I wonder if they used uranium from Hitlery’s Uranium One scandal that will never be pinned on her.
Another possibility is use of a waste product produced from the civilian grade material containing 241Pu. Various isotopes of Americium are fissionable materials which in theory might be useful as fuel for a small and light weight reactor. A variant of a nuclear battery using this material as the energy source has been proposed as a power source for the space station. Some speculation posits that with a proper design, a very light device suitable for aerospace applications could be built.