6 ms·

It was mainly an engineering issue: materials, manufacturing and assembling. It is too big to fail right now, and most issues have been solved. It never was as

by DrNuke 6y ago

It was mainly an engineering issue: materials, manufacturing and assembling. It is too big to fail right now, and most issues have been solved. It never was as simple as webinars from scientists would make it. The funniest joke within nuclear eng insiders is the marvels of paper reactors pretty always make real reactors just seem glorified boilers.

cromwellian 6y ago
ITER's too big the fail. But again, the parameters were known. The magnets give you the field strength, the field strength tells you the radius, the radius^3 gives you the cost, and also, some measure of the construction time. This is one of the great things about Elon Musk -- he looks at things from first principles. When it looked like he needed 1000 Gigafactories to reach his goal, he went back to the drawing board on decades of battery manufacturing, to come up with the Terafactory. When carbon composite rockets looked to be too hard to manufacture, and have too many other detriments, despite the clear wins in strength-to-weight, he dropped it and went with stainless steel. I'm pretty sure if he was staring at the basic Tokamak equations, he would have long again saw the economic and time dependence on R, and the massive benefits to improving B, and that would have driven him to look for alternatives. Too many researchers engage in sunk cost / dollar auctions, doubling down on obvious wrong approaches, because they've already spent so much. This is also why DeepMind won CASP again, because rather than try to iteratively improve their 2018 result, they dropped it as a dead end and restarted with a completely new approach, even though the 2018 approach was also a revolutionary breakthrough. What I'm getting at is, being able to let go of your previous projects if they are stalling, with huge cost over runs, and a mediocre future return, is a value we should seek in fusion research, and elsewhere.
- DrNuke 6y ago
  Ok but ITER was much more than engineering: soft diplomacy, supranational bureaucracy, manufacturing modernisation. Musk comes from a different era and a different environment but, again, launching rockets successfully, with humans in them safely going and coming back, was achieved well before him. Stable nuclear fusion is still unclaimed as a milestone, even if sustainable nuclear fusion might well come from different, smaller approaches the likes we are seeing from United Kingdom and South Korea.
- pfdietz 6y ago
  Going back to first principles is how you conclude DT fusion is a dead end. And this has been known for decades. http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trouble-With-Fusion_MIT_Tech_Review_1983.pdf http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trou... (That prescient article has stood the test of time, except that advanced fuels were mostly ruled out also.)
  - cromwellian 6y ago
    Except the article is wrong, because it makes fundamental assumptions about the vacuum wall and lithium blanket, and even the superconductors. The ARC reactor, for example, doesn't use a solid sandwich style blanket, it uses a volumetric blanket of FLiBe, a liquid that acts as the moderator that absorbs neutrons, the breeder, the magnetic shield, and the heat exchanger -- and has proven to work in molten salt reactor prototypes. And unlike the designs he claims that are "essentially unchanged", this significantly reduces the cost and mass of the reactor, reduces the so-called "danger" of lithium, and leverages the fact that high energy fusion neutrons travel further, as it increases the efficacy of the liquid blanket. The claim that neutrons will damage the metal structure is also handled by many aspects of the design: easy reparability thanks to modular, segmented magnets, being completely submerged in the liquid blanket, low activation steel for structure, and the pulse design which runs the reactor in a way that reduces overall temperature of the walls. Plus, he brings up the ole aneutronic fusion dream, except that creating a confined Boron-11 plasma is much more difficult, outside the realm of tokamaks, and typically proposes using laser internal confinement fusion at the Petawatt scale. More than 20 papers were published on ARC, heavily vetted in journals like Nature, and pretty much all of the peer review concluded the design will work, and if it does work, then it will be much cheaper than ITER, simpler than ITER, and thus refute your paper. We'll know in about 4 years.
    - pfdietz 6y ago
      No. The article makes no assumptions about superconductors. The argument makes no assumption even about plasma confinement. It's all about the limits on areal power density at the reactor walls. The conclusion he reaches, that fusion reactors will have a volumetric power density at least an order of magnitude lower than a fission reactor, is not contradicted by ARC. The volumetric power density of ARC (from the ARC paper I linked to elsewhere in these comments) is 0.5 MW(th)/m^3 (counting the volume of the entire reactor, not just the plasma) vs. 20 MW(th)/m^3 for the primary reactor vessel of a PWR -- a factor of 40 worse. His suggestion to look at aneutronic plasmas didn't pan out, as you note, but that doesn't save DT fusion. I'll note that it's his PhD student Todd Rider who shot down the non-Maxwellian schemes that aneutronic fuels would have needed. After that, Lidsky switched to working on fission for the rest of career and life.

