TOKYO (Reuters) - Water containing radioactive materials leaked inside a nuclear power plant in southwestern Japan, but was contained and did not escape into the environment, the Nuclear and Industrial Safety Agency said on Saturday.
About 1.8 tonnes of water leaked from a pump at Kyushu Electric Power Co's Genkai No.3 reactor on Friday, Tetsuya Saito, an official at the agency said.
The reactor has been closed since December last year for maintenance.
"The cause of the leakage is still unknown. Kyushu Electric is investigating now," Saito said.
The issue about nuclear power safety is sensitive in Japan as the country is trying to stabilize Tokyo Electric Power's Fukushima Daiichi nuclear power plant, which was damaged after the March 11 massive earthquake and tsunami.
On Friday, Kyushu Electric issued a statement saying it had detected a rise in temperature at the base of one of the pumps which had triggered an alarm. But the statement did not refer to any leakage, although the company separately informed the nuclear agency about it, Saito said.
(Reporting by Chikafumi Hodo; Editing by Sanjeev Miglani)