http://www.guardian.co.uk/world/2011/may/13/fukushima-reactor-meltdown-flooding-warning* As if they would listen to Greenpeace, but it's interesting the article is written as if they were able to communicate with Tepco
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Greenpeace has urged Tepco to abandon plans to flood the container with water, given the likelihood that melted fuel has damaged it. Shaun Burnie, nuclear adviser to Greenpeace Germany, said: "Flooding a reactor that has fuel
through the pressure vessel is not a good idea."
Outlining a worst-case scenario, Burnie said very large amounts of cold water hitting the melted fuel could cause an explosion, trigger substantial damage to the reactor and create a "high risk of atmospheric release running for days, if not weeks." He added: "I think will now be scrapped."
Greenpeace said problems could escalate rapidly if the fuel melted through the reactor vessel. "As the fuel rods were fully exposed and subsequently melted, it is highly likely that the core's integrity is compromised and that there is larger amount of melted fuel at the bottom of the reactor pressure vessel." John Large, an independent nuclear engineering consultant in London, said Tepco's plan to flood the reactor was riddled with "potential risks". It appeared not to have factored in the extent of damage to the fuel rods and the structural state of the containment vessel, including whether it was watertight. "It seems to be poorly thought through," he said, adding that the firm had not demonstrated that the strategy could work.
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