I read that fusion is safer than fission because it emits less particles and is harder to cause a 10k year meltdown. Is that accurate?
The reaction itself kicks off a huge amount of neutron radiation, which eventually makes the reactor chamber radioactive - that is the only radioactive waste that will have to be disposed safely eventually. But neither the fuel nor the resulting product are radioactive.
I don’t think the reactor would be scrapped, just shutdown for maintenance.
So most of the heat will have to be extracted from a radioactive material, with similar precautions like in fission reactors, where the heat is extracted from the radioactive nuclear fuel.
I am very skeptical that fusion of deuterium with tritium or of deuterium with deuterium will ever produce "clean energy", even if they are the easiest fusion reactions, due to the relatively low temperatures required for them.
It still remains to be proven whether the radioactive waste for a fusion reactor of the kinds attempted now will be less than for a fission reactor.
I wonder, how can this possibly be even a question? Fission based reactors obviously have the same or worse problem of irradiating the entire reactor enclosure and everything around it, so that's at best the same as a fusion reactor + they produce tonnes of very highly radioactive waste that will be radioactive for millennia.
Materials activated through neutron bombardment aren't radioactive for anywhere near as long. And to add to that, nearly all elements produced in a fission reactor are highly toxic in addition to being radioactive - in a fusion reactor if your steel containment chamber becomes activated, you just have radioactive steel, not one of the many many dangerous heavy metals produced through fission.
LFTR would be far better. Neutrons breed new fuel, and it consumes virtually all the radioactive fuel with "waste" that rapidly becomes non-dangerous within a month.
So I would guess neutron degradation of the equipment/vessel/reactor will probably be a similar problem in both cases.
IIRC people have stated that the breeding could also reprocess the bad millenial-scale waste from LWR into usable fuel or other isotopes in MSRs, although maybe not in LFTR.
If we had a decent LFTR industry, we could probably have more specialized MSRs to deal with the "legacy" waste and breeder reprocess into new fuel or other stuff.
The chemists from ORNL seemed pretty amazing. They had all the work done for separating out the byproducts for use in other applications.
It's basically the hottest plasma we can make suspended in a magnetic donut surrounding by near absolute zero temperatures.
Also, per unit volume, the sun produces about as much power as a compost pile.
In fusion on earth, we want to be considerably more efficient than the fusion process in the sun, as we don't have as much space to work with. ITER is already a pretty big machine.
We still have plenty of helium. It's a byproduct of oil extraction and is still often vented because it would not be profitable of capturing it.
Certainly not in the conventional sense (although perhaps there's another way that helium might act similarly to a GHG that I'm not aware of).
Greenhouse gasses are molecules, i.e. multiple atoms bonded together. Those molecules can absorb photons of infrared light, which cause them to vibrate (as if the atoms were held together by springs). After some time, the vibration stops and an infrared photon is emitted.
The problem is: those photons are emitted in a random direction, unrelated to the photon that was absorbed. Half the time they will go roughly upwards, half the time they'll go downwards.
A photon of visible light (from the Sun) can travel down through the atmosphere without interacting much with the greenhouse gasses, since it has too much energy to be absorbed. This visible photon can be absorbed by other materials at ground level, e.g. by a plant, and its energy will eventually result in around 20 lower-energy infrared photons being emitted back up (on average).
These 20 infrared photons are readily absorbed by the greenhouse gasses, and each time they're absorbed, they get re-emitted in a random direction: half the time heading upwards again, but half the time heading back to the ground. This is how energy gets "trapped" by greenhouse gasses.
Helium is almost completely unreactive: it doesn't form molecules in the atmosphere, it just bounces around as individual atoms. Without bonds to vibrate (or asymmetries to spin), the only way it can absorb energy is by speeding up, and even this isn't very effective since its mass is so low. Fast-moving helium is also more likely to escape the Earth's gravity completely.
The frequency band for absorption and emission might be different, but the helium could absorb a shorter wavelength, then release a longer wavelength (not infrared) that can be absorbed by something else, then emitted yet again to be infrared
The lower the temperature, the higher your critical current is for a given superconductor. The reason HTS are a big deal isn't that you can have a superconductor at liquid nitrogen temperatures, but that you can have a very high field at liquid helium temperatures.
Fission requires effort to control. When things go wrong it isn't controlled.
Fusion requires effort to create. When things go wrong it isn't created.
Yes, they are massively energetic, (we wouldn't be harvesting power from it if they weren't.) However, they require a very high input energy to trigger the release of the output energy.
With a fission reactor meltdown, the way you get there is by pulling out dampening rods or boiling off all the water, but otherwise leaving the fission rods in the same place.
