Storage tanks for contaminated water – a major challenge at the Fukushima Daiichi site. Highly contaminated water in the basement of the reactor buildings is pumped out and treated to reduce the level of radionuclides, particularly caesium, then recirculated to cool the reactor cores. But every day an additional 400 tonnes of groundwater seeps into the damaged reactor and turbine buildings, meaning that an ever-increasing amount of treated and untreated water needs to be stored. The total capacity of existing tanks is just over 240,000 cubic metres, and more are being built, putting a strain on available space. Fukushima Daiichi Nuclear Power Plant. 18 December 2012.

Further information see the wikipedia article of Discharge of radioactive water of the Fukushima Daiichi Nuclear Power Plant.