4 ms·

Could you explain why or link a relevant source?

pfdietz 7y ago
ITER has a design gross fusion power of about 400 MW. If you compute the thermal power/volume ratio of the reactor, it's about 50 kW/m^3. In comparison, the thermal power/volume ratio of a commercial PWR fission reactor is about 20 MW/m^3 -- 400 times higher. A commercial tokamak would have a somewhat higher power, but not enormously higher. If based on ITER, the power density would be two orders of magnitude worse than a fission reactor. And since the complexity of a fusion reactor is far higher than a fission reactor core, the cost ratio of the reactors (for a given power output) would be even larger. Since fission reactors are having desperate trouble being competitive today, how is making the reactor core orders of magnitude more expensive going to lead anywhere useful?
- Ygg2 7y ago
  I believe your assumptions are faulty. Nothing about ITER suggest that it's volume or performance is indicative of what future reactor design will look like. Stronger super-magnets, different designs could lead to smaller reactors. As to why is it useful? A zero emissions powerplant, with minimal environment impact that is immune to core meltdown. Sure we don't have the tech to build it profitabily. Yet. But doesn't mean we never will.
  - socialdemocrat 7y ago
    I support the effort, but in terms of solving global warming problems this is IMHO a total dead end. The progress is far too slow. It takes far too long time to build these reactors. They are expensive and complicated. Say we get commercial reactors in 2050. If these are anything like building fission reactors, we will start getting these commercial reactors online in 2060. That is very late. Within that time we can massively expand solar power and wind power. As renewable energy start dominating the grid, ultra low spot prices on power will spur a huge cottage industry of businesses relying on buying this power cheap, storing it and selling it later. Alternatively factories will be built to take advantage of it. E.g. only running power hungry processes in periods of low power prices.
    - Ygg2 7y ago
      Sure. But you will need power after 2060. Just because you went neutral doesn't mean you suddenly don't need extra energy. ATM fission, with its Chernobyl and Fukushima is still safer than solar and wind. And overall better for environment. Fusion in theory promises even more - low environment impact plus no risk of disaster. I don't see variability as a positive trait. From what I remember, renewables, really suck for the grid, as it wasn't designed for too much variability or diffusion in mind.
      - pfdietz 7y ago
        Given the rate of decline of cost of renewables, a fission reactor anything like ITER by 2060 will be museumware. I don't think DEMO is ever getting built, btw. I suspect ITER is not going to have a very happy operational experience either (disruptions, maintainability). If ITER cannot effectively control disruptions they won't ever operate it with DT. The idea that "renewables suck for the grid" is not correct. The very low levelized price of renewables means there's a lot of economic headroom to deal with intermittency.
        Ygg2 7y ago
        > Given the rate of decline of cost of renewables, Don't mistake current trends for future prognosis. Even if costs are falling at the moment, there is no reason future fusion technology will be museumware. At worst we'll discover new data on plasma behavior. At best we have a possible tech for colonizing the Milky Way. > I don't think DEMO is ever getting built, It's ok. I don't think we'll transfer to renewables before it's too late anyway. > The very low levelized price of renewables means there's a lot of economic headroom to deal with intermittency. So you're saying that economics will change grid design? That grids designed for single way of transmitting energy will somehow reconfigure to allow consumers to stream energy to the source?
        pfdietz 7y ago
        The trend of decreasing costs for PV has followed an empirical experience curve for decades, with an exponent of about -0.2 (giving cost as a function of cumulative production). There are perennially assertions this trend has ended, but those assertions have never been correct. Is there any reason to think they will be correct now? I assert no: PV modules are still well away from the costs of the material and energy inputs. I'll add that fusion economic studies have to posit large learning effects as well, so the "N-th of a Kind" plant is much cheaper than the first. And there, this assumption is dubious, since the closest technology (fission) has not shown good learning effects. That's why fission is failing now -- any technology that doesn't improve eventually gets killed as the competition does. > It's ok. I don't think we'll transfer to renewables before it's too late anyway. And you think the transition to fusion would be FASTER? My mind boggles at your double think. > So you're saying that economics will change grid design? That grids designed for single way of transmitting energy will somehow reconfigure to allow consumers to stream energy to the source? It's bizarre you think dealing with intermittency would require impossible, or even particularly difficult, changes. If you notice, grids are already becoming smarter, with power markets dispatching on short term prices. Storage and dispatchable demand fit nicely into this system. The market is going to force things in the right direction, which is renewables/storage and not high cost baseload sources.
