5 ms·

One thing I’ve never figured out about fusion - how do you get the heat out and turned into electricity? (Presumably, water to steam then turbines, like everyt

One thing I’ve never figured out about fusion - how do you get the heat out and turned into electricity? (Presumably, water to steam then turbines, like everything, but how do you get the heat out from the reaction?)

jamiek88 3y ago
That's kinda on the 'we'll figure it out later' track. Materials are being investigated that can withstand the heat and neutron bombardment to attach a steam turbine the old fashioned way. But we ain't there yet, not without having to constantly change the 'walls'. > Most of the energy produced inside a fusion reactor is emitted in the form of neutrons, which heat a material surrounding the fusing plasma, called a blanket. In a power-producing plant, that heated blanket would in turn be used to drive a generating turbine
- DennisP 3y ago
  Zap Energy is using a "waterfall" of molten lead-lithium for its inner wall. They're planning to attempt net power this year.
Tuna-Fish 3y ago
The simplest answer that's part of the plan for most DT reactors is "as neutrons". The fraction of the energy that is retained as velocity of particles with a charge vs that is lost as the velocity of neutrons turns out to be conveniently just about where you'd want it to be. So, to capture the energy you need to surround your reactor with something that effectively converts fast neutrons to heat, such as a blanket of molten lithium, which you then use as a heat source. Lithium is proposed because it would also breed the necessary tritium.
- aziaziazi 3y ago
  Does that mean you need to “feed” with new lithium regularly ? Any idea on the frequency, like lithium gram*watt produced ?
  - dmurray 3y ago
    Assuming you need enough lithium to replace the tritium, and 100% energy efficiency, one atom of lithium makes one atom of tritium which makes 17.6 MeV of energy [0]. That's an energy output of 7 x 10^7 Wh per gram [1], or alternatively, a 70MW reactor needs one gram per hour, or alternatively, a very large 3.5GW plant needs 500 grams per hour, roughly the equivalent of the water drunk by a single thirsty person. [0] https://en.wikipedia.org/wiki/Deuterium%E2%80%93tritium_fusion https://en.wikipedia.org/wiki/Deuterium%E2%80%93tritium_fusi... [1] https://www.wolframalpha.com/input?i=17.6+MeV+divided+by+atomic+mass+of+lithium+in+watt+hours+per+gram https://www.wolframalpha.com/input?i=17.6+MeV+divided+by+ato...
    - aziaziazi 3y ago
      Thanks ! Following up on the napkin : The world final energy consumption (2018) [0] is around 9717Toe or 9,717*11.63=113,009TWh 1g for 70MW = 1T for 70TWh 113,009 / 70 = 1614 1614 ton of lithium every hour seems huge to me, does my calculations are wrong ? [0] https://en.m.wikipedia.org/wiki/World_energy_supply_and_consumption https://en.m.wikipedia.org/wiki/World_energy_supply_and_cons...
      - Tuna-Fish 3y ago
        They are wrong. The worldwide primary energy consumption is ~600EJ. 1g/70MWh * 600EJ ~= 2400t per year.
      - dmurray 3y ago
        You turned TWh/year into TWh/hour at some point, adding a factor of 8,760.
        aziaziazi 3y ago
        Thanks !
  - willis936 3y ago
    More than likely a plant will have a lifetime supply of lithium and other blanket materials on site before it is turned on. The fuel costs really do drop to effectively zero on MCF devices. Cost of cryogens, cost of steel, cost of working nitronic, cost of Beryllium, and cost of superconductors are the dominant sources to track.
apendleton 3y ago
Depends on the reaction. Most efforts are around deuterium-tritium fusion (that's the pair that's easiest to make fuse), which emits most of its energy as high-energy neutrons. So for these, yes, like the peer comment said, the neutrons are hitting something that heats up (that's the "blanket," which might be made of molten salt or metal), and then you can get the heat out of that with a heat exchanger. The company described in this article is aiming for D-T fusion. There are other reactions one can pursue that produce charged particles instead of neutrons. With these reactions, there are alternative energy conversion pathways that turn the kinetic energy of these charged particles directly into voltage, and you can skip the turbine. Of the fusion startups, Helion is probably the most prominent pursuing this kind of approach, with a D-He3 reaction. See https://en.wikipedia.org/wiki/Direct_energy_conversion https://en.wikipedia.org/wiki/Direct_energy_conversion for more info on this general approach.
- rgmerk 3y ago
  If the plan for energy conversion is a steam turbine, it’s never going to be economically competitive. New-build coal isn’t economically competitive anywhere, even where you get the coal essentially for free.
  - willis936 3y ago
    Source please.
    - rgmerk 3y ago
      The only place where new coal plants are being constructed is Asia. This article from DW explains it doesn’t make economic sense there either: https://www.dw.com/en/why-build-600-new-unprofitable-coal-plants/a-58095657 https://www.dw.com/en/why-build-600-new-unprofitable-coal-pl...
      - willis936 3y ago
        I wasn't asking about coal. That's obvious/non-controversial. Provide a source or your own analysis for this claim: >If the plan for energy conversion is a steam turbine, it’s never going to be economically competitive.
deleted 3y ago
[deleted]

jamiek88 3y ago

That's kinda on the 'we'll figure it out later' track. Materials are being investigated that can withstand the heat and neutron bombardment to attach a steam turbine the old fashioned way. But we ain't there yet, not without having to constantly change the 'walls'. > Most of the energy produced inside a fusion reactor is emitted in the form of neutrons, which heat a material surrounding the fusing plasma, called a blanket. In a power-producing plant, that heated blanket would in turn be used to drive a generating turbine

