Curious that they do not mention the far more developed fusion reactor in France, but anyway while I prize research in general I always reiterate that we can and MUST dream, but at a society scale, not company, not lab, we need thing that work for sure NOW.
Witch means that's hyper-right funding a PUBLIC research on fusion energy even if it demand *centuries* before showing usable results, BUT we have an energy production issue now and we need to sort it out quickly for real, not in a potential future...
ITER was mentioned several times in the article. I am guessing that's what you meant by "far more developed fusion reactor in France", even though "far more developed" could be argued since it's still under heavy construction and has not started operation, and thus has produced no results as of yet. D-T operations are scheduled for 2035, and it will most certainly miss that target. Plus, it's still an experimental reactor and meant to be a proof of concept. DEMO, a commercial reactor, would then be designed and constructed using the learnings of ITER (if it turns out feasible, which is unproven at this point).
Moonshots need a focused direction of R&D, not design by committee. ITER is the definition of design by committee. VC backed funding is a much better model for this kind of idea where the tech is _almost_ there but need capital intensive build outs to validate it.
Apollo was also a dead end. It resulted in a system that was so expensive not even the government wanted to keep using it. It's taken a private approach to get launch costs down to the point that returning the moon may be practical.
If we had stuck with the Saturn V and conducted one moon landing per year, it would have been far cheaper than the Space Shuttle program.
I applaud the private sector’s results, but the Apollo program was a national triumph and should in no way be considered a dead end technologically. It was the politicians that failed the program, not the other way around.
The Shuttle was an abomination of a program. At no point during the Shuttle program would it have been a mistake to shitcan the whole thing. Pointing to it does nothing to justify Apollo.
I'm not sure how you're failing to understand. Apollo was a dead end, obviously, since we gave the entire thing up and still haven't been back. It was an artificially inflated exercise in national ego. In no way was it worth the money expended on it.
(If you bring up science or spinoff arguments, I will demolish those in detail.)
More broadly, if we include Mercury and Gemini, it was a tremendous success in the sense of developing Astronautics as a whole. I won’t cite specific spin-offs, but the impetus to land on the moon so rapidly necessarily meant learning how to do things like rendezvous and establish communication networks.
>”It was an artificially inflated exercise in national ego. In no way was it worth the money expended on it.”
There is way more to it than mere pride. President Kennedy and LBJ decided to push hard with the space race as a means of economic warfare against the Soviets. The strategy was twofold: one, to get the Soviets to commit resources to their own moonshot program when they otherwise would not. We were betting on our economy being stronger than theirs, and we could force them to catch up to us. Two, to develop American industry and expertise when we had clearly fallen behind. The spending might seem wasteful but it created a ton of jobs and bootstrapped our space industry. We essentially closed the whole “missile gap” in about 7 years as a result.
If you want to spend for energy production, fusion is, by far, a worse choice than most alternatives.
Spend on building out existing solar and wind. Spend on building out transmission lines. Spend on improved solar, e.g longer-lived perovskites. Spend on a wider variety of storage media. Spend on cheaper electric-driven ammonia synthesis.
"The incoming fusion neutrons sustain the temperature of the circulating liquid metal, whose heat would be extracted to drive a turbine."
I assume this means a steam turbine (heat engine). With the losses inherent in that process, I assume the idea is we'll have a "limitless" source of heat anyway?
Or is heat transfer inherently better with this fusion design?
If fusion relies on a steam turbine, it's going to be economically infeasible. Natural gas power is cheaper than either coal and fission power because they both rely on big, heavy, expensive, inefficient steam turbines.
And solar power and wind is cheaper than natural gas, even with batteries.
- "Natural gas power is cheaper than either coal and fission power because they both rely on big, heavy, expensive, inefficient steam turbines."
Most natural gas power plants in the USA use steam turbines. The most common setup is a two-stage "combined cycle": first, an internal-combustion gas turbine, whose waste heat powers a lower temperature steam turbine.
Because it is still very much up in the air if fusion is cost effective. If the price to build a plant is astronomical it can not make enough energy to pay for itself.
A better question is why we are not investing in solar, wind and hydrogen more.
Yes, but they have the incredible advantage that they produce large amounts of energy economically today, whereas, as the article states, it is not yet clear whether fusion will ever be able to produce significant energy, let alone economically.
Wind and solar only produce energy when the weather is cooperating, and it's difficult to predict how climate change will impact future availability. Hydrogen might be economical someday, but currently it's rather difficult to generate, store, and transport.
Hand-waving away the transmission/storage required to make intermittent energy sources "reliable" does not magically make them trivial, or even solved, problems.
I don't really care whether or not nukes are cheap when they're the only reliable low-carbon energy source we have, and when they're the safest energy source we have. Some things are more fundamentally important than economics.
We can look at simulations using actual historical weather data and actual cost estimates to determine how much it would cost to deal with intermittency of wind/solar using storage. The result is something that looks cheaper than fission (or cheap than fusion is likely to achieve.)
Fusion does not "offer benefits" of any energetic or economic kind. It is interesting in the same ways that microkelvin cryogenic and gigapascal hyperpressure are, exercising extreme physics.
Fusion does not offer energy density even approaching commercial fission.
> A better question is why we are not investing in solar, wind and hydrogen more.
This always comes up in discussions about fusion but do you really think we aren't? Solar didn't get where it is now from a lack of funding. A lot of money and time and effort has gone into it, just not mostly into one boondoggle project everyone can point to.
I would really like to hear numbers to back up the idea that investment into these (esp. solar and wind) is "small" in total because I'd easily bet on it being several orders of magnitude more invested in than fusion.
Sure, I agree with that. But when you raise this in the context of fusion it implies that you think fusion is somehow preventing this, so where's the evidence?
If you took every dollar of ITER and put it into solar would it make a meaningful difference? Probably not. It just reads as extremely misdirected, and maybe even sealioning.
And to be clear, I think ITER specifically probably is a waste of money, but it's a waste of money on a shockingly tiny scale for how much negative attention it draws, it's by far the bulk of spending on fusion, and none of it really has much to do with anything to do with scaling out manufacturing and deployment of proven technology.
Add up the money spent on fusion over decades. Imagine it spent instead, at the time, on improving solar panel manufacturing processes, initiating the exponential decline in cost two decades earlier than we got it.
But just now probably the biggest effect is confusing people about the cost structure of power generation, leading them to believe that lots of heat per unit mass input results in cheap power.
Again, I really don't think as much is spent on fusion -- or as little on solar -- as you seem to think. People keep throwing this idea around but it's not clear where they get it or they have literally anything to back it up. Fusion spending has amounted to maybe a few billion dollars a year since it began to be something anyone was willing to spend any money on at all, and that's being generous to the idea that a lot is being spent on it. I can find sources that talk about the investments that have gotten us to this point in solar being on the order of trillions of dollars[1].
It's likely that in a parallel universe where 0 investment into fusion happened, and most of it was pumped into solar, the difference might be something like:
- One small city might be covered in solar panels.
- We'd be farther behind on some areas of material science, superconductor research, and fundamental physics than we are by a bit.
