Commercially Feasible Fusion Reactor

[lekh2003]

I read an article: https://mashable.com/2017/12/19/nuclear-fusion-company-plans-to-make-carbon-free-energy/ about a company named General Fusion who aim to use plasma balls and pressurized steam pistons to create a 150 million degrees celsius environment for fusion to occur.

I also found a youtube video by Linus Tech Tips on the same fusion reactor where he tours the facility and gives a run down of the tech at General Fusion.

What are everybody's thoughts?

 

[Drakkith]

My understanding was that it's mostly nonsense. The design might turn out to be workable, but not in the near future. Almost certainly not before other types of reactors, such as tokamaks, become operational.

 

[lekh2003]

My understanding was that it's mostly nonsense.

That's what I thought as well. Seemed too hopeful. It is trying to solve a problem though. Toroidal fusion reactors use more energy than it produces from fusion.

Some tokamaks have been tested, but only to be a waste of energy. Let's hope we find a neat way to produce energy safely soon.

 

[Drakkith]

Some tokamaks have been tested, but only to be a waste of energy.

The difference is that tokamaks have shown a steady improvement over the last few decades, whereas no reactors of this new design have even been built yet.

 

[lekh2003]

new design have even been built yet.

It's definitely a unique design.

 

[CWatters]

I remembered that there has been at least one claim for an over unity fusion reaction...

http://www.kurzweilai.net/scientists-achieve-fuel-gain-exceeding-unity-in-confined-fusion-implosion

 

[Bigjoemonger]

When ITER is finished it should prove the viability of fusion for commercial use.

 

[jimgraber]

https://thebulletin.org/iter-showcase-drawbacks-fusion-energy11512
An interesting and well done pessimistic assessment.

 

[Drakkith]

https://thebulletin.org/iter-showcase-drawbacks-fusion-energy11512
An interesting and well done pessimistic assessment.

Interesting perhaps, but not particularly well done in my opinion. I think some of the author's arguments are shallow and nearsighted and aren't supported particularly well. Particularly the section detailing how much energy and materials are going into the construction of ITER.

 

[mfb]

Someone who calls ITER a prototype for a (electricity generating) fusion reactor either didn't understand anything or is deliberately misleading readers. Both are good reasons to ignore the article.

The construction images do remind me of some other machine.

 

[girts]

maybe not to make a new thread about this since the title of this one perfectly suits my commentary.
I did a few small calculations and please tell me what do you think about this.

say we are speaking about a tokamak fusion idea. looking at the ITER proposed numbers and tokamaks in general they require quite a lot of electrical energy input.
So let's say some 100MW of electrical input is necessary for a certain size device, (I am not sure about ITER numbers , they say its 50MW but other sources claim that that number is the proposed future one and actual starting and test input levels will be higher)
so staying with our 100MW input, we then need for the electrical output after thermal to mechanical to electrical conversion to be atleast 200MW correct?
In other words any fusion powerstation would need to output at least twice as it's input consumption is to be commercially feasible.
because if the powerstation say consumes 100MW but outputs 150 then sure that too is 50 more than nothing but from a purely grid perspective you have to have all those extra switch yards and transformers etc just to run the station and the output is kind of little compared to that, so how does this transform into numbers and money terms? Would it be feasible to run a tokamak say that outputs just 1/2 more than it consumes?

I assume if my numbers are correct, fission power plants consume something like 2% to 4% of their total electrical output , or someone can correct these numbers since I have no chart at the moment to illustrate these.

So what are your thoughts

 

[mfb]

It would have to be much more. 200 MW thermal output could be converted to something like 70 MW to 100 MW electrical power, and the 100 MW going into the plasma need more than 100 MW electrical power to produce them.

The ITER design is 500 MW thermal power from 50 MW heating (ratio Q=10), at this point you could produce more electricity than you have to put in, but it is still not enough to be interesting commercially. A power plant should run at Q=25 or higher. Ideally the fusion itself produces the heat to keep the reactor running.

 

[girts]

yes thanks mfb that was my point i just forgot to mentioned that I was talking about MW with regards to electric consumption specifically, although I am not sure of the specific numbers for ITER, I simply assumed based on a simple paper calculation that no matter how much electricity in terms of MW such a power plant consumes it must put out no less than twice as much also in electric MW to the grid to be feasible correct?

now maybe someone knows the specific efficiencies of plasma heating devices like neutral particle injection, ohmic heating and microwave or RF heating? I assume ohmic being resistive is the most efficient one where most of the electricity is converted to heat much like in a regular conductor heater?
well we must also include the cryogenic pumps for the magnets and magnets themselves although I guess that under superconducting state the magnets use very little power?

well it is much easier with the output , if we assume they don't use direct conversion (charged particles striking and anode/cathode then the typical thermodynamic efficiency of water/steam is no more than 35% I guess with some molten salts or gases having a higher efficiency if implemented.

