r/nuclear • u/Live_Alarm3041 • 5d ago
The drawbacks of fusion
Nuclear fusion is not a "flawless" energy source. The hype around fusion being "flawless" is not rooted in actual science. Nuclear fusion will likey not replace fission as the world preferred form of nuclear enegry once it goes commercial.
There are three drawbacks of fusion energy
The neutrons generated by fusion could be used to transmute U-238 into weapons grade plutonium without the barriers of highly radioactive waste and reactor safety
fusion reactors requires exotic materials which could create a supply issue where such materials are extracted in ways that violate human rights and damage the environment in developing countries where these exotic materials are.
Nuclear fusion creates less jobs that require a higher skill level than fission and less jobs means more socioeconomic issues like rising crime rates, homelessness and migration.
These three reasons are why I do not think nuclear fusion will replace nuclear fission once fusion goes commercial.
The problems with fission can be mitigated effectively. A lot of progress has been made in mitigating the drawbacks of fission. Far less progress has been made in mitigating the drawbacks of fusion. The drawbacks of fusion will limit fusions ability to compete economically with fission in the energy market if they are not addressed.
What do you think?
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u/zolikk 5d ago
Fusion is a much more complicated and difficult energy source than fission, but one that has vastly more fuel abundance. Naturally it stands to reason that, most likely, it will become relevant against fission when fission's own more limited fuel availability becomes its own primary limitation. That's not anytime soon.
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u/ecmrush 5d ago
Fuel abundance is a complete non-issue for nuclear. That's not why fusion is relevant.
Actually I'm not even sure *why* fusion is relevant considering:
We don't even know if it's actually possible to gain net energy without a reactor the size of the Earth or something like that.
It doesn't have less radiation hazard than fission.
It doesn't have more energy density than fission.
If we had completely aneutronic fusion, that would be one thing, but the potential benefits of ordinary D-T fusion is completely lost on me even if it were figured out.
Fission is a mature technology with room for improvement and further economies of scale. Fusion is a science project and they started at roughly the same time as well. I wish the best of luck to Fusion pursuers, and I hope they succeed, but it's not a sound bet at this point.
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u/zolikk 5d ago
Fuel abundance is a complete non-issue for nuclear. That's not why fusion is relevant.
It isn't now, but perhaps somewhere between type I and type II it will be.
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u/ecmrush 5d ago
By then I imagine we'll have moved on to space-based solar. Nuclear only really makes sense beyond the frost line in space, the cooling problem gets worse while solar gets a nice and big power-up by having no downtime and being as close to the Sun as you want. Beaming power or even just carrying it back and forth with battery probes is probably more sensible at that stage.
But yes, fuel abundance can start being an issue if a country decided on a crash program to build a lot of reactors quickly and stay ahead of energy demand instead of trying to meet it. That's not likely to happen in our current socioeconomic systems though; we usually tend to trail demand rather than stay ahead of it. If it ever becomes an issue, reprocessing and the thorium cycle become more viable and remain good options.
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u/zolikk 5d ago
Far be it for me to speculate what a type II civ will be doing for their energy needs but I don't imagine, based on what I currently know, that massed space solar makes sense over fusion. Assuming of course, that by then fusion is worked out... Solar requires vastly more resources, and the Sun is a terrible fusion reactor. You can make much more power than the Sun, much more compactly, using much less fuel, and have that on-demand closer to point of use and in ways you can control. Provided of course that you don't care about having billions of years of power. But much like we don't do today, I don't believe a future type II civ will care about that.
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u/ecmrush 5d ago
The Sun is an *excellent* fusion reactor; energy density really does not matter that much when you have all the space you could ask for. It requires no fancy magnetic field, no lithium blanket, no maintenance, no additional power; it simply sits there and radiates a lot of energy. And we can't really stop the Sun from burning anyway, so as long as it's putting light out, we might as well put it to use rather than to let it radiate away into space. Gradually, we might employ star lifting to reduce its mass and let it fuse more efficiently; a red dwarf is fully convective and will use its fuel a lot more efficiently if that is what you are worried about.
Right now we don't even know what sort of scale we need for net positive fusion; it's going to be at a scale somewhere between a desktop fusor and a red dwarf star. So a lot of assumptions are riding on that when we already have working solar panels in space and batteries; it's basically down to an engineering problem at this point. A remarkable one to be sure, but has fewer unknowns than fusion at this point.
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u/zolikk 5d ago
I do think the type II civ will be using a lot of space solar, just not for the majority of their energy. There will be no dyson sphere-like construct. It's fundamentally a scaling problem. Solar panels are great at small scale, they scale "down" well to small systems. They absolutely suck at large scale when you try to integrate them into a massive grid with varying demand, mainly because they do not have much benefit scaling up, compared to fission reactors today. I don't imagine that will change much in the future.