Again, I compared research on fusion against the prospect of research to make manufacturing solar cheap decades earlier than the Chinese government finally commissioned that work, leading to the present miracle. The consequence could have been solar built out decades earlier, millions of tons more coal left in the ground, and climate catastrophe pushed back.
Back when that spending might have made a difference, there was no work on superconduction for fusion, because high-temperature superconductors were not a gleam in anybody's eye.
That said, it is possible that training up and employing plasma fluid dynamics physicists could yet have unforeseeably consequential results that might yet (as it were) eclipse the effects of cheap solar PV.
Do you really believe fusion research is the least useful thing the usgov spends $1b a year on? My issue here comes down to "why is fusion the thing you pick on"? They're both energy projects but so are thousands of other more expensive, more dangerous to the climate things.
Anyways I suspect $1b of 2022 dollars wouldn't go nearly as far in 1980 or 1990 in terms of advancing solar tech. It's not like all that happened in a vacuum, semiconductor tech likely had to get to a certain point before this explosion could meaningfully happen, and there's never been a shortage of investment into semiconductors.
In this whole thread you've provided no evidence or reason to believe fusion research was in any way inhibiting solar research. You just seem to have a feeling it's true, but what, specifically, would those dollars have done for solar, and why are they somehow uniquely suited to being repurposed towards solar? If it's so glaringly obvious you should be able to explain more deeply.
I don't see any problem with doing the research involved in trying to get fusion working. There are plenty of practical problems that provoke creative attempts at solutions, which are at least educational and might actually advance the state of this or that art.
The problem is promoting the work as if it might ever lead to practical power generation.
The first is the same as all other research. The other is just lying. I don't like lying. That is all.
It is worse when they claim yet another "breakthrough".
The best information available says fusion as pursued will never be anywhere close to competitive even with fission (which is not today economically competitive), never mind with photovoltaic solar panels (which are).
Fusion research is cool beans, but not for any plausible practical reason.
Given that, all the work on making it happen at big scale is a wholly wasted. The companies issued billion-dollar contracts to build parts of it do not see those contracts as wasteful, and hope we won't.
Probably because it's not a solved problem that simply needs money to scale up?
If you think about it, you can't simply give money to JS developers to do fusion research instead of making HTML buttons for internal use.
Those who can work in the field already do but so far there's nothing to show in terms of practical solutions. They even receive fair bit of criticism for misrepresenting the outcomes of their work to get more funding. Every now and then a startup or something will come up to claim that they thought of something novel that will solve all of the problems and how the people who work in expensive government funded programs are amateurs with no creativity, then disappear in the valley of vaporware dreams.
Humanity is deeply invested in it, it's just that it's really hard.
Oh, BTW, We already have a reliable and extremely powerful nuclear fusion reactor in the sky. We can actually pour enormous amount of our resources into harnessing it and succeed but it is considered a divisive topic.
The storage is not an unsolved mystery at all, we have many methods to store energy. Maybe it's not perfected yet and not optimal and cost effective as we would like it to be yet but it's nowhere near the situation with fusion technology. Unlike the fusion, the science of it is well developed and it boils down to its commercialisation optimisation.
Besides, as we are creatures who sleep roughly in sync with the fusion in the sky, we don't really need to have 24/7 constant energy input. Combination of storage and older tech like good old fission energy and natural gas can be enough.
I guess we take as a given we were there for cynical oil based reasons?
> War in Ukraine? Just stop giving Russia fossil fuel money
The oil/gas doesn't cease to have value under sanctions, at worst it can all be consumed internally to drive their war machine. Climate change isn't driving Russia to desire Ukraine, it just does.
> Climate change? Let’s just not.
The government we are cynical of now has the power to control climate and our cynicism vanishes?
1) yes definitely. The only reason anyone in the west cares about the Middle East is the oil.
2) it they have less value, to the point you wouldn’t have to be a slave to the producers of energy.
3) even cynics can’t sell ice to eskimos. If fusion really did pan out and make energy abundant it doesn’t matter if they have lots of oil and gas. No one would need it.
As many other comments have pointed out though, fusion seems kinda unlikely to actually do that, but arguing that even if it did it wouldn’t change anything is a bit pessimistic for me.
I sort of feel this way, but the problem seems sufficiently complex that the solution is "path dependent," much in the way chip process generations are (we couldn't have jumped straight from a 100nm process to the present 5nm processes just by spending all of our money on it). Just spewing out money would likely lead to lots of fraud, and the outcome would be similar to the current funding regime.
Politicians aren't here to offer to solution or to improve the state of the country, they are here to maintain themselves in power and reward their friends. Their friends don't like fusion, and supporting fusion would make it less likely for them get reelected.
Until the winds change and supporting fusion would make it more likely for them to get reelected, they will be making up all sort of stuff of why we should waste money in less proven and more unreliable, and possibly dirtier sources of energy.
Because the whole field is an easy to debunk bullshit which is worthless in practice.
If today somebody came up with a working thermonuclear reactor with a positive energy output, nothing at all will change in energy markets, because it basically means you are getting a complex and expensive steam boiler that runs on effectively free fuel. But even electricity made from coal has only 20% of the coal price in it, meaning, there won't be a dramatic improvement in energy cost if fossil fuels were free.
Renewable energy today provides very cheap energy inputs and no improvement in this field can yield any dramatic difference. And everything that comes further downstream has to be paid, anyway.
Research in it is still a good thing though because a lot of other discoveries and technology improvements are done on the way, bringing benefit even if result itself is useless (like with the moon landing).
There's no guarantee it's a solvable problem. With the Manhattan Project we knew it was feasible and how to do it, all we needed was engineering.
With fusion we don't know how to do it. There are many, many ideas we could pursue, and they are being pursued, but we have no idea if any of them will actually work. It's quite possible none of them will, or that solving it might take enabling technology we haven't even thought of developing yet.
For context we have already spent several Manhattan Projects worth of fund on fusion research, in inflation adjusted terms.
You made 10+ comments along those lines, just for this article. How about providing at least some justification, rather than making absolutist statements?
DT fusion has inherently lousy volumetric power density. ITER's thermal power density, for example, is 400x worse than a commercial pressurized water reactor's primary reactor vessel. ARC's is 40x worse. Now couple that with those cores being far more complex than a fission core, and the difficulty of maintenance (they will be too activated for hands on maintenance.)
IMO, the only fusion company that has a real chance is Helion. Most of the breathless hype runs into generic showstopping issues like the ones above. If someone presents a new fusion concept, ask them about their power density, and how much complexity there is in that core.
And there's the more insidious variant of this: to solve it we need new physics. I say it's more insidious because, if we used all the money in current approaches, we would be diverting it from the research that could really solve it.
We need to understand the nuclei. The only way to do that is to create macro-scale working models of nuclei, to see what happens inside them. The «walking droplet» kind of experiment is a step in the right direction. These experiments are much, much cheaper than any other experiment in quantum or nuclear physics, but nobody wants to fund them.
> There's no guarantee it's a solvable problem. With the Manhattan Project we knew it was feasible and how to do it, all we needed was engineering.
