Re: the medical instrument - why isn't bleach used in such a case then, or even as a standard procedure before autoclaving? (Or does that just damage the metal instead?)
Looks like bleach (sodium hypochlorite) plus autoclaving is a method recommended by the World Health Organization (WHO), for whatever that's worth.
https://en.wikipedia.org/wiki/Prion#Sterilization
Bleach is like $1 and a lot of the instruments thrown away are hundreds of dollars, and the hospital administration knows both of these figures.
I'm assuming that bleach is insufficient for this purpose.
Idk about bleach, but if you look at some of the studies, 600deg treatment for over a day and similar protocols were being evaluated, and even those scales of energy weren't clearly enough.