3 ms·

In every article about thorium reactors, I never see any real discussion of drawbacks, or why uranium triumphed over thorium early, so I asked here the last tim

by fatbird 14y ago

In every article about thorium reactors, I never see any real discussion of drawbacks, or why uranium triumphed over thorium early, so I asked here the last time this author's article was linked. I got good answers: http://news.ycombinator.com/item?id=4912614 http://news.ycombinator.com/item?id=4912614 The short version is that the typical thorium reaction still requires/produces U-232, which is weapons grade uranium, so you have all the same problems as before regarding proliferation concerns; and more seriously, the product U-233 produces a lot of gamma radiation, which is really deadly at a distance and terribly difficult/expensive to shield against by comparison to the radioactive products of U-235/238 fission reactors. Also, there's a general engineering issue that lots of work and research has been done on current reactor designs, while little has been done on thorium reactors, comparatively. Thorium looks good on paper, but there are bound to be a bunch of practical issues that come up that raise the expense and mitigate the advantages. Basically, uranium fission is far more advanced, practically speaking, so a better bet for commercial applications. ETA: And on reading the article linked above, I find that Mr. Reinhart addresses neither of these two issues.

msandford 14y ago
I believe that because the thorium is "burned" so effectively you don't see much in the way of U232 for the amount of energy output. I would be worried about a plant that can make many kilograms of fissile material per year. I wouldn't be worried about a plant that can make many grams of fissile material per year.
thingification 14y ago
"there's a general engineering issue...": This is quite right. However, that is a general-purpose argument to dismiss any new technology. I don't think the rational response to that is to not develop new technologies that show promise to be significantly better than the old ones, as this one does. While nobody could disagree that we don't know for sure how much it will cost before actually commercialising it, if we want to learn more about whether it is worth a try, the argument has to focus on the specific issues, such as the one you raise in your previous paragraph. (I think it is worth a try, because there are reasons to expect that it will be cheaper and safer.) To address your specific point about U 232: First, you have 232 and 233 reversed: it's the U 232 and not the U 233 that causes significant gamma emission [1], and the U 233 that is bred from the Th for use as fissile nuclear fuel. U 233 production from Th 232 also unavoidably produces a small amount of U 232. The gamma emissions from the U 232 are a problem for handling of U 233. However, the gamma rays (easy to spot from space) and the tricky handling are both unattractive properties for U 233 as a weapons material. The pro-Th argument goes that this means that it is much easier to enrich U 235 than it is to work with U 233. If that is the case, the proliferation properties of U 233 are arguably not relevant to the LFTR debate (I'm personally not yet convinced that it is the case). You say that the gamma rays are "really deadly at a distance". Can you cite a reference please? I don't think it is necessary to fully shield the gamma rays, unless you are building a nuclear weapon and don't want it to be seen by a monitoring satellite. Certainly the gamma emitters here don't constitute a nuclear waste issue, because the reaction takes place quickly. [1] http://www.princeton.edu/sgs/publications/sgs/pdf/9_1kang.pdf http://www.princeton.edu/sgs/publications/sgs/pdf/9_1kang.pd...
- fatbird 14y ago
  This isn't an area of my expertise. I was only trying to summarize the response to my earlier question. I think I understand the issues generally, but please look at the linked conversation for more details. I agree that engineering inexperience with thorium isn't a reason to dismiss it. I just find it a bit telling that thorium boosters like Reinhold don't address that discrepancy, in the same way they tend to be silent on the issues with U-232/233. Regarding gamma radiation, by "deadly at a distance" I mean that they're a coherent threat to health at a much greater distance because gamma radiation travels further than alpha or beta radiation because it's much higher energy. Likewise, that greater energy imposes a much higher cost on shielding: a sheet of paper blocks alpha, heavy clothing blocks beta, but you need significant amounts of dense material like lead or packed earth or granite to block gamma radiation. Presumably, this imposes a significant extra expense on a thorium reactor that's breeding U-232. My source to back up my vaguely recalled knowledge is this: http://www.epa.gov/rpdweb00/understand/protection_basics.html http://www.epa.gov/rpdweb00/understand/protection_basics.htm....
  - 7402 14y ago
    Gamma radiation is not "higher energy" than alpha or beta radiation. And the energy of particle is not by itself significant as far as radiation damage is concerned - what matters is how that radiation is deposited in you as the particle passes through you. An extremely high-energy neutrino could pass through you with no effect whatsoever. Materials such as a sheet of paper or piece of cloth have a higher stopping power (loss of energy per unit distance) for alpha particles (helium nuclei of charge +2) and beta particles (electrons of charge -1) than for gamma rays (photons - uncharged particles). This is why an alpha emitter is much less significant if it's outside your body, but much more significant if it's in your lungs - because it dumps all its energy inside you where it can cause damage.
    - lostlogin 14y ago
      I'm not sure if this is semantics or not. Yes, low energy and high energy radiation both can cause bad damage and a DNA hit from one is as bad as that from another, but that isn't the point. Standing in a 20KV beam is going to do you more damage than standing in a 500KV beam on a photon by photon basis - but only because more of the 500kV beam will go straight through you. An I missing your point though? Edit: Yes I am. Your talking about alpha versus gamma, not low energy damage versus high energy damage.

