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Fusion reactors: Not what they’re cracked up to be

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Re: Fusion reactors: Not what they’re cracked up to be

#31

Post by Robotbeat »

sjcsjc wrote: post #28
Robotbeat wrote: post #26

There's nothing quite like trying to get fusion to work for a while to make you appreciate how awesome fission technology is. If we applied even half the cleverness needed for fusion to making better fission technology, we'd probably be way better off. ...and then there's solar. Why even bother with producing the energy, just capture it with a very thin solid state device! Just need to automate the planting of solar…

Re solar: not just deserts (there aren't many in the UK) - https://www.fastcompany.com/3053998/these-sky-high-balloons-...

Yes, I was being US-centric. I know most about the energy situation in the US, and I happen to live here. :)

Thinking deeper into the future, floating solar farms could also be a thing. The oceans are huge, and most nations are not land-locked. They'd have their own engineering challenges, for sure, but those challenges look like patty-cake compared to fusion power.

Re: Fusion reactors: Not what they’re cracked up to be

#32

Post by jerf »

leephillips wrote: post #18
adrianN wrote: post #16

Releasing Tritium is no problem, even if it's in kilogram amounts, because, as the author himself notes, the half life is less than two weeks. Edit: My reading comprehension is clearly lacking...

Where does the author note that? "Tritium has a half life of 12.3 years which means it will be dangerous for at least 120 years, since the hazardous life for a radionuclide is ten to twenty times longer than its half-life"¹ If you come in contact with it during that time you will get cancer. [1] https://www.nirs.org/wp-content/uploads/factsheets/tritiumba...

If tritium is released in its atomic form, it is only a hyper-local threat, both geographically and temporally. I wasn't able to confirm this with a quick Google, but I imagine tritium will just want to go up, up, up as fast as it can, where it will never bother anybody again. (It's heavier than hydrogen but still lighter per-atom than helium, which has the same behavior). It doesn't have the problem fission fuels have where they like to seep into ground water, and be both heavy metals and radioactive.

Plus, there won't necessarily be a lot of it in a plant. Even if you're accustomed to the surprisingly large energy density of fission fuels, you're still not used to the even larger power density of fusion fuels. We're not talking moving tritium around by the tons... we're talking by the kilogram, or tens of kilograms. Compared to the difficulty of building the fusion plant in the first place, handling a few pounds of tritium safely isn't challenging at all.

Re: Fusion reactors: Not what they’re cracked up to be

#33

Post by Recurecur »

_rpd wrote: post #27
Recurecur wrote: post #12

I'm interested in the approach being investigated at LPPFusion, on a shoestring budget no less. http://lppfusion.com/ LPPFusion is attempting to harness hydrogen-boron fusion, which doesn't produce neutrons, only gamma radiation and helium nuclei (alpha particles). Both the gamma radiation and the alpha particles can be directly converted into electricity. There are many potential benefits of this approach, but a pri…

There are a whole bunch of options for aneutronic fusion ... https://en.wikipedia.org/wiki/Aneutronic_fusion

True, but there are many engineering tradeoffs. Any of the listed reactions involving deuterium produce some neutrons, so those aren't desirable (plus deuterium and tritium are rare).

Of the other reactions, neither Li-6 or N-15 are readily available, plus lithium is highly chemically reactive. The proton-boron reaction requires the lowest input energy (temperature) of the desirable aneutronic reactions, so it's the hot ticket...so to speak.

Re: Fusion reactors: Not what they’re cracked up to be

#34

Post by mrfusion »

Robotbeat wrote: post #26

There's nothing quite like trying to get fusion to work for a while to make you appreciate how awesome fission technology is. If we applied even half the cleverness needed for fusion to making better fission technology, we'd probably be way better off. ...and then there's solar. Why even bother with producing the energy, just capture it with a very thin solid state device! Just need to automate the planting of solar…

Not just deserts. You could also float them in the ocean, no? We have 70% of our planet we're not using.

Spread them far enough apart and add some movement and shadows wouldn't hurt wildlife much.

Re: Fusion reactors: Not what they’re cracked up to be

#35

Post by Robotbeat »

(Thinking about the far future, here.) Inertial fusion using Deuterum and Helium 3 would solve a lot of these problems. Of course, He3 is rare here on Earth.

I don't think mining the Moon for He3 makes much sense. It's just too rare in the lunar soil.

Instead, my favorite concept is mining it from Uranus (whose gravity at Earth-like pressures is actually slightly less than 1g...). There's vast amounts available at useful concentrations (in addition to deuterium). You'd need a reusable two-stage nuclear thermal rocket to get it back to orbit, but luckily there's lots of hydrogen for propellant in the atmosphere (unlike Earth where that hydrogen must be chemically split from water or methane) and we've built and tested nuclear thermal rockets before (with more recent NTR designs achieving sufficient performance for such a vehicle to close). I'm not a fan of NTR for Earth launch (a lot of cost, plus it actually requires a lot more energy since all the propellant is hydrogen, instead of a mix of methane and mostly oxygen), but it would be enabling for Uranus launch.

