The plan for Fukushima was unveiled following the Tokyo Electric Power Company's admission on Aug. 20 that some 300 tons of radioactive water had leaked from storage tanks built to hold the water, which has been used to cool the plant's reactors and highly radioactive spent fuel since March 2011. This followed an admission a month earlier that contaminated water from the plant was leaking into the sea.
At the same time, some 400 tons of groundwater are said to be flowing into the plant's environs each day, where it seeps into the damaged buildings and mixes with contaminated water before making its way to the sea.
The sea-side power plant, located at Okuma on the east coast of Japan's largest island, Honshu, was devastated by a series of safety-system failures following a magnitude 9 earthquake offshore that sent a 45-foot tsunami sweeping across the nuclear plant as it moved inland. Follow-up investigations showed that the utility underestimated the tsunami hazard the plant faced, leading to design flaws that left it more vulnerable to tsunamis than it might otherwise have been.
The plant was built above sea-level, but the tsunami still covered the site with up to 16 feet of water as it moved inland. All of the main and back-up systems designed to provide power to the plant's cooling systems failed. Hydrogen gas built up in three of the plant's six reactor buildings, triggering explosions that also damaged a fourth reactor building.
The explosions and subsequent fires released a radioactive plume that within three weeks of the accident was detected over southern Spain. The plant's owner, Tepco, has been pouring water over the damaged reactors and the spent-fuel pools ever since to keep heat from doing further damage to the reactors and spent-fuel assemblies.