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The article mentions losses at the hohlraum but doesn't mention losses in the laser. "Ignition" means they controled the implosion well enough to break (almost) even on laser energy, but the laser itself is less than 1% efficient on wall power. Input energy to the entire system is over 400 MJ per shot. Even at max theoretical fusion yield, it wouldn't come close to breakeven.

There's also a firing rate issue. Even if the system produced net power, significant production would require many shots per second. Currently, the laser flash lamps are expendable and it takes on the order of a day (and lots of money) to prep for each shot.

Some of these drawbacks were addressed in the LIFE proposal, which would use fusion neutrons to burn fission fuel in a blanket around the fusion chamber. You could burn spent reactor fuel subcritically (no fission chain reaction), for example. But then it's a fission machine, and criticality excursions aren't much of an issue in conventional fission reactors. In the end, there are many drawbacks and little benefit with such a setup -- even if it worked.

I love lasers, and NIF is a marvel. But there really is no sensical story about power production in it. Even the machine's stated purpose -- stockpile maintenence -- is highly dubious. It is really an elaborate welfare machine, given to weapons scientists in exchange for their support of testing bans.

I think your take on this is accurate, but it’s a little deeper than a welfare program. The government needs to maintain a population of cleared scientists who know how to calculate things like fusion yields, simulated with classified codes. These fake fusion energy programs contribute to that; some of the most capable scientists don’t want to work on weapons, so they can kid themselves that they are working on “energy”.

There is no reasonably foreseeable future with fusion as part of the electricity grid. Even if we got fantastically lucky and were able to build a practical (magnetic or inertial) reactor in 50 years, by that time improvements in energy storage and transmission technologies will have allowed renewable energy to dominate, and no government would be crazy enough to permit it to be built.


> some of the most capable scientists don’t want to work on weapons, so they can kid themselves that they are working on “energy”.

This should be highlighted.

Anecdotally, I have a friend who worked at Macdonald-Detweiller on algorithms for handling the controlled descent of autonomously-guided aircraft when lacking propulsion and relying solely on gliding. She was horrified when I told her she was working on smart bomb guidance systems.

By what deductive reasoning process, and evidence, made you come to that conclusion?

The flight profiles of a guided bomb - and a glider aircraft - are very different. I appreciate there’s a lot of dual-use, but I’m skeptical someone could be working on something so central to the system and not know what it’s really for - all of the stories of internal-disinformation I’ve heard about from the defence sector were all to keep “peripheral” workers quiet.

Nope, newer guided bombs are almost all of the glide variety, see the SDB/Stormbearker and JSOW. They can achieve high glide ratios similar to aircraft, can follow pre programmed waypoints, have variable terminal profiles including the ability to attack from different directions, and can loiter. Speaking as someone who just left that industry, she was 100% working on glide bombs.

I'll admit I was thinking more of JDAMs than those glide-bombs... huh TIL! Thanks!

She gave me a great many more details than what I shared, and they weren't important for sharing the anecdote.

That anecdote reminds me of the big twist in "Real Genius", an otherwise comedic film.

Wow, what did she think it was for?

Clearly, delivering cuddles and cookies to the destitute.

In a sense, we programmers who work on ML are just as guilty. It seems to be used primarily for for surveillance and reliably scalable automation of centralised control of industry and society.

We're just cattle killing cattle

Defeatist. Most of us are able to say no to such jobs.

Not OP, but it could also be used in engine-out situations on drones or de-orbiting satellites.

She'll probably be suitably shocked again for the next guy that comes along and explains what she's really doing to her.

What motivation is there for her to falsely say she's shocked?

Not wanting to admit that she knows perfectly well what it is she is doing, seems to be the obvious explanation. Like, what else could it be; how could one not understand that this must be it?

Couldn't she have just not told dleslie the details? dleslie said the friend gave dleslie many more details. If the friend was ashamed of what she was doing, I think it would have been much simpler for her to only say very briefly what she worked on, like flight control software, but not go into any details and say it's confidential.

Intentionally giving a ton of details that will lead to dleslie figuring it out seems counter to her goal of not admitting what she's doing. Also her giving out this information sounds like it might actually be breaking confidentiality agreements.

If you're not familiar with different types of bombs and weapons then you might not have even heard of a glide bomb before. And someone else suggested engine-out situations on drones or de-orbiting satellites.

Spoiler alert, but this reminds me of that Orson Scott Card novel

> These fake fusion energy programs contribute to that; some of the most capable scientists don’t want to work on weapons, so they can kid themselves that they are working on “energy”.

This sounds quite anti-progressive and anti-scientific, I have trouble understanding where this sentiment comes from. If Fusion reactors could be realized, this would solve all energy problems. As you mention, renewables done right doesn't stop at production but also includes global deployment of Smart Grids and Energy storage capabilities. It's nuclear energy done in a reasonable way. Apart from that, it's really not clear if production fusion reactors will ever be possible so it's clearly a research topic. Perhaps better availability of computing power (to engineer the confining magnetic fields) and better abilities to orchestrate such complex projects will also help if you look at the challenges of the ITER project.

“This sounds quite anti-progressive and anti-scientific, I have trouble understanding where this sentiment comes from.”

