"Fukushima has 9 days to prevent ‘unsafe’ overheating"

As reported by RT, Fukushima Daiichi Unit 5's high-level radioactive waste storage pool cooling system has suffered a leak, requiring its being shut down while repairs are made. If cooling is not restored in the next nine days, the pool water temperature could rise to dangerous levels.

If cooling is disrupted for a long enough period of time (days or weeks, depending on how recently extremely thermally hot irradiated nuclear fuel from an operating reactor core was transferred into the pool), the pool water can boil. If it boils down to just above the tops of the irradiated nuclear fuel assemblies stored in the bottom of the pool, gamma radiation dose rates in the immediate vicinity would become quickly lethal, blocking any further worker intervention to mitigate the crisis.

If irradiated nuclear fuel is uncovered, depending on how densely packed the storage pool is, it could quickly reach the ignition temperature of its zirconium metal cladding. The ensuing "pool fire" could then spread to the entire inventory of irradiated fuel in the pool, resulting in a catastrophic release of radioactivity to the environment. Storage pools are not located within robust radiological containment structures, but rather mere industrial warehouse-like buildings.

Update on July 8, 2014 by admin

On July 8th, TEPCO posted additional information about the cooling system leak, including a photo of the 3 mm hole before and after its attempted repairs.