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Why is nuclear fusion so hard?

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Re: Why is nuclear fusion so hard?

#101

Post by earthboundkid »

vegetablepotpie wrote: post #47
candiodari wrote: post #38

Earlier quoted context omitted.

Yeah this is something people keep forgetting. The reason fossil fuels have such an impact is because the industry is happening at such a scale. Solar and wind are working at miniscule size ... and ... "no" impact (well, wind clearly has impact already, but ... let's forget that). Well actually, solar does have an impact. In Spain there's a couple large wind farms I visited and ... not that it should surprise anyone…

I think Fission would be great if we had somewhere to put the waste, if it didn't cost $10 billion dollars to set up a plant and people weren't phobic of it. Overall Nuclear makes more sense than coal and arguably more sense than wind and solar. But then there's the risk of the meltdown. No politician, no utility CEO, no corporation commission is going to take the risk of a meltdown when the political cost of pumping…

I can believe that human beings can run one nuclear fission plant successfully for one hundred years without a serious accident. I cannot believe that we can run thousands of plants for hundreds of years without a serious accident. There is too much complexity to prevent a black swan event, and in the case of nuclear fission, a black swan renders the surrounding area uninhabitable for an immensely long time. Nuclear fission is a fine bridge technology, but we cannot build systems that rely on it and expect them to be sustainable.

Re: Why is nuclear fusion so hard?

#102

Post by earthboundkid »

eloff wrote: post #88
martythemaniak wrote: post #82

Earlier quoted context omitted.

Yeah, it's probably a conservative number. But the Toronto area (~20% of Canada's population) would not be much different from Chicago, New York, Boston, Philadelphia, etc. And yeah, Canada has a lot of land, but once we ask Canadians "How would you like to chop down 5 Torontos worth of forest to cover them in silicon panels and make it into a lifeless desert?", then maybe some people will reconsider the relative mer…

5 Torontos worth of forest is nothing. In BC for just the last two years we lost forest half the size of Switzerland to fires. If you think how much land is cleared and maintained clear for agriculture in Canada, 5 Torontos is a rounding error. Land is cheap and abundant it's a non-issue for the kind of area we'd need to even power the whole world 100% on solar. Habit losses would be more than made up for by not cont…

Also, you can put solar panels on the roof of buildings in actual Toronto and not have to lose any additional footprint.

Re: Why is nuclear fusion so hard?

#103

Post by acqq »

fromMars wrote: post #85
zipwitch wrote: post #68

Earlier quoted context omitted.

My big problem with nuclear (fission) is that while on paper it looks like a great solution, in practice our civilizational apparatus does not appear to be up to the task of long-term responsible implementation. Fission power looks like a long game of hot potato, where everyone hopes they won't be the ones on the hook when the eventual equipment failure, natural disaster, or time to decommission eventually arrives. (…

I posted further up thread, and I am not an expert, that thorium based nuclear power may be safer with less dangerous waste and potential for weaponization.

https://www.theguardian.com/environment/2011/jun/23/thorium-...

"Don't believe the spin on thorium being a greener nuclear option"

and

https://thebulletin.org/2018/08/thorium-power-has-a-protacti...

"Protactinium separations provide a pathway for obtaining highly attractive weapons-grade uranium 233 from thorium fuel cycles. The difficulties of safeguarding commercial spent fuel reprocessing are significant for any type of fuel cycle, and thorium is no exception."

Re: Why is nuclear fusion so hard?

#104

Post by the8472 »

Creatccount wrote: post #43

Would zero gravity be helpful in order to make it easier to get fusion working?

Space also comes with a natural vacuum, not just zero-g. That might be more interesting for a reactor since you would only have to care about shielding the magnetic coils instead of building and cooling a vacuum vessel at the same time.

Re: Why is nuclear fusion so hard?

#105

Post by Animats »

Plasma instability is just awful. See [1]. I thought he was going to go on about some approach to active stabilization of plasmas. But no. There's been work done on that, but it's been years. Anyone following that?