- T-A 7y ago
  Let me guess: you implicitly assume that cost is proportional to volume, because that is roughly true for a fission reactor, which is filled with fuel and control rods. But in a tokamak reactor, you have a large container with all the expensive engineered stuff placed around its surface, so cost should be roughly proportional to surface area, or volume^(2/3).
  - pfdietz 7y ago
    Fusion reactors are MUCH more complex than fission reactors. So, just comparing volume is being very favorable to fusion. There should be a complexity multiplier in there as well, but that's difficult to quantify. This complexity also means keeping that fusion reactor running would be a nightmare. Complex things break, and the fusion reactor will be so irradiated that hands on maintenance will be impossible. I will add that fission power plants are uncompetitive even if you ignore the cost of the reactor itself.
    - T-A 7y ago
      > Fusion reactors are MUCH more complex than fission reactors. So, just comparing volume is being very favorable to fusion. That's a non sequitur. Your volume comparison can, at best, tell you how cost scales with reactor power. If the exponent is wrong, it serves no valid purpose at all.
      - pfdietz 7y ago
        Complex things being more expensive than simple things is a non sequitur? Surely your apparent position, that something made of superconductors is going to be just as cheap as something made of steel, is much more supportable! /s And I wasn't talking about an exponent there.
        T-A 7y ago
        > Complex things being more expensive than simple things is a non sequitur? No. The statement "Fusion reactors are MUCH more complex than fission reactors." followed by "So, just comparing volume is being very favorable to fusion." is a non sequitur. > And I wasn't talking about an exponent there. Your compared power/volume ratio, implying that cost is proportional to volume (otherwise, the comparison is pointless). I pointed out that the different operating principles of fission and fusion reactors suggest cost proportional to volume^(2/3) for the latter (which of course implies that there is a size beyond which a fusion reactor will be more cost efficient than a fission one). The 2/3 is known as an exponent. I believe exponents are part of the K-12 math curriculum, and definitely propaedeutic to nuclear engineering.

ITER has a design gross fusion power of about 400 MW. If you compute the thermal power/volume ratio of the reactor, it's about 50 kW/m^3. In comparison, the thermal power/volume ratio of a commercial PWR fission reactor is about 20 MW/m^3 -- 400 times higher. A commercial tokamak would have a somewhat higher power, but not enormously higher. If based on ITER, the power density would be two orders of magnitude worse than a fission reactor. And since the complexity of a fusion reactor is far higher than a fission reactor core, the cost ratio of the reactors (for a given power output) would be even larger. Since fission reactors are having desperate trouble being competitive today, how is making the reactor core orders of magnitude more expensive going to lead anywhere useful?

Ygg2 7y ago
I believe your assumptions are faulty. Nothing about ITER suggest that it's volume or performance is indicative of what future reactor design will look like. Stronger super-magnets, different designs could lead to smaller reactors. As to why is it useful? A zero emissions powerplant, with minimal environment impact that is immune to core meltdown. Sure we don't have the tech to build it profitabily. Yet. But doesn't mean we never will.
- socialdemocrat 7y ago
  I support the effort, but in terms of solving global warming problems this is IMHO a total dead end. The progress is far too slow. It takes far too long time to build these reactors. They are expensive and complicated. Say we get commercial reactors in 2050. If these are anything like building fission reactors, we will start getting these commercial reactors online in 2060. That is very late. Within that time we can massively expand solar power and wind power. As renewable energy start dominating the grid, ultra low spot prices on power will spur a huge cottage industry of businesses relying on buying this power cheap, storing it and selling it later. Alternatively factories will be built to take advantage of it. E.g. only running power hungry processes in periods of low power prices.
  - Ygg2 7y ago
    Sure. But you will need power after 2060. Just because you went neutral doesn't mean you suddenly don't need extra energy. ATM fission, with its Chernobyl and Fukushima is still safer than solar and wind. And overall better for environment. Fusion in theory promises even more - low environment impact plus no risk of disaster. I don't see variability as a positive trait. From what I remember, renewables, really suck for the grid, as it wasn't designed for too much variability or diffusion in mind.
