Tokyo Electric Power said the power failure at the Fukushima Daiichi plant was brief at its command centre but continued for hours at three of the seven fuel storage pools and at several other facilities, including one that treats water contaminated with radioactivity.
Tepco said the reactors were unaffected and no other abnormalities were found. Tepco spokesperson Takeo Iwamoto said the utility plans to restore power to the pool cooling systems as soon as it can determine the cause of the failure.
The utility said the nuclear fuel stored in the pools will remain safe for at least four days without fresh cooling water.
The 11 March 2011, earthquake and tsunami destroyed the plant's power and cooling systems, causing three reactor cores to melt and fuel storage pools to overheat. The plant is now using makeshift systems.