6 ms·

> Tokamak fusion can only ever be far more expensive, per watt and per watt-hour, than existing fission. Why?

ncmncm 5y ago
The energy flux density in the most compressed plasma imaginable is orders of magnitude less than in fissile uranium. So, to match power out, it has to be big. Really, really big. And a fusion reaction chamber is a much more expensive affair than a fission pile: super high-tech materials and construction, enormous magnets (blasted by the hot-neutron flux output), piping for thousands of tons of melted lithium that have to be replaced (by robots! because super radioactive) every couple of years as the neutrons destroy them. The (radioactive) lithium itself, and containment for if it breaks out of the piping. Continuous processing of the lithium to extract synthetic tritium for fuel. Heat exchangers for lithium to a working fluid that won't pick up radioactivity, and more heat exchangers from that to water for steam. And then the usual steam turbines, which demand regular, very expensive maintenance. Cooling towers to condense the steam, after. A hundred billion dollars estimated for one several GW plant, and decades for construction. Meanwhile, solar and wind get cheaper every year, with no bottom in sight. The longer they take on fusion, the less competitive it gets, and it starts out way behind, with no possibility of ever catching up.
- _0w8t 5y ago
  This was with previous designs of fusion reactors. Read about proposed Ark and currently constructing Spark reactors. By using stronger superconductive magnets it was possible to reduce the size of the plant by order of magnitude. Spark even has a chance to get to Q>1 before ITER and it’s chamber is less than 2m in diameter. Plus it is possible to replace its parts without disassembling the whole reactor. [1] - https://en.m.wikipedia.org/wiki/SPARC_(tokamak) https://en.m.wikipedia.org/wiki/SPARC_(tokamak)
  - ncmncm 5y ago
    That might be nice if they had solutions to the other problems not addressed (see above). But operating it will necessarily still be enormously more expensive than solar or wind, which cost practically nothing. Somebody with one leg can do a lot better in a race than somebody with none, but that is not the measure to consider when the competition is with two-legged runners. (Hint: they win.)
    - _0w8t 5y ago
      In Europe after the last autumn when for months there were little wind and cloudy sky there is a realization that energy based purely on renewables will require much bigger storage and much more solar or at least significantly more expensive solar that works under clouds. Doable, but cost is non-trivial. So if any of fusion startups can make operating plant within the next 20 years, it can be used. But if that takes longer, then I agree that large-scale fusion will not happen.
      - pfdietz 5y ago
        Long term darkness/calm is solved with hydrogen. Europe has plenty of underground geology suitable for mass hydrogen storage (it's just like natural gas is stored.) Most of the energy still would go directly from solar/wind to the grid, or through efficient batteries, so the low round trip efficiency of power to gas to power doesn't matter much.
        gmueckl 5y ago
        If hydrogen is produced from electricity at scale, it won't be used for energy storage. It'll get sold to chemical plants first. They'll pay good prices.
        pfdietz 5y ago
        Yes, surely that will be a major market. It just makes the case easier for renewables, as that's a major source of dispatchable demand that can smooth variation in renewable output without having to pay a cost for turning it back to electric power later.
  - panick21_ 5y ago
    Compare that to a simple molten salt fission reactor. It will simply never be cheaper.
    - _0w8t 5y ago
      Molten solt reactors do not solve the problem of nuclear waste. It is very expensive to deal with it as it has to be stored for hundreds of years unless some technology would appear to separate that cheaply. Fusion produce like order of magnitude less radioactive waste which will be short-lived. Plus a fusion plant can be very quick to start and shutdown or throttle down which is very useful for base load.
