I don't understand how even a 19 year old can make such a huge error as to believe that weapons grade material is not currently being used.
This material is very much not "collecting dust on shelves". Under the "Megatons to Megawatts" program the US has spent a considerable amount of money to acquire highly enriched Uranium from Russia, from decommissioned warheads, and has reformulated it into fuel rods. The US does the same thing with its own decommissioned weapons.