[pfdietz]

I don't think it's necessary for the pipes in the piles to be operating at the pressure of the steam in the turbines. There could be an intermediate heat exchanger to transfer heat from the low density steam (or air) in the pipes to the high pressure steam in the turbine loop.

[kragen]

Yes, that is what I meant to propose, but when you have that additional heat exchanger, why would you use steam rather than air (or some other fluid like helium or argon) in the low-pressure pipes?

[pfdietz]

An expensive gas would present the problem of leakage. If that could be cheaply addressed, great, otherwise go with something where making up small leaks is not expensive. That probably means steam or air.

I think steam would have better heat transfer properties than air, maybe?

I do wonder how much we should worry about oxidation of the pipes. Stainless is certainly fine at 600 C in an oxidizing atmosphere, but what about cheaper steel?