Tokyo Electric Power Company (Tepco) said that it has lost power that is used to cool spent uranium fuel rods at its Fukushima Daiichi nuclear plant in Japan.
On Monday, Tepco said that there was no immediate threat of overheating or radiation releases after the loss of electricity.
The company partially restored power by Tuesday afternoon, reported Reuters.
The loss of power has revealed that that the plant is still in an unstable state after it was damaged due to an earthquake and tsunami in March 2011.
Tepco general manager Masayuki Ono was quoted by the news agency as saying, "We have time to find a solution before the temperature gets out of hand and then also the ability to inject water into the pools if needed."
The company began operations in the cooling system at the No.1 reactor, while it expects cooling operations to restart at the No.3 and No.4 reactors later on Tuesday, and the shared pool on Wednesday morning.
It is expected that to take a minimum of four days for the spent fuel pool at the No.4 reactor to exceed the legal limit of 65 degrees Celsius (149 degrees Fahrenheit) if the power stays off and no additional water is added.