Tokyo Electric Power Company says it has determined that water containing radioactive substances leaked from a tank at the Fukushima Daiichi nuclear plant for more than two years. The company says there is no impact on the environment.
The utility says workers discovered water from an unknown source in an underground tunnel on January 10th at the plant.
The reactor complex was heavily damaged by the earthquake and tsunami in March 2011.
Officials later found that the water level of a nearby tank had dropped since around November 2016. They say about 300 tons of water leaked from the tank.
The officials say the water contained 120,000 becquerels of tritium per liter. That is twice the allowable level for the release of contaminated water at a nuclear plant operating normally.
The officials report that the tritium level of the water found in the tunnel was below the standard.
They believe the water flowed into the turbine building for the number four reactor through pipes.
The officials say the tank's water level declined by about 1.7 meters during the period, but measurements conducted four times each day failed to detect the tiny difference from the previous check.
The company will now work to uncover the cause.