With a fusion reaction, you have to be constantly providing both the energy to keep the fusion going AND the input material to be fused. Interrupt one or the other and fusion stops.
I know it seems weird that the bigger energy release is safer, but that's how it is. It's the difference between requiring constant input into the system to produce power vs an idle system with no input producing power.
I'm not trying to scaremonger fusion energy, but I think it's intellectually dishonest to portray is as fundamentally sound, with a binary outcome of either inertia or safe energy. This design relies on spherical compression to both initiate and confine the fusion. We should not discount the possibility that if it instead creates a cylindrical or elliptical confinement due to malfunction, it will just explode, at a minimum destroying the device. We know it is possible to initiate fusion with radial compression in a cylinder, because that's how an H-bomb secondary works.
The main safety factor in these things comes from the fact that a fusion weapon needs hundreds of kilos of hydrogen, and they are experimenting with much smaller masses. That limits the destructive potential.
1) There isn't a reality in which these devices get scaled up to that size. 2) The real danger with fission is radiation, not explosions, which fusion reactors will produce in smaller quantities than a banana farm.
Pure fusion power, even in its largest, most powerful, Elon Musk fever-dream incarnation, is safer than even the safest fission reactor, because there is no way for it to create a boom larger than it's vessel was designed to produce.
No offense but I think this sentiment is a huge problem with Hacker News. I have a minimal understanding of fusion energy production from an engineering perspective but I know more than the vast majority of the world due to my background.
You are smart but not a subject matter expert in this topic. Fusion is not a sustainable a reaction while fission is. Fission happens on its own, fusion requires something else to happen first (on Earth). Please don't insult the people in this thread who are subject matter experts in the field by implying they are intellectually dishonest. I am not a subject matter expert but recognize that a few of them are commenting in this thread with details that I have learned from other experts.
Fusion in theory has no pollution at all, but that's theoretical until large scale fusion plants are built.
Of course, repairing things inside a fission reactor is no less nasty, but fission reactors are comparably much simpler and much smaller. Swapping a fission reactor out with a new one is comparably much easier than with a fusion reactor.
MIT's Commonwealth uses an inner wall that's 3D-printed and designed to be replaced annually. They've tested joints in their superconducting tape, which will let them open up the coils on hinges so they can drop in a new inner wall. They'll surround that with liquid beryllium/lithium as coolant and breeding blanket.
With a fission reactor you have to expose uranium to those neutrons and when it gets hit it either splits into dangerously radioactive components or absorbs a neutron and becomes dangerously radioactive plutonium. There are pipes and stuff that become a bit radioactive too but that's not the part that people are afraid of when an accident happens. Also, the dangerously radioactive byproducts continue to release a lot of energy after the chain reaction is shut down, about 10% of the power the reactor was run at. So even after a fission reactor is shut down you need to keep cooling it otherwise things melt and people become unhappy.
With fusion you do need to keep exposing lithium to the neutrons from the reaction to make more tritium fuel. And tritium is radioactive. But if it escapes it'll go straight up into the upper atmosphere where it won't particularly bother people and then dilute. You've still got the radioactive pipes problem you do with fission but, again, that's not really the part that people are afraid of. And once you stop containing the plasma energy generation stops instantly.
I'm generally inclined to say that the risks involved in fission are worth the benefits but those risks are worth taking seriously and require careful government regulation more so than other forms of power. With fusion, on the other hand, I'd a lot less concerned with someone building a power plant up wind of me than a coal plant even with similar levels of regulation. Just as long as they aren't deliberately exposing uranium to the neutrons or something like that.
Fission byproducts are well known to just be a ton of heavy metal junk that decays over thousands of years.
I'm sure there's fusion byproducts that are nasty too, but fundamentally you can't get byproducts as high up on the elemental chart as you can with fission strictly because fusion is merging 2 smaller atoms into 1 larger atom. With fission you start with a larger atom and break it into 2 smaller ones. Oversimplified, but you get the idea.
- Method to Reduce Long-lived Fission Products by Nuclear Transmutations with Fast Spectrum Reactors https://www.nature.com/articles/s41598-017-14319-7
- Fast-neutron reactor https://en.wikipedia.org/wiki/Fast-neutron_reactor
- Evolution of transuranium isotopic composition in power reactors and innovative nuclear systems for transmutation https://inspirehep.net/literature/1243003
And few other things. It is possible to have nuclear power with shorter byproducts than thousands of years.
Newer reactors and spent fuel reprocessing are definitely ways to solve the issue, but the fact is you still create those nasty byproducts in the traditional reactors today.
[1]: https://en.wikipedia.org/wiki/Nuclear_power_in_the_United_St...