I only wish I had even a hint of what that really means. Kinda sounds like he was trying to make Uranium cross-dress and apply for a goobermint-funded operation.
Simply put, transUranium Elements are all the ones above Uranium on the Periodic Table. They are larger than Uranium, and less stable the larger they get. Most, if not all, did not exist in nature at the time of Marie Curie's research. Some may have been discovered, many were man-made. While it does exist in nature, it's only in trace amounts embedded in Uranium. The first truly man-made Element was Curium, and Glenn T. Seaborg was one of a team of scientists who did it.
I'm oversimplifying a bit, but when we first started developing a nuclear weapon, our materials of choice were Uranium and Plutonium, which we had learned to synthesize (from Uranium) in 1940. Creating the conditions for fission was easier with the correct isotope of Uranium (235), but Uranium ore is about 99.25% U-238, so it had to be purified to have a much higher 235 content (this is done in centrifuges, which is why Iran has so many and it's such a concern). Plutonium 239 was easier to synthesize than U-235 was to purify, but it was more difficult to create the conditions for fission. Little-Boy used on Hiroshima was U-235, and Fat-Man on Nagasaki (and the Trinity test in NM) were P-239.
P-239 is the material of choice for most modern nuclear reactors, but U-238 is a vital raw material to make it, which is why Russia wanted it so badly they bribed Hillary Clinton to get it.
Like I said, over simplified and you probably already knew all this. I'm sure
@Smokin Joe will come along and fill in the missing bits (he studied this a lot more than I).
