Storing and piping molten salt proved too unreliable for the Crescent Dunes solar collector. Swapping out the simple and free heat source with a much more complex nuclear reactor doesn’t seem like a good idea.
Mostly because of problems with foundations and the power-tower architecture. And note that other molten salt concentrated solar plants have done just fine, and that nuclear power is much more highly regulated and requires a higher degree of engineering analysis than a concentrated solar plant (that's why it's so expensive, in large part!)