It can’t be, it was first published in the Progressive.

It comes from my scientific knowledge of the field and is my factual description of what I personally observed, working on-and-off in both magnetic and inertial fusion for many years. My motivation is not anti-scientific but in defense of real science that is not getting done because of the billions wasted on fake energy projects.

I read your article here [1] and I've found it a bit problematic.

You don't give a real foundation impetus to 'stop' fusion research other than the perception not making enough progress in general terms, and that the money could be used on renewables.

It's a problematic argument because 'a few billion' is a very, very small amount of investment for an energy potentially which could yield significant results, even decades away.

It maybe a 80 year-long project, even then, it would be worth it.

Renewables are not suffering from money otherwise allocated to Fusion.

I think if you gave some very specific arguments as to why some investment will not work - even as an experimental vehicle - that would lend more credibility to your argument, but then you'd also have to have that view corroborated in some way aka 'this experiment does not materially advance science, and they know it, here is the evidence or logic'.

[1] https://progressive.org/op-eds/let-cut-our-losses-on-fusion-...

Are you saying that no energy projects should be funded or that there are better uses of energy funding (and if so which areas)?

"there are better uses of energy funding (and if so which areas)?"

He said so somewhere else. I would assume:

batterie, electrolyse, fuel cells, more flexible energy grid, solar panel as light weight foil ... all that works already today and can be greatly improved.

Fusion is awesome. And we can greatly benefit from it, someday. But to me it sounds like scam if it is advertised as the energy solution. Not when we are still at the stage of basic research (except for bombs).

Till then I would rely on the very big working fusion reactor we have: the sun.

> If Fusion reactors could be realized, this would solve all energy problems.

If fusion reactors could be realized, they'd likely be so Rube Goldbergish and expensive that no one would want them.

There's this tendency to conflate "getting a fusion reactor" and "getting a fusion reactor that actually makes sense to use". The former, while difficult, is likely MUCH easier than the latter.

The first computers were massive Rube Goldberg machines the size of industrial buildings which cost a fortune and were useful only for the militaries of nation states. Now machines with a billion times the number of transistors fit in our pockets.

Projects like ITER and NIF are monstrously complex because they are science experiments where lots of things need to be varied and we don't even know what it is we need to do. An economical reactor designed by people who knew how to make such a reactor would look remarkably different.

Reasoning by analogy is not valid reasoning.

With old and new computers, the physics are different - what makes the principles still work is that logics are the same, both have gates, memory etc.

With fusion you still have the same physical substrate you need to affect.

Also you have something backwards in your reasoning. Real production systems are usually much more complicated because they need to stay up all the time, witness real nuclear power plants with their little armies of engineers, operators etc. versus the simple research reactors of old times.

I was not reasoning by analogy, I presented an example that contradicts the claim that machines meant for widespread adoption must resemble their experimental form.

The laws of physics are unchanged, computers improved because of clever workarounds that allowed us to accomplish the same tasks in easier ways. Practical fusion reactors need to produce power via fusion, but beyond that the how is irrelevant. Swap out different lasers, different magnets, different power supplies, hell even the fuels might be different, it's frankly ignorant to claim that these changes are the same physics but "use a shorter wavelength in your fab" isn't.

A modern computer in terms of number of logic gates is astronomically more complex than ENIAC, however what matters for practicality is not complexity but cost. The cost of complexity decreases as you learn what you're doing. Chicago Pile 1 cost $17 million in today's dollars to produce about half a watt of thermal power, or $34,000,000/Wth. A modern nuclear plant costs about $2/Wth. ITER will cost $45 Billion to generate 500 MW. If fusion sees 0.001% of the economic improvement that fission experienced, that's $0.52/Wth.

The conclusion that DT fusion reactors will be expensive follows from basic engineering considerations on heat transfer, not from specifics of any design. The volumetric power density will be lousy, so cost will be high.

> A modern nuclear plant costs about $2/Wth

This may have been the projection before the AP1000 and the EPR flamed out. In practice, the cost can escalate well above that. Their complexity made them difficult to build. And yet, these designs have reactor power densities orders of magnitude better than ITER, and are far simpler (and more fault tolerant) than a fusion reactor would be.

The cost is not a function of volumetric power density. I believe we have had this conversation before.

The most expensive nuclear plant projected to be constructed is the Hinkley Point C reactor. With all its overruns, it's projected that the cost will be £23 Billion, which works out to $3.37/Wth. $2/Wth is a $6 billion 1000 MWe plant, quite typical. Note that this is for reactors in the west, in China, where non-technical issues like NIMBYism aren't a concern, the cost is closer to $1/Wth.

> The cost is not a function of volumetric power density. I believe we have had this conversation before.

Yes, and you failed to make the case that larger things aren't more expensive than smaller things (all else being equal, but note that fission reactors are made of steel, not the complex sophisticated equipment of fusion reactors). We can continue the argument here, if you can come up with any argument for your position that makes any sense.

We have simple research "fusion reactors", to the point where we know a lot about fusion. That's not the hard part. Making the real production system is the hard part.

