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The Trouble with Fusion (1983) [pdf]

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Re: The Trouble with Fusion (1983) [pdf]

#21

Post by willis936 »

pfdietz wrote: post #18
willis936 wrote: post #13

Earlier quoted context omitted.

So I’m a few pages further and I fear I will not be finishing this paper. I am surprised it was published and is still referenced. Where are the citations? Where is the analysis? You can’t just say “fusion reactors need to be ten times bigger than fission reactors”. It’s frankly embarrassing to MIT that they would allow egregious, unfounded claims to be published. Peer review exists to shred such unsupported statemen…

This was a semi-popular article. You can find more technical analyses in the literature. The specific points made in the article have stood the test of time. Lidsky said the power density of a DT fusion reactor would be at least an order of magnitude worse than that of a fission reactor. And if you look at existing reactors and concepts, this is true. Compare to a commercial PWR, in which (thermal power)/(volume of r…

My outrage is from making scientific conclusions before the science has been done. A hard justification of power density limitations And it’s economic meaning is necessary before you can make a blanket statement like “D+T magnetic confinement will never be economically viable”. The price of electricity is always changing, and public opinion is shifting towards the idea that we have been grossly underpaying for our electricity.

Re: The Trouble with Fusion (1983) [pdf]

#22

Post by pfdietz »

willis936 wrote: post #21
pfdietz wrote: post #18

Earlier quoted context omitted.

This was a semi-popular article. You can find more technical analyses in the literature. The specific points made in the article have stood the test of time. Lidsky said the power density of a DT fusion reactor would be at least an order of magnitude worse than that of a fission reactor. And if you look at existing reactors and concepts, this is true. Compare to a commercial PWR, in which (thermal power)/(volume of r…

My outrage is from making scientific conclusions before the science has been done. A hard justification of power density limitations And it’s economic meaning is necessary before you can make a blanket statement like “D+T magnetic confinement will never be economically viable”. The price of electricity is always changing, and public opinion is shifting towards the idea that we have been grossly underpaying for our el…

You're just passive-aggressively rejecting his argument on facile grounds, that this specific popular exposition didn't include the details you demand. It's sad you don't have enough self awareness to see what you're doing here.

If you want more detail of this sort of analysis, look at the Pfirsch & Schmitter paper from 1987 I linked to below. Lidsky also had a paper in the technical literature going into more details, although I don't have that reference. The basic argument as given by Lidsky in TTWF is not difficult to understand though, if you allow yourself to try to understand it.

In any case, the experience since then confirms what he was saying. Why don't you show me a fusion reactor concept with a power density approaching that of a fission reactor? Someone, somewhere must have been able to produce such a schematic if Lidsky's analysis was wrong, yes? Understand Lidsky's point is independent of limits due to plasma physics.

Re: The Trouble with Fusion (1983) [pdf]

#23

Post by Symmetry »

pfdietz wrote: post #18
willis936 wrote: post #13

Earlier quoted context omitted.

So I’m a few pages further and I fear I will not be finishing this paper. I am surprised it was published and is still referenced. Where are the citations? Where is the analysis? You can’t just say “fusion reactors need to be ten times bigger than fission reactors”. It’s frankly embarrassing to MIT that they would allow egregious, unfounded claims to be published. Peer review exists to shred such unsupported statemen…

This was a semi-popular article. You can find more technical analyses in the literature. The specific points made in the article have stood the test of time. Lidsky said the power density of a DT fusion reactor would be at least an order of magnitude worse than that of a fission reactor. And if you look at existing reactors and concepts, this is true. Compare to a commercial PWR, in which (thermal power)/(volume of r…

The paper made many good points but I found the power density argument by far the weakest. Yes a fusion reactor will necessarily weight more than a fission reactor of the same output and if we assume a constant price per pound across fission and fusion reactors this means it will be more expensive. But the reactor itself is only a small fraction of the weight of a fission plant. And of course we have every reason to think that the cost per pound of reactors across different reactor types will be entirely different.

