Officials: Cold shutdown has been achieved

Original story By KAZUAKI NAGATA 17 Dec 2011

The government and Tokyo Electric Power Co. declared Friday the three crippled reactors at the Fukushima No. 1 plant are in cold shutdown and no longer leaking large amounts of radiation.

If the authorities are correct and cooling of the reactors is stable, it would be an important milestone in ending the world’s worst nuclear accident since the 1986 Chernobyl crisis. But many skeptics believe the declaration is little more than political grandstanding, given the revised definition of what constitutes cold shutdown and the date of the declaration, which had been reported long in advance, and are concerned about the long-term stability of the plant’s critical coolant system.

A cold shutdown usually means the reactor core coolant temperatures are below 100 degrees, ensuring that coolant water is not boiling and that radioactive material are not escaping from the cores in significant amounts.

But reactors 1, 2 and 3 have been damaged and much of the melted fuel is believed to have penetrated through the pressure vessels and fallen to the bottom of the outer containment vessels. Tepco has been unable to take direct measurements of the temperatures at the bottoms of the containment vessels.

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