Tokyo Electric Power Co. said Wednesday the radioactive coolant water leaked from a broken pipe in reactor 4 of the stricken Fukushima Daiichi nuclear plant, but the water did not flow outside the plant, Kyodo News reported.
The nuclear plant was crippled by an earthquake and a tsunami in March 2011.
The Kyodo report quoted TEPCO officials as saying the water containing radioactive materials from the fuel pool had leaked on to the floor of the reactor 4 building Tuesday but the problem was fixed within 13 minutes by closing a valve.
The Kyodo report said TEPCO, which is investigating the pipe damage, said it suspects the leak was caused either by the recent cold weather or the hydrogen explosions that occurred immediately following the crisis.
The quake disaster at Fukushima set off the world's worst nuclear crisis since the 1986 Chernobyl disaster.
The Fukushima crisis has hit Japan's nuclear power industry hard. Most of Japan's remaining 54 nuclear reactors have been shut down for safety checks, while the government has set aside its plan to generate more than 50 percent of its energy from nuclear power by 2030, the Voice of America reported.
The Japanese cabinet approved a bill this week for a new nuclear watchdog. The bill would limit a new nuclear reactor's operational life to 40 years.