Maybe some vested interests don't want to solve energy problems. Didn't the cotton industry kill hemp in the early 30s or so? And created the whole Reefer Madness scare?

Why wouldn't the natgas and upstream/downstream petroleum industry want to do the same thing with any potential competitors? There is already propaganda about windmills killing seagulls and windmills being ugly, so why not take it an extra step and flash pictures of thalidomide babies and then say "wow do you really want this?" with respect to nuclear? Seems totally within the realm of possibility.

EDIT: Correction - I think I actually meant the petroleum industry when I was referring to cotton in this post. What killed the hemp industry in the 50s (I said 30s earlier but I made a mistake) apparently was the availability of inexpensive, manufactured synthetic fibers.

This is deeply fascinating to read.

But what about projects like Iter? There's a lot going on in fusion that has no alternative government justification. Surely those provide little to no value for weapons programs.

If fusion for grid-scale energy is really accepted to be non-viable (and if we're honest... it is) then that has some pretty far-reaching consequences.

I don't think that fusion is categorically non-viable, but the approaches of the currently funded megaprojects all seem to be. More creative and compact approaches could still have potential. Of course, there's always PACER, which illustrates our cognitive dissonance.

There are plenty of true believers working in fusion energy. Enough to support big projects like ITER.

But consider this analogous situation. I was working in a government physics lab when Star Wars (excuse me—SDI) was still a program that you could get money from for all kinds of projects. Nobody—I mean nobody—actually doing research believed in the program. That we would actually build a Star Wars defense shield to make Ronald Reagan proud. But they happily sent off grant proposals and were glad to accept money to work on various things. You can spin lots of pet projects so it sounds like they are all about missile defense. But the algorithms I worked on, during my brief involvement, would have been more useful for game design.

Out of curiosity, are you familiar with Project Excalibur at all? I’m curious how the simultaneous-targeting of dozens of reentry vehicles from a single fission-explosion-powered sea-urchin multi-laser was supposed to work. Going by leaked and declassified material I’ve seen the concept was too far developed for it to have been laughed-out of the room, so what’s the story?

…or any other juicy bits you got for us?

Doesn’t ring a bell, but I’m not an expert in Star Wars stuff. I don’t know if this qualifies as juicy, but let me just point out, as a general strategy, that if your boss puts you on a project that you don‘t want to work on, and you are in a position to ensure that the project will lose its funding by failing to meet its milestones...well, you can‘t work on a project that doesn’t exist.

> you can‘t work on a project that doesn’t exist.

You've lost me :S

It's still around, they just changed the name. And it's still a boondoggle.

Fusion isn’t just about grid power. In terms of covering the needs for food, shelter, etc the Hubble telescope, cassini probe, large hadron collider etc are useless. However, there’s plenty of economic capacity to push limits simply to explore what’s possible and what’s out there.

Fusion is likely the energy source of the future and that’s ok. It’s ok to dream of far future deep space colonization, and take just one tiny step closer to that dream.

Mass, sustainable renewables with large energy-storage systems do kinda make fusion unnecessary though.

Places with existing gas and oil, and maybe even coal, power stations aren’t going to tear them down when fusion becomes do-able or even economically viable. Not just due to the sunk-cost fallacy but because they don’t want 10,000+ newly unemployed workers who honestly probably won’t retrain for fusion. And more reasons like that.

I think you overestimate how much companies care about their existing employees. If firing 90% of them is significantly more profitable that’s what their going to do. Solar is so cheap largely because it needs very few workers per GWh so they can fire people.

I personally doubt Fusion will be significantly cheaper than Fission let alone coal any time soon. But, if it happens their not going to care about their workforce. That said, fission > fusion isn’t going to require more training for most of the workers. In many locations they would both have identical cooling towers for example.

Who knows, fusion could be key to accessing the next order-of-magnitude level for society. Perhaps it'll be key to large scale carbon sequestration to stabilize future climate change effects.

If we had cheap Fusion tomorrow we could replace much of fossil fuels with synth fuels with neutral CO2 cycle. We get to reuse existing infrastructure but without massive co2.

It could, but IMO it's a very low odds bet. There are fundamental physical reasons why fusion reactors will struggle to compete. Fusion is a technology that IMO persists on cultural momentum, a meme technology that is part of the future because that's a story that we've been told since the 1950s. I think the most likely end will be that controlled fusion will go into a similar niche as dirigibles and vacuum tubes as a retrofuturistic anachronism. It will be recognized as something that used to be part of the future, but no longer is.

It might be be cheaper than fission. More complex reactor vs less need for thick containment walls and likely fewer NIMBY issues. Decommissioning costs are likely significantly lower. Operating costs and downtime are more questionable as you don’t need nearly as much security or to deal with enrichment and spent fuel. No need for radioactive plumbing etc. Even just constructing fuel rods is shockingly expensive.

D-T requires extracting tritium from a breeder blanket which will likely be very expensive. But the ratio of T:D can be lowered the more efficient the design, with pure D-D designs avoiding that issue entirely.