I mean, the Manhattan project wasn't about trying to figure out how to harness nuclear power, it was about how to deliver a nuclear explosion. getting some energy out of fission was never really a particularly hard problem once we understood what was going on (it's literally so easy that it's a problem), getting it to explode from a package you could load into a b-52 was the harder problem.
The difference isn't really about what we know is possible, it's that unlike fission, making a fusion bomb is easier than making fusion power, so the military funding dried up before it made much progress, like a person's interest in a porno once the fun part is done.
We could also look at simpler ways of living. Simply not using that much energy. Politically that's a suicide move (to promote), but it can happen on a grassroots level. Housing policy for example would need to change. People should be able to build simple houses using natural methods without having to comply with complex building codes.
A bigger problem is making people less career-driven and settle for a simpler life, small-scale farming, permaculture etc. Photosynthesis is free and abundant!
But we're locked into this mental trap of constant growth. We just assume that the only way should be up - more energy, more people, more stuff...
There's an interesting analogy about how we've been depleting our huge supplies of fossil fuels at an alarming rate, causing the population to spike out of control, with little planning ahead for when they eventually run out (the effects of which we've already started to see the effects of):
"On the far end of the overshoot spectrum are situations in which a community of living things receives a surplus of energy through some accidental event that happens only once. Imagine how the lives of field mice would be transformed if a truck full of grain overturned on the nearby freeway and spilled its load in their meadow. The mice suddenly have more energy than they can use and their population soars far beyond the meadow’s carrying capacity. As the number of mice in the meadow grows, though, the rate at which the grain is consumed also rises, until the grain begins to run short. At this point nothing the mice can do will spare them from dieoff; most of the mice will starve, and the survivors’ struggle to keep themselves fed may damage the meadow badly enough to decrease its carrying capacity over the long term. Years later, the meadow may still not support as many mice as it did the day before the truck overturned."
From John Michael Greer's book The Ecotechnic Future
> there are daunting engineering challenges involved in stabilizing a torus where the inboard legs of the magnet coils are subjected to extraordinarily high electromechanical stresses and overturning moments.
True, but MIT (and by extension CFS) has more experience with this than anyone. Their Alcator C-Mod had the strongest magnetic field of any tokamak. I got a tour of it once, and a grad student showed us a metal tie rod, about a meter long. He said they'd calculated that two of them could have held down the Space Shuttle when it was trying to launch. To keep the reactor from flying apart, they needed 38 of them.
> In any case, improving cost-effectiveness is surely a distraction for MCF research when there have been no advances in Q
Except smaller, cheaper reactors mean you can iterate experiments a lot faster.
> two of them could have held down the Space Shuttle when it was trying to launch. To keep the reactor from flying apart, they needed 38
And all that for a reactor that was unable to break even in energy terms, let alone ignite and break even economically.
It perfectly illustrates the folly of magnetic confinement: to hold the plasma you need fields so strong and equipment so massive and expensive that the capital expenses get out of control, fully negating any advantage fusion might have over fission. We already know how to make capital intensive energy - the fueling costs are negligible for a fission reactor, yet those largely failed in the market. An even more expensive and capital intensive solution is dead in the water for economic reasons regardless of any theoretical merits.
If you look at the 2014 ARC paper, you will discover that 60% of the mass of the reactor is the stainless steel structure for resisting the JxB forces on the magnets.
I never said it was. But a device that needs multiple square feet of high tensile steel to hold together will have immense costs because it also includes gigantic superconducting magnets, vats of cryo-coolant and myriad of custom, unique parts made of exotic materials for exorbitant money.
The billion price tags of tokamak experiments is not a scientific oddity, it's a fundamental economic issue with the approach that will carry on to any production plant, that as far as we can conjuncture will need to be even larger and more expensive.
Nonsense. That's all gravy. The cost difference between experiments and reactors is scale. ITER is a good example to point to. If reactors needed to be the size of ITER mankind could never deploy them at scale because we simply don't have the resources. If ITER was 5x smaller: it's a different story.
Since ITER's volumetric power density is 400x worse than an existing commercial PWR's reactor (+ its pressure vessel), we'd need quite a bit more than a 5x reduction in volume. Even a 5x reduction in linear dimensions (likely impossible at the same power output, due to wall loading 25x higher) may not be enough.
> mankind could never deploy them at scale because we simply don't have the resources.
I don't understand what your objection exactly is. That's just a way to rephrase my statement: magnetic confinement, as it stands, is too capital intensive to ever break even financially, regardless of the experimental success ITER/DEMO might have.
And if you're ever thinking about building one at home, just try not to cause an accident. What's more dangerous than playing with fire? Playing with smoke detectors.
Both stellarators and tokamaks appear as Möbius strips to confined charged particles. The key difference is that the toroidal transform is applied via induced toroidal current in a tokamak whereas it's inherent in the magnetic field geometry of a stellarator. We're in the middle of the golden age of stellarator geometry research and optimization. It's a very interesting problem with large payoffs for modest investment.
It would take a square bar of regular old 250MPa structural steel about 32x32cm to hold the space shuttle, at full throttle, and it's solid rocket boosters down.
Or 38 square bars about 5x5cm.
And 250MPa is just it's yield strength, that type of steel work hardens and has an ultimate tensile strength usually in excess of 350MPa.
There are, of course, much stronger varieties of steel.
For sure, you'd likely have heard of chrom-molly steels.
Got example, 4140 is a 1% chromium - molybdenum medium hardenability general purpose high tensile steel - generally supplied hardened and tempered in the tensile range of 850 - 1000 Mpa.
Three to four times greater tensile strength, so two 127mm (5") diameter rods would do it at 1000 MPa.
- "The in-plane loads are carried from the covers to the cylinder by 96 INCONEL® 718 draw bars with a yield strength of 1 GPa." [0]
- "The wedged conductors are CD107 copper, bonded to flat Inconel 718 plates, with a 4:1 copper/reinforcement ratio over the central column area. The yield strength of the copper is 310 MPa, up to 100 °C, while the yield strength of the Inconel plates is 1130-1300 MPa. The peak Tresca stress on the Inconel at the inside radius is calculated to be 580 MPa, while that in the copper is 310 MPa." [1]
Speaking of fruit, I’m interpreting this as an apples and oranges situation. If we’re talking about trust of the engine that’s one thing, but holding back a launching rocket is different. That is the absolute worst case for the rocket (and best case for the rod) due to the weight of the heavy fueled up rocket fighting the trust along with the rod
> It is likely unachievable anytime in the next half a century.
It is very important for this message to get through. Fusion is not "just around the corner".
By the way, the energy generated by fusion is higher than that generated by fission, but not by a huge amount. Only by a factor of 4.
The energy density of Deuterium+Tritium is 337 TJ/kg. The energy density of Uranium is 81 TJ/kg. For comparison, the energy density of methane is 56 MJ/kg or more than 1 million times lower than that of Uranium.
1 kg of deuterium is a lot friendlier to be around and less alarming to find anywhere on the planet than 1 kg of U-235. 1 kg of tritium is a hazard, but it's also more than the global annual production of tritium and any DT reactor would be engineered to have low tritium inventories and a controllable breed rate.
