How would electricity be generated from a nuclear fusion reactor?

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Summary
How would we get energy from a fusion power plant?
How would electricity be generated from a nuclear fusion reactor?

How soon do you think that fusion power plants will become a reality?
 

phinds

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Summary: How would we get energy from a fusion power plant?

How would electricity be generated from a nuclear fusion reactor?

How soon do you think that fusion power plants will become a reality?
What research have you done on this so far? What have you found out?
 

russ_watters

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How would electricity be generated from a nuclear fusion reactor?
Same way most of our power is generated now: by boiling water and running it through a turbine.
How soon do you think that fusion power plants will become a reality?
The joke is that it is always 30 years away (and has been for 60 years). Scientists seem pretty confident that the next project will achieve break-even and the one after that will be a prototype power reactor. So 3 more generations of projects; still at least 30 years if the optimism is warranted.

And then we can answer the question of whether we want it or not.
 

gleem

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Same way most of our power is generated now: by boiling water and running it through a turbine.
Good old 19 th century technology.

How soon do you think that fusion power plants will become a reality?
Researcher have been promising fusion for decades. MIT is promising a small reactor (100 MW) by 2025 don't know about the big industrial sizes that we need.
 

anorlunda

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Does anyone remember Chaos Manner, the Jerry Pournoule column in Byte Magazine? His favorite phrase applies here. Fusion will arrive "real soon now."
 

berkeman

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How would electricity be generated from a nuclear fusion reactor?
I took a class on plasma physics and fusion reactors many years ago. I seem to remember that the instructor mentioned that one of the harder fusion reactions to get working would have the advantage of being able to use Magneto Hydrodynamic (MHD) power generation instead of a thermal cycle. But my Google-foo is failing me now -- Does anybody know which fusion Rx that might be, and why it lends itself to MHD power generation?
 

Astronuc

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I took a class on plasma physics and fusion reactors many years ago. I seem to remember that the instructor mentioned that one of the harder fusion reactions to get working would have the advantage of being able to use Magneto Hydrodynamic (MHD) power generation instead of a thermal cycle. But my Google-foo is failing me now -- Does anybody know which fusion Rx that might be, and why it lends itself to MHD power generation?
Likely, it was an aneutronic reaction, such as DD or D3He. There were numerous concepts on 'direct energy conversion', in which one would want most, if not all, energy in the form of nuclei and electrons.

See the section on Induction > conduction systems
 
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Read a random thing the other day that said D-T fusion produces about 80% of its energy in the form of high energy neutrons (~14MeV), the hard part is slowing them down to get the heat out (thermalize them), also bit of a problem for any materials => resulting in potentially large amounts of radioactive waste due to the neutron bombardment of previously not radioactive materials.

Interestingly it was also mentioned that there is a significant proliferation risk since production of Pu239 is relatively easy by just putting some uranium (depleted or other wise) somewhere near those neutrons.
 

etudiant

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Think that is perhaps why none of the fusion efforts are getting enthusiastic government support.
The idea of creating electricity from star fire by boiling water seems a little incongruous, sort of like the early requirement to have a man with a flag precede motor vehicles. Plus the current ITER concept is proving to be so expensive that it produce power economically, even in the revised improved follow on design. It will hopefully prove that fusion is practicable, then the engineers will work to make a viable system starting from there.
 

anorlunda

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By the way, do they have a plan for the Tokamak type fusion reactors to convert the energy to steam?
 

etudiant

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Afaik, the idea is that ITER provides proof of concept, based on which an actual prototype fusion power plant would be built around 2050. That was briefed as a steam turbine based concept when I visited ITER some years ago. I don't know whether anything has changed since.
 

anorlunda

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What about power density and temperature gradients in the steam production?

One article (sorry, lost the link) said that we would need 10000 MW/m3 power density, and 1 million degrees K per m temperature gradient. It is not easy dealing with such extremes.

Does anyone have a source on those issues?
 
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What about power density and temperature gradients in the steam production?

One article (sorry, lost the link) said that we would need 10000 MW/m3 power density, and 1 million degrees K per m temperature gradient. It is not easy dealing with such extremes.

Does anyone have a source on those issues?
Why do we have to use steam turbines? Again, that’s the technology of yesterday, too bulky and too many processes of energy conversion (radiation→Heat of reaction chamber→Heat of H2O→Kinetic energy of turbines→electricity) something that often seen in a Rube Goldberg machine... If we have to use the heat generated by fusion (actually, I believe that heat should be maintaining the fusion reaction. So we don’t have to pump extra heat to the plasma) why don’t just convert the heat directly into heat via thermoelectric materials?
607DC743-B6D7-4319-B89C-5398096B7079.png

Or in the other case we convert the kinetic energy of charged particles to electricity (direct energy conversion)
8FA07A53-BD38-4151-9754-BFAD6AA941CB.jpeg
 
