Yes, and the bottoming steam turbine is 1/3 the size of a steam turbine rated for the full power output so… radical capital cost reduction.

It isn’t just the turbine but the heat exchangers, in a PWR the ‘steam generators’ are water-water heat exchangers that are usually larger in volume than the reactor vessel. Many LMFBRs had two stages of heat exchangers (sodium-sodium and sodium-water) even larger heat on the water though SuperPhenix has relatively affordable secondary heat exchangers and never had them catch on fire.

> Yes, and the bottoming steam turbine is 1/3 the size of a steam turbine rated for the full power output so… radical capital cost reduction.

It's a cost reduction, but likely not radical when talking about a nuclear power plant. For a cost breakdown of a nuclear plant see

https://world-nuclear.org/information-library/economic-aspec...

So the "conventional island", which would include the steam turbines, condensers, generators etc. is about 15% of the cost. Reduce that to a 1/3 the size, and cost drops to 5% of the total, a savings of 10%. Probably even not that much, since a steam turbine 1/3 the size probably costs more than 1/3 the cost of a "1/1" size turbine. And then the remaining 2/3 of the power output would have to be generated some other way, so would shift cost somewhere else. Of course, some part of the cost of the nuclear island can be attributed to steam production as well. In any case, all in all I don't see this as making or breaking the economics of a nuclear plant. The issues that cause nuclear plant costs to skyrocket lie elsewhere (and no, just blaming regulations is overly simplifying it as well, though a popular scapegoat).

(I'm not sure, but I suspect what's making coal non-competitive with gas isn't so much the steam turbines, but rather that there's more labor and machinery involved in burning coal than gas, from mining, transportation, pulverizers, and then all kinds of exhaust gas treatment used at least in the civilized world, ash handling etc.)

> It isn’t just the turbine but the heat exchangers, in a PWR the ‘steam generators’ are water-water heat exchangers that are usually larger in volume than the reactor vessel.

Yes, that's true. The BWRX300, which of the current crop of SMR's is probably the one with the most realistic prospects of actually being built somewhere, is a BWR, and the maker claims one reason for the supposedly good economics is that they have spent a lot of effort on minimizing construction cost and equipment needed. We'll see, I guess. I think historically the economics of BWR's vs PWR's is mostly a wash.

> Many LMFBRs had two stages of heat exchangers (sodium-sodium and sodium-water) even larger heat on the water though SuperPhenix has relatively affordable secondary heat exchangers and never had them catch on fire.

The follow-up ASTRID project, which never left the drawing board, used a sodium-air (or might have been nitrogen, to avoid issues with trace contaminants in air since it was all closed cycle anyway?) heat exchanger and Brayton cycle turbomachinery, to avoid any potential issues with sodium and water. I think it was supposed to have slightly lower thermal efficiency than an equivalent steam plant, but maybe somewhat lower capital cost.