[ghaff]

One of the issues with metal is that it starts out as a ductile material and neutrons can embrittle it by introducing voids and dislocations. (i.e. basically moving the atoms around from their ordered crystal state) I'm sure some of the same mechanisms apply to ceramics but they're fairly brittle to start with so designs/applications using ceramics need to account for the fact that they're brittle from Day One.