Four fuel storage pools at the Fukushima nuclear plant were without fresh cooling water for nearly 20 hours after a power outage hit the tsunami-crippled facility, its operator has announced.

Tokyo Electric Power Co. said Tuesday that pool temperatures at the plant were well within safe levels, and that pools would remain safe for at least four days without fresh cooling water. Earlier, it was forced to suspend systems to cool spent fuel pools at three reactor units, reports AFP. The pools are needed to prevent spontaneous nuclear reactions.

The number 1, 2 and 3 reactors, which suffered core meltdowns soon after the March 2011 nuclear crisis, were unaffected and no other abnormalities were found, the Nuclear Regulation Authority (NRA) said, according to Japan-based Kyodo News.

The used fuel pool at reactor 4 could reach 65 degrees (149 degrees Fahrenheit) – the upper safety margin limit – within four days if no cooling steps are taken. “We are trying to restore power by then,” TEPCO said.

Workers were scrambling to repair a broken switchboard that might have caused the problem, TEPCO spokesman Masayuki Ono said, adding that they will utilize a backup water injection system in case the repairs didn’t fix the issue.

TEPCO has been criticized for downplaying the scale of the disaster and has since admitted covering up the consequences because of financial and reputation risks, reports Aljazeera.