U-235 has a half life of 700 million years. When it decays, it releases alpha radiation (Helium neclei), which is not that dangerous. As long as you don’t ingest or inhale it, U-235 is harmless. If you do ingest or inhale it, it will probably harm you more because it is a heavy metal than because it is radioactive.
I don't fully understand where you're going with this question.
Maybe you are implying a terrorist could get their hands on 1kg of U-235 and either make a dirty bomb or a nuke. A dirty bomb would not really be more dangerous than a dirty bomb made with Cadmium. As for a nuke, 1kg is well below the minimum necessary to make a nuclear bomb, which is about 15 kg. But that's not the only thing. You need weapons grade Uranium for that, i.e. Uranium where U-235 constitutes at least 85% of the whole. Civilian reactors use Uranium that is enriched to much lower levels. Currently, the vast majority of the civilian reactors use Uranium enriched to 4.5%. A terrorist who gets their hands on that, can forget about building a nuclear bomb, except if they have means to further enrich that Uranium. In other words, if they have centrifuges, like Iran does. I might remind you that Iran is a state, not a single person. In any case, if you have centrifuges, you might as well start with Uranium ore, there's no point in stealing from an existing civilian reactor.
Unlike in most cases, where there is a conflation of fissile and radioctive substances, I believe that the parent comment was actually referring the the problem that occurs when you allow people to get their hands on too much enriched uranium.
I mean I sort of see why you’ve been downvoted (this is off-topic and adds nothing to the discussion), but you’re also not wrong.
Extraordinary claims require extraordinary evidence, which is a lesson that we learned a million different hard ways and which has been almost completely forgotten.
> It is very important for this message to get through. Fusion is not "just around the corner".
Only if you keep reading articles written by people who don't know what they're talking about. Fusion power break even will happen in roughly 5 years with MIT's/Commonwealth Fusion's SPARC test reactor.
How does tokamak fusion interpolate between pure D-D and 50/50 D-T? Like, responsive to footnote cite [30], if tritium recovery falls short, could you run a sustainable D-rich D+T mixture, where D+D helps provide more neutrons for breeding tritium? Or does it only make sense to jump *all the way* to pure D+D (like the author argues in OP). What exists in the intermediate zone?
This is really the most comprehensive write-up of nuclear fusion R & D I've ever come across. However, the conclusions aren't that hopeful for the notion of nuclear fusion as a useful energy source anytime soon. On the technological scale, it seems closer to the likelihood of terraforming Venus, rather than the much more feasible notion of colonizing Mars.
Basically it seems like the ICF method is more effective and as an experimental system, uses much less tritium, but using it to drive a power production system (converting heat to electric power) is much more difficult than with the MCF system, if even possible. The MCF system on the other hand seems nowhere near reaching breakeven.
ICF is even less practical than MCF, and MCF is not.
We will with certainty not get commercially competitive, or even usable, energy from fusion. Any money spent on that prospect is badly misdirected. Support fusion research to direct money to support plasma physicists, or to keep certain exotic-tech military contractors afloat, or to drive superconducting electromagnetics.
Daniel Jassby is a tiresome crank. Always quoted in the media as the sole critic of fusion. He runs a website devoted to blowing things out of proportion. In this article, he says that SPARC and ITER will both achieve first plasma around the same date (2025) but that SPARC will take another ten years to burn DT fuel because ITER is taking ten years.
ITER is taking ten years because the equipment required for DT operation won't be installed until 2035, after their second maintenance shutdown. SPARC is intended to progress to DT operation as soon as possible after first plasma assuming all the equipment checks out.
He poo-poos tritium breeding, referring to an article he wrote 5 years ago about the faults of a solid blanket, neglecting to mention that the ARC design has been based on a liquid blanket.
If he wants to criticize the MIT/CFS SPARC/ARC design, he should by all means just go ahead and do so, but this lazy approach of his is just plain dumb and tiresome.
I'm glad you saved me the effort of reading this article. I've been following fusion for years, and have been cautiously optimistic. Recently, with the progress of both Commonwealth Fusion Systems and Tokamak Energy, both startups with private funding which aim to develop commercially viable Tokamaks, I'm ready to throw caution to the wind.
Tokamaks work, high temp superconductors work, and the combination is likely to result in working fusion reactors. If it doesn't, then at least we'll know soon enough via these two private companies. It doesn't make sense to write articles heckling companies which have literally put millions of dollars where their mouths are. Just let them get on with the work, and if they fail, they fail, and we learn something.
This author wrings their hands a lot and says "gosh that engineering sounds hard" and then stops there. Look at the stated timelines of ongoing projects and watch the news. Armchair engineers ought not be confident.
“This author wrings [his] hands a lot and says "gosh that engineering sounds hard" and then stops there.”
But that itself is a useful contribution to the discussion around the fantasy of fusion energy, when the national labs are constantly seeding the media with deceptive press releases.
It isn't useful because it says "the devil's in the details but I don't know any of the details. Isn't that scary?" Are you going to make decisions based on that? Armchair speculation costs nothing if you're wrong.
Also, linking your own fluff op-ed to support your point is a bad look. Consider moving the bio photo to after the conclusion.
In order to direct that much laser energy on target, they had to expend far more energy than the claimed output. Never forget, the laser system is far less than 10% efficient.
> There are two broad approaches toward achieving terrestrial fusion. In magnetic confinement fusion (MCF), magnetic fields are used to confine the hot fusion fuel in the form of a fully ionized gas or plasma that persists for seconds or longer. In inertial confinement fusion (ICF), laser or particle beams are used to compress and heat a tiny capsule of fusion fuel to generate a micro-explosion of a nanosecond duration.
I thought there were now 2 more: projectile method via gas gun and piston containment of molten lead
There's an even better one that for some reason gets ignored all the time. Fusion-fission hybrid. Use a fusion reactor that is well below break-even as a neutron source for a fission reactor.
Currently all fission reactors have a common safety problem: their fuel has to be very nearly critical. More precisely, there are 2 types of criticality, delayed criticality and prompt criticality. Prompt needs a higher concentration of fissile material than delayed, or delayed needs a higher amount of moderator (like graphite rods) than prompt. In any case, you absolutely don't want your reactor to become prompt critical. It did happen at Chernobyl, but I think you don't want to be in that company.
All reactors need to be just ever so slightly above delayed criticality some of the time. You can think of it as the R0 for Covid. When R0 is above 1, the disease spreads exponentially. If it's below, it dies down. You want it at a constant level. In this case "disease" is fission. You need R0 to be slightly above 1 a bit of the time, and slightly below 1 some of the time, so the fission keeps going, but does not go out of hand. The thing is this narrow band around 1 needs to be really, really narrow. We are talking 0.999 to 1.001 or so. Why? If for Covid a generation is about 3 days, for nuclear fission, a generation is about 1 millisecond (delayed fission, not prompt one; for that one, a generation is about 10 microseconds, which the funny guys at Los Alamos called "one shake"). If you have an R0 of 1.01, then after 1 second (1000 generations) you get 22000 more fission, and after 2 seconds you get half a billion more fission events than at time 0. That looks an awful lot like an explosion.
Keeping the R0 in a very narrow band is not that easy. It is for sure doable, and that's how all reactors work. But the specter of R0 going to 1.01 is never that far away.