    - pfdietz 7y ago
      Given the rate of decline of cost of renewables, a fission reactor anything like ITER by 2060 will be museumware. I don't think DEMO is ever getting built, btw. I suspect ITER is not going to have a very happy operational experience either (disruptions, maintainability). If ITER cannot effectively control disruptions they won't ever operate it with DT. The idea that "renewables suck for the grid" is not correct. The very low levelized price of renewables means there's a lot of economic headroom to deal with intermittency.
      - Ygg2 7y ago
        > Given the rate of decline of cost of renewables, Don't mistake current trends for future prognosis. Even if costs are falling at the moment, there is no reason future fusion technology will be museumware. At worst we'll discover new data on plasma behavior. At best we have a possible tech for colonizing the Milky Way. > I don't think DEMO is ever getting built, It's ok. I don't think we'll transfer to renewables before it's too late anyway. > The very low levelized price of renewables means there's a lot of economic headroom to deal with intermittency. So you're saying that economics will change grid design? That grids designed for single way of transmitting energy will somehow reconfigure to allow consumers to stream energy to the source?
        pfdietz 7y ago
        The trend of decreasing costs for PV has followed an empirical experience curve for decades, with an exponent of about -0.2 (giving cost as a function of cumulative production). There are perennially assertions this trend has ended, but those assertions have never been correct. Is there any reason to think they will be correct now? I assert no: PV modules are still well away from the costs of the material and energy inputs. I'll add that fusion economic studies have to posit large learning effects as well, so the "N-th of a Kind" plant is much cheaper than the first. And there, this assumption is dubious, since the closest technology (fission) has not shown good learning effects. That's why fission is failing now -- any technology that doesn't improve eventually gets killed as the competition does. > It's ok. I don't think we'll transfer to renewables before it's too late anyway. And you think the transition to fusion would be FASTER? My mind boggles at your double think. > So you're saying that economics will change grid design? That grids designed for single way of transmitting energy will somehow reconfigure to allow consumers to stream energy to the source? It's bizarre you think dealing with intermittency would require impossible, or even particularly difficult, changes. If you notice, grids are already becoming smarter, with power markets dispatching on short term prices. Storage and dispatchable demand fit nicely into this system. The market is going to force things in the right direction, which is renewables/storage and not high cost baseload sources.
T-A 7y ago
Let me guess: you implicitly assume that cost is proportional to volume, because that is roughly true for a fission reactor, which is filled with fuel and control rods. But in a tokamak reactor, you have a large container with all the expensive engineered stuff placed around its surface, so cost should be roughly proportional to surface area, or volume^(2/3).
- pfdietz 7y ago
  Fusion reactors are MUCH more complex than fission reactors. So, just comparing volume is being very favorable to fusion. There should be a complexity multiplier in there as well, but that's difficult to quantify. This complexity also means keeping that fusion reactor running would be a nightmare. Complex things break, and the fusion reactor will be so irradiated that hands on maintenance will be impossible. I will add that fission power plants are uncompetitive even if you ignore the cost of the reactor itself.
  - T-A 7y ago
    > Fusion reactors are MUCH more complex than fission reactors. So, just comparing volume is being very favorable to fusion. That's a non sequitur. Your volume comparison can, at best, tell you how cost scales with reactor power. If the exponent is wrong, it serves no valid purpose at all.
    - pfdietz 7y ago
      Complex things being more expensive than simple things is a non sequitur? Surely your apparent position, that something made of superconductors is going to be just as cheap as something made of steel, is much more supportable! /s And I wasn't talking about an exponent there.
      - T-A 7y ago
        > Complex things being more expensive than simple things is a non sequitur? No. The statement "Fusion reactors are MUCH more complex than fission reactors." followed by "So, just comparing volume is being very favorable to fusion." is a non sequitur. > And I wasn't talking about an exponent there. Your compared power/volume ratio, implying that cost is proportional to volume (otherwise, the comparison is pointless). I pointed out that the different operating principles of fission and fusion reactors suggest cost proportional to volume^(2/3) for the latter (which of course implies that there is a size beyond which a fusion reactor will be more cost efficient than a fission one). The 2/3 is known as an exponent. I believe exponents are part of the K-12 math curriculum, and definitely propaedeutic to nuclear engineering.