Uranium

Uranium was a dangerously radioactive metal. (PROSE: Venusian Lullaby)

This material was found on the the planet Desrault, where the Sontarans were negotiating with the Time Lords and the Order of the Black Sun for the element. (COMIC: Black Sun Rising)

Sebastian Grayle, under the guise of "Leofric of Exeter" and with the aid of the Nimon, mined uranium and converted it to plutonium in order to power the transport capsules for the Nimon. The Nimon taught Sebastian where and how to mine the uranium. (AUDIO: Seasons of Fear)

The planet Megerra was rich in valuable minerals such as uranium. (PROSE: Shakedown)

Ian Chesterton noted that Destination ore had the same properties as uranium. (AUDIO: The Destination Wars)

Uranium-235 was often used in nuclear power plants, where it was used to produce electricity via the process of nuclear fission. (AUDIO: Power Play)

Uranium was essential for the proper function of the Doctor's TARDIS, although thorium could be used in its place. (AUDIO: The Fragile Yellow Arc of Fragrance)