On the contrary to nuclear fusion, nuclear fission of any kind is not tolerable. Apparently very few have learned a lesson from neither Chernobyl nor Fukushima.

On the contrary, fusion research hasn't panned-out, so on the supply side, it's solar, wind, water, geothermal, biomass and fission to stop the climate catastrophy. However, molten Salt is anything but proven with significant challenges to be overcome. Nonetheless, it seems doable, though it will quite likely never be as economical as the renewable alternatives. Very significant progress will come from opportunities on the demand side and with efficiencies such as thermoelectric. It just can't come soon enough.

yoatmon, you want to eschew something that works in favor of something that has never been a net energy source, and has even more of the same problem (massive physical size) which makes conventional nuclear plants expensive to build because everything has to be done on-site?  Get your feet back on the ground.

Since this is a fluoride-salt reactor, it's going to be thermal spectrum.  So far so good.  If they're looking at net breeding it means it'll be thorium-U233, because the neutronics of U235/Pu aren't good enough to breed in a thermal spectrum.

Molten-salt reactors have a number of advantages over solid-fuel reactors, one of which is that there's no fuel fabrication cost.  Another is that there is no excess reactivity and thus no need for burnable poisons.  There is a very strong negative temperature coefficient; overheat the salt and it expands, leaking more neutrons and shutting down the chain reaction.  You regulate the temperature by managing the concentration of fissiles.  Gaseous fission products like xenon and krypton don't swell the fuel and suck up neutrons, they simply bubble out.  Last is that chloride and fluoride salts have very high boiling points, allowing these reactors to operate at atmospheric pressure and eliminating the heavy, costly pressure vessels required for water-cooled reactors.  This means no heavy forges are required to fabricate parts, allowing much faster and cheaper construction.

If Seaborg and SHI can lick the materials problems required to hit 1000°C temperatures, their reactor could be used to make hydrogen thermochemically by the sulfur-iodine cycle.  This can hit 52% efficiency at 1000°C.  From there, making ammonia is all downhill.

Frankly, I think the sulfur-iodine cycle is pure genius.  You mix iodine, SO2 and water at around 100°C.  What you get is hydrogen iodide (HI) and H2SO4.  HI boils at around -35 C and thus off-gasses very easily, separating the hydrogen.  HI cracks to H2 and I2 at around 450°C.  The critical point of iodine is about 546 C and 117 bar, so the iodine can be condensed and taken off as a liquid while the hydrogen can be filtered off through something like a palladium membrane.  Cracking H2SO4 back to SO2, H2O and ½O2 requires the 1000°C temperatures to hit the 52% efficiency point, but that frees your oxygen.  The SO2 and iodine recycle completely; there are no effluents, only products.

I wish Seaborg and SHI the best of luck, and the rest of them too.  Let a thousand Cherenkov glows bloom.

The new generation of reactors certainly have the potential to enhance safety manifold.
The shame in my view is that the acceptance of linear no threshold for nuclear reactors, the notion based on very little evidence that any level of radioactivity is proportionately as dangerous as high levels, is that changing or improving anything in the nuclear industry is massively expensive, so passive safety designs have been held back unduly.

Small factory built reactors have the potential to greatly reduce costs, and economically provide district heating and/or hydrogen.

They complement renewables very well, as they use little space, and in the event of, say, a major volcanic eruption significantly reducing solar panel output, make the system more robust.

It ain't either/or, it is 'all of the above, please' and getting rid of CO2 emissions.

@ EP:
Back in 1972 - 73, I was engaged in deploying a monitoring system for a molten salt reactor in Milano, Italy. I don't know what progress has been made in the mean time on this reactor type. If the progress hasn't been immense since then I'd recommend to keep hands off.

@yoatmon, If you read Engineer-poet valid comments, or did not, here is another perspective from a well informed neutral scientist:

Is Nuclear Power Green?
https://www.youtube.com/watch?v=0kahih8RT1k

Personally I expect nuclear to fill niches where it's higher cost than solar, wind, and cheap batteries is acceptable. The H2 or NH3 co-generation angle may be a key.

I think the views from both the opposing camps rely on unduly pessimistic assessments of the other technology.

It is not a suitable forum for a full analysis, but the renewables only camp should make themselves more fully aware of, for instance, the potential of mass factory built passively safe 4th generation reactors to radically reduce costs whilst the safety levels climb enormously, and for ultra-high efficiencies through a variety of methods, including using waste heat for district heating and turning out hydrogen at minimal energy cost.

Nor are these reliant on far fetched and difficult to achieve breakthroughs, but several of the potential designs being near to deployability, with the main obstacle being the massive costs imposed on the nuclear industry by regulation, which perversely leads to it being cheaper to build more high cost per unit and inherently less safe reactors.

Administrative and regulatory obstacles should not be confused with technical impossibility.

On the other hand, criticisms of the supposed impossibility of providing round the clock and round the year power using renewables is equally one-eyed and confounds present practice with technical possibility.

There is loads of lithium in the sea, and extracting it as and when it becomes necessary is fairly well understood.

But for stationary storage, just because its use in cars has driven costs down so as to make it a ready to hand alternative, does not mean that that is the chemistry which is most likely to be deployed in stationary storage at scale, where weight does not count for much.

I could name half a dozen alternatives off the top of my head, including CATL's sodium batteries, various flow batteries, thermal storage and the production of hydrogen and its derivatives.

Nor are these far off alternatives, reliant on massive breakthroughs.

Personally I favour combining nuclear with renewables, and think either side seeking to write off the other at best premature, and reliant on unduly pessimistic assessments of the technology apparently to be simply written off on very sketchy grounds simply because the 'alternative' is fancied.

How much storage renewables need is dependent on where they are, and 100% is far harder than even, say , 90%

Using figures appropriate for the latitude of the US, let alone Europe, greatly exaggerates the issue for where most people now, and even more so in 2050, live.

Mostly they live way closer to the equator, with far less seasonal variation, so relatively little storage is needed, compared to, say, Europe or New York State.

And other low carbon technologies, for instance nuclear, can go some way to closing the gap.

We are in the wonderful position, which I would never have thought likely 20 years ago, of having the potential to produce much of the world's energy incredibly cheaply, and with very low carbon.

Sure, storage is an issue, and we don't currently have perfect solutions, but the suit of technologies including nuclear and artificial fuels are impressive, and becoming ever more cost competitive.