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Last login: Sunday, June 16, 2013
DonWood, when fuel rods are highly radioactive, it isn't because of plutonium in them. Recall the young Queen Elizabeth 2 being allowed to touch a piece of the stuff through gloves (although that was probably weapon plutonium, purer and less radioactive than the power-only stuff that power plants produce).
Plutonium's hazard is entirely due to its radioactivity, and in the time when nuclear waste is really dangerous, it is so because of other, much hotter materials than plutonium. The arithmetic for making these comparisons is quite difficult, so much so that even when computer programs such as ORIGEN2 make it easy, it's still difficult.
However, "Spent Fuel Explorer", a front end for presenting some ORIGEN2 results, is free on the web, and is another step up in accessibility for those results.
With its "decay heat" setting we can learn that 1.1 days after shutdown, nuclear fuel that has been working at 39 thermal megawatts per tonne is still producing 0.1925 megawatts per tonne.
There is a timeline with a slider you can drag with your mouse, and a pie chart showing how the heat production is divided between isotopes. Slide it far enough to the right and the red pie slices that represent plutonium grow to half of the total. This happens at 1220 years, and the heat due to plutonium is 0.00002676 megawatts per tonne.
Because its half-lives are so long, this is pretty much the same heat it was producing at 1.1 days. So at 1.1 days, the fraction of the rays that are due to it is rather small: 0.00002676/0.1925.
If there were genuine, informed concern over plutonium, the Greenpeace associate photographed with a nuclear icebreaker at http://www.projectthinice.org/blog/vi... might be expected to be about 1925/0.2676 times more concerned, 7200 times more concerned, about the other radioactivity in that boat's two reactor cores.
(Actually more than 7200, because that fuel is either working at the very moment the photo was taken, or switched off just minutes before, not 1.1 days before. I asked the author of SFE why it doesn't go to zero days, but apparently it just doesn't.)
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I haven't seen Pandora's Promise but I understand it does advocate recycling plutonium. This makes it into fission products, the things that make spent fuel rods dangerous in the short term, but -- as above said -- they don't last as long. They naturally can't, since they have less energy, having given up so much.
June 16, 2013 at 4:52 a.m.
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