Here's a concept for mining Helium 3 in Uranus using floating hot-air balloon mining facilities: https://solarsystem.nasa.gov/docs/5.6_Reinert.pdf

Re: Fusion reactors: Not what they’re cracked up to be

#36

Post by Recurecur »

mrfusion wrote: post #34
Robotbeat wrote: post #26

There's nothing quite like trying to get fusion to work for a while to make you appreciate how awesome fission technology is. If we applied even half the cleverness needed for fusion to making better fission technology, we'd probably be way better off. ...and then there's solar. Why even bother with producing the energy, just capture it with a very thin solid state device! Just need to automate the planting of solar…

Not just deserts. You could also float them in the ocean, no? We have 70% of our planet we're not using. Spread them far enough apart and add some movement and shadows wouldn't hurt wildlife much.

The ocean environment isn't easy on equipment, plus storms are a major issue. Then there's cabling...

Re: Fusion reactors: Not what they’re cracked up to be

#37

Post by KnightOfWords »

Robotbeat wrote: post #26

There's nothing quite like trying to get fusion to work for a while to make you appreciate how awesome fission technology is. If we applied even half the cleverness needed for fusion to making better fission technology, we'd probably be way better off. ...and then there's solar. Why even bother with producing the energy, just capture it with a very thin solid state device! Just need to automate the planting of solar…

Turns out those deserts may not be so useless after all I'm afraid, for example dust blown from the Sahara fertilizes the Amazon: https://www.nasa.gov/content/goddard/nasa-satellite-reveals-...

Solar has become more efficient and economic in recent years but remains only a small part of the energy puzzle for various reasons.

Re: Fusion reactors: Not what they’re cracked up to be

#38

Post by Spare_account »

SomeStupidPoint wrote: post #17
leephillips wrote: post #11

Earlier quoted context omitted.

No, they haven't, not even in single events, although their press releases claim that they have. Their actual papers make it clear that the claim of >1 energy gain is a result of somewhat arbitrary definitions. There has not been a single shot on the NIF where more energy was supplied by the fusion reaction than was used to fire the lasers - it's not even close.

Are you guys talking about different things? One seems to be talking about energy released by while the other is talking about energy captured from. I think GP was criticizing the news for making it sound like the first hasn't happened when only the second hasn't happened. (At least, in my understanding.)

The BBC article linked above describes a very specific scenario which matches neither of your described options.

"The amount of energy released through the fusion reaction exceeded the amount of energy being absorbed by the fuel"

This doesn't describe the relationship between the amount of energy injected by the lasers and the energy emitted by the fusion reaction. Presumably a lot of the energy injected by the lasers is wasted, some of it is absorbed by the fuel and it is this absorbed amount that was exceeded by the energy released.

There is even a clearer statement in the article:

"This is a step short of the lab's stated goal of "ignition", where nuclear fusion generates as much energy as the lasers supply."

It seems to me that the following order of energy levels exists with present technology:

Energy supplied to Lasers > Energy injected into system by lasers > Energy absorbed by fuel > Energy released by fuel > Energy captured to generate electricity from

Re: Fusion reactors: Not what they’re cracked up to be

#39

Post by DigitalJack »

Robotbeat wrote: post #26

There's nothing quite like trying to get fusion to work for a while to make you appreciate how awesome fission technology is. If we applied even half the cleverness needed for fusion to making better fission technology, we'd probably be way better off. ...and then there's solar. Why even bother with producing the energy, just capture it with a very thin solid state device! Just need to automate the planting of solar…

I have to think there are major ecological concerns with blocking sunlight over large areas. They may not be negative impacts, but surely it isn't a no-impact situation.

Re: Fusion reactors: Not what they’re cracked up to be

#40

Post by short_sells_poo »

Robotbeat wrote: post #26

There's nothing quite like trying to get fusion to work for a while to make you appreciate how awesome fission technology is. If we applied even half the cleverness needed for fusion to making better fission technology, we'd probably be way better off. ...and then there's solar. Why even bother with producing the energy, just capture it with a very thin solid state device! Just need to automate the planting of solar…

How exactly do you propose to get that electricity from the desert to say Finland?

Furthermore, you need to plaster a vast area in the desert with solar plants, which brings along all sorts of concentrated security risks. The alternative is to have many smaller plants dispersed, which results in a big loss of efficiency.

I'm all for clean energy, but you seem to be handwaving away pretty huge issues as "thought exercise". Our inability to store energy is not just some side concern that will go away any time now. There is a reason carbon fuels are so prevalent - their energy density is far above what we can store in batteries. Without scalable and high density energy storage, unpredictable energy sources like solar or wind are much less useful because often there is no sun or wind at high demand and on the contrary there can be an overproduction during low demand. Germany already causes serious headaches for the European grid when it floods the network with electricity on sunny/windy days. They actually have to pay other countries to take over the extra capacity.

Solar, wind, tidal etc... energy are all awesome and clean (if we disregard the land that they take up), but there are many difficult issues that remain to be solved before they can become a core part of the energy production.

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