I had posted this in another thread as a joke, but the idea actually seems plausible (in the realm of TPT, at least). I've seen Tritium being suggested countless times, so I put a slight spin on the commonly-suggested compound:

URTM (Uritium): A simple mixture of Tritium+Uranium that has the properties of both elements/compounds (creates heat under pressure + rapid oxidizing). It would help boost Plutonium's fission rate while also saving space (pure Uranium would not be needed). Since it releases a considerable amount of heat/neutrons while oxidizing, it wouldn't hamper the explosive force of a "normal" (by TPT standards) nuclear weapon, unlike pure Uranium, which tends to retard the blast by "locking" the neutrons in the center of the bomb.

Uritium could be synthesized by bombarding pure Uranium with Neutrons and Deuterium during a high-temperature low-pressure situation (+9000 degrees, -100 pressure). It doesn't seem realistic at all, but it seems like it'd be fun.

Now, it wouldn't remove the usefulness of pure Uranium (especially when it comes to nuclear reactors) since the Uritium would deplete, while Uranium does not. On the other hand, it would most likely supplant Deuterium, so I'm trying to find other uses for it and any suggestions/criticism would be greatly appreciated.

On second thought, this is relatively useless. Uritium would basically do the same thing that Plutonium already does (becomes unstable under pressure/releases heat+neutrons). Didn't think this one through, damn it.