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This article perpetuates a common misunderstanding about radioactive half-lives, which is that shorter ones are better because the waste isn't dangerous as long
by apendleton 10y ago
This article perpetuates a common misunderstanding about radioactive half-lives, which is that shorter ones are better because the waste isn't dangerous as long. Actually, isotopes with short half-lives are undergoing radioactive decay very quickly, and are thus much more highly radioactive than substances with longer half-lives. There are radioactive isotopes in dirt, vegetables, etc., but they pose us no risk because their half-lives are so long as to not radiate significantly enough for it to matter. Fission byproducts with 300-year half-lives are actually super dangerous.
Interestingly, most thorium proponents point to this danger inherent in the thorium fuel cycle as a selling point, because it makes thorium waste so difficult to handle as to be a hindrance to proliferation.
In general, even speaking as someone who's generally pretty excited about thorium power, I'm not a huge fan of this article because I don't get the sense that this author has a super-solid handle on the science.
- outworlder 10y agoIf a "waste product" is still that energetic, then is it waste after all?
- apendleton 10y agoAs I understand it, the main waste product of concern is Uranium-232, which is highly radioactive (half-life of ~70 years) but not fissile. Conceivably you could maybe use it for power generation in some other way, though, like with a radioisotype thermoelectric generator? I'm not sure it would be worth the effort, though.
- JoshTriplett 10y agoI do find it sad that we don't yet have a more efficient means of capturing the output of a nuclear reactor than heating liquid to power a turbine. Seems like there should be a more direct (and more efficient) path from fission or fusion to electricity.
- lmm 10y agoUsing the difference between a hot and cold reservoir to do work is a very fundamental, pure way to look at energy. It seems very natural to me.
- rosser 10y agoI don't think the GP is bemoaning how "natural" the process seems, but how inefficient it is. It's pretty much the best we've got currently, given the choices we've made (including those broadly detailed in The Fine Article). That said, there's an aesthetic level at which you kinda have to look at the thermal efficiency of a nuclear power plant — which is, AFAIK, like 30-some percent — and wish we could somehow do better, given all the infrastructure and risk involved.
- dv_dt 10y agoSo has anyone ever calculated the effect of the heat output if all of our power consumption were supplied by nuclear power? (at 30% conversion efficiency). Would the earth just radiate that extra heat off, is it negligible for all practical purposes?
- rosser 10y agoProbably not much different. I'm pretty sure most fossil fuel power plants have comparable efficiencies. It's not like the steam produced by burning dinosaurs is somehow less capable of driving a turbine than what comes from splitting atoms.
- mikeash 10y agoSo much of the nuclear reaction ends up just wiggling the atoms around, so it's tough to do anything smarter than a heat engine. It is possible to generate power by other means. For example, you can use radioactive isotopes which emit beta radiation to generate electricity directly, since beta radiation is just free electrons. With fusion (ignoring the important problem of breakeven) you have an energetic plasma, and you can extract energy using magnetic fields rather than with turbines. For fission, the energy produced goes into moving neutrons and the fragments of the nuclei, which I don't think can really be captured other than as heat.
- VLM 10y agoU232 is not fun to work with, well into the "robot arms" level of gamma radiation output. U235 and P239 are like "wear gloves, glovebox" In a lab, or WRT inevitable accidents and contamination, its like the difference between working with strong industrial acids vs nerve gases. Its really a huge pain. The article author seems to have hand waved away several practical engineering problems like this. Also see his interesting hand waving away of the steam cycle as we know it, hand wave away molten salt moderator issues, etc. Some things are a practical pain because nobody's given the engineers enough $$$ yet, some things are a pain because of basic physics and chemistry reasons. I think the article author is confusing those two. Certainly, the nuclear industry over the last 70 years has not lacked for money or brainpower.
- static_noise 10y agoVery short half-life-times in the minute regime and below are actually pretty great because you can just keep that stuff in a container for some time and it decays away exponentially.