But a fusion-fission reactor can achieve just that. The fission part of the reactor can be kept well below R0=1. You can keep it at 0.98 for example. And then you need to provide an extra 2% of neutrons coming from the fusion part of the reactor. If anything goes out of hand, you just shut down the fusion reaction, and the fission reaction dies down right away.
That's a good link. But a fairly shallow dismissal.
Both yours (you are quite an active participant on HN, so you are very likely aware of the site's guidelines) and theirs (the authors of the presentation).
The wikipedia article on fusion-fission presents the downsides of the idea much better I think.
The link you provided appears to be some type of high-school debate level of argumentation.
The final report issued by MIT [1] at that 2009 fusion-fission forum is much more balanced (and more informative).
But overall, the negative tone of the report rests on the assumption that fusion is "just around the corner". It is not.
Their argument is roughly: we need research both for a pure fusion reactor and for a fusion-fission hybrid. Let's not get distracted with the fusion-fission, and invest fully in fusion. Which they call "the grand challenge" and "transformative".
The thing is, we don't need "grand challenges" and "transformative" things for their own sake. We need stuff that works. Fusion-fission reactor may be complex, but is clearly achievable. Fusion by itself, not in the foreseeable future.
That link was on slides presented at a professional workshop. If you judge slides by whether they are flashy ppt files, well bless your heart.
I agree that the slides maybe slanted too much in the direction of fusion being just around the corner. But that hardly helps hybrid reactors! If fusion is more problematic that promised, that tilts the table even more toward just using fission, with no fusion component whatsoever.
The major problem of fission is not safety, or waste disposal, or (near term) fuel availability. The major problem is cost. It's difficult to see how hybrid reactors would improve cost. As the slides say, the focus on hybrids is more of matter of "how can we make our fusion work appear more relevant", not "what would customers actually want?"
Maybe a little analogy would help: well before thermonuclear bombs were developed, people started using fusion in the so called "boosted bombs" [1]. In that design (which dominates to this day), the implosion of the Plutonium pit triggers a fission chain reaction, but it also triggers the fusion of a small amount of D+T mix. That fusion adds a tiny bit of energy to the whole explosion, but it also produces a huge amount of fast neutrons, which increases the number of Pu nuclei that split by about 30%.
Of course, we eventually had above-breakeven fusion in nuclear weapons too. But the below-breakeven was and continues to be useful (although some people debate the entire idea of usefulness in the context of nuclear weapons).
> The major problem of fission is not safety, or waste disposal, or (near term) fuel availability. The major problem is cost.
You sound like one of those opponents of nuclear reactors who doesn't understand that cost is driven by regulations, which in turn are driven by safety.
Increasing safety will decrease costs.
But that's not all. A fusion-fission reactor can burn much more of the Uranium/Plutonium/Thorium core. While the fuel cost is not that important in the economics of a nuclear reactor, the costs associated with refueling are. If you don't need to refuel every 18 months, but rather every 15 years, then this changes drastically the economics.
Of course, producing less waste is great too.
Now, you can say (and you said) that fast fission reactors can achieve the same result. The Department of Energy recently let the startup Oklo operate an experimental liquid metal fast reactor [2]. That's great, and I really hope Oklo will succeed getting their NRC approval the second time around.
But pure fission reactors have this problem with criticality. The presentation you linked to dismissed this
Criticality control, while important, does not dominate fission reactor safety.
This is a very strange thing to say. The safety of fission reactors is dominated by what is in people's mind. And two things are in people's mind: Chernobyl and Fukushima. The first got critical, and the second one may have. The world just does not have the appetite for another one of these. Consequently, the regulators are very concerned with criticality.
Take a look at NRC's assessment of NuScale's design [3], and check how many times they talk about the control rods and their role in criticality.
The linked wiki article doesnt go into the reasons why so many hybrid fission-fusion projects have been abandoned, this technology seems so promising that there must be good reasons why.
I think after Fukushima the R&D budget for nuclear fission research has gone down.
For example, the latest Department of Energy budget proposal [1] asks for $1.7 BN for civilian fission-related projects (page 58) and for $0.7 BN for fusion science (page 36). The fission budget is still higher, but fission is something concrete, the US has 100 nuclear power plants still running.
In any case, anything related to nuclear research is expensive. So, even if fusion-fission is promising, it won't get done without quite a few billion being invested in it. This is not something that can happen without government support.
Looking at the Department of Energy portfolio of projects on the fission side, I can't say I don't agree with it. They are ranging from low hanging fruit (like the SMR where NuScale already got the NRC approval) to somewhat higher risk-reward profile. Still the risk-reward profile for fusion-fission appears to be even higher. So, I don't blame them for picking their current priorities.
I could blame them for continuing to pump money in ITER, but I think that's more of an international relations project, so the money needs to go that way.
Fusion energy has been "coming in 5 years" ever since 1960. Just like Gallium Arsenide will replace Silicon. Except neither has happened and the reasons are physics!!
Not meaningfully. Physicists can roughly calculate how much energy will be liberated inside the reactor over its power, or a laser's efficiency, but not (for example) whether their grant money will be available in 2 years, whether oil and gas reserves will open up, in general how much oil and gas are available on Earth, the atmospheric budgets, whether some (un)friendly political group will gain influence, etc.
So sometimes innovations don't work because of things like economics, geoscience, politics, funding, and other times it's fair to say that it's the physics that doesn't play. It communicates more by using an accurate word, while "everything is physics" communicates nothing at all?
As an accountant, the technology doesn't make sense to me, but taking nuclear fission as a case study in capital costs makes me certain that this fusion won't happen on a reasonable time scale. I'd love to be wrong though!
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[ 4.2 ms ] story [ 77.1 ms ] threadWitch means that's hyper-right funding a PUBLIC research on fusion energy even if it demand *centuries* before showing usable results, BUT we have an energy production issue now and we need to sort it out quickly for real, not in a potential future...
I applaud the private sector’s results, but the Apollo program was a national triumph and should in no way be considered a dead end technologically. It was the politicians that failed the program, not the other way around.
(If you bring up science or spinoff arguments, I will demolish those in detail.)
>”It was an artificially inflated exercise in national ego. In no way was it worth the money expended on it.”
There is way more to it than mere pride. President Kennedy and LBJ decided to push hard with the space race as a means of economic warfare against the Soviets. The strategy was twofold: one, to get the Soviets to commit resources to their own moonshot program when they otherwise would not. We were betting on our economy being stronger than theirs, and we could force them to catch up to us. Two, to develop American industry and expertise when we had clearly fallen behind. The spending might seem wasteful but it created a ton of jobs and bootstrapped our space industry. We essentially closed the whole “missile gap” in about 7 years as a result.
Spend on building out existing solar and wind. Spend on building out transmission lines. Spend on improved solar, e.g longer-lived perovskites. Spend on a wider variety of storage media. Spend on cheaper electric-driven ammonia synthesis.
I assume this means a steam turbine (heat engine). With the losses inherent in that process, I assume the idea is we'll have a "limitless" source of heat anyway?
Or is heat transfer inherently better with this fusion design?
And solar power and wind is cheaper than natural gas, even with batteries.
