> It's a powder form of purified uranium

It is not purified uranium. It is uranium oxide. Before being reduced to the metal.

https://en.wikipedia.org/wiki/Yellowcake

>Yellowcake (also called urania) is a type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before fuel fabrication or uranium enrichment.