- mapt 10y agoNot the best direct source, but this is asserted to be from Nuclear Engineering International magazine in November 2009 http://www.greenpeace.org/international/community_images/88/2288/98676_156425.jpg http://www.greenpeace.org/international/community_images/88/... via http://www.greenpeace.org/international/en/news/Blogs/nuclear-reaction/the-mythologies-of-thorium-and-uranium/blog/48625/ http://www.greenpeace.org/international/en/news/Blogs/nuclea... Thorium waste appears substantially less radioactive at shorter timescales we care about. On really long (10^4 - 10^6 years) timescales the proactinium-231 becomes an issue and uranium waste pulls ahead of thorium waste slightly. As we don't really have any idea how to plan on those timescales anyway (it's not like they're still going to be sitting in casks in a pool of water in New Jersey in 10^4 years), I think thorium is a lot better candidate from this perspective.
- hexane360 10y agoThat writing was even worse than the OP!
- thelonecabbage 10y agoI'm not sure exactly why a non-fissile material with a half life this long is a "problem". By definition it's not. Beside these are the burnup rates for Once-Through solid fuel cycles. In Uranium reactors this is only recommended if you are actively trying to create weapons material, and in Throium it simply doesn't work. Not sure what the relevance of these articles is.
- robinhoodexe 10y agoGood point. I work a bit with PET-related isotopes, mostly fluor-18 and carbon-11, which has half-lives of 110 and 20 minutes, respectively. You gotta be careful with that stuff, the radiation (β-minus) is pretty dangerous if you're exposed for long (usually there's 5-30 GBq per vial), but again, it's pretty neat that if something happens (you spill something for example), you can just leave the room and clean it the next day without any problems. Overall, there's really no radioactive waste, since after 24 hours it's darn safe (and the FDG turned to sugarwater, literally).
- personjerry 10y ago> you can just leave the room and clean it the next day without any problems Wouldn't it radiate into the room and make the room... bad? (Sorry, I'm clueless about this subject)
- Gibbon1 10y agoUsually it's neutron radiation that makes things radioactive[1]. Really energetic particles can do the same[2]. But the positron emission from Flourine-18 I don't think has enough energy to do that. [1] Being neutral particles they can easily be absorbed by the nucleus of whatever. Adding an extra neutron may result in an unstable nucleolus. [2] Friend that worked at SLAC (big linear accelerator) gave us a tour and mentioned the block of aluminum they use to backstop the beam. He said it gets slightly radioactive. http://www.slac.stanford.edu/pubs/slacpubs/1250/slac-pub-1406.pdf http://www.slac.stanford.edu/pubs/slacpubs/1250/slac-pub-140...
- deleted 10y ago[deleted]
- hexane360 10y agoRadiation is very different from radioactivity. It's sort of like the idea that a microwave can be dangerous running exposed, but it's fine the moment the magnetron stops. If you have a rapidly decaying isotope, it will produce lots of radiation. However, most of that radiation will be harmless. Some ionizing radiation will be able to change the atoms that make up surrounding materials, but most of that will remain harmless, and very little will become radioactive.
- neutronicus 10y agoThorium and Uranium waste profiles are pretty similar with respect to the shorter-half-life stuff (fission fragments unstable against beta-minus decay because they've got too many neutrons for their own good).
- iaw 10y agoAgreed. There's also a lack of understanding of the economics behind the construction of industrial power generation facilities. In short: there is virtually no environment in the US where it's a financially sound decision to build any new nuclear power facilities.
- pfarnsworth 10y agoA nuclear engineer once told me that you could eat more plutonium than you could caffeine, because the caffeine would instantly kill you, but the half life of plutonium was much longer and it would pass in and out of you before anything actually happened.
- rosser 10y agoThat claim is usually sourced to a guy named Bernard Cohen, who once volunteered to eat as much pure plutonium as Ralph Nader did caffeine. Nader demurred, and most people disavow Cohen, because who'd actually do that? That said, consider Albert Stevens. He was (unknowingly) injected with 131 kBq of Pu, accumulating a lifetime dose of ~64 Sv, and died of heart disease some 20 years later.