Most natural gas power plants in the USA use steam turbines. The most common setup is a two-stage "combined cycle": first, an internal-combustion gas turbine, whose waste heat powers a lower temperature steam turbine.
https://en.wikipedia.org/wiki/Combined_cycle_power_plant
https://www.eia.gov/todayinenergy/detail.php?id=39012 (~90% of natural gas kWh)
All these methods are really sophisticated ways to heat stuff and rotate a turbine.
War in iraq? Why bother.
War in Ukraine? Just stop giving Russia fossil fuel money
Climate change? Let’s just not.
Why aren’t we just spending _all_ the money on this?
A better question is why we are not investing in solar, wind and hydrogen more.
Both of those are cheap. People advocating nukes wish they were not.
I don't really care whether or not nukes are cheap when they're the only reliable low-carbon energy source we have, and when they're the safest energy source we have. Some things are more fundamentally important than economics.
https://model.energy/
Fusion does not offer energy density even approaching commercial fission.
This always comes up in discussions about fusion but do you really think we aren't? Solar didn't get where it is now from a lack of funding. A lot of money and time and effort has gone into it, just not mostly into one boondoggle project everyone can point to.
I would really like to hear numbers to back up the idea that investment into these (esp. solar and wind) is "small" in total because I'd easily bet on it being several orders of magnitude more invested in than fusion.
If you took every dollar of ITER and put it into solar would it make a meaningful difference? Probably not. It just reads as extremely misdirected, and maybe even sealioning.
And to be clear, I think ITER specifically probably is a waste of money, but it's a waste of money on a shockingly tiny scale for how much negative attention it draws, it's by far the bulk of spending on fusion, and none of it really has much to do with anything to do with scaling out manufacturing and deployment of proven technology.
But just now probably the biggest effect is confusing people about the cost structure of power generation, leading them to believe that lots of heat per unit mass input results in cheap power.
It's likely that in a parallel universe where 0 investment into fusion happened, and most of it was pumped into solar, the difference might be something like:
- One small city might be covered in solar panels.
- We'd be farther behind on some areas of material science, superconductor research, and fundamental physics than we are by a bit.
[1] eg. https://www.unep.org/news-and-stories/press-release/decade-r...
Back when that spending might have made a difference, there was no work on superconduction for fusion, because high-temperature superconductors were not a gleam in anybody's eye.
That said, it is possible that training up and employing plasma fluid dynamics physicists could yet have unforeseeably consequential results that might yet (as it were) eclipse the effects of cheap solar PV.
Anyways I suspect $1b of 2022 dollars wouldn't go nearly as far in 1980 or 1990 in terms of advancing solar tech. It's not like all that happened in a vacuum, semiconductor tech likely had to get to a certain point before this explosion could meaningfully happen, and there's never been a shortage of investment into semiconductors.
In this whole thread you've provided no evidence or reason to believe fusion research was in any way inhibiting solar research. You just seem to have a feeling it's true, but what, specifically, would those dollars have done for solar, and why are they somehow uniquely suited to being repurposed towards solar? If it's so glaringly obvious you should be able to explain more deeply.
The problem is promoting the work as if it might ever lead to practical power generation.
The first is the same as all other research. The other is just lying. I don't like lying. That is all.
It is worse when they claim yet another "breakthrough".
More butts than seats on that fast-moving ride.
Fusion research is cool beans, but not for any plausible practical reason.
Given that, all the work on making it happen at big scale is a wholly wasted. The companies issued billion-dollar contracts to build parts of it do not see those contracts as wasteful, and hope we won't.
If you think about it, you can't simply give money to JS developers to do fusion research instead of making HTML buttons for internal use.
Those who can work in the field already do but so far there's nothing to show in terms of practical solutions. They even receive fair bit of criticism for misrepresenting the outcomes of their work to get more funding. Every now and then a startup or something will come up to claim that they thought of something novel that will solve all of the problems and how the people who work in expensive government funded programs are amateurs with no creativity, then disappear in the valley of vaporware dreams.
Humanity is deeply invested in it, it's just that it's really hard.
Oh, BTW, We already have a reliable and extremely powerful nuclear fusion reactor in the sky. We can actually pour enormous amount of our resources into harnessing it and succeed but it is considered a divisive topic.
On HN, anyway. The wider world is all in on solar, except where it might compete with oil extraction subsidy.
It is like planning a project and ignoring half of issues which will make or break your project.
Besides, as we are creatures who sleep roughly in sync with the fusion in the sky, we don't really need to have 24/7 constant energy input. Combination of storage and older tech like good old fission energy and natural gas can be enough.
Also there is lot of things going on at night - people are heating their homes or charging their BEVs.
I guess we take as a given we were there for cynical oil based reasons?
> War in Ukraine? Just stop giving Russia fossil fuel money
The oil/gas doesn't cease to have value under sanctions, at worst it can all be consumed internally to drive their war machine. Climate change isn't driving Russia to desire Ukraine, it just does.
> Climate change? Let’s just not.
The government we are cynical of now has the power to control climate and our cynicism vanishes?
2) it they have less value, to the point you wouldn’t have to be a slave to the producers of energy.
3) even cynics can’t sell ice to eskimos. If fusion really did pan out and make energy abundant it doesn’t matter if they have lots of oil and gas. No one would need it.
As many other comments have pointed out though, fusion seems kinda unlikely to actually do that, but arguing that even if it did it wouldn’t change anything is a bit pessimistic for me.
Until the winds change and supporting fusion would make it more likely for them to get reelected, they will be making up all sort of stuff of why we should waste money in less proven and more unreliable, and possibly dirtier sources of energy.
Renewable energy today provides very cheap energy inputs and no improvement in this field can yield any dramatic difference. And everything that comes further downstream has to be paid, anyway.
Research in it is still a good thing though because a lot of other discoveries and technology improvements are done on the way, bringing benefit even if result itself is useless (like with the moon landing).
With fusion we don't know how to do it. There are many, many ideas we could pursue, and they are being pursued, but we have no idea if any of them will actually work. It's quite possible none of them will, or that solving it might take enabling technology we haven't even thought of developing yet.
For context we have already spent several Manhattan Projects worth of fund on fusion research, in inflation adjusted terms.
Fusion can never even come close to competing with fission, and fission is not today competitive. It gets less so every year.
IMO, the only fusion company that has a real chance is Helion. Most of the breathless hype runs into generic showstopping issues like the ones above. If someone presents a new fusion concept, ask them about their power density, and how much complexity there is in that core.
And there's the more insidious variant of this: to solve it we need new physics. I say it's more insidious because, if we used all the money in current approaches, we would be diverting it from the research that could really solve it.
I mean, the Manhattan project wasn't about trying to figure out how to harness nuclear power, it was about how to deliver a nuclear explosion. getting some energy out of fission was never really a particularly hard problem once we understood what was going on (it's literally so easy that it's a problem), getting it to explode from a package you could load into a b-52 was the harder problem.
The difference isn't really about what we know is possible, it's that unlike fission, making a fusion bomb is easier than making fusion power, so the military funding dried up before it made much progress, like a person's interest in a porno once the fun part is done.
