This just gives me spec-evo ideas for a person who does the shin-godzilla schtick where they ingest radioactive material and then use their inner fluids, either blood or some secondary circulatory system, as a coolant for the internal bio-reactor digestive system.

Either developing sail-hawks and sail-backs to expose as much surface area as possible, or Kit-Fisto style tail-locks with the same purpose.

Maybe a mix of both with the sail fans migrating to be like bat wings for that extra surface area cooling combined with high altitude chill.

Surprisingly I'd actually imagine this creature getting smaller, more use out of every bit of material they can find, and smaller creatures radiate heat more quickly than larger ones, so even more bio-coolant features to keep the reactor from making biological corium.