Workers at the crippled Fukushima Daiichi nuclear power plant discovered a problem with the outdoor vent of a filtering device.
ADVERTISEMENTHighly radioactive water has leaked from a machine to treat contaminated water at the tsunami-hit Fukushima Daiichi nuclear power plant, though radiation monitoring reportedly shows no impact to the outside environment so far.
The plant operator, Tokyo Electric Power Company (TEPCO), said the water – some of which may have seeped into the ground – is believed to have contained 220 times the standard level of radioactive substances that has to be reported to the government.
The filtering machine, known as SARRY, has been idled for maintenance work.
According to TEPCO, 10 of the machine's 16 valves, which were supposed to be closed, were left open. The result is that water may have entered an air vent through which it leaked out of the facility, dripping down to the ground.
The company plans to remove the soil that the leaked radioactive water is believed to have reached.
So far, levels of radiation on monitors around the plant and those inside gutters on the compound have shown no increase.
The meltdown at the Fukushima Daiichi plant on 11 March 2011, which was caused by an earthquake and ensuing tsunami, was the world's worst nuclear accident since the 1986 Chernobyl disaster.
Tens of thousands of residents around the Fukushima plant were ordered to evacuate their homes or chose to do so. Around 18,500 people died or remain missing in northeast Japan, many of them killed by the tsunami.
Several workers deployed to the plant contracted cancer after being exposed to radiation, and have received compensation from the government because the cases were recognised as occupational diseases.