Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Why is nuclear fusion so hard?

blog.sigfpe.com

Post reply on HN
Print view View original

131–140 of 182 posts

Re: Why is nuclear fusion so hard?

#131

Post by narag »

Koshkin wrote: post #127
narag wrote: post #112

Earlier quoted context omitted.

Nuclear tech is not even a century old. The idea that we can't do any better in a thousand or a million years seems so improbable to me that I can't take it seriously. There is some kind of extrange pessimism around that mindset: that we will be extinct much sooner, or that the Sun will die and thus Humanity, as if there's no obvious way to escape that apocalypsis.

> do any better in a thousand or a million years From what I can tell, there is a much bigger chance that we'll do much worse - and much sooner.

And I was afraid someone would call me Dr. Freud for mentioning the pessimism...

Re: Why is nuclear fusion so hard?

#132

Post by losteric »

mdpopescu wrote: post #115
aurizon wrote: post #93

Here is a thought experiment( no cats harmed or wetted). Show a cat how the toilet flushes, then try to flush the cat. You have two hands, the cat has 4 paws, with sharp claws as well as teeth. This will give you an idea.... Stars have gravity and mass- we do not, so we must try and compress the plasma, heat it AND stops the paws from grabbing the exterior. In truth magnetic confinement is a poor way to constrain a p…

Controlled fusion has always been 5 to 10 years away, just as we've always been at war with Eurasia.

All deadlines have an implied "with equivalently aggressive funding" addendum

Re: Why is nuclear fusion so hard?

#133

Post by fusiaoids »

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.

These are called self-stable plasmas, and are already been explored. For example, TAE's field-reversed configuration.

Re: Why is nuclear fusion so hard?

#134

Post by dangjc »

Does fusion still have much of a role now that renewables are increasingly competetive? We can pretty much already harness infinite energy for all our needs from an already working fusion generator our planet happens to orbit around.

Re: Why is nuclear fusion so hard?

#135

Post by sethrin »

narag wrote: post #112
simonh wrote: post #96

Earlier quoted context omitted.

I suppose the universe doesn't owe us a cheap, easy, unlimited source of energy. A lot of people seem to think that it's inevitable we will achieve amazing, magical feats of technology given sufficient time and effort that are unthinkable today. Maybe. But it's also just as possible that we already know most of the general parameters of what is possible in the universe, and the peak practical feats of technology that…

Nuclear tech is not even a century old. The idea that we can't do any better in a thousand or a million years seems so improbable to me that I can't take it seriously. There is some kind of extrange pessimism around that mindset: that we will be extinct much sooner, or that the Sun will die and thus Humanity, as if there's no obvious way to escape that apocalypsis.

I don't know what it is about the idea of the far future that makes people so willing to throw out fundamental physical laws. The relevant point here would be that there are fundamental limits to heat transfer, and a finite amount of work which can be done on Earth-as-we-know-it for a given unit of time, irrespective of the energy source. An "unlimited" source of energy would be in practice limited by its heat output.

Re: Why is nuclear fusion so hard?

#136

Post by ethbro »

dangjc wrote: post #134

Does fusion still have much of a role now that renewables are increasingly competetive? We can pretty much already harness infinite energy for all our needs from an already working fusion generator our planet happens to orbit around.

> now that renewables are increasingly competetive...

... with legacy energy sources.

When talking about fusion / nuclear vs renewables, think in terms of max energy produced per site, not cost per unit.

Similar to total thrust vs specific impulse.

The largest respective power generation stations by source -- Three Gorges Dam / Itaipu Dam (Hydro, 22,500 MW capacity, ~100 TWh/yr), Kashiwazaki-Kariwa (Nuclear, 7,965 MW capacity, 60 TWh/yr, currently suspended for earthquake-proofing), Tengger Desert Solar Park (Solar, 1,547 MW capacity, ? TWh/yr), Alta Wind Energy Center (Onshore Wind, 1,547 MW capacity, 2.68 TWh/yr, Gansu not included due to utilization issues), Walney Wind Farm (Offshore Wind, ~1,000 MW capacity, >1.3 TWh/yr?).

