“I’m not an electrician but it’s always seemed to me
to be somewhat anachronistic to use atomic power to
run a steam turbine to make electricity.”
Bingo. The giant energy problem of the next decade(s) ISN’T where are we going to find stuff to burn.
The problem is: Where, on a planet where only one percent of the water on it is fresh water, are we going to find sufficient water for both energy exploration AS WELL AS production.
Consider this, however:
A generator is nothing more than a piece of iron spinning inside a magnetic field. The core of the earth is made up of nickel and iron. It rotates within a giant magnetosphere. Where does that electrical current manifest itself? Does that current require water to produce?
As you correctly point out, all that is required is a conductor moving in an electromagnetic field (specific conductors, such as iron and nickel are not required.) Or [what relativistically amounts to the same thing] a stationary conductor inside a time varying electromagnetic field will also function as a generator.
The expansion of water from the nuclear pile's heat is just a way to move the turbine. That's all. Any way you could convert the heat into some way of moving the conductor through the field works just fine. As it turns out, for many reasons including the enormous amounts available and its low toxicity, water is actually a pretty good fluid to use.