I already said that they need radiation (read: Heavy Metal Poisoning) to survive, but if you want to get it told the long way...
CU7 (translated) wrote:
Radiation Norns, Ettins and Grendels need - as their homonymous relatives from C2- from the lifestage "adolescent" radioactivity and heavy metals to survive. Ideal conditions for them are so in the Ettindesert, where the Volcano provides a regulated release of radioactive matter. Radiation Norns are not much interested in lifts; Radiation Grendels grow slower; Radiation Ettins steal no gadgets.
Appearance: Radiation Norns use the sprites of the C3 Civet Norns (Norn Slot C), Radiation Ettins the ones of the C3 Ettins (Ettin Slot A), Radiation Grendels the ones of the C3 Grendels (Grendel Slot A).
Colorgenes: extended, modified, lifestage-constant
Translation enough?