      - panick21_ 5y ago
        Molten salt reactors inherently don't. But you can burn up higher actinides resulting in waste that only needs to be stored a few 100 years and pose very little danger even in the most absurd scenarios. You don't need to separate all the different parts. You reprocess our old waste into fuel for modern reactors. In those reactors higher actinides will be burned up. And the resulting output does not have higher actinides and only needs to be stored as long. Moltex Energy is currently engaged with the Canadian regulator for such a facility, the process is called WATSS. Doing this is actually cheaper then the deep storage storage facilities proposed in many countries. Sadly because of political bullshit reprocessing has been made illegal in the US. Such things would have been doable decades ago, and the money for it is already on bank accounts in most countries. But politician force the 'dig a hole for everything' solutions instead. > Plus a fusion plant can be very quick to start and shutdown or throttle down which is very useful for base load. Next generation fusion would also be very reactive to changes. Far more then traditional. But the reality is you actually want to run full power as much as you can, no matter if fission or fusion.
      - pfdietz 5y ago
        Nuclear waste is not the major problem with fission, capital cost is. Fusion solves a minor problem of fission while making the major problem worse. It's a great example of misplaced focus. Cooling down the magnets of a fusion plant is not a quick process, btw. Hell, just getting a fusion plant built with RAFM steel up to operating temperature is a delicate process. Once irradiated, the temperature window that material can operate at is rather narrow (300 C to 550 C; below that it's too brittle and above that it creeps.)
  - pfdietz 5y ago
    You are making a commonly seen mistake there. Yes, making magnetic fields stronger can give one higher power density than ITER. But one runs into a limit because of power density at the wall. Once you're at that limit, higher magnetic fields don't really help. ARC's volumetric thermal power density (volume of reactor, not of the plasma) is just 1/40th that of the primary reactor vessel of a commercial pressurized water fission reactor. 60% of the mass of an ARC reactor is in the steel structural supports for the magnets, so it's about at the upper limit for steady magnetic fields in a fusion reactor.
- Aeolun 5y ago
  I find it hard to believe that people would be seriously researching this if we already knew there could never be any sensible commercial application. More likely we just don’t know the way to make it viable yet.
  - ncmncm 5y ago
    In some hypothetically possible world, policy choices are based the best reasoning from the latest information. We, alas, live in this world, where policy is mainly a product of history. The H bomb legacy looms large here. We are in the position of the person whose car keys were lost somewhere, but we are looking only under the D-T fusion streetlight because we can't see anywhere else.
- marcosdumay 5y ago
  > So, to match power out, it has to be big. Really, really big. Fusion has all of the characteristics of something you'll want to do if you are in space. Add to that the fact that its fuel is much easier to acquire than fission and that solar isn't available everywhere and you have a winner. Meanwhile down to Earth, yes, most likely it will never be an important energy source.
  - pfdietz 5y ago
    I must strongly disagree, particularly for DT fusion. DT fusion reactors would be very heavy. ARC, for example, would have the weight of a couple of US WW2 destroyers. DT fusion delivers its energy as heat. A fission reactor would be far smaller, simpler, cheaper, and more reliable. You might make the case for advanced fuels, but that likely means you have to get 3He from somewhere. I suspect beamed power will beat even advanced fuel fusion in all missions in the future (a weak prediction as I will not be around to see.)
  - Paradigma11 5y ago
    But you dont need a lot of fuel for fission and you also need many other things to keep a ship/station running. Isnt fuel in the ballpark of just one of many consumables that you need?
    - ncmncm 5y ago
      Fission-powered ion propulsion is the best mature tech we have. In space, the fission doesn't need containment, or even much shielding if it is far enough away from the rest of the ship. In the cloud tops of Titan, Venus, Saturn, Uranus, or Neptune, a nuclear power plant may be as simple as a naked pile suspended near the bottom of a big fabric tube with wind turbines at the top. The radioactively-heated, buoyant air inside holds it up, and, escaping through the turbine, generates power. (Enough is held back so it stays up.) Perhaps surprisingly, gravity is almost Earth-normal on all four planets. Perhaps more surprisingly, the temperature at a not unreasonably-high pressure is also close to Earth-normal (except on Titan). But getting back to orbit from any of the last three would be very, very difficult, so such a reactor would only ever power robots. Getting back to orbit from Titan is easy. From Venus, it is pretty hard; and once in orbit you would need to refuel to get anywhere else.