I see this argument a lot in discussions around rockets where some people assume that if one rocket weighs less than another per pound delivered to space it must necessarily be cheaper when in fact the effort required to make it lighter almost always means it's more expensive. I think the rise of SpaceX has finally put an end to that argument, at least.

Re: The Trouble with Fusion (1983) [pdf]

#24

Post by Symmetry »

pfdietz wrote: post #2

This old critique has aged fairly well. It was too optimistic about advanced fission, and the suggestion to move to advanced fuels for fusion was mostly shot down by Lidsky's student, Todd Rider. https://pdfs.semanticscholar.org/fce7/a35629488ec030d983025a... https://dspace.mit.edu/handle/1721.1/11412 A similar critique was being made around the same time by Pfirsch and Schmitter in Europe. https://pure.mpg.de/rest/i…

There are a few parts that have been overtaken by advances. Improvements in superconductors have driven the minimum size for a fusion reactor far down, for instance.

Re: The Trouble with Fusion (1983) [pdf]

#25

Post by willis936 »

pfdietz wrote: post #22
willis936 wrote: post #21

Earlier quoted context omitted.

My outrage is from making scientific conclusions before the science has been done. A hard justification of power density limitations And it’s economic meaning is necessary before you can make a blanket statement like “D+T magnetic confinement will never be economically viable”. The price of electricity is always changing, and public opinion is shifting towards the idea that we have been grossly underpaying for our el…

You're just passive-aggressively rejecting his argument on facile grounds, that this specific popular exposition didn't include the details you demand. It's sad you don't have enough self awareness to see what you're doing here. If you want more detail of this sort of analysis, look at the Pfirsch & Schmitter paper from 1987 I linked to below. Lidsky also had a paper in the technical literature going into more detail…

Even if the point of power density is conceded, the work necessary for economic analysis has not been done anywhere I have looked. If you would focus on my points, and not try to project some psychological model on someone you’re having a conversation with (a proper dick move, you won’t make friends that way), then you wouldn’t be pointing at papers talking about power density.

Where is the cost analysis that prices future fusion plants out of reasonability? Where is the cost analysis that takes the hidden cost of CO2 emission into account? What is the societal value of producing an on demand energy source that lasts millions of years, rather than hundreds? The burden is not on me to find these answers, because I did not make cavalier statements that will be discussed 40 years later. Unchecked publications are why I became heated, not the content.

Re: The Trouble with Fusion (1983) [pdf]

#26

Post by pietjepuk88 »

pfdietz wrote: post #7
maxharris wrote: post #6

Commonwealth Fusion Systems was formed out of the work presented here: https://www.youtube.com/watch?v=KkpqA8yG9T4 A lot has changed since 1983. The superconducting materials that CFS depends on weren't even discovered until the late 80s, and it took a very long time for that to become practical. Fast-forward to today and you can buy this stuff on Alibaba!

Lidsky's arguments against fusion apply to the ARC design. Its overall volumetric power density is 0.5 MW/m^3, 40 times less than a PWR reactor vessel.

What defines the volume to get to that number? From what I can tell from the ARC specs the plasma volume is 141 m3, and the expected power output is 200-300 MWe, which makes it 1.5-2 MWe/m3.

Do you have some numbers on a PWR reactor vessel? I was trying to look up some details on the APR-1400, but could not find any.

Re: The Trouble with Fusion (1983) [pdf]

#27

Post by pfdietz »

Symmetry wrote: post #23
pfdietz wrote: post #18

Earlier quoted context omitted.

This was a semi-popular article. You can find more technical analyses in the literature. The specific points made in the article have stood the test of time. Lidsky said the power density of a DT fusion reactor would be at least an order of magnitude worse than that of a fission reactor. And if you look at existing reactors and concepts, this is true. Compare to a commercial PWR, in which (thermal power)/(volume of r…

The paper made many good points but I found the power density argument by far the weakest. Yes a fusion reactor will necessarily weight more than a fission reactor of the same output and if we assume a constant price per pound across fission and fusion reactors this means it will be more expensive. But the reactor itself is only a small fraction of the weight of a fission plant. And of course we have every reason to…

Fission reactor cores and reactor vessels are made of fuel and steel. They are very simple compared to fusion reactors. Fission reactors can therefore be expected to be much cheaper than fusion reactors, even on a per-pound or per-volume basis. They can also be expected to be much more reliable.

