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Author Topic:   Japan
Posts: 4555
From: Oregon, USA
Joined: 08-27-2006
Member Rating: 4.0

Message 61 of 175 (609012)
03-15-2011 9:47 PM
Reply to: Message 57 by Rahvin
03-15-2011 7:43 PM

Re: "Worst case scenario"
Rahvin, thanks for the interesting and informative posts.
I find it hard to imagine what all the effects of a worst case scenario would consist of. If a full meltdown occurred the fuel would melt through the bottom of primary and secondary containment, and possibly some distance into the ground below the reactor. It is possible that the fission reaction would continue until the fuel was spent and it might be molten all that time. Some of the daughter products of Uranium such at Radium-226 are water soluble and could enter the aquifer and with a 2200 year half-life would be a serious contamination for a long time. Once the sustained fission reaction stopped there would still be a considerable amount of Uranium left that through normal radioactive decay would continue to create radioactive daughter nuclides.
At Chernobyl the loss of control of the reaction caused the core to become so hot that there was a massive explosion, and the graphite moderator that the core was embedded in caught on fire and burned so fiercely that it could not be extinguished. They tried to smother it with Boron laced sand dropped from helicopters but that did not work. I can't remember how long it burned but I think it was close to a week. The fire caused the spread of radioactive nuclides to be much worse. I actually had a very small sample of material from Chernobyl in the gamma spectrometry lab where I worked years ago and the number a radionuclides and the level of activity was pretty amazing.
An interesting effect happens when Zirconium (the tube that contains the fuel pellets) gets hot enough. It catches on fire and burns at a temperature that is hot enough to disassociate water into Hydrogen and Oxygen. And it burns readily under water. This may have been where the hydrogen bubble came from that exposed the top of the core at Three Mile Island.
I support safer nuclear power and I think the lessons learned from this disaster should guide retrofits of the existing power plants and future designs. Today on NPR I heard that Three Mile Island was the most studied accident in history and I imagine that the Japanese disaster will surpass that. I think the spent fuel and waste is still the most serious long term problem that needs a solution.

Tactimatically speaking, the molecubes are out of alignment. -- S.Valley
What if Eleanor Roosevelt had wings? -- Monty Python
You can't build a Time Machine without Weird Optics -- S. Valley

This message is a reply to:
 Message 57 by Rahvin, posted 03-15-2011 7:43 PM Rahvin has not replied

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