Talk:Radioactive waste

From Academic Kids

More could be added to describe the vitrification plants being built by the US government.

True enough, IP 12.150.68.29 (http://en.wikipedia.org/w/wiki.phtml?title=Special:Contributions&target=12.150.68.29). Andrewa 16:52, 27 Oct 2004 (UTC)

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There's probably room for some more explanation of the way radioactive decay and particularly decay chains impact waste management. The statement The radioactivity of all nuclear waste diminishes with time seems obvious but it's perhaps misleading. It will eventually be true for any radioactive material, but there can be periods of time when waste increases in radioactivity owing to the buildup of decay products which are more radioactive than the waste was. It's quite common for waste to increase in radioactivity for a while and then decrease, other waste decreases then increases then decreases, some has even more wobbles in the curve. The best example is probably a fresh, unused uranium reactor fuel element... You can stand next to it now, but if it's stored for a few hundred years the decay products will build up again, and yowie! Thorium is even worse. Andrewa 16:52, 27 Oct 2004 (UTC)

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How relevent is this article. They say that waste should not be burried, so where does that leave the US government program to burry the waste under some mountain? [1] (http://news.bbc.co.uk/2/hi/science/nature/4407421.stm)

more!

I think this article needs to contain more information about high-level waste:

the contents of high-level waste

quantitative evaluation of the hazards and evolution with time

make the paragraph about waste disposal more clear

--Philipum 11:32, 25 May 2005 (UTC)

Philipum:

Good source material for "the contents of high-level waste", or at least for the fission products in used fuel: [2] (http://ie.lbl.gov/fission.html)

Andrewa:

Build up of decay products in uranium eventually would make it about seven times as radioactive as it was when it was fresh - but this takes hundreds of thousands of years. A few hundred years results in only a small increase. Natural uranium ores are likewise about seven times as radioactive as the uranium they contain, the difference being the decay products.

Fresh thorium is only about 1/3 as radioactive as uranium, but its decay chain establishes equilibrium relatively quickly - over only a few decades - at a little over 3 times the initial radioactivity.

This is all fairly easily calculated using source material at [3] (http://atom.kaeri.re.kr/ton/)

Build-up of radioactivity can occur, but it's not a significant issue.

There's a fair amount of work needed on the waste disposal bit - I'll take a look when I've got time.

Proliferation

Pu240 is roughly four times as radioactive as Pu239, because it has 1/4 the half-life (6564 as against 24110 years, see |data on nuclides (http://atom.kaeri.re.kr/ton/)). However, this half-life is still so long that the increasing purity of Pu239 as Pu240 decays really doesn't affect the proliferation argument significantly.

Actually, handling ANY sort of plutonium is very difficult: it's all highly radioactive, regardless of any contaminants.

Yes, you are right about the half-lives. However, I think it should be a period between 10000 years and 20000 years after disposal (rather a long time anyway) where we have rather pure isotopic content of Pu239 in still large amounts, that can be relatively easily chemically separated from the rest of the waste. --Philipum 15:20, 26 May 2005 (UTC)

Around 10,000 to 20,000 years from now, the amount of Pu240 contaminating the Pu239 in these "mines" will be around 25% to 50% of what it is now, whatever that happens to be for any particular batch.

I think it's right to be concerned about leaving dangerous radioactive materials where future generations might be affected by them. However, I think the risk we should be mainly considering is that of leakage of these materials into the environment by various routes, both foreseen and unforeseen. One of the possible routes is indeed mining, where future generations' mining operations intersect long-forgotten waste depositories.

I don't think the far-future proliferation issue is really an important scenario. Either our techological civilization will have advanced to the point where the availability of relatively pure plutonium in mines is an irrelevance, or the people around won't have the faintest idea what plutonium is or what they could do with it.

Near term proliferation is a real issue, and it's perfectly possible to make bombs using reactor-grade plutonium. It's just not the material you'd use if you had the choice. evilC 18:06, 26 May 2005 (UTC)

No, I don't agree with you. The half-life of Pu240 is about 6500 years and that means that 50% the amount will have decayed after 6500 years and 75% after 13000 years and 88% after 20000 years. Thus, around 13000 to 20000 years from now, the remaining amount will be 12% to 25% of what it is now. But I agree with you this is not a real issue, however the point here is to be precise in the article.

In the near term, I would not say it is perfectly possible to make bombs using reactor-grade plutonium. I would rather say it is possible, but unpractical: when detonating a plutonium nuclear bomb, you have to start the chain reaction at a very precise time in the implosion process (chemical explosives surrounding the bomb would be blown first), and the fact the Pu240 is a proliferous neutron emitter causes the trigger to start too early. As a result, the bomb is not reliable: it can fizzle, or explode with greatly reduced power. Moreover, Pu240 is very hot and radioactive and it makes the bomb manufacturing very difficult. --Philipum 07:06, 27 May 2005 (UTC)

Don't forget that after 10,000 years the amount of Pu239 will also have decreased; after 20,000 years it'll be little more than half what it is now. Your 10,000 and 20,000 years were approximate; so are my 50% and 25%.

