I’m skeptical of their material choices. Gold plated copper 8km underground? If the gold gets damaged, it seems like they may have a problem. What’s wrong with

I’m skeptical of their material choices. Gold plated copper 8km underground? If the gold gets damaged, it seems like they may have a problem. What’s wrong with stainless steel? And pumping 90000 gpm of demineralized water through hot copper doesn’t sound like a very nice thing to do with the copper, although I have no actual experience with this. (Certainly, various water compositions are quite corrosive to copper at room temperature, and I’ve seen copper damaged by corrosive water.) Also, this thing is 8km deep, and it will have water going down one way and steam going back up the other way. The fluids are moving, which complicates things, but the hydrostatic pressure of 8km of water is 11k psi, and the hydrostatic pressure of 8km of steam is much much less, and there will be some gnarly dynamics involved. (As a relevant example, a tube of water that’s sealed and hot at the bottom makes a geyser!). And any residual solids in the water going down will stay down the hole as scale. If I were designing this thing, I would seriously consider a working fluid that is liquid over the entire operating range.