Fukushima nuclear plant loses power Japan's crippled Fukushima Daiichi nuclear station suffered a power failure on Monday night, and some systems, including cooling mechanisms for several pools storing radioactive fuel rods, remained offline on Tuesday morning. Tokyo Electric Power (Tepco), the plant's owner, said there was no immediate danger because the pools have been cooled to well below safe levels since the accident at the plant in March 2011. But if power is not restored, temperatures inside one pool could rise to levels deemed unsafe in a little over four days. The breakdown of such a critical system is a reminder that the situation at Fukushima Daiichi remains tenuous even after a two-year repair effort. The plant reached a state of relatively safe "cold shutdown" nine months after the accident, but full disposal of the dangerous materials inside will take years. Tepco said it was investigating the power failure, which also affected the plant's control room and a system for purifying the thousands of tonnes of water that is constantly cycled through the reactors and spent-fuel pools to keep them cool. It said water supply to the three reactor cores that melted down during the accident was not interrupted. Power was restored quickly to the control room, but the purification system remained offline on Tuesday morning, as did cooling mechanisms at three of four fuel storage pools inside the damaged reactor buildings, as well as a larger collective storage pool on the site. Together, the affected pools contain about 9,000 uranium fuel rods that had been removed from the reactor cores before the accident. Temperatures inside the pools were between 15 and 30 degrees Celsius as of 10am Japan time on Tuesday, Tepco said. The utility estimated that one of the reactors" pools would reach 65 degrees - the upper end of the threshold that regulators regard as safe - in four and a half days. The other pools, meanwhile, are likely to take between seven and 27 days. During the accident, water reached boiling point and evaporated, leaving fuel rods exposed to the air and releasing radiation.