There's no radiation in the subterranean oceans, which is what they are investigating.

(Radiation shielding is an exponential function; a few meters of water is, for most purposes, total shielding [0]. The major radiation source on Europa is solar particles trapped in Jupiter's magnet belts, which bombard Europa's airless surface. The ocean begins multiple tens of kilometers below that surface).

[0] https://what-if.xkcd.com/29/