Here is an article about the probably unavoidable downsides of fusion [0], from the Bulletin of Atomic Scientists. To summarize their points:

- neutron bombardment, the unavoidable consequence of the only realistic fusion reaction, deuterium + tritium, turns every known material brittle and radioactive; and can be trivially used for uranium enrichment

- tritium is almost impossible to contain, and requires fission plants to create - the fusion plants could theoretically create a surplus, but they would have to recapture essentially 100% of a very hard to capture gas (today they normally leak about 10% of the injected tritium)

- fusion plants need to be massive to be even close to break-even - the energy drain of the facility consumes a sizeable portion of the generated energy; most of this power drain is still required while the facility is not operating the reactor, increasing projected costs of running a facility

- ICF tech is very close to fusion weapon tech, so there is a massive risk for proliferation from there as well; MCF tech is not, thankfully

[0] https://thebulletin.org/2017/04/fusion-reactors-not-what-the...

I don't think the containment (and a containment will be needed) will be significantly cheaper. The fusion reactor itself is much larger, and accessing it (like, lifting the top off an ARC reactor) will require considerable volume. ITER has a large volume around it where robotic servicing equipment can be arranged to get inside the reactor.

All this volume will have to be hermetically sealed from the outside world, since it will become permeated with tritium. Keeping that tritium from escaping the building will be a major headache (polymer seals cannot be used on penetrations, as tritium permeates through polymers). This will be true in any fuel cycle using deuterium, not just DT, since D+D -> T+p reactions will be occurring.

> Keeping that tritium from escaping the building will be a major headache

JET already had robust procedures for handling Tritium. It wasn’t that difficult because we are talking about such small amounts and the T is lighter than air so minute releases aren’t a major public hazard. Don’t forget Fission reactors actually produce Tritium.

A commercial reactor will involve far larger amounts of tritium, and the structure of the reactor will be so hot that tritium will permeate through it. The amount of tritium made and consumed in a 1 GW(e) DT fusion reactor in a year would be enough, if it were all released, to raise two months of the entire flow of the Mississippi River above the legal limit for drinking water. Containment is going to have to be extremely good.

Their never going to have a full years tritium on hand so that’s kind of an odd benchmark. Getting the cost of Tritium down to $10,000 per gram is somewhat optimistic, significant effort is going to be used to recover it.

As to the Mississippi River flow estimate that’s something like 6 orders of magnitude larger than what I am referring to. Still, the other way of looking at that statistic is if half of the Tritium used per day was dumped into the Missisippi every day it would be considered safe to drink when well mixed.

That figure was to point out the large volume flowing through the system. Containment will have to be very good. Only a tiny percentage of that tritium can be allowed to escape.

Realize also that what has to be constrained is the cumulative leakage from all fusion power plants, not just a single one. The world would need on the order of 10,000 1GW power plants, to displace fossil fuels.

That’s moving the goalposts, the US only has 95.5 gigawatts of nuclear power and it’s moving away from nuclear. At that level even just 99.9% containment you can replace all US fission reactors and have 1/10th the annual releases your concerned about spread across a much larger area.

Globally, I do think fission or potentially fusion has a minor role because it could be important for a few countries locally even if it’s not cost effective in most areas. But realistically their only really competing with each other.

It's not moving the goalposts, it's describing the scale of the problem. If fusion won't be addressing a significant fraction of the CO2 problem, it will be because it's inferior to the non-fossil energy sources that are. In which case, why is it even needed?

Nuclear fission looks unable to compete with renewables at current prices in almost all the world. There's a zone around Poland where it does the best. But even those zones go away as renewables and storage proceed down their experience curves. If there are very minor niche uses, fission would work just fine vs. fusion, particularly in high latitude countries that are already members of the nuclear club.

> In which case, why is it even needed?

Circling back to my original post, it’s clearly not needed any time soon. I think it’s worth doing in much the same way building the ISS was worth doing. That said, I was trying to avoid being dismissive of possible upsides which seem unlikely but still possible.

Whatever the opposite of devils advocate is.

Don't get too fascinated by the takes you hear about on Hacker News, as many of these comments are written by software engineers as they are by deeply embedded domain experts.

A lot of the posters on hacker news have just mastered the cynical take. It’s an ego booster for people who can’t handle that there are other people out there accomplishing things.

The cynical take is a product of talking to engineers, not scientists.

The tragedy of engineering is that in any market niche, generally only one technology can win. The others are driven to extinction. It's like ecology's "one niche, one species" rule. As Freeman Dyson pointed out, this is not like science, where multiple complementary theories may coexist. We build chips from silicon, not GaAs or superconducting niobium or any of the other possible technologies that were considered over the decades.

An engineer, if he's old enough, will have seen many technologies come up then fail and die. There are more ways to solve problems than there are sufficiently distinct problems, so this is inevitable. When fusion competes with fission, and wind, and solar, and geothermal, and..., it's a fight to the death. The notion that fusion is inevitable is a stacking of the mental deck to just assume fusion will win this competition.

A HN user’s cynical take on other HN users’ cynical takes. Masterful.

I'll take that bet - say, $500 in 2021 dollars, that a fusion power plant is selling energy to the grid? I'll even make it easier and halve the time you suggested to 25 years, so we can settle the bet in 2046.

