Nuclear material refers to the metals uranium, plutonium, and thorium, in any form, according to the IAEA. Nuclear materials most commonly refers to fissile materials that are capable of sustaining a chain reaction in a process that releases energy called nuclear fission. The materials include isotopes of uranium, thorium, and plutonium. These materials are distinct from radiological materials like cobalt and cesium, which are used for a variety of civilian purposes, including medical procedures. The nuclear materials most commonly used for nuclear energy and nuclear weapons are uranium and plutonium in various forms. The principles for using nuclear power to produce electricity are the same for most types of reactor. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines which produce electricity (as in most fossil fuel plants).