A lot of the natural gas plants are combined cycle, which includes a steam Rankine bottoming cycle.

perihelions 3 days ago | parent | next [-]

I don't see how this isn't dispositive on the economics question. That markets (overwhelmingly) choose to build combined-cycle natural gas plants, choose to add the Rankine bottoming cycle, means the marginal cost of the steam turbine is *less* than the marginal cost of the fuel saved by the efficiency gain. That's the case even in the USA; and natural gas elsewhere in the industrial world is integer-multiples more expensive.

The natural gas plants without steam turbines are precisely the load-following plants that run for a fraction of the time (or at a fraction of their capacity); the relative weight of capital vs. fuel costs is inverted. (Or those, like xAI in Memphis, which are rapidly assembled in rushed desperation. I wonder if that will be a trend in the datacenter boom: designs limited, not by costs under normal market conditions, but bottlenecks affecting rushed projects. Nuclear SMR's would seem to be worst at this—the designs they expect to use haven't even been built yet!)

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PaulHoule 3 days ago | parent | prev [-]

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.

	▲	jabl 2 days ago \| parent [-]
		> 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.