I’m interested, but the bet needs another condition, to exclude toy demonstration projects. The reactor will have to generate at least 100MW (far less than existing coal plants) and be in operation for an integrated time of at least 90 days over the course of any one year on or before 2046. Accept?

100MW seems like a substantial moving of the goalposts, given your earlier statement that "there is no reasonably foreseeable future with fusion as part of the electricity grid" and that I've already cut the timetable by 25 years :) That said, I'll still accept - I'm emailing you at your profile address for the details!

"Practical" is in there.

A price competitive 10 MW generator probably meets that standard though (Islands, small towns, isolated mills, etc).

...very fast spaceships for the solar system, interstellar big ones probably. With continous thrust.

That would likely not demonstrate grid comparable cost though.

I didn’t mean to move the goalposts. I just want to exclude demonstration projects that might produce some net energy but not be serious commercial sources of electricity. But thanks for accepting anyway.

I've sent an message to the address listed in your profile, it's coming from a nonstandard domain though, so if you don't see it, it may be in spam. Also, I now realize that the longbet page is still under review, so you might not be able to see that either until the staff approve it.

I wonder how many of the bets on the longbets site stem from HN discussions. Probably not a significant number, but it would be deeply interesting to go back and read the discussions that spawned them.

Longbets should include a link to the thread in question in the bet.

Edit: Would be nice to have a link to refer back to the discussion that led to the bet. To my knowledge, most bets do not provide such a citation.

Is that a prescriptive or descriptive statement? I just looked at about 20 and didn't see anything immediately obvious, but that was with in page text search, and not actually paying attention enough to tell whether it's common or encouraged to include a link to online discussions in general (and I would happily search for a data set or scrape the data if I could expect to find it there).

Seems like any profitable plant should count. Some designs work best at smaller scales, but if they worked out they'd be cheap and for more power you just build a lot of them. Even in fission, there's a big push now to build reactors small enough to mass-produce in factories. Maybe say at least 100MW total power?

Energy has the most externalized costs of any industry.

The 5th fleet is in the Gulf to protect the flow of Oil.

The USD is backed to some extent by petrodollar, and that is a geopolitical hammer the Americans like to use at least to some extent.

So what does 'profitable' mean?

If Climate Change gets really problematic quickly, then guess what, all Nuclear Plants become considerably more profitable because the government will socialize the losses in case of catastrophic failure meaning owners don't pay for massive insurance costs which are a problem for profitability today give the possibility of $100B payouts in the case of failure.

I'm wary of the commentator's cynicism. If we can make demo plants operating at some scale, close to break even in 25 years ... then that's a strong hint there's material progress, and that those plants could be breaking even another 25 years later.

It also easily justifies a number of scientists working on it now even if only pans out in 50 years. The long term surpluses are potentially ginormous, like, to the point where they existentially shape the future, much like carbon fuels triggered the industrial revolution.

Yeah maybe leave out "profitable," it's too fuzzy and hard to verify. One of the bettors simply expressed skepticism that there would be "fusion as part of the electricity grid," period, so just leave it at that. At least, that's what I would want if I were betting.

(I do think it's entirely possible that fusion will be solidly profitable, especially with carbon pricing.)

That would be my favored platform!

I like what Tim Bray's doing with his time. https://longbets.org/863/

I'd bet a bitcoin against him.

I think this is a safe bet. Between Commonwealth Fusion's Arc/Sparc, or General Fusion's spinning glob of hot metal, or TAE systems, or any of the others, I think you have a better than average chance of settling this bet within 20 years.

ARC has a power density 40x worse than a LWR's primary reactor vessel.

General Fusion abandoned their first scheme because of at least three showstoppers (vaporization of the liquid metal wall, Richtmyer-Meshkov instability turning the implosion into jets of metal, and stochastic magnetic field lines in the spheromak causing unacceptable loss of energy via electrons to the metal). The new scheme has extremely serious engineering problems (the central pillar will be in a radiation/thermal environment orders of magnitude worse than the walls of ITER, and subject to extreme JxB forces). And they've never produced a neutron, as far as I know.

Rostoker et al. were told 20+ years ago that their p-11B concept couldn't work, for at least eight different reasons.


If I had to bet on any current private fusion effort I'd choose either Zap Energy or Helion.

Why is the power density of the ARC/SPARC reactor problematic?

Lower power density implies larger size, which implies higher cost. Since the parts outside the reactors themselves (the turbines, generators, heat sink, etc.) will be similar, this means a fusion power plant will cost more to build that a fission power plant.

The other problem is that size is also related to reliability. A fusion reactor will have many more parts than a fission reactor. It will also be much more complex, and operate at higher radiation and thermal stresses. This is particularly important because it is very difficult to repair something that is so radioactive that hands-on access is not possible.

> no government would be crazy enough to permit it to be built

Why? Nuclear fusion doesn't have the meltdown risk or waste problems of fission.

Fusion still has to deal with waste, just not high-level waste. Through the process of neutron activation all of the parts exposed to neutrons eventually become radioactive enough to be treated as low-level waste. In a reactor large enough to produce energy for the grid these parts could be very large (and expensive) to deal with (not to mention replace).