The energy flux density in the most compressed plasma imaginable is orders of magnitude less than in fissile uranium. So, to match power out, it has to be big. Really, really big. And a fusion reaction chamber is a much more expensive affair than a fission pile: super high-tech materials and construction, enormous magnets (blasted by the hot-neutron flux output), piping for thousands of tons of melted lithium that have to be replaced (by robots! because super radioactive) every couple of years as the neutrons destroy them. The (radioactive) lithium itself, and containment for if it breaks out of the piping. Continuous processing of the lithium to extract synthetic tritium for fuel. Heat exchangers for lithium to a working fluid that won't pick up radioactivity, and more heat exchangers from that to water for steam. And then the usual steam turbines, which demand regular, very expensive maintenance. Cooling towers to condense the steam, after. A hundred billion dollars estimated for one several GW plant, and decades for construction. Meanwhile, solar and wind get cheaper every year, with no bottom in sight. The longer they take on fusion, the less competitive it gets, and it starts out way behind, with no possibility of ever catching up.

_0w8t 5y ago
This was with previous designs of fusion reactors. Read about proposed Ark and currently constructing Spark reactors. By using stronger superconductive magnets it was possible to reduce the size of the plant by order of magnitude. Spark even has a chance to get to Q>1 before ITER and it’s chamber is less than 2m in diameter. Plus it is possible to replace its parts without disassembling the whole reactor. [1] - https://en.m.wikipedia.org/wiki/SPARC_(tokamak) https://en.m.wikipedia.org/wiki/SPARC_(tokamak)
- ncmncm 5y ago
  That might be nice if they had solutions to the other problems not addressed (see above). But operating it will necessarily still be enormously more expensive than solar or wind, which cost practically nothing. Somebody with one leg can do a lot better in a race than somebody with none, but that is not the measure to consider when the competition is with two-legged runners. (Hint: they win.)
  - _0w8t 5y ago
    In Europe after the last autumn when for months there were little wind and cloudy sky there is a realization that energy based purely on renewables will require much bigger storage and much more solar or at least significantly more expensive solar that works under clouds. Doable, but cost is non-trivial. So if any of fusion startups can make operating plant within the next 20 years, it can be used. But if that takes longer, then I agree that large-scale fusion will not happen.
    - pfdietz 5y ago
      Long term darkness/calm is solved with hydrogen. Europe has plenty of underground geology suitable for mass hydrogen storage (it's just like natural gas is stored.) Most of the energy still would go directly from solar/wind to the grid, or through efficient batteries, so the low round trip efficiency of power to gas to power doesn't matter much.
      - gmueckl 5y ago
        If hydrogen is produced from electricity at scale, it won't be used for energy storage. It'll get sold to chemical plants first. They'll pay good prices.
        pfdietz 5y ago
        Yes, surely that will be a major market. It just makes the case easier for renewables, as that's a major source of dispatchable demand that can smooth variation in renewable output without having to pay a cost for turning it back to electric power later.
- panick21_ 5y ago
  Compare that to a simple molten salt fission reactor. It will simply never be cheaper.
  - _0w8t 5y ago
    Molten solt reactors do not solve the problem of nuclear waste. It is very expensive to deal with it as it has to be stored for hundreds of years unless some technology would appear to separate that cheaply. Fusion produce like order of magnitude less radioactive waste which will be short-lived. Plus a fusion plant can be very quick to start and shutdown or throttle down which is very useful for base load.
