Aren't beta particles electrons, and as such will shy away from molecules that aren't "missing" one? Or are they just too high-powered in this case to give a crap about their charge?
While this was covered in Elementary and re-covered in high-school (or whatever you call it), I didn't remember particle radiation being THAT weak. Although, come to think of it, my teacher did bring in some radioactive materials one day, and we discovered that you could block the particles with a newspaper or two, so sure.
Puny particle radiation aside, what about gamma radiation then? It is a reactor after all.
H2O, even "pure" such, will form ions, and therefore conduct some electricity.