Kyushu Electric Power Co. has said 1.8 tons of radioactive water leaked in the purification system of a reactor at the Genkai power plant in Japan's Saga Prefecture.
Though the utility had detected the leakage on December 9, it informed local government after facing pump trouble in the No. 3 reactor.
The utility was criticised by local government, including Genkai Mayor Hideo Kishimoto for failing to promptly inform about the leak.
"It should have been reported properly (to the town of Genkai and Saga Prefecture). I have been repeatedly telling Kyushu Electric to change its corporate culture," the Japan Times quoted Kishimoto, as saying.
Kyushu Electric Power Co said the water leaked from an area involving the pumps, but all radioactive materials were contained within the reactor building.
The intensity of radioactive matter in the water was yet not clear, it added.
The company said the alarm went off on December 9 indicating a leak but could not immediately detected as the leaked water was contained within the purification system.
The Nuclear and Industrial Safety Agency ruled out that leak within the purification system posed a safety threat and urged Kyushu Electric to probe the issue.
Genkai power plant's reactor 4 had resumed operation in early November, becoming the first to be restarted since the March 11 Fukushima nuclear crisis.