Japan’s Tepco is working to control a leak of highly radioactive water from a storage tank at Fukushima Daiichi nuclear power plant. Observers are calling the incident the worst radioactive water seepage since the disaster which took place in March 2011.

Water escaped from the tank and then reached the environment through a rainwater valve in the surrounding dam. The cooling of the reactor cores damaged in March 2011 still requires a constant flow of water, which circulates through the power plant basements before treatment and storage in a complex of large tanks. The water becomes highly radioactive after contact with the cores and is pumped to a storage and treatment facility.


Personnel at the site found water leaking from a rainwater drain valve in a dam that surrounds a tank of pre-treated water on Tuesday.

Investigations showed that the level of water in the tank was about 3 metres lower than expected, indicating that some 300 cubic metres had escaped. The water was said to be highly radioactive: 80,000 becquerels per cubic centimetre.

The drain valve has now been successfully closed. Water from the failed tank is currently being pumped to other tanks and Tepco is removing water from within the dam to a temporary tank before it will be added to other tanks at the facility.

According to Tepco, there is no evidence that the water entered a drainage ditch, said Tepco, meaning it is unlikely to have left the area or reached the sea.

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