Upgrading living standards for poor people is (or should/would be) easy: https://www.youtube.com/watch?v=VtbjQ51NvDg
A bigger problem is making people less career-driven and settle for a simpler life, small-scale farming, permaculture etc. Photosynthesis is free and abundant!
But we're locked into this mental trap of constant growth. We just assume that the only way should be up - more energy, more people, more stuff...
"On the far end of the overshoot spectrum are situations in which a community of living things receives a surplus of energy through some accidental event that happens only once. Imagine how the lives of field mice would be transformed if a truck full of grain overturned on the nearby freeway and spilled its load in their meadow. The mice suddenly have more energy than they can use and their population soars far beyond the meadow’s carrying capacity. As the number of mice in the meadow grows, though, the rate at which the grain is consumed also rises, until the grain begins to run short. At this point nothing the mice can do will spare them from dieoff; most of the mice will starve, and the survivors’ struggle to keep themselves fed may damage the meadow badly enough to decrease its carrying capacity over the long term. Years later, the meadow may still not support as many mice as it did the day before the truck overturned."
From John Michael Greer's book The Ecotechnic Future
True, but MIT (and by extension CFS) has more experience with this than anyone. Their Alcator C-Mod had the strongest magnetic field of any tokamak. I got a tour of it once, and a grad student showed us a metal tie rod, about a meter long. He said they'd calculated that two of them could have held down the Space Shuttle when it was trying to launch. To keep the reactor from flying apart, they needed 38 of them.
> In any case, improving cost-effectiveness is surely a distraction for MCF research when there have been no advances in Q
Except smaller, cheaper reactors mean you can iterate experiments a lot faster.
And all that for a reactor that was unable to break even in energy terms, let alone ignite and break even economically.
It perfectly illustrates the folly of magnetic confinement: to hold the plasma you need fields so strong and equipment so massive and expensive that the capital expenses get out of control, fully negating any advantage fusion might have over fission. We already know how to make capital intensive energy - the fueling costs are negligible for a fission reactor, yet those largely failed in the market. An even more expensive and capital intensive solution is dead in the water for economic reasons regardless of any theoretical merits.
The billion price tags of tokamak experiments is not a scientific oddity, it's a fundamental economic issue with the approach that will carry on to any production plant, that as far as we can conjuncture will need to be even larger and more expensive.
I don't understand what your objection exactly is. That's just a way to rephrase my statement: magnetic confinement, as it stands, is too capital intensive to ever break even financially, regardless of the experimental success ITER/DEMO might have.
Some light reading on this:
https://www.cambridge.org/core/journals/journal-of-plasma-ph...
After a brief bit of web searching, it turns out that the design exists, and it's called a Stellarator:
https://en.wikipedia.org/wiki/Stellarator
And if you're ever thinking about building one at home, just try not to cause an accident. What's more dangerous than playing with fire? Playing with smoke detectors.
It would take a square bar of regular old 250MPa structural steel about 32x32cm to hold the space shuttle, at full throttle, and it's solid rocket boosters down.
Or 38 square bars about 5x5cm.
And 250MPa is just it's yield strength, that type of steel work hardens and has an ultimate tensile strength usually in excess of 350MPa.
There are, of course, much stronger varieties of steel.
Steel is strong
Got example, 4140 is a 1% chromium - molybdenum medium hardenability general purpose high tensile steel - generally supplied hardened and tempered in the tensile range of 850 - 1000 Mpa.
Three to four times greater tensile strength, so two 127mm (5") diameter rods would do it at 1000 MPa.
- "The in-plane loads are carried from the covers to the cylinder by 96 INCONEL® 718 draw bars with a yield strength of 1 GPa." [0]
- "The wedged conductors are CD107 copper, bonded to flat Inconel 718 plates, with a 4:1 copper/reinforcement ratio over the central column area. The yield strength of the copper is 310 MPa, up to 100 °C, while the yield strength of the Inconel plates is 1130-1300 MPa. The peak Tresca stress on the Inconel at the inside radius is calculated to be 580 MPa, while that in the copper is 310 MPa." [1]
[0] https://www-internal.psfc.mit.edu/research/alcator/data/fst_...
[1] https://dspace.mit.edu/bitstream/handle/1721.1/94967/87ja040...
It is very important for this message to get through. Fusion is not "just around the corner".
By the way, the energy generated by fusion is higher than that generated by fission, but not by a huge amount. Only by a factor of 4.
The energy density of Deuterium+Tritium is 337 TJ/kg. The energy density of Uranium is 81 TJ/kg. For comparison, the energy density of methane is 56 MJ/kg or more than 1 million times lower than that of Uranium.
Maybe you are implying a terrorist could get their hands on 1kg of U-235 and either make a dirty bomb or a nuke. A dirty bomb would not really be more dangerous than a dirty bomb made with Cadmium. As for a nuke, 1kg is well below the minimum necessary to make a nuclear bomb, which is about 15 kg. But that's not the only thing. You need weapons grade Uranium for that, i.e. Uranium where U-235 constitutes at least 85% of the whole. Civilian reactors use Uranium that is enriched to much lower levels. Currently, the vast majority of the civilian reactors use Uranium enriched to 4.5%. A terrorist who gets their hands on that, can forget about building a nuclear bomb, except if they have means to further enrich that Uranium. In other words, if they have centrifuges, like Iran does. I might remind you that Iran is a state, not a single person. In any case, if you have centrifuges, you might as well start with Uranium ore, there's no point in stealing from an existing civilian reactor.
It's always the same.
Reminds me of a well known electric car CEO that says self-driving cars are 3 years away and has been saying that for 10 years.
Extraordinary claims require extraordinary evidence, which is a lesson that we learned a million different hard ways and which has been almost completely forgotten.
Only if you keep reading articles written by people who don't know what they're talking about. Fusion power break even will happen in roughly 5 years with MIT's/Commonwealth Fusion's SPARC test reactor.
So it is only a matter of what can appear to produce any apparent results, enough to unlock further grant funding.
Basically it seems like the ICF method is more effective and as an experimental system, uses much less tritium, but using it to drive a power production system (converting heat to electric power) is much more difficult than with the MCF system, if even possible. The MCF system on the other hand seems nowhere near reaching breakeven.
We will with certainty not get commercially competitive, or even usable, energy from fusion. Any money spent on that prospect is badly misdirected. Support fusion research to direct money to support plasma physicists, or to keep certain exotic-tech military contractors afloat, or to drive superconducting electromagnetics.
Any money spent on it is not at all badly misdirected, it's rather accurately directed, you could say.
ITER is taking ten years because the equipment required for DT operation won't be installed until 2035, after their second maintenance shutdown. SPARC is intended to progress to DT operation as soon as possible after first plasma assuming all the equipment checks out.
He poo-poos tritium breeding, referring to an article he wrote 5 years ago about the faults of a solid blanket, neglecting to mention that the ARC design has been based on a liquid blanket.
If he wants to criticize the MIT/CFS SPARC/ARC design, he should by all means just go ahead and do so, but this lazy approach of his is just plain dumb and tiresome.
