adding that while engineers did not yet know the cause, there was no immediate danger.
"Electricity has been cut to pools used to cool spent fuel at the reactor 1, 3 and 4 units" as well as to the equipment to treat contaminated discharge including radioactive caesium, TEPCO spokesman Kenichi Tanabe said.
However the incident had not so far affected cooling-water injection to the number 1, 2 and 3 reactors, which suffered core meltdowns soon after the start of the March 2011 nuclear crisis, he said.
The temperature at the pool for spent fuel from reactor number 4 was believed to be the highest and slightly above 25 degrees Celsius (77 degrees Fahrenheit), still well below the safety limit of 65 degrees, he said, adding it was rising by 0.3-0.4 degrees every hour.
If the system is not restored, it will take four more days for that pool to reach the limit, he said.
"We are trying to restore power by then," he said, adding the deadline would be about 14 days and 26 days for the other two.
"No major changes have been observed in radioactivity levels detected by (nearby) monitoring posts" after the incident, he said.
TEPCO was to brief reporters on the incident later Tuesday.
The meltdowns of three of Fukushima's six reactors occurred after the March 11, 2011, earthquake and ensuing huge tsunami shut off the power supply and cooling system.