Seems like these problems would not be a consideration if they used a heat exchanger system where the water, or some other fluid, was circulated through the hot areas to pick up the heat but never actually came in contact with whatever is down there.
I can see where pumping water down there and then collecting the steam, along with all the contaminants, would foul pipes and valves. But a sealed system would not seem to me to have that drawback.
You external (metal) casing is always exposed.
The solution is to cement it in, but good luck getting a good squeeze job at the depths in question.