Japan’s Fukushima plant has leaked more than 600 litres of water, forcing it to briefly suspend cooling operations at a spent-fuel pond at the weekend.
Fukushima, on the coast north of Tokyo, was wrecked by a huge earthquake and tsunami in March last year, triggering the evacuation of around 80,000 people in the world's worst nuclear crisis in 25 years.
The operator of the complex, the Tokyo Electric Power Co (Tepco), reported two main leakages on its website on Sunday, one from a pump near the plant's office building and another from a back-up cooling system at reactor No.4.
"The cooling water is from a filtrate tank for fire extinction and doesn't contain radioactive materials," Tepco said of the incident at reactor No. 4. It added that some water from the other leakage had flowed into a drain and "we are examining whether this water has flowed into the ocean or not".
The Nikkei newspaper on Monday quoted Tepco as saying around 40 litres had leaked from the pool-cooling system of the No. 4 reactor on Sunday morning, with probably 600 litres of purified water leaking from another point. Water had also leaked at other facilities within the complex, the Nikkei added.
However, the Nikkei newspaper quoted Tepco on Monday as saying that it believed no water had escaped into the sea.
"The leakage is believed to have been caused by freezing due to cold weather, and the leaked water included radioactively contaminated water that has been purified," the Nikkei said in its online edition, quoting Tepco.
"The contamination level is low."