Pu240 is only four times more radioactive than Pu239. Pu239 is too radioactive to handle without heavy shielding and remote handling equipment. The presence of a few percent, or even 30%, of Pu240 makes no real difference to this.

The fact that Pu240 is a neutron emitter makes the design of a nuclear bomb using reactor grade plutonium more like the design of a bomb using enriched uranium: you wouldn't rely on a trigger at all. You're right about the uncertainty of the yield of such a bomb, although even a minor rogue state could do "better" than a fizzle, and a terrorist organization couldn't make any kind of plutonium bomb. However, a bomb of admittedly rather uncertain yield would actually be easier to make with reactor grade plutonium, than with bomb grade plutonium.

evilC 07:49, 27 May 2005 (UTC)

Yes, sorry, you were right with the 25% to 50%, I were wrongly giving the 240Pu contents relative to the initial plutonium, but I forgot that the Pu239 content decreases as well. Concerning how impractical it is to build a bomb with reactor-grade plutonium, I found my information in the book Before it's too late - A scientist's Case for Nuclear Energy by B.L. Cohen (Plenum Press 1983). By looking at the references the author gives I judge what he says is reliable, althought the way he has to describe it is probably biased in favour of nuclear energy. Maybe you are right that a state could make reasonable bombs with reactor-grade plutonium, while terrorists would't have any chance. However, I still disagree with your last statement that the bomb would actually be easier to make with reactor grade plutonium, than with bomb grade plutonium. I think it is the opposite: a plutonium production reactor, designed not to produce energy but rather to provide easy and rapid fuel removal, can be operated at low temperature and normal pressure, and use natural uranium. It is also cheaper and smaller. --Philipum 10:20, 27 May 2005 (UTC)

Ah, yes, we're talking at cross-purposes a bit. A state wanting to make a plutonium bomb would almost certainly make its own bomb grade plutonium in such a reactor. But if we're worrying about someone mining an old waste depository for plutonium to make bombs, either reactor grade or bomb grade would suit their purposes. The reactor grade bomb would be easier for them to make (basically, like Little Boy rather than the much more sophisticated Fat Man), but would be "inferior" in yield and predictability. 193.131.176.54 11:31, 27 May 2005 (UTC)

Still, I believe that it would be easier to make weapon-grade plutonium than to mine plutonium from a deep repository. --Philipum 06:44, 30 May 2005 (UTC)

I'm not sure. I think it depends partly on whether the plutonium is mixed with fission products. If it's already separated, that's one major job already done for you, to weigh against the mining work. It's also not all that easy to build plutonium production reactors: you need substantial quantities of high purity graphite or heavy water, if you're using natural uranium. Clive 08:41, 31 May 2005 (UTC)

No one buries separated plutonium. The US considered it once to eliminate surplus weapons grade plutonium, but decided to burn it in a reactor as MOX. Some countries intend to bury nuclear fuel without reprocessing to save reprocessing costs. Others reprocess so they can extract the plutonium and burn it as MOX. pstudier 23:12, 2005 May 31 (UTC)

It's still under consideration in the UK, see the |Report of the Working Group on Plutonium (http://www.the-environment-council.org.uk/docs/PuWG_Report_Mar_03.pdf) - the reason being that there's already far more separated plutonium in the UK than existing reactors can burn as MOX in their projected lifetimes, and there are currently no plans to build any new reactors. Reprocessing is also used to extract unburnt uranium from used fuel, because neutron absorbing fission products poison the chain reaction long before all the U235 is consumed. Clive 06:39, 1 Jun 2005 (UTC)

Bernard Cohen

I'm not sure about the Bernard Cohen book that you've provided a link to, Pstudier. I think it ought to be marked in some way as "disputed". Where an article in Wikipedia itself is disputed, there's a clear method of stating that; but I'm not sure how to mark a reference.

I'm not even sure that a reference to it is called for, since you're not referring to it as a source of any information. Many of the claims made in it, if presented as fact in Wikipedia itself, would cause uproar.Clive

As discussed above, I have read works of Bernard Cohen. Thank you for pointing out he is disputed! His books are dangerously convincing. The author has a very skilful way of providing precise information while omitting aspects that do not serve his purposes. A good basis for debates! --Philipum 06:55, 30 May 2005 (UTC)

I think that if the nuclear power article can include a link to the explicitly anti-nuclear World Information Service on Energy (WISE) (http://www.antenna.nl/wise/index.html), then this article can include the Cohen link. Perhaps the link should read

• The Nuclear Energy Option (http://www.phyast.pitt.edu/~blc/book/BOOK.html), pro-nuclear book online by Bernard L. Cohen with chapter on nuclear waste.

or

• The Nuclear Energy Option (http://www.phyast.pitt.edu/~blc/book/BOOK.html), controversial pro-nuclear book online by Bernard L. Cohen with chapter on nuclear waste.

pstudier 21:37, 2005 May 30 (UTC)

That sounds entirely fair. I hadn't followed the WISE link - I wasn't aware what it was like! Clive 08:07, 31 May 2005 (UTC)