4 ms·

could you outline the problems with thorium reactors that you know of? i've been searching high and low to figure out what they are. obviously they exist, but t

by pkrein 14y ago

could you outline the problems with thorium reactors that you know of? i've been searching high and low to figure out what they are. obviously they exist, but they often seem brushed over and ill-defined. any extra light you can shed on it would be useful. thanks!

jakozaur 14y ago
Thorium is not a fuel that could be use alone, you still need an enriched uranium: http://ieer.org/wp/wp-content/uploads/2012/04/thorium2009factsheet.pdf http://ieer.org/wp/wp-content/uploads/2012/04/thorium2009fac... So thorium reactors will still have some problems similar to uranium reactors.
- thingification 14y ago
  Need for enriched Uranium: that is correct, though liquid fueled Th reactors are designed to operate as a closed system that breed and "burn" their own Uranium from the Th, starting from an initial supply of neutron flux to start the process. That source of neutrons, it's usually assumed, will be Uranium. LFTR designs breed U233 (as opposed to the U235 used in conventional "thermal" reactors). The people trying to revive liquid-fueled reactor development say that U233 is by far the most practical "starter" to provide the neutrons to start a reactor going. The US has a stockpile of U233, which would provide a significant advantage for in the US any race to develop the technology. Sadly, the US has a program costing hundreds of millions of dollars to destroy its stock of U233, thus throwing away that advantage, for dubious gain. Last I heard, they were due to have started by now. Video on the subject from the guy who did the excellent Thorium remix 2011 video (on skimming it seems it doesn't really explain why U233 is better than alternative neutron sources as a way to start the reaction): https://www.youtube.com/watch?v=-p49Sq7mbpE https://www.youtube.com/watch?v=-p49Sq7mbpE I don't think they're done destroying it: if you're a US citizen, I guess there's still time to write to your member of congress. "some problems similar to uranium reactors": I think you need to be much more specific for the comment to be useful.
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...
InclinedPlane 14y ago
Wikipedia has a decent list: http://en.wikipedia.org/wiki/LFTR#Disadvantages http://en.wikipedia.org/wiki/LFTR#Disadvantages Though it's missing a few key elements. Note that a lot of the advantages of LFTR designs rely on technology that hasn't been invented let alone demoed or proven yet. For example, in-situ fuel reprocessing. The biggest thing is that nearly every aspect of building and operating a LFTR is completely new. From how to keep the reactor humming along and avoid having a criticality excursion or avoid accidentally quenching the reaction to how you get power out of the heat from the reaction to how you refuel it. Damned near everything is untried and untested. It's going to take a lot of iterations to smooth out the bumps, even if we accept the idea that the overall inherent safety of the design is superior.
- KitemanSA 14y ago
  This statement is completely false. All _required_ aspects of fuel reprocessing have been demonstrated. And it has been demonstrated in two reactors with all three fissile fuels the LFTR cores are inherently stable. We have over two full-power years of experience with a LFTR core over a ~five year period

by pkrein 14y ago

jakozaur 14y ago

Thorium is not a fuel that could be use alone, you still need an enriched uranium: http://ieer.org/wp/wp-content/uploads/2012/04/thorium2009factsheet.pdf http://ieer.org/wp/wp-content/uploads/2012/04/thorium2009fac... So thorium reactors will still have some problems similar to uranium reactors.

thingification 14y ago
Need for enriched Uranium: that is correct, though liquid fueled Th reactors are designed to operate as a closed system that breed and "burn" their own Uranium from the Th, starting from an initial supply of neutron flux to start the process. That source of neutrons, it's usually assumed, will be Uranium. LFTR designs breed U233 (as opposed to the U235 used in conventional "thermal" reactors). The people trying to revive liquid-fueled reactor development say that U233 is by far the most practical "starter" to provide the neutrons to start a reactor going. The US has a stockpile of U233, which would provide a significant advantage for in the US any race to develop the technology. Sadly, the US has a program costing hundreds of millions of dollars to destroy its stock of U233, thus throwing away that advantage, for dubious gain. Last I heard, they were due to have started by now. Video on the subject from the guy who did the excellent Thorium remix 2011 video (on skimming it seems it doesn't really explain why U233 is better than alternative neutron sources as a way to start the reaction): https://www.youtube.com/watch?v=-p49Sq7mbpE https://www.youtube.com/watch?v=-p49Sq7mbpE I don't think they're done destroying it: if you're a US citizen, I guess there's still time to write to your member of congress. "some problems similar to uranium reactors": I think you need to be much more specific for the comment to be useful.

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...

InclinedPlane 14y ago

Wikipedia has a decent list: http://en.wikipedia.org/wiki/LFTR#Disadvantages http://en.wikipedia.org/wiki/LFTR#Disadvantages Though it's missing a few key elements. Note that a lot of the advantages of LFTR designs rely on technology that hasn't been invented let alone demoed or proven yet. For example, in-situ fuel reprocessing. The biggest thing is that nearly every aspect of building and operating a LFTR is completely new. From how to keep the reactor humming along and avoid having a criticality excursion or avoid accidentally quenching the reaction to how you get power out of the heat from the reaction to how you refuel it. Damned near everything is untried and untested. It's going to take a lot of iterations to smooth out the bumps, even if we accept the idea that the overall inherent safety of the design is superior.

KitemanSA 14y ago
This statement is completely false. All _required_ aspects of fuel reprocessing have been demonstrated. And it has been demonstrated in two reactors with all three fissile fuels the LFTR cores are inherently stable. We have over two full-power years of experience with a LFTR core over a ~five year period