My guess: expensive. Gas turbine power plants are not cheap, but fuel wasn't that expensive back then. I'd expect the replacement to either use hydrogen with h

My guess: expensive. Gas turbine power plants are not cheap, but fuel wasn't that expensive back then. I'd expect the replacement to either use hydrogen with hydrogen-resistant steel, or, more likely, helium. I think carbon-carbon composite can handle extreme temperatures in a helium atmosphere, beyond what you can reasonably reach with a fuel flame. However, the temperatures should be feasible for fusion power plants, which could use helium or another noble gas (in case helium diffuses too fast) to cool the chamber-facing tiles. The light gas would be for power density by way of having a high speed-of-sound. Also, we mostly switched to Rankine cycle for external combustion power plants. Steam turbines are quite good at what they're doing.