As reported by the Asahi Shimbun, a series of leaks at the Fukushima Daiichi Units #5 and 6 have continued throughout this month, right up to the present. The leaks are occuring in piping attached to the high-level radioactive waste storage pools, which still do hold irradiated nuclear fuel. Apparently, valves are failing on the pools' cooling system piping.
Loss of cooling to irradiated nuclear fuel can lead to catastrophic consequences. A sudden pool drain down could lead to an irradiated nuclear fuel fire in a matter of hours. A slower motion pool boil down could still result in an irradiated nuclear fuel fire, if the water loss proceeds to uncover the stored assemblies. Storage pools not only hold large quantities of hazardous irradiated nuclear fuel, they also are not located within robust radiological containment structures. Very large-scale radioactivity releases are possible, directly into the environment.
Units #5 and 6 were not operating on 3/11/11, and were largely undamaged by the earthquake, tsunami, and nuclear catastrophe. However, Tokyo Electric Power Company has decided to retire them nonetheless, and is converting them into training centers for nuclear decommissioning. The lessons learned will be applied later at the devastated Fukushima Daiichi Units 1, 2, 3 (all melted down) and 4 (also not operating on 3/11/11, but still severely damaged by a hydrogen explosion).
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