Tokamaks work, high temp superconductors work, and the combination is likely to result in working fusion reactors. If it doesn't, then at least we'll know soon enough via these two private companies. It doesn't make sense to write articles heckling companies which have literally put millions of dollars where their mouths are. Just let them get on with the work, and if they fail, they fail, and we learn something.
I've heard from multiple experts now that you may have this backwards. SpaceTime even made a video about it long ago [1]
1. https://www.youtube.com/watch?v=gJ5KV3rzuag
But that itself is a useful contribution to the discussion around the fantasy of fusion energy, when the national labs are constantly seeding the media with deceptive press releases.
https://progressive.org/op-eds/let-cut-our-losses-on-fusion-...
Also, linking your own fluff op-ed to support your point is a bad look. Consider moving the bio photo to after the conclusion.
NIF
https://www.youtube.com/watch?v=zWeQICvl42k
I thought there were now 2 more: projectile method via gas gun and piston containment of molten lead
Currently all fission reactors have a common safety problem: their fuel has to be very nearly critical. More precisely, there are 2 types of criticality, delayed criticality and prompt criticality. Prompt needs a higher concentration of fissile material than delayed, or delayed needs a higher amount of moderator (like graphite rods) than prompt. In any case, you absolutely don't want your reactor to become prompt critical. It did happen at Chernobyl, but I think you don't want to be in that company.
All reactors need to be just ever so slightly above delayed criticality some of the time. You can think of it as the R0 for Covid. When R0 is above 1, the disease spreads exponentially. If it's below, it dies down. You want it at a constant level. In this case "disease" is fission. You need R0 to be slightly above 1 a bit of the time, and slightly below 1 some of the time, so the fission keeps going, but does not go out of hand. The thing is this narrow band around 1 needs to be really, really narrow. We are talking 0.999 to 1.001 or so. Why? If for Covid a generation is about 3 days, for nuclear fission, a generation is about 1 millisecond (delayed fission, not prompt one; for that one, a generation is about 10 microseconds, which the funny guys at Los Alamos called "one shake"). If you have an R0 of 1.01, then after 1 second (1000 generations) you get 22000 more fission, and after 2 seconds you get half a billion more fission events than at time 0. That looks an awful lot like an explosion.
Keeping the R0 in a very narrow band is not that easy. It is for sure doable, and that's how all reactors work. But the specter of R0 going to 1.01 is never that far away.
But a fusion-fission reactor can achieve just that. The fission part of the reactor can be kept well below R0=1. You can keep it at 0.98 for example. And then you need to provide an extra 2% of neutrons coming from the fusion part of the reactor. If anything goes out of hand, you just shut down the fusion reaction, and the fission reaction dies down right away.
[1] https://en.wikipedia.org/wiki/Nuclear_fusion%E2%80%93fission...
Bad features of fission: generation of large amounts of radioactivity, proliferation, waste disposal, afterheat/meltdown concerns.
Bad features of fusion: complexity, cost, reliability.
http://web.mit.edu/fusion-fission/WorkshopTalks/skepticsvg.p...
Both yours (you are quite an active participant on HN, so you are very likely aware of the site's guidelines) and theirs (the authors of the presentation).
The wikipedia article on fusion-fission presents the downsides of the idea much better I think.
The link you provided appears to be some type of high-school debate level of argumentation.
The final report issued by MIT [1] at that 2009 fusion-fission forum is much more balanced (and more informative).
But overall, the negative tone of the report rests on the assumption that fusion is "just around the corner". It is not.
Their argument is roughly: we need research both for a pure fusion reactor and for a fusion-fission hybrid. Let's not get distracted with the fusion-fission, and invest fully in fusion. Which they call "the grand challenge" and "transformative".
The thing is, we don't need "grand challenges" and "transformative" things for their own sake. We need stuff that works. Fusion-fission reactor may be complex, but is clearly achievable. Fusion by itself, not in the foreseeable future.
[1] http://web.mit.edu/fusion-fission/Hybrid_Report_Final.pdf
I agree that the slides maybe slanted too much in the direction of fusion being just around the corner. But that hardly helps hybrid reactors! If fusion is more problematic that promised, that tilts the table even more toward just using fission, with no fusion component whatsoever.
The major problem of fission is not safety, or waste disposal, or (near term) fuel availability. The major problem is cost. It's difficult to see how hybrid reactors would improve cost. As the slides say, the focus on hybrids is more of matter of "how can we make our fusion work appear more relevant", not "what would customers actually want?"
Of course, we eventually had above-breakeven fusion in nuclear weapons too. But the below-breakeven was and continues to be useful (although some people debate the entire idea of usefulness in the context of nuclear weapons).
> The major problem of fission is not safety, or waste disposal, or (near term) fuel availability. The major problem is cost.
You sound like one of those opponents of nuclear reactors who doesn't understand that cost is driven by regulations, which in turn are driven by safety.
Increasing safety will decrease costs.
But that's not all. A fusion-fission reactor can burn much more of the Uranium/Plutonium/Thorium core. While the fuel cost is not that important in the economics of a nuclear reactor, the costs associated with refueling are. If you don't need to refuel every 18 months, but rather every 15 years, then this changes drastically the economics.
Of course, producing less waste is great too.
Now, you can say (and you said) that fast fission reactors can achieve the same result. The Department of Energy recently let the startup Oklo operate an experimental liquid metal fast reactor [2]. That's great, and I really hope Oklo will succeed getting their NRC approval the second time around.
But pure fission reactors have this problem with criticality. The presentation you linked to dismissed this
This is a very strange thing to say. The safety of fission reactors is dominated by what is in people's mind. And two things are in people's mind: Chernobyl and Fukushima. The first got critical, and the second one may have. The world just does not have the appetite for another one of these. Consequently, the regulators are very concerned with criticality.Take a look at NRC's assessment of NuScale's design [3], and check how many times they talk about the control rods and their role in criticality.
[1] https://en.wikipedia.org/wiki/Boosted_fission_weapon
[2] https://www.energy.gov/ne/articles/argonne-adds-new-testing-...
[3] https://www.nrc.gov/docs/ML2022/ML20224A508.pdf
For example, the latest Department of Energy budget proposal [1] asks for $1.7 BN for civilian fission-related projects (page 58) and for $0.7 BN for fusion science (page 36). The fission budget is still higher, but fission is something concrete, the US has 100 nuclear power plants still running.
In any case, anything related to nuclear research is expensive. So, even if fusion-fission is promising, it won't get done without quite a few billion being invested in it. This is not something that can happen without government support.
Looking at the Department of Energy portfolio of projects on the fission side, I can't say I don't agree with it. They are ranging from low hanging fruit (like the SMR where NuScale already got the NRC approval) to somewhat higher risk-reward profile. Still the risk-reward profile for fusion-fission appears to be even higher. So, I don't blame them for picking their current priorities.
I could blame them for continuing to pump money in ITER, but I think that's more of an international relations project, so the money needs to go that way.
[1] https://www.energy.gov/sites/default/files/2022-04/doe-fy202...
Gödel just found it.
So sometimes innovations don't work because of things like economics, geoscience, politics, funding, and other times it's fair to say that it's the physics that doesn't play. It communicates more by using an accurate word, while "everything is physics" communicates nothing at all?