The power outage occurred at 6:57 p.m. Monday, 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 cesium, 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.