Then there's the first wall problem.[2] Fusion generates heat and neutrons. Lots of neutrons, which break atoms apart. Finding something which will stand up to that in an experimental machine has been tough. Finding something which will stand up to that in a long term production environment is really tough. In a fission reactor, you can use water to slow and stop the neutrons, and you just get some tritium as a byproduct. A fusion reactor's first wall faces a vacuum, so that's out.

[1] https://en.wikipedia.org/wiki/Plasma_stability

[2] https://en.wikipedia.org/wiki/Plasma-facing_material

Re: Why is nuclear fusion so hard?

#106

Post by adrianmonk »

lisper wrote: post #76

> Some kinds of instability are slow enough that we can control them. For example bicycles are unstable, but many of us eventually learn to ride them. Actually, bicycles are only unstable when they are moving slowly (or stopped), and most people never learn how to stabilize one in this unstable regime. It can be done, but it's very, very hard.

Now, what would be great is if that analogy could be stretched further. It would pretty wonderful if someone found a way to do fusion where, like a bike, it's stable once it gets going.

Re: Why is nuclear fusion so hard?

#107

Post by thomasahle »

mannykannot wrote: post #41

This is somewhat tangential to the specific issue here, but I was surprised by this: At the center of the Sun, fusion power is estimated by models to be about 276.5 watts/m3. Despite its intense temperature, the peak power generating density of the core overall is similar to an active compost heap, and is lower than the power density produced by the metabolism of an adult human.[1] So practical fusion power requires…

It continues like this though:

> The low power outputs occurring inside the fusion core of the Sun may also be surprising, considering the large power which might be predicted by a simple application of the Stefan–Boltzmann law for temperatures of 10 to 15 million kelvins. However, layers of the Sun are radiating to outer layers only slightly lower in temperature, and it is this difference in radiation powers between layers which determines net power generation and transfer in the solar core.

So if a m^3 of sun core was moved to a powerplant it would generate a lot more energy.

Re: Why is nuclear fusion so hard?

#108

Post by abecedarius »

rkagerer wrote: post #91

This is probably another ignorant question, but why can't we "aim" and shoot protons at each other to make them smack together without requiring all that heat and pressure?

I've wondered, aren't there any fusible elements that can be solids in vacuum? Then shoot pellets at each other at a sizable fraction of c. Way better density than a particle beam.

For instance, lithium-6 is a stable solid metal with the right nucleon composition and binding energy to fuse into carbon-12. I have no idea if it actually would to a useful degree.

Re: Why is nuclear fusion so hard?

#109

Post by lisper »

adrianmonk wrote: post #106
lisper wrote: post #76

> Some kinds of instability are slow enough that we can control them. For example bicycles are unstable, but many of us eventually learn to ride them. Actually, bicycles are only unstable when they are moving slowly (or stopped), and most people never learn how to stabilize one in this unstable regime. It can be done, but it's very, very hard.

Now, what would be great is if that analogy could be stretched further. It would pretty wonderful if someone found a way to do fusion where, like a bike, it's stable once it gets going.

Well, that is actually possible. That's what happens in stars and hydrogen bombs. The problem, of course, is that "getting going" for fusion means getting very big. The reason fusion energy is hard is precisely because to be practical and safe we have to "ride slowly".

Re: Why is nuclear fusion so hard?

#110

Post by [deleted] »

mikeash wrote: post #46
mannykannot wrote: post #41

This is somewhat tangential to the specific issue here, but I was surprised by this: At the center of the Sun, fusion power is estimated by models to be about 276.5 watts/m3. Despite its intense temperature, the peak power generating density of the core overall is similar to an active compost heap, and is lower than the power density produced by the metabolism of an adult human.[1] So practical fusion power requires…

That also shows why fusion power always centers around exotic isotopes like deuterium and tritium rather than plain hydrogen. The reaction paths needed to fuse plain hydrogen are so improbable that they don’t happen fast enough to be useful.

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