What is the sort of lifetime (ball-park) that one might expect before neutron saturation of the reactor walls becomes a serious concern and the reactor has to be scrapped?
You can read about stuff like that in some of the ITER technical reports. They actually want to use that neutron radiation to generate tritium, and feed that back into the reactor.
I don’t think the reactor would be scrapped, just shutdown for maintenance.
The General Fusion design covers the walls with a molten mix of lead and lithium held in place by spinning the chamber. The lithium turns to tritium when you bang on it with a neutron to crease more inputs to the D-T fusion process. And lead doesn't really mind getting hit with neutrons. From the diagrams on Wikipedia[1] it looks like there is some normal metal exposed which might get neutron activated.