All in all the question is can a tokamak be efficient enough to give out more than it consumes counting away the losses both in input and output conversions.
I suppose that many of the plasma heating techniques are already maximized in their efficiencies and there is not much headroom to grow into?

 

[rootone]

I think it's a scale thing.
The Sun is a perfect demonstration of a working fusion reactor, fusion works.
Can we make what are in effect tiny Suns though?
I guess it has to be called work in progress.

 

[lekh2003]

Can we make what are in effect tiny Suns though?

Yup, the big problem. Can we make balls of plasma with temperatures that could annihilate us. What could be more simple?

 

[mfb]

I simply assumed based on a simple paper calculation that no matter how much electricity in terms of MW such a power plant consumes it must put out no less than twice as much also in electric MW to the grid to be feasible correct?

If you have a free machine that can output 5% more electricity than you put in it would be commercially feasible to use this machine. The only hard threshold is the obvious one - you need to get more out than you put in (this includes the whole potential power plant - cooling, tritium cycle, ...). After that it is just a matter of cost.

 

[rootone]

If we do get there, we get Helium as waste.
Helium is quite useful, not stuff you have to bury in the ground and hope it doesn't cause trouble.

 

[Bystander]

https://www.physicsforums.com/search/65268239/?q=sun%2C+compost&o=relevance

 

[mfb]

If we do get there, we get Helium as waste.
Helium is quite useful, not stuff you have to bury in the ground and hope it doesn't cause trouble.

Not enough helium to be interesting.
Fusion reactors produce radioactive reactor walls. Fission reactors produce isotopes useful for spaceflight and medicine.
Things are not as black and white as your post suggests.

 

[rootone]

Reactor walls meaning some outer containment of neutrons and other particles emitted from the reactor core?
Could those walls be constructed in a way that produces useful isotopes when they are worn out so have to be recycled.

 

[lekh2003]

After that it is just a matter of cost.

To overcome this cost, you would ultimately require an energy yield of at least 200% of the amount of energy you put in as suggested. Otherwise, it wouldn't be commercially feasible in a reasonable time period, but only energy yielding.

 

[mfb]

Reactor walls meaning some outer containment of neutrons and other particles emitted from the reactor core?

Yes.

Could those walls be constructed in a way that produces useful isotopes when they are worn out so have to be recycled.

It is challenging enough to find any material that can withstand the intense heat and radiation damage without needing a replacement every year or even every month. It is even more challenging to find a material that doesn't produce too much problematic waste.
Finding a material that can satisfy all this while also producing something useful? Good luck.

To overcome this cost, you would ultimately require an energy yield of at least 200% of the amount of energy you put in as suggested.

Where does that number 200% come from? It looks too low for realistic concepts.

 

[lekh2003]

Where does that number 200% come from? It looks too low for realistic concepts.

Just off the top of my head, I didn't put much thought into the number, double seemed like a neat scheme. But it would still be realistically feasible as compared to 5%...

 

[mfb]

Well, the experts expect that you need much more than a factor of 2.
Be careful with made-up numbers. Ideally don't just make up numbers.

 

[lekh2003]

Well, the experts expect that you need much more than a factor of 2.
Be careful with made-up numbers. Ideally don't just make up numbers.

Ok sir.

 

[girts]

well anyway , we can make fusion now just not efficiently and we also know the basic ways by which we can achieve fusion, basically it is just a matter of pushing the numbers in our favor but that is the hard part.
given how much a fusion plant costs anything less than twice output vs input in electrical MW would probably not lift off the ground...
well maybe only when any other energy resource would cost the same or more for the same amount of net gain electricity.I assume the problem in fusion is not the price of the fuel unlike it is in all other resources like oil, gas, etc, but the problem is the complexity and price of the technology itself and the technology is not even self sustaining yet

could it be with fusion like it is with other technologies that the more precise and result yielding it is the more expensive it is?
or could the scenario be like with computers that at first they were very expensive and rather rare but then as the years went by the price for a given performance dropped as the technology was better understood and more mass produced?

 

[mfb]

Things nearly always get cheaper if you have more experience building it, if you build it larger, and if you build more of it.

Electronics are an extreme case with the miniaturization, that is not possible elsewhere, but you still see that trend in many places. Cars, batteries and electric cars, photovoltaics, ...

 

[Drakkith]

I assume the problem in fusion is not the price of the fuel unlike it is in all other resources like oil, gas, etc, but the problem is the complexity and price of the technology itself and the technology is not even self sustaining yet

Pretty much. Tritium is essentially nonexistent on Earth since it has a half-life of about 15 years. Any reactor using tritium as a fuel will have to breed tritium itself. Deuterium is readily available in water everywhere, but deuterium-only fuels are much more difficult to fuse. However the main problem is just getting fusion to work well enough to be a useful power generation technology in the first place.

could it be with fusion like it is with other technologies that the more precise and result yielding it is the more expensive it is?
or could the scenario be like with computers that at first they were very expensive and rather rare but then as the years went by the price for a given performance dropped as the technology was better understood and more mass produced?