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The typical efficiency of TEGs is around 5-8%
Well, there is no reason to think of this efficiency will not improve. TEG isn’t ready yet, but so is fusion. Consider the first generation of steam engines have a very low efficiency (below 5%) and now these gas turbines still can reach 50% or more... by the time fusion is ready, these TEGs should have enough efficiency though. And I believe TEGs are one of the key technologies that make miniature fusion generators possible.
Other than the thermoelectric cycle, I prefer more of the DEC cycle for aneutronic fusion (D-He3 is 16 times harder than D-T though) ... by directing the vector of speed of the charged particles, we focus them in a beam and harness their kinetic energy. This should be as efficient as a electric motor (since they works about the same) and up to 90% of efficiency (that’s way above the best turbines!) . Plus, Wikipedia says “Direct energy conversion (DEC) or simply direct conversion converts a charged particle's kinetic energy into a voltage. It is a scheme for power extraction from nuclear fusion.” This technology is optimized for fusion!
You got to see this! https://en.m.wikipedia.org/wiki/Direct_energy_conversion
 

russ_watters

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Well, there is no reason to think of this efficiency will not improve.
Wishful thinking is not engineering.
Why do we have to use steam turbines? Again, that’s the technology of yesterday...
Not that it actually matters, but thermoelectric generators are about 2/3 as old as steam engines.
 

anorlunda

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Even if we had direct conversion that is 90% (more likely 50%) efficient, there is still a huge amount of waste heat to get rid of. The problems with power density and thermal gradients remain.

At what temperature does a direct conversion device melt?
 
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It might be efficient, but boiling water and power a turbine might be common somehow, but it will be very bulky (not ideal if we want to fit it onto a spacecraft, or a ship (like carriers and nuclear subs).
Actually today's carriers and nuclear subs do use steam turbines to convert the heat produced in their (fission) reactors to propulsion. What seems Rube Goldberg to some is proven technology, reliable and well-understood.

Spacecraft is another realm completely, you're probably right about that.
 

DEvens

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How would electricity be generated from a nuclear fusion reactor?
For several designs that's a difficult point.

Most of the variations on magnetic confinement are doing their absolute best to keep the heat in. So far, nobody has included any place to transport heat out to any kind of converter. So this would need to be at the next stage of development. You'd need to have some way to open some kind of passage for the heat. Maybe you have a "dump heat to the generator" mode in the magnetic field. So you might push the plasma to it's hottest, then dump the heat to a specially designed port or panel or something. Dump some heat then go back to normal operation mode. This is still to be worked out.

Possibly inertial confinement has an easier job on that point. The fusion lasts a very short time producing a pulse of energy that can be captured in any convenient format.

There is one outside-the-main-line design that has this already worked out. The General Fusion design uses molten lead as the wall of the fusion chamber. It circulates in, picks up the heat, and circulates out. Then the lead goes through a fairly familiar heat exchanger to pass the heat to turbines.


How soon do you think that fusion power plants will become a reality?
I'd say there are too many unknowns to hazard a guess. Primarily it's a question of exactly what is possible. We don't know yet which method or design will work. Or even if any of the current designs will work in an acceptable fashion.

After that there are tons of motivation questions. How much do people want it? What will be the price of fossil fuels? What will be the attitude towards fission reactors and what will be the price of Uranium or Thorium? What will be people's ideas about carbon into the atmosphere? How much electricity, and other forms of power, do people want? Will we continue to convert to electric cars and so need much more electricity generation? And bunches of other questions I've not thought of. These considerations will determine how much funding fusion gets, and so how hard people work at it.

In the meanwhile, we should not be ignoring things like improved fission reactors. And improved generation of all kinds. Fossil, wind, solar, tidal, geothermal, even things like burning garbage and waste products from saw mills should be investigated for improvement. Improved energy supply is important for nearly every activity of modern society. We should keep as many options going as we can afford.
 

anorlunda

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So you might push the plasma to it's hottest, then dump the heat to a specially designed port or panel or something.
Am I correct that the chamber holding the plasma is maintained in vacuum?

If so, then the port would need to be transparent to particles and radiation, but also act as a pressure barrier to protect the vacuum. Are there any preliminary ideas for such a port?
 
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well maybe i'm mistaken and did not catch your idea here quite clearly but wasn't ITER and any major tokamak or spheromak design all about having the alpha particles help with plasma heating (after all they are charged and so can't escape the plasma easily) and the neutrons escaping the plasma doing the heating in the "blanket" from which heat is taken off by plain old circulation?
As far as I know there is no direct conversion for ITER and most other magnetic confinement designs , it's all about keeping the plasma "burn time" for as long as possible , taking off the heat produced by neutrons to convert to electricity and then recharging the torus plasma vessel by taking fused plasma leftovers out and fresh DT fuel in, I suppose in gas form which then gets ingnited once again and so the cycle repeats.
 
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@artis: Right.

Getting the energy out is easy - it is unavoidable in DT fusion. The heat goes to the walls, the cooling fluid heats up, the rest is similar to a fission reactor.
 

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