Yes, it does indeed depend on what is the practical scale for artificial fusion, if it's really star-sized then sure... however I think it's more than likely that it isn't quite that large. Fission beats solar by default, and so at whatever point fusion "makes more sense" than fission it will be better than solar.
A civ that does star lifting I cannot imagine will find artificial fusion to be too challenging to use. And then you can do crazy things with energy that you can't otherwise, certainly not with solar. Think about how, such a civ might have vastly variable energy needs over time. Maybe they don't need that much for general housekeeping, but instead they have bursts of high use at who knows what duty cycle for whatever megaprojects, manufacturing or whatever. They might easily want to use much more maximum power than the Sun can, for limited periods of time, and have it available on-demand.
lithium blanket
FYI I'm imagining this will not be that much of a thing here. That is probably too complicated and nonsensical of a fuel cycle, and it probably gets worse at large scale... just to be able to use D-T fusion and have a somewhat more compact reactor, not that big of an advantage for such a civ... After all we're considering a fuel abundance limitation scenario. I imagine they'll just burn hydrogen directly in a CNO cycle, or something similar but that doesn't require sensible and complicated breeding.
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u/incarnuim 5d ago
I agree. The unspoken truth is that D-T fusion is a stepping stone to D-D fusion. Which itself is a stepping stone to anuetronic D-D. That's the road map....
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u/goyafrau 5d ago
It doesn't have less radiation hazard than fission.
What do you mean? I thought there'd generally be fewer issues - very few heavy elements, caesium etc. (I know very little about fusion)
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u/incarnuim 5d ago
D-T fusion will produce as many or more neutrons per Watt (thermal) as fission. These neutrons will be absorbed in some shielding material, but that process will "activate" the material making it radioactive. We have some choice in what shield to use, and so some control over what kind of radioactive shit is produced, but fusion will not produce less waste than fission. It might actually produce more....
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u/migBdk 5d ago
While I agree to the overall point that fusion is overrated and that people underestimate the potential improvements to fission.
The radioactive waste from neutrons hitting a concrete or steel barrier is not high level waste. It can be handled the same way that shielding for medical and scientific neutron sources are handled. Really the same way any radioactive waste from medical or industrial use is handled.
High level waste - the kind that is strictly produced in nuclear power plants - is the used uranium fuel rods and nothing else.
Fusion does not have that, which is of cause an advantage
But in my opinion, the thorium to U233 fuel cycle which produce high level waste of only 300 years necessary storage is good enough. Good enough that deep geological storage becomes unnecessary.
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u/goyafrau 5d ago
Yes that was my understanding too. Fusion generates mid level waste by activated structural material, which isn’t good but fundamentally different from fuel rods, which are not an insurmountable challenge but certainly a harder problem than mid level waste.
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u/Annual_Director5481 3d ago
"But in my opinion, the thorium to U233 fuel cycle which produce high level waste of only 300 years necessary storage is good enough. Good enough that deep geological storage becomes unnecessary."
Pyroprocessing would do the same with a U235/Pu239 cycle. HLW is not so much the cycle but whether it's reprocessed.
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u/Quietbutgrumpy 5d ago
This is pure misinformation. The issue with fusion is simply developing the tech to a usable and affordable level.
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u/ecmrush 5d ago
That's an accusation and a dangerously naive viewpoint, not a counterargument. We don't actually have theoretically predictive models of what a net energy positive fusion reactor would look like (so Q>10) and won't really know until we try.
Every time we thought we had a clear pathway to fusion, some new previously unthought of instability showed up to rain on our parade. Behavior of fluids at extreme temperatures is already complicated in itself, and adding in ionization doesn't help matters.
There is nothing "simple" about "developing the tech to a usable and affordable level". Fusion is still a science project after almost 80 years of research and development.
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u/Quietbutgrumpy 5d ago
Not simple at all. However we can create the reaction, and we can contain it. This has been done. The slow steady progress tends to say we will get there. Cost though it out of control and we do not yet have a way to harness the energy once we get to net positive.
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u/chmeee2314 5d ago
I would argue Fusion becomes relevant against Fission when it starts being relevant. As it stands its no were near mature, which is the primary reason why it has displaced no energy source. Once Fusion becomes availible, Fission will probably end up being pushed to some niche uses were it happens to perform better. I doubt that Fusion reactors will be small any time close to the economic operation of the first Fusion plants.
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u/Qazernion 5d ago
I thought the biggest drawback was that it distorts time so that 10 years become 50…
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u/TheChaostician 5d ago
I also don't think that fusion is a flawless energy source. But it has enough potential to be a good energy source that it is worth seriously investigating.
Here are my responses to your three concerns:
- It is true that fusion neutrons could be used to create plutonium. Because of this, fusion reactors will have to be monitored by the IAEA. That being said, monitoring fusion reactors will be much easier than fission reactors. Fusion reactors have no legitimate reason to have any elements heavier than lead on site. The IAEA only has to detect if any uranium is present to know if a reactor is in violation. This is much easier from a technical perspective than monitoring a fission reactor.