And then realize that hydro & wind are both location-limited. And solar has a large footprint: Tengger is 43km^2.

Nuclear (and eventually fusion) scales footprint much more slowly with capacity. Kashiwazaki-Kariwa is 4.2km^2.

Re: Why is nuclear fusion so hard?

#137

Post by sova »

voidmain wrote: post #114
sova wrote: post #113

Earlier quoted context omitted.

Provided you could keep the plasma contained in magnetic fields, it would certainly generate plenty of free neutrons to provide heat for substantial power generation.

If you let it cool, it would stop fusing. The fusion power wouldn't magically go up.

fusion halts harmlessly when conditions are unmet

Re: Why is nuclear fusion so hard?

#138

Post by pontifier »

ballenarosada wrote: post #70
Creatccount wrote: post #43

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

Good question. Under the influence of a magnetic field, charged particles do all sorts of counterintuitive things due to the Lorentz force, which acts at right angles to the particle velocity and the field. One example is a sideways precession due to the interaction between gravitational acceleration g and the Lorentz force. Fortunately this effect is basically negligible, because gravity is so much weaker than the e…

My understanding is that stellarators are designed in such a way that this sideways drift in one part of the device is canceled by opposite drift in another part due to the twisting of the field.

Re: Why is nuclear fusion so hard?

#139

Post by robertsteinhaus »

Mankind is currently in possession of a practical fusion technology.

It might be worthwhile to remember that Ivy-Mike fission-fusion technology worked the very first time it was tried in 1952. Mike technology was the basis of the first thermonuclear weapons in the US arsenal. Adapting Mike technology to be pure hybrid DT-DD fusion opens up many new applications in economical power generation.

In 60 years, no other fusion technology (Magnetic Confinement or Inertial Confinement) has ever produced any net energy (more energy out of the fusion reaction than it takes to get the fusion plasma to fusion conditions).

In 60 years, all existing MCF and ICF fusion systems have never worked (in the sense that they have not produced more energy from fusion than it took to get the fusion plasma to fusion conditions).

Mike fission-fusion technology worked the first time it was tried and produced huge amounts of net energy (and has never failed).

Rather than placing our faith in scaling laws while we build ever larger and more expensive Magnetic Confinement fusion experiments (tokamaks and stellarators) while trying to achieve break even energy generation - why not go back to the field and adapt technology that has never failed to finally find success in fusion?

Re: Why is nuclear fusion so hard?

#140

Post by acqq »

fromMars wrote: post #125
acqq wrote: post #103

Earlier quoted context omitted.

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 t…

What I got from the first article you linked is that Thorium reactors produce less radioactive waste but are unproven technologies.

Don't stop at the first sentence. Read the whole article. It answers the propaganda claim of "less radioactive waste":

"Less" is only if need thorium would magically materialize out of nothing, that is, if you ignore the whole process. In reality, thorium inevitably has to be prepared with uranium rectors:

"Thorium cannot in itself power a reactor; unlike natural uranium, it does not contain enough fissile material to initiate a nuclear chain reaction. As a result it must first be bombarded with neutrons to produce the highly radioactive isotope uranium-233 – 'so these are really U-233 reactors,' says Karamoskos.

This isotope is more hazardous than the U-235 used in conventional reactors, he adds, because it produces U-232 as a side effect (half life: 160,000 years), on top of familiar fission by-products such as technetium-99 (half life: up to 300,000 years) and iodine-129 (half life: 15.7 million years). Add in actinides such as protactinium-231 (half life: 33,000 years) and it soon becomes apparent that thorium's superficial cleanliness will still depend on digging some pretty deep holes to bury the highly radioactive waste."

Not to mention that these hypothetical reactors simply don't work: if they would be viable means to produce energy, nobody would wait for the taxpayer subsidies, there's enough money which couldn't wait to make huge profits, if they were possible:

"'Without exception, [thorium reactors] have never been commercially viable, nor do any of the intended new designs even remotely seem to be viable. Like all nuclear power production they rely on extensive taxpayer subsidies; the only difference is that with thorium and other breeder reactors these are of an order of magnitude greater, which is why no government has ever continued their funding.'"

Post reply on HN