Reprocessing refers to the chemical separation of fissionable uranium and plutonium from spent fuel. Coal ash contains the radioactive elements uranium and thorium. In practice, bombs do not contain hundreds of tons of uranium or plutonium. Ru is a product of fission of a nucleus of uranium or plutonium. Tobacco contains traces of thorium, polonium and uranium. They occur in the decay chains of primordial isotopes of uranium or thorium. These rock formations contain rich deposits of valuable minerals like coal, limestone, uranium and sillimanite. Handling uranium hexafluoride is well established in enrichment. Residues from processing of uranium ore can also be a source of radon. Both metallic depleted uranium and depleted uranium dioxide are used for radiation shielding. However, trace amounts occur naturally as a product of transmutation reactions in uranium ores. The reactor required an enormous amount of graphite blocks and uranium pellets. Concerns relate to the health risks and environmental damage from uranium mining. Krypton is one of the products of uranium fission. Marshall also examined possible genetic effects due to radiation from depleted uranium.