The main parts of a commercial tokamak would be huge. I read once that due to thermal stresses, replacement might be needed annually. I seem to recall that the STARFIRE project[1] estimated nearly 60 tons of low-grade radioactive waste per year of the operational lifetime.

[1] https://www.sciencedirect.com/science/article/abs/pii/002954...

Power plant waste:

60T/y for 1200 MWe = 50g / kWe·y = 1.6 mg/MJ

Coal energy density:

24 MJ/kg = 0.024 MJ/g -> 42 g/MJ

Not perfect, but depending on what the waste is, doesn't seem too bad.

Coal is absolutely the worst so it may not be a fair comparison. How would fusion compare to renewables like solar or wind?

Yes, though the article consists almost entirely of reasons why aneutronic fusion is really hard ("the conditions required to harness aneutronic fusion are much more extreme than those required for deuterium-tritium fusion being investigated in ITER").

Note that the "Candidate fuels" section is not part of "Technical Challenges", but it might as well be. Helium-3, by far the easiest, is vanishingly rare. Deuterium would not really be aneutronic. Then further down is a list of worse and worse headaches.

The leading scenario for acquiring the most convenient fuel candidate is "mining it on the moon". (The alternative scenario being to scale up production of tritium by existing heavy-water reactors from the nuclear weapons program, which decays into helium-3... and defeats the point of researching extremely complex, clean, aneutronic fusion reactors)

I want to like aneutronic fusion, but it takes an objective that is several breakthroughs away and plays the game on nightmare mode.

Anything beyond D-3He or D-D is likely impossible. And any fuel with deuterium will still make enough neutrons to render the reactor inaccessible to hands-on maintenance. So there will still be a waste problem (as well as a huge reliability and maintenance problem). The reactor might not AS MUCH radioactivity, but much of the cost of dealing with it will scale with the mass of the contaminated material, not its activity. And fusion reactors will be very large. The cost of dealing with the activated material might end up higher than the cost of dealing with spent fission reactor fuel.

...is even further from breakeven than deuterium+tritium fusion.

There is no meltdown risk with modern fission reactor designs. But there is the waste problem.

If you follow the links my Op-Ed, you’ll find articles describing the radioactive waste and proliferation risks that will accompany any fusion reactor. Not as great as fission, but far from zero. And there is the problem of production and transportation of tritium, a very nasty substance.

A commercial fusion reactor would be fantastically expensive and complex, and require a huge infrastructure to support it.

"Does Fusion produce radioactive nuclear waste the same way fission does?

Nuclear fission power plants have the disadvantage of generating unstable nuclei; some of these are radioactive for millions of years. Fusion on the other hand does not create any long-lived radioactive nuclear waste.

Can fusion reactors be used to produce weapons?



> Can fusion reactors be used to produce weapons?

> No.

That is a deeply misleading answer. While this would likely be easy to detect by international observers, it is not hard to enrich uranium in a fusion plant [0]. So fusion reactors, like fission reactors (though with less chance of clandestine operation) are still a nuclear weapon proliferation risk.

[0] https://web.mit.edu/fusion-fission/HybridsPubli/Fusion_Proli...

Couldn't you use regular fusor to generate neutrons to enrich uranium? Do you specifically need neutrons with the 14.1Mev energy produced by D-T fusion (which you can make in a regular fusor, if you have the tritium for it) or is there a path starting from lower energy levels? Or do fusors just not make enough neutrons for enrichment to be practical?

You probably could. However, the question wasn't whether fusion power plants are a bigger risk for nuclear weapons proliferation than other technologies, it was simply if they can be used for nuclear weapon development, to which the answer is yes, but not as easily as you can with fission power plants.

Right, as other commenters have pointed out, this is low-level radioactive waste. It, along with tritium, is great for dirty bombs and catnip to terrorists.

A dirty bomb is a weapon. They are talking about “atom bombs”.

> is great for dirty bombs and catnip to terrorists.

This is another variant of “think of the children”. How many terrorists have built these dirty bombs?

I saw it in at least two movies.

They haven’t been able to yet, because we don’t have any fusion reactors out there.

Is the risk any worse than a terrorist making a bomb that spreads a bunch of non-radioactive heavy metals, or any other toxic substance? What about when compared to the general damage caused by mining and burning coal?

Not necessarily, if I take “any other” literally.

Tritium’s low molecular weight means that a bomb can disperse it over a large area. It has a half-life of 12.5 years and its beta radiation is known to be carcinogenic from animal studies. An inhaled, microscopic bit of tritium will be irradiating your lung tissue for many years, although the actual effects of this are not known. However, it is very strictly controlled, and you need all kinds of special licences and certifications to use it in your laboratory, for these reasons.

So the lure for the terrorist is just that: it’s good for terror, because of the psychological effect.

“What about when compared to the general damage caused by mining and burning coal?”

If the choice were between coal and fusion, for me there would be no contest. We would have to put everything into developing fusion power. Fortunately, there are alternatives that are better than either and are already working.

> Fortunately, there are alternatives that are better than either and are already working.

Agreed, I would love to see more spending for things like, CSP molten salt research and storage systems in the public domain. That way, even if countries like the US are still captive by certain industries to not adapt it at scale, countries like Chile with +100MW systems with 17h of molten salt storage that are grid connected now, can benefit.

