[PaulHoule]

No it is the steam turbine (& associated heat exchangers) that makes the economics of the lwr impossible. It is what made the economics of the old-school coal burning power plants impossible in most places compared to the methane fueled gas turbine not to mention wind and other renewables.

The power density of a gas turbine is so much greater than that of a steam turbine that a closed-cycle gas turbine powerset for a sodium cooled fast reactor would fit in the employee break room of the turbine hall of an lwr. Running at higher temperatures with liquid metal, molten salt, or gas-cooled reactors poses many practical problems, but means building a machine that processes more energy with less mass thus drastically lower capital cost.

[pfdietz]

The advantage of combustion turbines is that there is much less transfer of heat across fluid/solid interfaces. In a simple cycle combustion turbine, no such transfer is needed. The heat is generated by combustion in the working fluid, which carries away the waste heat after expansion. Combined cycle does add a steam bottoming cycle that needs heat exchangers (before and after) and cooling towers, but most of the power is still coming from the combustion turbine, so the steam part is much smaller than in a pure steam plant of the same rated power.

[DennisP]

Also, a big reason LWRs use so much reinforced concrete is that they have huge containment domes. The reason they're so big is that the water is pressurized at around 100 atmospheres, and if there's a pipe break it'll flash into steam at a thousand times the volume. You need plenty of space for the steam to expand inside containment.

A molten salt reactor is at atmospheric pressure and has nothing to cause a chemical explosion. You still need containment, but you don't need to contain a large empty space.

[PaulHoule]

Yep.

A supercritical CO2 turbine runs at 1000+ psi but if the pipes broke and the CO2 sprayed out into that salt, you might get an overpressure around 10 psi in a not-too-big confinement because the volume of working fluid is tiny.

[pfdietz]

You would not even run the CO2 plumbing into the containment building. There would be a secondary salt loop leaving that building.

[andromeduck]

By gas turbines do you mean scCO2 tech?

[PaulHoule]

That is one kind, yes.