While any new technology is most expensive when it is in its infancy, the sheer size of a fusion power plant means that it will always cost a significant amount of money to build and maintain. On top of that, fusion-specific problems, like disposal of radioactive waste, also increase the cost.

 

[anorlunda]

There is more to commercially viable than energy production, and more than just cost.

Extracting the heat from a tokamak reactor requires dealing with extremely high temperature gradients (degrees K/m) and power densities (MW/m^2), not to mention radiation (as @mfb pointed out). A bottomless budget and determination may not be enough to assure success overcoming problems like that.

From an engineering point of view, it would be much easier to make a power plant with laser implosions of fuel pellets. It would be easier because the temperature gradients and power densities would be more reasonable in magnitude and easier to control. But too bad, those laser approaches haven't been shown to work well enough yet.

 

[BWV]

I think there will continue to be only one commercially viable fusion reactor over any of our lifetimes

 

[etudiant]

At an ITER visit two years ago, a senior specialist from the PPPL showed a chart tracking the figure of merit of fusion devices, a combination of temperature and confinement time, over the past 50 plus years. The improvement trend was pretty linear and about 10 years away from reaching levels sufficient for viable fusion.
So I'm much more hopeful than most here that there will be practical fusion devices by 2030, even though ITER will still only be in its shakedown phase at that point.

 

[girts]

I remember reading some popular science articles about fusion VS fission some time ago and what I noticed is that many of them echo some slogans like fusion is much cleaner etc (to which i know the answers myself) but what especially attracted my attention was the emphasis that fusion would produce much more power than fission, which I think comes from the fact that the fusion of certain light elements release more energy per nucleon than fission of the known fissile elements like Uranium or Plutonium per nucleon, which I assume is true.

But isn't this notion false or at least not objective because even if the per nucleon energies are higher, any practical devices have other constraints like particle density and confinement times etc aka Lawson criteria.
As far as I can see current fusion devices are far less energy dense than current fission reactors so for a given size would produce less thermal energy correct?
Because enriched U235 fuel rods are very dense so even if the per nucleon energy is lower there are many more of them in a given space while in a fusion reactor the per nucleon energy is higher but there are far far less nucleons in a given space not to mention the fact that only a small fraction of those nucleons fuse at any given time, so would it be fair to say that current fusion energy density is much worse than that of fission devices?What is there to do to increase the fusion energy density? Do we have to increase the density of plasma and it's fusion rate?

 

[mfb]

Comparing the power per fuel mass across different energy sources is meaningless if you don't take the different availability, cost and so on of these things into account.
Both deuterium and lithium are easily available, luckily.

The power per volume would be roughly similar, the power per mass would be much higher for fusion, the available energy per volume of the fuel would be much lower for fusion. As corollary, fusion reactors would exchange their fuel much more often (on a timescale of minutes instead of months).

 

[girts]

Ok so basically what you are saying is that if we took 1kg worth of U235 and put next 1kg worth of deuterium and tritium (500g each) the power we could extract from DT using fusion would be much more than the maximum power we could extract from fission using U235, because the fusion process of DT releases something like 17.6Mev per nucleon? while fission of U235 was 7Mew?

but because U235 is a solid heavy metal while Deuterium and Tritium are gaseous under atmospheric temp and conditions that 1kg worth of fuel takes up much more space right so from an energy density per volume viewpoint it being a gas is far worse?

Does this mean that once we arrive at a 1000 MW or more fusion generating plant it would need very large tanks for deuterium and tritium storage so that it is readily available if peak power is demanded from the machine?
I assume one can cool deuterium and tritium to very low temps using cryogenics and then they could be stored as liquids greatly reducing the space but that would require energy, I wonder how much though?

 

[mfb]

Fission of one uranium nucleus releases about 200 MeV, a bit less than 1 MeV per nucleon.
DT fusion releases about 18 MeV, a bit more than 3 MeV per nucleon (~4.5 MeV per nucleon if we don't consider the neutron which is recycled to breed new tritium).

but because U235 is a solid heavy metal while Deuterium and Tritium are gaseous under atmospheric temp and conditions that 1kg worth of fuel takes up much more space right so from an energy density per volume viewpoint it being a gas is far worse?

Sure, but it does not matter, as storage costs for both are negligible. A fusion power plant would work with a few kilograms of deuterium and tritium on site, enough to power it for days. Handling tritium is a bit difficult due to its radioactivity, but the deuterium to run a power plant for years can easily be stored in a small room.