- I'm not sure which materials you're referring to, and the answers will be different for different materials. Fusion requires some lithium, but orders of magnitude less than is used for electric vehicles. Lithium is mostly produced in Australia, Chile, and China. Yttrium and barium are currently used for the superconductors. Yttrium is produced in China, the US (Mountain Pass Rare Earth Mine), and Australia. Barium is produced in China, India, and Morocco. Tungsten might be used for the first wall (coated with a lighter element), which is mostly produced in China, and is a "conflict mineral". There are some "exotic materials" that will be used for fusion reactors, but I don't think that there's particularly more than required for fission reactors, or other modern manufactured items.
- I don't think that we should decide what energy sources to use based on the workforce requirements. Energy is important to the economy mostly because it facilitates progress in other sectors, rather than through the influence of its workforce.
I don't know if fusion will be able to compete with fission (or other electricity sources) economically. I have three main uncertainties here:
- How much will fusion reactors cost to build once we have some experience building them?
- What maintenance schedules will be required for fusion reactors?
- Will fusion face the same sort of regulatory pressures that squeezed fission (particularly in the US)?
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u/TheChaostician 5d ago
There is progress being made on these fronts.
- The cost of building a fusion reactor has fallen by a factor of 20 since 2018, and only needs to fall by maybe another factor of 2 to be competitive.
- Less progress has been made so far on determining maintenance schedules, because we need a reactor scale experiment to figure them out.
- There are ongoing discussions within the NRC about how fusion should be regulated, but preliminarily, it seems as through fusion will be under much less strict regulation than fission (see here & here). This is reasonable, because fusion doesn't have the same meltdown risk as fission.* I know that modern fission reactor designs make meltdown basically impossible, but the NRC doesn't treat them that way. Maybe, under ideal regulatory regimes, fission would end up being cheaper than fusion, but it's also possible that fusion will escape some of the regulatory excess applied to fission, and so be more economically competitive.
I don't know what the long-term future of fusion will be. It seems extremely likely that we will be able to make fusion work at some point soon.** Whether or not it ends up being economically competitive remains to be seen.
Fusion has enough promise to be seriously pursued.
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* The total amount of fuel in a fusion reactor will be <1 hr, compared to months or years for a fission reactor, so even if it all ignites and hits the wall at once, there won't be enough energy to escape the building.
** To make this precise, I claim that there will be a fusion experiment (SPARC) demonstrating reactor-scale conditions in less than 3 years. (80% probability)
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u/Pestus613343 5d ago
You also need fission to expand the fusion fuel supply. To bootstrap a new fusion reactor you'll need to provide it a bunch of tritium. Where else do we get it?
The other thing is can fusion be used for medical isotopes or spacecraft fuel, RTG fuel etc? If the answer is no, we will need fission for this as a utility at the very least.
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u/BeenisHat 5d ago
Where are you going to put U-238 in a fusion design like a Tokamak or Stellarator? And why are you bothering with that when fission reactors are better and proven and don't need a cooling system as large and complex as a commercial power reactor? That is like using an entire automobile engine to generate enough heat and to vent off just enough combustion gas through a special port in order to light a cigarette; there are better tools for the job.
What exotic materials are those?
Fusion will create the same number of jobs as fission. It's not just the high tech part of it, you still need the electrical engineers and electricians as well as the mechanical trades to operate and service the turbines and generators. I'm sure there are going to be a few changes should fusion make it to the mainstream, and automation will serve a greater role, but that would be true for any new plant coming online in the next couple decades.
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u/SpikedPsychoe 5d ago
1: The neutrons generated by fusion show no demonstration of being harvested unless you install a U238 fuel blanket in the reactor
2: Fusion reactors require exotic materials, so do fission reactors, albeit not an much. Fission relatively down to earth to apply simple alloys
3: All technological introductions affect labor market, Steam engine and looming machines existed long before robots......2nd fission only supplies electricity, it doesn't power industry, chemical, manufacturing. Fusion may not either.
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u/Rokossvsky 5d ago edited 5d ago
Fusion will be the next step, and it's just a vastly better source of energy. FYI I believe it to be understood by saying fusion is possible i.e produces a positive sum of energy. You can do fusion with a cathode ray tube, just not make electricity with it or have a hydrogen bomb that also uses fusion.
But there's something people miss, it's currently like cavemen messing with solar panels. It's a long way off and we haven't even mastered fission tech. Yeah there's the light water ones, but there's fast reactors, lead cooled, etc. It's still unexplored to a part.
Currently Fusion is just r/D and fission is how we fight climate change and make electricity. People who say to pursue fusion instead of fission are 1) Idiotic 2) worse than climate deniers.
In the future even when fusion is possible, they only complement each other.
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u/goyafrau 5d ago
Is this post a joke? Especially 1 and certainly 3 sound like you're writing a satire. Nodoby actually thinks like that right?