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> Effectively unlimited clean energy is the goal. > Let that sink in. No, this was never the goal. At the beginning, ITER was a science project to get the US a
by credit_guy 2y ago
> Effectively unlimited clean energy is the goal.
> Let that sink in.
No, this was never the goal. At the beginning, ITER was a science project to get the US and the USSR to collaborate on something even if the Cold War was at its height. Similar to the International Space Station. Some project with no real scientific objective, but that could spur the enthusiasm of the masses, so politicians could gain popular support while covertly pursuing a path to rapprochement.
> Unlimited clean energy.
How exactly to you get the tritium? By running some fission reactors, right? Fission reactors are a reality today, and can provide unlimited clean energy already. Why don't they? Because they are expensive? And how do we know fusion reactors, if they ever show up, will be inexpensive?
Ok, here's something else to let sink in. The best fusion reaction out there (deuterium+tritium) yields only about 5 times as much energy per kg of fuel as the fission of uranium or plutonium. Only 5 times, not 50 times or 500 times.
And of course, we don't find tritium in nature, so we need to breed it from lithium using a source of neutrons. You could use a fusion reactor as the source of neutrons (deuterium + tritium = helium + neutron), as you can read on this ITER page [1]. What that page does not tell you is that you would need 100% efficiency to be able to breed your own tritium. Good luck with that. Any deficit will need to come from fission reactors.
Somehow the dream that is sold to people is that once we get fusion reactors, we can stop using the "dirty" fission reactors. It is just a lie.
[1] https://www.iter.org/mach/TritiumBreeding https://www.iter.org/mach/TritiumBreeding
- WorkLobster 2y ago> you would need 100% efficiency to be able to breed your own tritium How so? As I understand it, the breeding reaction is exothermic (Li-6 + n -> He-4 + T) so all you need are neutrons, for which (as someone pointed out to me two years ago[1]) neutron multipliers would be used. [1] https://news.ycombinator.com/item?id=32224650 https://news.ycombinator.com/item?id=32224650
- credit_guy 2y agoI was talking about the neutron efficiency, not the thermodynamic efficiency. As for neutron multipliers, they are currently so far from being realistic that they are essentially science-fiction.
- WorkLobster 2y agoI'm not sure I understand what's 'science-fiction' about lead or beryllium?
- credit_guy 2y agoHere's some articles about the neutron multipliers. You can go through them and see that they are all talking about feasibility and theoretical considerations. It's not just as simple as shooting some neutrons at a block of lead of beryllium on one side and more neutrons come on the other side. [1] https://www.sciencedirect.com/science/article/abs/pii/S0022311520312010 https://www.sciencedirect.com/science/article/abs/pii/S00223... [2] https://scipub.euro-fusion.org/wp-content/uploads/eurofusion/WPBBPR18_19890_submitted.pdf https://scipub.euro-fusion.org/wp-content/uploads/eurofusion... [3] https://publikationen.bibliothek.kit.edu/1000160103 https://publikationen.bibliothek.kit.edu/1000160103
- WorkLobster 2y agoNo, I agree, but you specifically mentioned "science-fiction" in the second post, and implicitly denied even their existence in the first post. I think there's a reasonable distance between that, and economic considerations / the fact that test hardware has yet to exist that's presented in those papers.
- ImHereToVote 2y agoSo best case scenario we have expensive fission nuclear reactors with marginally more output per plant. Why not just spend that money on fission plants. Also if all reactors are essentially based on boiling water. Why don't we just dig to depths were water is already boiling? I'm sure there are plenty of those areas on the globe.
- frankharv 2y agoWe are too busy driving rovers on Mars to explore our own planets inner structures. Many of the deepest shafts are commercial diamond mines. Not science. Imagine a Liquid Nitrogen cooled probe through the earths volcanic layers. There are probably organisms living there that we have no idea about.
- JoeAltmaier 2y agoNot right? Breeder reactors are not some sort of perpetual-motion device. They create energy, which can be used for lots of things including more reactions creating tritium by a 'cheaper' route from lithium. Like we use petroleum to power drilling equipment to get more petroleum. The energy released is the part that makes it 'free'. And isn't that 'four or five times' number, per reaction? Because deuterium and tritium are so much lighter than fissionable materials (by 10X) the energy per kg is truly 50X not 5X. Right?
- credit_guy 2y agoNo, the five times number is per weight, not per reaction. Per reaction, the fusion one Deuterium and one Tritium yields 17.6 MeV [1]. The atomic mass of the components is 5, so you get 3.5 MeV per one unit of atomic mass (also called a Dalton). Per reaction, fission produces between 190 and 200 MeV. Since the input is one nucleus of U-235 or Pu-239 and one neutron, the mass is either 236 or 240, so the yield is 0.8 MeV per Dalton. So the deuterium-tritium reaction is only 4.4 times more energetic than fission, per unit of mass. As for your first part, I didn't get what you were trying to say. > Breeder reactors are not some sort of perpetual-motion device. I don't think I implied they are, and I don't think anyone believes in perpetual-motion devices in 2024. [1] https://en.wikipedia.org/wiki/Nuclear_fusion#Criteria_and_candidates_for_terrestrial_reactions https://en.wikipedia.org/wiki/Nuclear_fusion#Criteria_and_ca...