They're still running a steam turbine but it is more compact and efficient.

Fourth-generation reactors won't be easy, but the motivation to develop them is strong.

Arguably there is a lot of experience with liquid metal fast reactors, many of the problems like sodium fires and problems with inspection are probably solved. Think

https://en.wikipedia.org/wiki/Fast_Flux_Test_Facility

as opposed to

https://en.wikipedia.org/wiki/Superph%C3%A9nix