Decay heat in Fukushima reactors, Union of Concerned Scientists, May 22, 2011:
As we noted last week, the Tokyo Electric Power Company (TEPCO) announced it believes the fuel in Fukushima Daiichi reactor 1—and possibly reactors 2 and 3—has melted and is sitting in a lump at the bottom of the reactor vessel. But it believes that workers have been able to keep the lump cool enough that it has not melted through the bottom of the reactor.
Such a melt-through is a concern since it would mean that highly radioactive gases released from the melting fuel would be released into the primary containment. Moreover, the molten fuel mass would then react with the concrete floor of the primary containment and create additional radioactive gases. If these are released to the atmosphere, either through venting or a leak in the containment (which could be caused by the molten fuel), it could add significantly to the total radiation released by the accident. [...]
Published: May 23rd, 2011 at 6:50 am ET