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Comment by eloff | Hacker News Reader

> 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).

https://en.wikipedia.org/wiki/Aneutronic_fusion

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

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.

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?

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?

No."

https://www.iaea.org/topics/energy/fusion/faqs

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.

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.

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.

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.

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.

> 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.

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.

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