I’m still only a few pages in. I don’t have the chance to read it all right now, but I will revisit this tomorrow morning. Here are my early thoughts. Disclaimer: I am an advocate of fusion and am moving into the field (professional electrical engineering support of an academic project).
We need to walk before we can run. D+T fusion is viable. Hull maintenance is a solvable problem. Economic studies come after we can walk. Similarly, actually realizable designs that can reach Lawson performance necessary for p+B11 won’t come before designs that can reach D+T are made.
There are compelling narratives around funding, but ultimately it seems they are simultaneously overly optimistic about our technical advancement and overly jaded about future prospects.
It’s important to note that there is no difference in a reactor design capable of different fusion fuels, other than its Lawson performance. You can fuse D+T just the same as p+B11 if your device is capable of p+B11. There is not magical jump in performance we can make. So why skip over D+T if we need to go through it anyway? If D+T is found to truly not be economically viable (which sounds inherently flawed, since prices go down as technology becomes more advanced) then we could still pursue confinement devices in the hopes of reaching more advanced fuels.
So I’m a few pages further and I fear I will not be finishing this paper. I am surprised it was published and is still referenced. Where are the citations? Where is the analysis? You can’t just say “fusion reactors need to be ten times bigger than fission reactors”. It’s frankly embarrassing to MIT that they would allow egregious, unfounded claims to be published. Peer review exists to shred such unsupported statements.
This was a semi-popular article. You can find more technical analyses in the literature.
The specific points made in the article have stood the test of time. Lidsky said the power density of a DT fusion reactor would be at least an order of magnitude worse than that of a fission reactor. And if you look at existing reactors and concepts, this is true. Compare to a commercial PWR, in which (thermal power)/(volume of reactor vessel) is about 20 MW/m^3. An order of magnitude worse than that would be 2 MW/m^3. The (thermal power)/(reactor volume) for ITER is about 0.05 MW/m^3. For ARC and Lockheed's concepts, about 0.5 MW/m^3.
Your outrage should not be directed at this article (although such outrage is sadly understandable, if this article is telling you things you don't want to hear.) Instead, it should be directed at the fusion community as a whole, which has downplayed these critiques and glad-handed the issues raised while marching confidently into a dead end.
Tokamaks may not even be viable for steady state D+T. The bootstrap current effect still needs to be explored further. Electrostatic confinement and inertial confinement are the only known viable options for p+B11. Electrostatic has serious issues related to conduction losses, but perhaps if they were large enough scaling laws may make them viable. It’s not well explored. Inertial confinement is getting a lot of funding and shows serious promise. However, inertial confinement is not a steady state design and its pulsed nature makes it difficult to make a power plant out of. No such engineering cliffs exist for tokamaks and stellarators. The performance just needs to keep marching towards success. Then the discussion of economics can begin in earnest.
This old critique has aged fairly well. It was too optimistic about advanced fission, and the suggestion to move to advanced fuels for fusion was mostly shot down by Lidsky's student, Todd Rider.
There are a few parts that have been overtaken by advances. Improvements in superconductors have driven the minimum size for a fusion reactor far down, for instance.
A lot has changed since 1983. The superconducting materials that CFS depends on weren't even discovered until the late 80s, and it took a very long time for that to become practical. Fast-forward to today and you can buy this stuff on Alibaba!
Lidsky's arguments against fusion apply to the ARC design. Its overall volumetric power density is 0.5 MW/m^3, 40 times less than a PWR reactor vessel.
What defines the volume to get to that number? From what I can tell from the ARC specs the plasma volume is 141 m3, and the expected power output is 200-300 MWe, which makes it 1.5-2 MWe/m3.
Do you have some numbers on a PWR reactor vessel? I was trying to look up some details on the APR-1400, but could not find any.
We know what the issue is--fusion never got a useful amount of funding.
Now, it is entirely possible that even given an enormous amount of funding--fusion might still not work. However, engineers with lots of money are remarkably clever and effective beasts (see: radio, semiconductors, plastics, steel).
Fusion has been funded at "Fusion Never" levels for almost 40 years while we subsidize every other significant energy source to the tune of billions or trillions of dollars every single year. (For example, how much money got poured into the technology that became "fracking"?)
No, that's not what the issue is. That's an effect, not a cause. The cause is that fusion turned out to be less promising than had been thought, and that led to budgets being tight. Lidsky's devastating critique was part of that (tokamaks not being as good as early hopes implied was another.)
> The cause is that fusion turned out to be less promising than had been thought
So did a whole lot of chemical rocketry. Instead of whining about it--we spent a lot of money on engineering, we made the Saturn V, and we went to the moon anyway.