DennisP 3y ago
Zap Energy is using a "waterfall" of molten lead-lithium for its inner wall. They're planning to attempt net power this year.

Tuna-Fish 3y ago

The simplest answer that's part of the plan for most DT reactors is "as neutrons". The fraction of the energy that is retained as velocity of particles with a charge vs that is lost as the velocity of neutrons turns out to be conveniently just about where you'd want it to be. So, to capture the energy you need to surround your reactor with something that effectively converts fast neutrons to heat, such as a blanket of molten lithium, which you then use as a heat source. Lithium is proposed because it would also breed the necessary tritium.

aziaziazi 3y ago
Does that mean you need to “feed” with new lithium regularly ? Any idea on the frequency, like lithium gram*watt produced ?
- dmurray 3y ago
  Assuming you need enough lithium to replace the tritium, and 100% energy efficiency, one atom of lithium makes one atom of tritium which makes 17.6 MeV of energy [0]. That's an energy output of 7 x 10^7 Wh per gram [1], or alternatively, a 70MW reactor needs one gram per hour, or alternatively, a very large 3.5GW plant needs 500 grams per hour, roughly the equivalent of the water drunk by a single thirsty person. [0] https://en.wikipedia.org/wiki/Deuterium%E2%80%93tritium_fusion https://en.wikipedia.org/wiki/Deuterium%E2%80%93tritium_fusi... [1] https://www.wolframalpha.com/input?i=17.6+MeV+divided+by+atomic+mass+of+lithium+in+watt+hours+per+gram https://www.wolframalpha.com/input?i=17.6+MeV+divided+by+ato...
  - aziaziazi 3y ago
    Thanks ! Following up on the napkin : The world final energy consumption (2018) [0] is around 9717Toe or 9,717*11.63=113,009TWh 1g for 70MW = 1T for 70TWh 113,009 / 70 = 1614 1614 ton of lithium every hour seems huge to me, does my calculations are wrong ? [0] https://en.m.wikipedia.org/wiki/World_energy_supply_and_consumption https://en.m.wikipedia.org/wiki/World_energy_supply_and_cons...
    - Tuna-Fish 3y ago
      They are wrong. The worldwide primary energy consumption is ~600EJ. 1g/70MWh * 600EJ ~= 2400t per year.
    - dmurray 3y ago
      You turned TWh/year into TWh/hour at some point, adding a factor of 8,760.
      - aziaziazi 3y ago
        Thanks !
- willis936 3y ago
  More than likely a plant will have a lifetime supply of lithium and other blanket materials on site before it is turned on. The fuel costs really do drop to effectively zero on MCF devices. Cost of cryogens, cost of steel, cost of working nitronic, cost of Beryllium, and cost of superconductors are the dominant sources to track.

apendleton 3y ago

Depends on the reaction. Most efforts are around deuterium-tritium fusion (that's the pair that's easiest to make fuse), which emits most of its energy as high-energy neutrons. So for these, yes, like the peer comment said, the neutrons are hitting something that heats up (that's the "blanket," which might be made of molten salt or metal), and then you can get the heat out of that with a heat exchanger. The company described in this article is aiming for D-T fusion. There are other reactions one can pursue that produce charged particles instead of neutrons. With these reactions, there are alternative energy conversion pathways that turn the kinetic energy of these charged particles directly into voltage, and you can skip the turbine. Of the fusion startups, Helion is probably the most prominent pursuing this kind of approach, with a D-He3 reaction. See https://en.wikipedia.org/wiki/Direct_energy_conversion https://en.wikipedia.org/wiki/Direct_energy_conversion for more info on this general approach.

rgmerk 3y ago
If the plan for energy conversion is a steam turbine, it’s never going to be economically competitive. New-build coal isn’t economically competitive anywhere, even where you get the coal essentially for free.
- willis936 3y ago
  Source please.
  - rgmerk 3y ago
    The only place where new coal plants are being constructed is Asia. This article from DW explains it doesn’t make economic sense there either: https://www.dw.com/en/why-build-600-new-unprofitable-coal-plants/a-58095657 https://www.dw.com/en/why-build-600-new-unprofitable-coal-pl...
    - willis936 3y ago
      I wasn't asking about coal. That's obvious/non-controversial. Provide a source or your own analysis for this claim: >If the plan for energy conversion is a steam turbine, it’s never going to be economically competitive.

deleted 3y ago

[deleted]