by DrNuke 6y ago

cromwellian 6y ago

ITER's too big the fail. But again, the parameters were known. The magnets give you the field strength, the field strength tells you the radius, the radius^3 gives you the cost, and also, some measure of the construction time. This is one of the great things about Elon Musk -- he looks at things from first principles. When it looked like he needed 1000 Gigafactories to reach his goal, he went back to the drawing board on decades of battery manufacturing, to come up with the Terafactory. When carbon composite rockets looked to be too hard to manufacture, and have too many other detriments, despite the clear wins in strength-to-weight, he dropped it and went with stainless steel. I'm pretty sure if he was staring at the basic Tokamak equations, he would have long again saw the economic and time dependence on R, and the massive benefits to improving B, and that would have driven him to look for alternatives. Too many researchers engage in sunk cost / dollar auctions, doubling down on obvious wrong approaches, because they've already spent so much. This is also why DeepMind won CASP again, because rather than try to iteratively improve their 2018 result, they dropped it as a dead end and restarted with a completely new approach, even though the 2018 approach was also a revolutionary breakthrough. What I'm getting at is, being able to let go of your previous projects if they are stalling, with huge cost over runs, and a mediocre future return, is a value we should seek in fusion research, and elsewhere.

DrNuke 6y ago
Ok but ITER was much more than engineering: soft diplomacy, supranational bureaucracy, manufacturing modernisation. Musk comes from a different era and a different environment but, again, launching rockets successfully, with humans in them safely going and coming back, was achieved well before him. Stable nuclear fusion is still unclaimed as a milestone, even if sustainable nuclear fusion might well come from different, smaller approaches the likes we are seeing from United Kingdom and South Korea.
pfdietz 6y ago
Going back to first principles is how you conclude DT fusion is a dead end. And this has been known for decades. http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trouble-With-Fusion_MIT_Tech_Review_1983.pdf http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trou... (That prescient article has stood the test of time, except that advanced fuels were mostly ruled out also.)
- cromwellian 6y ago
  Except the article is wrong, because it makes fundamental assumptions about the vacuum wall and lithium blanket, and even the superconductors. The ARC reactor, for example, doesn't use a solid sandwich style blanket, it uses a volumetric blanket of FLiBe, a liquid that acts as the moderator that absorbs neutrons, the breeder, the magnetic shield, and the heat exchanger -- and has proven to work in molten salt reactor prototypes. And unlike the designs he claims that are "essentially unchanged", this significantly reduces the cost and mass of the reactor, reduces the so-called "danger" of lithium, and leverages the fact that high energy fusion neutrons travel further, as it increases the efficacy of the liquid blanket. The claim that neutrons will damage the metal structure is also handled by many aspects of the design: easy reparability thanks to modular, segmented magnets, being completely submerged in the liquid blanket, low activation steel for structure, and the pulse design which runs the reactor in a way that reduces overall temperature of the walls. Plus, he brings up the ole aneutronic fusion dream, except that creating a confined Boron-11 plasma is much more difficult, outside the realm of tokamaks, and typically proposes using laser internal confinement fusion at the Petawatt scale. More than 20 papers were published on ARC, heavily vetted in journals like Nature, and pretty much all of the peer review concluded the design will work, and if it does work, then it will be much cheaper than ITER, simpler than ITER, and thus refute your paper. We'll know in about 4 years.
  - pfdietz 6y ago
    No. The article makes no assumptions about superconductors. The argument makes no assumption even about plasma confinement. It's all about the limits on areal power density at the reactor walls. The conclusion he reaches, that fusion reactors will have a volumetric power density at least an order of magnitude lower than a fission reactor, is not contradicted by ARC. The volumetric power density of ARC (from the ARC paper I linked to elsewhere in these comments) is 0.5 MW(th)/m^3 (counting the volume of the entire reactor, not just the plasma) vs. 20 MW(th)/m^3 for the primary reactor vessel of a PWR -- a factor of 40 worse. His suggestion to look at aneutronic plasmas didn't pan out, as you note, but that doesn't save DT fusion. I'll note that it's his PhD student Todd Rider who shot down the non-Maxwellian schemes that aneutronic fuels would have needed. After that, Lidsky switched to working on fission for the rest of career and life.