The issue is that fusion only has one end point--providing energy. Researching chemical rocketry made better weapons--so we funded the snot out of it. The DOE spent billions on the Unconventional Gas Research Programs and lined a lot of pockets.
Funding isn't guaranteed to make progress, but lack of funding practically guarantees lack of progress.
Didn't the feasibility of fusion increase with advances in magnets. I thought the much stronger magnets being available today allowed for much smaller (volume per watt generated) systems, smaller even than the Iter design.
I'm a layperson like everyone else here, so I'm just going to rely on the fact that fusion research is ongoing, well-supported by government and private sector investment, and is an active area of research for hundreds or thousands of intelligent and sane institutionally supported academics, as reasonable and practical justifications for my belief that fusion is not quite as problematic as laid out in Lidsky's dated and superseded work.
However, for a sketch of how to address the talking points of the more strident objectors one encounters in the wild, one can perhaps turn to https://fire.pppl.gov/fusion_critic_response_stacey.pdf for some ideas. Cheers!
"Based on our present understanding, D-T tokamak fusion reactors project a cost-of-electricity that is about 50% larger than the projected cost-of-electricity from advanced light-water reactors in the middle of the next century."
We all know what happened to the projected cost of fission reactors -- the projections turned out to be hopelessly optimistic, because of complexity and loss of experience. Fusion would face these problems in even worse form (indeed, ITER's cost ballooned 4x or more past the initial projections.)
The experience with fission has enabled us to calibrate the optimism bias in these projections, with damning results.
Simply being competitive with fission is no longer good enough for fusion to succeed. It has to be significantly better than fission.
There has never been any serious expectation of getting usable power from fusion. All the reactor designs worked on in mainstream research would destroy themselves in a short time by high-energy neutron flux.
Fusion research is, instead, a jobs program for high-neutron flux physicists, to provide a pool to draw on for weapons work.
There are interesting commercial projects for designs that do not suffer from high neutron flux, such as those pursuing pB reactions. I read of another where neutrons are emitted in a place some distance from where the expensive machine parts are.
You can tell if a fusion process is serious by whether they have an answer to the neutron problem. Tokamak doesn't.
Some tokamaks do. MIT's ARC, for example, uses jointed superconducting tapes that let the reactor be opened up to replace the inner wall. That's done annually, and the wall is 3D-printed. Surrounding the inner wall is molten FLiBe salt, which acts as coolant, neutron absorber, and breeding blanket. Commonwealth Fusion is attempting to commercialize the design.
High neutron flux is useful not only for weapons but for civilian purposes too, for example for "burning" nuclear waste, or for fusion-fission hybrid reactors. I wonder why the Department of Energy does not invest more in this area.
Fusion-fission hybrids combine the worst features of both. There is no user "pull" for the concept. If you want power with fission, just build a fission reactor; that's going to be simpler, cheaper, and altogether more sensible. If you want to dispose of waste, just seal it in dry casks and wait a century or three before deciding what to do with it. That will also be much simpler and (due to nonzero interest rates) cheaper.
"Fusion in a magnetically-shielded-grid inertial electrostatic confinement device"
> Theory for a gridded inertial electrostatic confinement (IEC) fusion system is presented that shows a net energy gain is possible if the grid is magnetically shielded from ion impact. A simplified grid geometry is studied, consisting of two negatively-biased coaxial current-carrying rings, oriented such that their opposing magnetic fields produce a spindle cusp. Our analysis indicates that better than break-even performance is possible even in a deuterium-deuterium system at bench-top scales. The proposed device has the unusual property that it can avoid both the cusp losses of traditional magnetic fusion systems and the grid losses of traditional IEC configurations.
I’m still only a few pages in. I don’t have the chance to read it all right now, but I will revisit this tomorrow morning. Here are my early thoughts. Disclaimer: I am an advocate of fusion and am moving into the field (professional electrical engineering support of an academic project).
We need to walk before we can run. D+T fusion is viable. Hull maintenance is a solvable problem. Economic studies come after we can walk. Similarly, actually realizable designs that can reach Lawson performance necessary for p+B11 won’t come before designs that can reach D+T are made.
There are compelling narratives around funding, but ultimately it seems they are simultaneously overly optimistic about our technical advancement and overly jaded about future prospects.
