> Fusion power plants can't "melt down"

Eh, a core-containment failure (in any magnetically-contained system) would involve superheated hydrogen getting friendly with oxygen. That, in turn, would give neutron-impregnated barrier materials a free ride on propellant. It's not strictly a melt down. But it's in the same practical category of failure.

▲

gmueckl 3 hours ago | parent | next [-]

Ths is a massive misunderstanding of the technology. First of all, the amount of hydrogen in the reactor is tiny. The magnetic confinement severely limits the density of the plasma. The inner containment vessel is a ultra high vacuum chamber. The chemical energy that would be released by a reaction between the hydrogen in the reactor amd oxygen from the air would be less than what is released by popping a hydrogen filled balloon with a lighter.

The truly concerning failure modes would be related to release of radiation or activated materials. But that would require damaging the reactor in ways that the reactor is incapable of imparting on itself.

Overall, the technology is remarkably safe.

▲

JumpCrisscross 2 hours ago | parent [-]

> chemical energy that would be released by a reaction between the hydrogen in the reactor amd oxygen from the air would be less than what is released by popping a hydrogen filled balloon with a lighter

Thanks for the correction. If you're breeding lithium in the walls, might that be an incendiary concern?

▲

pixl97 2 hours ago | parent | next [-]

There seems to be a number of different prototypes of blankets, but the average operating temperature seems to be 300-700C. Adding oxygen to some of these designs while that hot may cause metal burning. This said, many of them are ceramic designs and would likely resist combustion.

With all that said, it seems to be way less 'dangerous' material than would be in your average nuclear reactor, making it more of an industrial accident versus a planet contaminating mess.

▲

rnhmjoj 2 hours ago | parent | prev [-]

The breeding blanket is entirely contained inside a vacuum vessel, so there isn't any oxygen to react with. Also, the are many blanket designs, but the lithium is never present in its elemental form (precisely because it would be very reactive), but in a stable chemical bond with some neutron multiplier (like lithium-lead alloys or beryllium ceramics). In some design the lithium is even immersed in the coolant itself, which is high pressure helium, so it's not going to ignite in any reasonable way.

	▲	JumpCrisscross an hour ago \| parent [-]
		> breeding blanket is entirely contained inside a vacuum vessel, so there isn't any oxygen to react with When the vessel works. If the vessel breaches, that lithium could ignite. Note a showstopper. But I suppose a risk to be thought about by the engineers (probably not by policymakers).

▲

Symmetry 3 hours ago | parent | prev | next [-]

There's only a few grams of hydrogen in the reactor's plasma, it's reaction with oxygen wouldn't be much more exciting than just losing containment. There are engineering challenges that have to be addressed but no worse than the 6 MW research reactor I used to walk by every day to my college classes in the middle of a dense city.

The proliferation risk of someone using the neutron flux to produce an atomic or dirty bomb are real but that exists no matter where it is.

▲

Aardwolf 3 hours ago | parent | prev [-]

What's the effect of this in a populated area in a certain radius? Compared to nuclear power plants...

	▲	JumpCrisscross 3 hours ago \| parent \| next [-]
		> What's the effect of this in a populated area in a certain radius? I'd imagine this is, like with fission plants, deeply dependent on the specific design.
	▲	cyberax 2 hours ago \| parent \| prev [-]
		Radiologically? Pretty much nothing. The regular industrial safety concerns will matter more. The plant will have some tritium, and the material in reactor walls will get activated by the neutron flux. Some of the activated materials can disperse in case of a catastrophic explosion (e.g. a couple of large airplanes being flown the reactor building). But the material of the walls is not volatile, so it'll stay on the site. And tritium is very volatile, so it'll quickly disperse to safe levels. You'll be able to detect them with sensitive equipment, but it won't be dangerous.