Dominic Ziegler: A dozen years after the Fukushima nuclear plant meltdown, cleanup is still going on. The biggest issue is what to do with the contaminated water that's been used to cool the fuel rods and debris. There are 64 radionuclides in the water; an advanced filtration process has removed 62 of those. But tritium remains a problem as it can damage DNA - so Tapco proposes releasing 500 olympic-sized swimming pools worth of water into the ocean over the course of three decades.