To dump or not to dump a little-discussed substance is the question brewing in Japan as it grapples with the aftermath of the nuclear catastrophe in Fukushima five years ago. The substance is tritium. The radioactive material is nearly impossible to remove from the huge quantities of water used to cool melted-down reactors at the Fukushima Dai-ichi plant, which was wrecked by the massive tsunami in northeastern Japan in March 2011.

The water is still accumulating since 300 tons are needed every day to keep the reactors chilled. Some is leaking into the ocean. Huge tanks lined up around the plant, at last count 1,000 of them, each hold hundreds of tons of water that have been cleansed of radioactive cesium and strontium but not of tritium. FULL REPORT