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shallowdeep -> RE: How does the US proceed with nuclear power? (3/27/2011 1:46:58 AM)
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ORIGINAL: DarkSteven
I have been screaming for years that we need to recycle nuclear waste…
Depends some on what you mean, but there actually are some reasons for the open, once-through policy that's in place. I'm assuming you mean something like the fuel reprocessing in France?
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It would:
1. Reduce the amount of waste to be disposed of.
2. Reduce the amount of new fuel needed.
3. Reduce the size and amount of waste that terrorists could get to.
- That's true, but the ~10% reduction in mass would come pretty much exclusively in the form of less uranium… which really isn't a concern from a waste standpoint. As far as the more significantly radioactive stuff, you would certainly end up with less plutonium, but actually more of the nastier, if shorter-lived, actinides per unit of energy produced.
- True, but uranium oxide fuel isn't a particularly large fraction of a reactor's cost.
- I'm curious… what's your reasoning on this? I'd probably argue it's actually more of a risk.
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I heard it said (have not confirmed) that it was a Carter decision to NOT recycle. Allegedly because it would somehow pose a terrorist threat. (?) Why a former nuclear engineer would do something that asinine, I don't know...
Here's a document with some of the history regarding U.S. Policy on fuel reprocessing. Carter did have a significant role, but reprocessing was already falling out of favor. Carter's rationale, as I understand it, was more related to weapons proliferation than terrorism. The process used to reprocess spent fuel is the exact same one used to isolate plutonium for the purpose of making nuclear warheads. If reprocessing became standard, any country with a civilian fuel cycle would also essentially have a functional weapons program by default. Furthermore, there'd be separated plutonium moving around. For someone interested in causing harm to others, that's probably far, far more attractive than a dirty bomb they could make after getting their hands on some unprocessed spent fuel.
Another big roadblock with reprocessing here is the fact that it's significantly more expensive than just obtaining freshly mined uranium. Given that it isn't presently cost-competitive with a once-through fuel cycle, it's not viable without government backing.
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ORIGINAL: jlf1961
The thing is that you cannot recycle the fuel more than once.
Why not? It should be depleted to the same level every time it gets depleted..
Hmm… I'm guessing you may be envisioning fuel recycling as something other than what it actually is. Basically, the problem is the accumulation of isotopes with an even number of neutrons, like Pu-240, that aren't fissile in a thermal reactor. At the end of a pure uranium oxide fuel cycle, most of the plutonium present in spent fuel is Pu-239 – still a very usable reactor fuel. Since plutonium can be chemically separated from spent fuel with relative ease, reprocessing it into MOX fuel is an option. The spent MOX fuel that results from burning that up, however, has high concentrations of plutonium that captured a second neutron, turning it into chain reaction-killing Pu-240. There's no easy way to separate that from the chemically identical Pu-239, so sending it back for another cycle wouldn't work as well. You also get a buildup of minor actinides which would make reprocessing more difficult due to higher levels of radioactivity. The combined effect is that nobody reprocesses more than once.
There are other approaches, like fast reactors that could burn through the actinides (and breed fresh plutonium fuel in the process), but commercial ones don't exist. France's experience with Superphénix probably means you won't see them in the near future, either.
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