Don't worry I don't plan on setting off a nuke every time the character sits down XD. My idea is that the character is pretty much a living small scale nuclear reactor, meaning it creates its own radioactive energy but it can absorb it from other sources. it'd be able to use this energy to give itself superhuman strength and speed, flight, and being able to release the energy in the form of beams and bursts from its body. But I do like the idea that its energy does build up over time and it would have to release it in someway, like one big burst.