It’s important to note that there is no difference in a reactor design capable of different fusion fuels, other than its Lawson performance. You can fuse D+T just the same as p+B11 if your device is capable of p+B11. There is not magical jump in performance we can make. So why skip over D+T if we need to go through it anyway? If D+T is found to truly not be economically viable (which sounds inherently flawed, since prices go down as technology becomes more advanced) then we could still pursue confinement devices in the hopes of reaching more advanced fuels.
So I’m a few pages further and I fear I will not be finishing this paper. I am surprised it was published and is still referenced. Where are the citations? Where is the analysis? You can’t just say “fusion reactors need to be ten times bigger than fission reactors”. It’s frankly embarrassing to MIT that they would allow egregious, unfounded claims to be published. Peer review exists to shred such unsupported statements.
This was a semi-popular article. You can find more technical analyses in the literature.
The specific points made in the article have stood the test of time. Lidsky said the power density of a DT fusion reactor would be at least an order of magnitude worse than that of a fission reactor. And if you look at existing reactors and concepts, this is true. Compare to a commercial PWR, in which (thermal power)/(volume of reactor vessel) is about 20 MW/m^3. An order of magnitude worse than that would be 2 MW/m^3. The (thermal power)/(reactor volume) for ITER is about 0.05 MW/m^3. For ARC and Lockheed's concepts, about 0.5 MW/m^3.
Your outrage should not be directed at this article (although such outrage is sadly understandable, if this article is telling you things you don't want to hear.) Instead, it should be directed at the fusion community as a whole, which has downplayed these critiques and glad-handed the issues raised while marching confidently into a dead end.
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Not to mention D+T has 2500 times higher power density than p+B11.
> So why skip over D+T if we need to go through it anyway?
Because much of what you'd end up doing to "do" D+T will be worthless for H+11B. Tokamaks, for example, are useless for H+11B.
Tokamaks may not even be viable for steady state D+T. The bootstrap current effect still needs to be explored further. Electrostatic confinement and inertial confinement are the only known viable options for p+B11. Electrostatic has serious issues related to conduction losses, but perhaps if they were large enough scaling laws may make them viable. It’s not well explored. Inertial confinement is getting a lot of funding and shows serious promise. However, inertial confinement is not a steady state design and its pulsed nature makes it difficult to make a power plant out of. No such engineering cliffs exist for tokamaks and stellarators. The performance just needs to keep marching towards success. Then the discussion of economics can begin in earnest.
1 reply →
This old critique has aged fairly well. It was too optimistic about advanced fission, and the suggestion to move to advanced fuels for fusion was mostly shot down by Lidsky's student, Todd Rider.
https://pdfs.semanticscholar.org/fce7/a35629488ec030d983025a...
https://dspace.mit.edu/handle/1721.1/11412
A similar critique was being made around the same time by Pfirsch and Schmitter in Europe.
https://pure.mpg.de/rest/items/item_2131865/component/file_2...
There are a few parts that have been overtaken by advances. Improvements in superconductors have driven the minimum size for a fusion reactor far down, for instance.
Lidsky's argument is entirely unaffected by that advance. The power of his argument is that one can just ignore the plasma physics.
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Commonwealth Fusion Systems was formed out of the work presented here: https://www.youtube.com/watch?v=KkpqA8yG9T4
A lot has changed since 1983. The superconducting materials that CFS depends on weren't even discovered until the late 80s, and it took a very long time for that to become practical. Fast-forward to today and you can buy this stuff on Alibaba!
Lidsky's arguments against fusion apply to the ARC design. Its overall volumetric power density is 0.5 MW/m^3, 40 times less than a PWR reactor vessel.
What defines the volume to get to that number? From what I can tell from the ARC specs the plasma volume is 141 m3, and the expected power output is 200-300 MWe, which makes it 1.5-2 MWe/m3.
Do you have some numbers on a PWR reactor vessel? I was trying to look up some details on the APR-1400, but could not find any.
1 reply →
We know what the issue is--fusion never got a useful amount of funding.
Now, it is entirely possible that even given an enormous amount of funding--fusion might still not work. However, engineers with lots of money are remarkably clever and effective beasts (see: radio, semiconductors, plastics, steel).
Fusion has been funded at "Fusion Never" levels for almost 40 years while we subsidize every other significant energy source to the tune of billions or trillions of dollars every single year. (For example, how much money got poured into the technology that became "fracking"?)
No, that's not what the issue is. That's an effect, not a cause. The cause is that fusion turned out to be less promising than had been thought, and that led to budgets being tight. Lidsky's devastating critique was part of that (tokamaks not being as good as early hopes implied was another.)
