TOKYO, Feb. 1 (Kyodo) — Tokyo Electric Power Co. said Wednesday that 8.5 tons of radioactive water leaked from the No. 4 reactor of the crisis-hit Fukushima Daiichi power plant because a pipe connected to the reactor dropped off, but added that the liquid has not flowed outside the reactor building.

At the time of the devastating earthquake and tsunami last March 11, the reactor's fuel rods were in its spent fuel pool due to maintenance work that was taking place. The water contains radioactive materials as it is mixed up with water that is in contact with the fuel in the spent fuel tank.

According to the utility known as TEPCO, water was found to have leaked onto the floor of the No. 4 unit building at 10:30 p.m. Tuesday. The leak was stopped at 10:43 p.m. by closing a valve, officials said.

The total amount of leakage from the reactor was initially estimated to be 6 liters, but the utility revised the figure later Wednesday, adding that the leakage appears to have started at around 5 p.m. Monday.

The pipe may have dropped off because water inside increased in volume as it turned into ice due to cold temperatures.

The utility plans to check whether there are similar cases in the other crippled reactors.

The Nos. 1 to 3 reactors have fuel inside, which is believed to have melted in the early phase of the nuclear crisis because the plant lost its cooling functions following the natural disasters.

The No. 4 unit also lost the function to cool its spent fuel pool, but no serious damage is believed to have occurred in the fuel stored there.