(A fission reactor vessel will also last the lifetime of the power plant. A DT fusion reactor, not so much.)

(The average density of ITER is about the same as the average density of an unfueled PWR reactor vessel, btw.)

The analogy with rockets would be for those advocating air-breathing launchers. Make the launcher much more complex, just so one can save on LOX. Make the reactor much more complex, just so one can not pay for uranium. But LOX is cheap, and fuel is not a major cost driver for fission power.

Re: The Trouble with Fusion (1983) [pdf]

#28

Post by pfdietz »

willis936 wrote: post #25
pfdietz wrote: post #22

Earlier quoted context omitted.

You're just passive-aggressively rejecting his argument on facile grounds, that this specific popular exposition didn't include the details you demand. It's sad you don't have enough self awareness to see what you're doing here. If you want more detail of this sort of analysis, look at the Pfirsch & Schmitter paper from 1987 I linked to below. Lidsky also had a paper in the technical literature going into more detail…

Even if the point of power density is conceded, the work necessary for economic analysis has not been done anywhere I have looked. If you would focus on my points, and not try to project some psychological model on someone you’re having a conversation with (a proper dick move, you won’t make friends that way), then you wouldn’t be pointing at papers talking about power density. Where is the cost analysis that prices…

I'm having a hard time feeling charitable toward you when you are missing things that are blindingly obvious.

You are demanding an economic analysis to tell you that a much larger, much more complex piece of equipment, made from more exotic materials, is going to be more expensive than a much smaller, much less complex one? This is screaming passive-aggressive denial. It is very simple to understand that point, if you just allow yourself to think about it.

The CO2 point would be worthwhile if fusion were competing just with fossil fuels. But it fails against fission (for the simple reasons Lidsky explained), and fission now fails against renewables.

Re: The Trouble with Fusion (1983) [pdf]

#29

Post by moogly »

pfdietz wrote: post #18
willis936 wrote: post #13

Earlier quoted context omitted.

So I’m a few pages further and I fear I will not be finishing this paper. I am surprised it was published and is still referenced. Where are the citations? Where is the analysis? You can’t just say “fusion reactors need to be ten times bigger than fission reactors”. It’s frankly embarrassing to MIT that they would allow egregious, unfounded claims to be published. Peer review exists to shred such unsupported statemen…

This was a semi-popular article. You can find more technical analyses in the literature. The specific points made in the article have stood the test of time. Lidsky said the power density of a DT fusion reactor would be at least an order of magnitude worse than that of a fission reactor. And if you look at existing reactors and concepts, this is true. Compare to a commercial PWR, in which (thermal power)/(volume of r…

> The (thermal power)/(reactor volume) for ITER is about 0.05 MW/m^3.

https://www.f4e.europa.eu/understandingfusion/iterdevice.asp...

500/800 = 0.625 (plasma volume, not reactor volume)

In an interview with the Omega Tau podcast a while back, it was mentioned by ITER personnel that the DEMO plant that would be the successor to ITER was probably going to be designed as a 2000 MW reactor. Since the plasma is in shape of a torus, that volume increases pretty quickly with the size of the confinement vessel.

Also, per unit mass of fuel, magnetic confinement fusion is still posited to be thousands of times more efficient than fission power.

Re: The Trouble with Fusion (1983) [pdf]

#30

Post by moogly »

willis936 wrote: post #5

I’m still only a few pages in. I don’t have the chance to read it all right now, but I will revisit this tomorrow morning. Here are my early thoughts. Disclaimer: I am an advocate of fusion and am moving into the field (professional electrical engineering support of an academic project). We need to walk before we can run. D+T fusion is viable. Hull maintenance is a solvable problem. Economic studies come after we can…

Not to mention D+T has 2500 times higher power density than p+B11.
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