IRL? or TPT.

i would think so irl... which reminds me of this.

http://news.yahoo.com/radioactive-tritium-found-leak-south-carolina-nuclear-plant-215738052.html

<Offtopic> Behold the next generation of large, buff green men and women that have speech impediments and wield miniguns...

It's just an isotope of hydrogen, so yes. TPT's DEUT is deuterium oxide, aka heavy water. IRL heavy water isn't radioactive, and doesn't expand or contract when heated any more than regular water does.

I don't really understand why deuterium oxide is fissile in TPT. IRL, it's very similar to water, but about 11% heavier. Deuterium oxide is not flammable, but deuterium is (it's basically slightly denser hydrogen). I think that, in TPT, deuterium oxide is supposed to be like deuterium.