Dirty bombs are actually terribly ineffective weapons. The radiation would be unlikely to harm anyone who wasn't close enough to be killed by the conventional explosives unless they spent a considerable amount of time in the irradiated area afterwards without any sort of protection. While the cleanup operation could be expensive, the whole affair would be more an inconvenience than anything else. On the plus side though, now you can detect the terrorists' essentially conventional explosive which would otherwise be quite concealable with radiation detectors.

Also tritium is essentially harmless. It is an incredibly weak beta emitter - the electrons it emits won't make it through the upper layers of dead skin if it's outside of your body. It has an extremely short residency period in the body if it is ingested (a benefit of being chemically identical to hydrogen). It also will dissipate in an area rapidly - it rises quickly and even if it is in an enclosed space it will pass straight through the walls. Also it's worth noting that a fusion plant like ITER has less than a gram of tritium inside of it at any given time.

You’re correct about the skin penetration, but the risk with tritium is in inhalation. Experiments with mice demonstrate carcinogenesis. The increase in cancer risk from inhaled tritium in humans is unknown, but the substance is considered dangerous enough that it’s a pain in the ass to get the certifications to use it in your laboratory. It definitely should not be considered harmless.

I worked with Stephen Bodner on the fusion program mentioned in the fine article. We did our experiments with deuterium. The reason we did not use DT, which would have been better for the experiments, is because nobody wanted to (1) go through the hassle of getting the lab certified to handle tritium' (2) get anywhere near the stuff. It is considered very hazardous.

Tritium is a pain in the ass to get certifications for because it is so difficult to contain. Even in an airtight setup, it will leak. If you spend a substantial amount of time in lab with a tritium leak, and are inhaling the stuff over months or years, yes it's dangerous, but hydrogen doesn't remain in your body long enough for a single brief exposure to do anything.

Mercury vapor is very hazardous, that doesn't mean a mercury bomb is an effective weapon.

Your points are solid; I accept that this material would not be very effective as a weapon, except maybe in a confined space. But it’s still something whose possession we want to control, so handling and transporting it adds to the cost and complexity of operating a commercial fusion facility.

I have a watch with lume powered by phosphor-coated tritium vials. I’d better keep it safe from terrorists trying to build dirty bombs.

The problem with this statement is that you are assuming tritium would be “great for dirty bombs and catnip for terrorists”. But then you go on to say that it hasn't happened yet other than in films because there are no fusion reactors yet. This is, in other words, speculation.

The problem of fission isn't meltdown risk or waste (or fuel availability), the problem of fission is capital cost. The capital cost of a fusion power plant is likely to be much higher than that of a fission power plant of equal capacity.

> Even if we got fantastically lucky and were able to build a practical (magnetic or inertial) reactor in 50 years, by that time improvements in energy storage and transmission technologies will have allowed renewable energy to dominate, and no government would be crazy enough to permit it to be built.

Not so sure about that. Vast solar and wind farms are eyesores and are not environmentally benign.

You're right. they’re not. But no form of electricity production at the scale we need it, and the even more massive scale in the future, is environmentally benign. The challenge is to find the best way to leave chemical combustion behind, and fast. Notice the new interest in the old devil, nuclear fission, among various green groups.

That's mostly interest among astroturfers, not actual green groups. There was a bit of interest among some genuine greens about a decade ago, but that evaporated as solar and wind continued to decline in cost and the nuclear renaissance flamed out.

I think they're aesthetically pleasing, personally. Both solar and wind farms.

Would be nice to note the thing you linked to was written by yourself, for full disclosure.

Yeah. that was a big secret.

> and no government would be crazy enough to permit it to be built

I can imagine China building one simply for the national prestige. "China built the world's first commercial nuclear fusion power station". The Chinese government wants to prove itself the equal of other major world powers (especially the US) and being the first country to have commercial nuclear fusion would be a good way of sending that message. Even if it is more expensive and less safe than renewable energy.

And then the US government would build one to "counter the nuclear fusion gap with China" and "ensure American supremacy in nuclear fusion technology".

That said, this isn't going to be technically feasible for a few more decades (at least), and we don't know what the geopolitical situation will be like by then. Maybe China-US competition will still be as strong, even stronger, then as now. Maybe it will be in the past and the world will have moved on to something else. Who knows.

Now that you said it, a holhraum does bear a resemblance to a Teller-Ulam device.

Is NIF even a "fake fusion energy program"? TFA specifically mentions their goal of simulating fusion detonations in nuclear weapons.

Yeah, but they regularly send out press releases gushing about the energy application. This helps with Congressional funding.

Here is the head of the NNSA, the funding agency for the NIF, quoted in the fine article:

“It also offers potential new avenues of research into alternative energy sources that could aid economic development and help fight climate change”

That’s some finely tuned BS right there.

> mean that renewables will soon be able to supply all of our energy needs

pure propaganda. Otherwise why all the panic about global warming. If true we'll have no problem hitting all the targets to avoid the a global warming catastrophe.