    - panick21_ 5y ago
      Molten salt reactors inherently don't. But you can burn up higher actinides resulting in waste that only needs to be stored a few 100 years and pose very little danger even in the most absurd scenarios. You don't need to separate all the different parts. You reprocess our old waste into fuel for modern reactors. In those reactors higher actinides will be burned up. And the resulting output does not have higher actinides and only needs to be stored as long. Moltex Energy is currently engaged with the Canadian regulator for such a facility, the process is called WATSS. Doing this is actually cheaper then the deep storage storage facilities proposed in many countries. Sadly because of political bullshit reprocessing has been made illegal in the US. Such things would have been doable decades ago, and the money for it is already on bank accounts in most countries. But politician force the 'dig a hole for everything' solutions instead. > Plus a fusion plant can be very quick to start and shutdown or throttle down which is very useful for base load. Next generation fusion would also be very reactive to changes. Far more then traditional. But the reality is you actually want to run full power as much as you can, no matter if fission or fusion.
    - pfdietz 5y ago
      Nuclear waste is not the major problem with fission, capital cost is. Fusion solves a minor problem of fission while making the major problem worse. It's a great example of misplaced focus. Cooling down the magnets of a fusion plant is not a quick process, btw. Hell, just getting a fusion plant built with RAFM steel up to operating temperature is a delicate process. Once irradiated, the temperature window that material can operate at is rather narrow (300 C to 550 C; below that it's too brittle and above that it creeps.)
- pfdietz 5y ago
  You are making a commonly seen mistake there. Yes, making magnetic fields stronger can give one higher power density than ITER. But one runs into a limit because of power density at the wall. Once you're at that limit, higher magnetic fields don't really help. ARC's volumetric thermal power density (volume of reactor, not of the plasma) is just 1/40th that of the primary reactor vessel of a commercial pressurized water fission reactor. 60% of the mass of an ARC reactor is in the steel structural supports for the magnets, so it's about at the upper limit for steady magnetic fields in a fusion reactor.
Aeolun 5y ago
I find it hard to believe that people would be seriously researching this if we already knew there could never be any sensible commercial application. More likely we just don’t know the way to make it viable yet.
- ncmncm 5y ago
  In some hypothetically possible world, policy choices are based the best reasoning from the latest information. We, alas, live in this world, where policy is mainly a product of history. The H bomb legacy looms large here. We are in the position of the person whose car keys were lost somewhere, but we are looking only under the D-T fusion streetlight because we can't see anywhere else.
marcosdumay 5y ago
> So, to match power out, it has to be big. Really, really big. Fusion has all of the characteristics of something you'll want to do if you are in space. Add to that the fact that its fuel is much easier to acquire than fission and that solar isn't available everywhere and you have a winner. Meanwhile down to Earth, yes, most likely it will never be an important energy source.
- pfdietz 5y ago
  I must strongly disagree, particularly for DT fusion. DT fusion reactors would be very heavy. ARC, for example, would have the weight of a couple of US WW2 destroyers. DT fusion delivers its energy as heat. A fission reactor would be far smaller, simpler, cheaper, and more reliable. You might make the case for advanced fuels, but that likely means you have to get 3He from somewhere. I suspect beamed power will beat even advanced fuel fusion in all missions in the future (a weak prediction as I will not be around to see.)
- Paradigma11 5y ago
  But you dont need a lot of fuel for fission and you also need many other things to keep a ship/station running. Isnt fuel in the ballpark of just one of many consumables that you need?
  - ncmncm 5y ago
    Fission-powered ion propulsion is the best mature tech we have. In space, the fission doesn't need containment, or even much shielding if it is far enough away from the rest of the ship. In the cloud tops of Titan, Venus, Saturn, Uranus, or Neptune, a nuclear power plant may be as simple as a naked pile suspended near the bottom of a big fabric tube with wind turbines at the top. The radioactively-heated, buoyant air inside holds it up, and, escaping through the turbine, generates power. (Enough is held back so it stays up.) Perhaps surprisingly, gravity is almost Earth-normal on all four planets. Perhaps more surprisingly, the temperature at a not unreasonably-high pressure is also close to Earth-normal (except on Titan). But getting back to orbit from any of the last three would be very, very difficult, so such a reactor would only ever power robots. Getting back to orbit from Titan is easy. From Venus, it is pretty hard; and once in orbit you would need to refuel to get anywhere else.