About 400 liters of coolant water containing radioactive material leaked from a nonactive reactor at the Mihama nuclear power plant in Fukui Prefecture, but there was no danger of radiation escaping from the plant, its operator said Tuesday.

The leak was discovered by a worker who rushed to the scene after an alarm went off in the afternoon at Mihama's No. 3 reactor, according to Kansai Electric Power Co. spokesman Hiroshi Toshikiyo.

Some 400 liters of water spilled from the primary coolant tank into a catchment area, 26 liters of which then spilled onto the surrounding floor. No radiation leaked outside the compound and no one was exposed to radiation, Toshikiyo said.

The cause of the leak appeared that workers had improperly attached a pipe to the tank, he said.