In this case the "radiation" is the emission of high-energy neutron particles. Neutrons will run into anything *... and when they do, they transfer a ton of their energy into whatever they hit... causing "damage cascades" as atoms get tossed around (Wikipedia has a decent animation here: https://en.wikipedia.org/wiki/... ).
That atom-scale damage adds up after a while... causing material failure... regardless of the type of material.
For instance, inside of a reactor all of the steel holding all of the fuel in place is constantly bombarded... leading to all sorts of effects like radiation induced swelling and embrittlement.
In humans the primary issue is when those neutrons hit DNA / cells and damage them. It actually happens to us all day long from radiation around us... but our bodies can deal with a certain amount. Too much damage though... and your body can't cope any more.
In robots / electronics the issue is much the same. The neutrons run into _everything_ and degrade it. More sensitive pieces (like camera sensors) will degrade rather quickly while larger components (like structural steel) will most likely be fine for long periods of time.
* The probability that a neutron will hit a certain type of atom is called a "cross section" (XS) and is an _extremely_ well studied phenomenon. You can look at some here: https://www.nndc.bnl.gov/sigma... for instance, this is the probability for a neutron running into Hydrogen: https://www.nndc.bnl.gov/sigma...