> The cause is that fusion turned out to be less promising than had been thought
So did a whole lot of chemical rocketry. Instead of whining about it--we spent a lot of money on engineering, we made the Saturn V, and we went to the moon anyway.
The issue is that fusion only has one end point--providing energy. Researching chemical rocketry made better weapons--so we funded the snot out of it. The DOE spent billions on the Unconventional Gas Research Programs and lined a lot of pockets.
Funding isn't guaranteed to make progress, but lack of funding practically guarantees lack of progress.
4 replies →
Didn't the feasibility of fusion increase with advances in magnets. I thought the much stronger magnets being available today allowed for much smaller (volume per watt generated) systems, smaller even than the Iter design.
I'm a layperson like everyone else here, so I'm just going to rely on the fact that fusion research is ongoing, well-supported by government and private sector investment, and is an active area of research for hundreds or thousands of intelligent and sane institutionally supported academics, as reasonable and practical justifications for my belief that fusion is not quite as problematic as laid out in Lidsky's dated and superseded work.
However, for a sketch of how to address the talking points of the more strident objectors one encounters in the wild, one can perhaps turn to https://fire.pppl.gov/fusion_critic_response_stacey.pdf for some ideas. Cheers!
In fact, section III of that document specifically rebuts The Trouble with Fusion, based on the state of knowledge 16 years later.
This is all you really need to read from Stacey:
"Based on our present understanding, D-T tokamak fusion reactors project a cost-of-electricity that is about 50% larger than the projected cost-of-electricity from advanced light-water reactors in the middle of the next century."
We all know what happened to the projected cost of fission reactors -- the projections turned out to be hopelessly optimistic, because of complexity and loss of experience. Fusion would face these problems in even worse form (indeed, ITER's cost ballooned 4x or more past the initial projections.)
The experience with fission has enabled us to calibrate the optimism bias in these projections, with damning results.
Simply being competitive with fission is no longer good enough for fusion to succeed. It has to be significantly better than fission.
There has never been any serious expectation of getting usable power from fusion. All the reactor designs worked on in mainstream research would destroy themselves in a short time by high-energy neutron flux.
Fusion research is, instead, a jobs program for high-neutron flux physicists, to provide a pool to draw on for weapons work.
There are interesting commercial projects for designs that do not suffer from high neutron flux, such as those pursuing pB reactions. I read of another where neutrons are emitted in a place some distance from where the expensive machine parts are.
You can tell if a fusion process is serious by whether they have an answer to the neutron problem. Tokamak doesn't.
Some tokamaks do. MIT's ARC, for example, uses jointed superconducting tapes that let the reactor be opened up to replace the inner wall. That's done annually, and the wall is 3D-printed. Surrounding the inner wall is molten FLiBe salt, which acts as coolant, neutron absorber, and breeding blanket. Commonwealth Fusion is attempting to commercialize the design.
High neutron flux is useful not only for weapons but for civilian purposes too, for example for "burning" nuclear waste, or for fusion-fission hybrid reactors. I wonder why the Department of Energy does not invest more in this area.
Fusion-fission hybrids combine the worst features of both. There is no user "pull" for the concept. If you want power with fission, just build a fission reactor; that's going to be simpler, cheaper, and altogether more sensible. If you want to dispose of waste, just seal it in dry casks and wait a century or three before deciding what to do with it. That will also be much simpler and (due to nonzero interest rates) cheaper.
1 reply →
You are referring to TAE's design. The people behind that were told 20+ years ago the concept would not work.
https://www.researchgate.net/profile/Wallace_Manheimer/publi...
http://w3fusion.ph.utexas.edu/ifs/ifsreports/919_wong.pdf
The concerns and criticism make too much sense; as much as I want to believe a comic/movie density power solution (like arc reactors) can work...
I think the criticisms would have gone over better if something more than the implicit: 'look for better ideas' proposal had been included as a path.
It's been over 30 years; is there anything else as an idea in the field of power generation? (Preferably something we could also use in space)
"Fusion in a magnetically-shielded-grid inertial electrostatic confinement device"
> Theory for a gridded inertial electrostatic confinement (IEC) fusion system is presented that shows a net energy gain is possible if the grid is magnetically shielded from ion impact. A simplified grid geometry is studied, consisting of two negatively-biased coaxial current-carrying rings, oriented such that their opposing magnetic fields produce a spindle cusp. Our analysis indicates that better than break-even performance is possible even in a deuterium-deuterium system at bench-top scales. The proposed device has the unusual property that it can avoid both the cusp losses of traditional magnetic fusion systems and the grid losses of traditional IEC configurations.
https://arxiv.org/abs/1510.01788