Unrefined: Despite being known for radioactivity, your most plentiful isotope is U238, which is only weakly radioactive. In order to become extremely radioactive, you'll have to undergo refinement to reach U235. To do this, you'll need Flourine to form Uranium Hexaflouride. You can accomplish this by simply being in the same room as Flourine. To enrich the Uranium Hexaflouride, you must use a gas centrifuge.