Plütonyum is a radioactive chemical element with the symbol Pu and atomic number 94. It is a silvery-gray metal that is dense and heavy, primarily used as a fuel in nuclear reactors and in the production of nuclear weapons. Discovered in 1940, it is named after the dwarf planet Pluto. Plütonyum is not found naturally in significant amounts and is typically produced in nuclear reactors through the irradiation of uranium. Due to its radioactivity, it poses health risks, requiring careful handling and storage to prevent contamination and exposure.