by fatbird 14y ago

msandford 14y ago

I believe that because the thorium is "burned" so effectively you don't see much in the way of U232 for the amount of energy output. I would be worried about a plant that can make many kilograms of fissile material per year. I wouldn't be worried about a plant that can make many grams of fissile material per year.

thingification 14y ago

"there's a general engineering issue...": This is quite right. However, that is a general-purpose argument to dismiss any new technology. I don't think the rational response to that is to not develop new technologies that show promise to be significantly better than the old ones, as this one does. While nobody could disagree that we don't know for sure how much it will cost before actually commercialising it, if we want to learn more about whether it is worth a try, the argument has to focus on the specific issues, such as the one you raise in your previous paragraph. (I think it is worth a try, because there are reasons to expect that it will be cheaper and safer.) To address your specific point about U 232: First, you have 232 and 233 reversed: it's the U 232 and not the U 233 that causes significant gamma emission [1], and the U 233 that is bred from the Th for use as fissile nuclear fuel. U 233 production from Th 232 also unavoidably produces a small amount of U 232. The gamma emissions from the U 232 are a problem for handling of U 233. However, the gamma rays (easy to spot from space) and the tricky handling are both unattractive properties for U 233 as a weapons material. The pro-Th argument goes that this means that it is much easier to enrich U 235 than it is to work with U 233. If that is the case, the proliferation properties of U 233 are arguably not relevant to the LFTR debate (I'm personally not yet convinced that it is the case). You say that the gamma rays are "really deadly at a distance". Can you cite a reference please? I don't think it is necessary to fully shield the gamma rays, unless you are building a nuclear weapon and don't want it to be seen by a monitoring satellite. Certainly the gamma emitters here don't constitute a nuclear waste issue, because the reaction takes place quickly. [1] http://www.princeton.edu/sgs/publications/sgs/pdf/9_1kang.pdf http://www.princeton.edu/sgs/publications/sgs/pdf/9_1kang.pd...

fatbird 14y ago
This isn't an area of my expertise. I was only trying to summarize the response to my earlier question. I think I understand the issues generally, but please look at the linked conversation for more details. I agree that engineering inexperience with thorium isn't a reason to dismiss it. I just find it a bit telling that thorium boosters like Reinhold don't address that discrepancy, in the same way they tend to be silent on the issues with U-232/233. Regarding gamma radiation, by "deadly at a distance" I mean that they're a coherent threat to health at a much greater distance because gamma radiation travels further than alpha or beta radiation because it's much higher energy. Likewise, that greater energy imposes a much higher cost on shielding: a sheet of paper blocks alpha, heavy clothing blocks beta, but you need significant amounts of dense material like lead or packed earth or granite to block gamma radiation. Presumably, this imposes a significant extra expense on a thorium reactor that's breeding U-232. My source to back up my vaguely recalled knowledge is this: http://www.epa.gov/rpdweb00/understand/protection_basics.html http://www.epa.gov/rpdweb00/understand/protection_basics.htm....
- 7402 14y ago
  Gamma radiation is not "higher energy" than alpha or beta radiation. And the energy of particle is not by itself significant as far as radiation damage is concerned - what matters is how that radiation is deposited in you as the particle passes through you. An extremely high-energy neutrino could pass through you with no effect whatsoever. Materials such as a sheet of paper or piece of cloth have a higher stopping power (loss of energy per unit distance) for alpha particles (helium nuclei of charge +2) and beta particles (electrons of charge -1) than for gamma rays (photons - uncharged particles). This is why an alpha emitter is much less significant if it's outside your body, but much more significant if it's in your lungs - because it dumps all its energy inside you where it can cause damage.
  - lostlogin 14y ago
    I'm not sure if this is semantics or not. Yes, low energy and high energy radiation both can cause bad damage and a DNA hit from one is as bad as that from another, but that isn't the point. Standing in a 20KV beam is going to do you more damage than standing in a 500KV beam on a photon by photon basis - but only because more of the 500kV beam will go straight through you. An I missing your point though? Edit: Yes I am. Your talking about alpha versus gamma, not low energy damage versus high energy damage.