My understanding from a friend who worked on nuclear subs was that transmutation due to radiation is what makes working with reactors so complicated and error prone. You can't assume anything about common tools and materials since the metallurgy becomes quite important in ways that we're not used to.
Well, tools better not be exposed to much neutron radiation, or else the person holding the tools will be in trouble. :)
What he may have been talking about is activation of troublesome elements that cause contamination that interferes with access. A prime example of this is the wear resistant alloy Stellite, used in valve seats. It's an alloy of cobalt. Some cobalt does wear off, gets circulated through the reactor, and is transmuted to 60Co, which increases the radiation field around all the piping.
All the materials in your reactor that are exposed to neutrons need to be purged of troublesome trace elements that can cause this sort of activation.
