The Tokyo Electric Power Company is pumping water nonstop through the three reactors to cool melted fuel that remains too hot and radioactive to remove. About 400 tons of water passes through the reactors every day, including groundwater that seeps in. The water picks up radiation in the reactors and then is diverted into a decontamination facility.

But the decontamination filters cannot remove all the radioactive material. So for now, all this water is being stored in 1,000 gray, blue and white tanks on the grounds. The tanks already hold 962,000 tons of contaminated water, and Tokyo Electric is installing more tanks. It is also trying to slow the flow of groundwater through the reactors by building an underground ice wall.