> Otherwise why all the panic about global warming

Because it doesn't just need to be feasible, it also has to be actually implemented. That costs a lot, and comes with a shit ton of friction. The fossil economy is a massive beast to try to turn around, and it would be so even if aliens landed and gave us the schematics to a perfectly working dream fusion reactor right now. That's why there is a "panic".

I agree, except in 50 years the productivity of the world will be so high that building this, even if it costs 500B in today's dollars, someone will pay.

Would they be useful in space?

No DT reactor will be useful in space. The size of the reactor will dwarf that of a fission reactor of equal output.

What about SPARC and ARC?

Building enough ARC reactors to supply the world primary energy demand require beryllium 100x more than the estimated global resource of that element. A single ARC reactor uses 40% of the current world annual production of Be.

"Renewable" maximalists are such bores.

On the contrary, it will be so much energy it will be like a new agrarian revolution. No society outside the be able to resist it.

Having toured NIF a few times and worked in one of the buildings adjacent to it a few summers ago, I will say the energy stuff always seemed more like a way to get funding. The main use and aim for NIF is and always has been to re-create some of the conditions inside nuclear weapons and similar fusion-based reactions.

The whole NIF building has the ability to switch modes between classified and unclassified. They wouldn't have gone through the trouble of making this a toggleable feature on the building if they weren't actively using it for both.

> The whole NIF building has the ability to switch modes between classified and unclassified.

Interesting, can you explain this more? What gets hidden?

I don't know the specifics but I imagine most of it is waving a magic wand and saying poof now this room is classified. But there are logistics that go with that, certain door technologies that have to be in place, probably some complex security procedure for "switching" between modes, (i.e. I would think they need to clear the building of uncleared personnel and be 100% sure there isn't someone hiding in a bathroom somewhere) etc etc, and it's enough of a pain that most buildings are either one or the other all the time. The ability to switch on the fly for a large facility like that is super rare and indicative of there being a real need for switching.

All I know for sure is on the tour they mention they can switch the whole building to be unclassified or classified and during the tour it is in unclassified mode.

I imagine a big chunk of switching to classified is shooing the un-cleared visitors.

Likewise for going from classified mode to unclassified mode they would have to sweep the whole facility for sensitive material

I'd imagine waste disposal processes and cleaning staff to be major headlines in the switching procedures.

Cleaning staff usually have TS clearance at places like this oddly enough, and are usually on a pension and work there for life.

I've heard that, at an air force base where civilians work, there's a blue light that turns on both on the door and inside the room, when that room is in "classified" mode, and they are only allowed to do classified work when the light is on and the door closed.

To be clear though, I don't think anything about NIF's actual design is classified. Maybe the parameters they use on some tests and the angles on some of the lenses and/or target design/composition are, but the actual setup is all publicly documented AFAIK.

The aliens have to go to their cryopods :).

>> There's also a firing rate issue. Even if the system produced net power, significant production would require many shots per second. Currently, the laser flash lamps are expendable and it takes on the order of a day (and lots of money) to prep for each shot.

Oh, but then there's this part:

>> Further experiments will require the manufacture of additional fuel capsules and hohlraums. These may not be ready until at least October, Herrmann says. The nanocrystalline diamond-coated capsule that was imploded in this month’s event took six months to grow at General Atomics, which has long worked with LLNL on fabricating capsules. The spheres have to be polished and the core’s interior etched with tools inserted through a 2-micron-diameter hole drilled into it. The tritium–deuterium mixture is injected through a tiny fill tube just prior to the shot.

Well, it is aweseom tech. But probably nothing I would bet we can rely on, soon.

That's actually uplifting to read! Even if we don't end up getting fusion power out of this, it's got to be helping fund improvements in nano-manufacturing!

for the love of god, someone please rename these "diluthium crystals"!

> There's also a firing rate issue ...

The NIF goal was ignition, not continuous power production. The original spec was one shot every four hours. Achieving one shot per day is close.

The nuclear stockpile bit is kind of true, although it's sort of true, HEDP systems are the only way in a controlled setting to create nuclear level conditions without setting off a nuke. That said, NIF at least from the energy perspective just like ITER was just to push the research forward than it was to produce break-even fusion in 10 years. If you really want that you'll need gobs of money, probably even beyond the level of things like the LHC. The reason we don't have fusion in either field (MCF or ICF) is because we don't fund it to that level.

EDIT: on funding, this[0] image shows what is neccessary and the level we actually funded. It's been around for a while but it may prove informative for the uninitiated.


I get the point the graph’s authors are making, but I wonder how those projections (made in the 70s) would hold up today, knowing what we know about the engineering challenges for each fusion approach.

In other words, I’d love to see a 2021 recreation of that graph.

> the LIFE proposal, which would use fusion neutrons to burn fission fuel in a blanket around the fusion chamber.

This is crazy. If you are going to have fission and fission products, you might as well just build a fission reactor. It would be vastly simpler, smaller, and cheaper.


My money is on stellarators. Just saw Wendelstein in the newsfeed here: https://news.ycombinator.com/item?id=28211413

Stellarators face many of the same likely showstoppers as tokamaks. Power density, materials, maintainability, complexity, cost.

In the utmost respect, you sound like Lazlo from the movie Real Geniuses.


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