Of all the actinide elements, plutonium (element 94) is among the most controversial and chemically complex. It is the fuel of nuclear energy and nuclear weapons. Trace amounts of plutonium are present in nature, such as in uranium mines, but virtually all plutonium in the world today is produced synthetically as a byproduct of the fission process in nuclear reactors.
 

Like uranium and neptunium, plutonium’s name also derives from a celestial body, Pluto. It is a grey colored metal that tarnishes in air. Plutonium was first produced and identified in 1940 by Seaborg, McMillan, Kennedy, and Wahl. Since then, multiple isotopes (varying in the number of neutrons in their nuclei) have been synthesized. All of these isotopes are radioactive, though they differ in their properties and hence are used for different purposes and applications. Among the most notable isotopes are Pu-239 and Pu-238.

The most important of these isotopes is Pu-239 as it is the fuel of nuclear energy and also nuclear weapons. 1 kilogram of Pu-239 produces approximately 8 million kilowatt hours of electricity, which is enough to power about 730 U.S. homes for one year. In commercial nuclear reactors, multiple isotopes of plutonium are produced from the nuclear processes that occur. Plutonium that comes from commercial nuclear reactors (referred to as reactor grade plutonium or ‘civil plutonium’) contains approximately 50% of Pu-239 and over 19% of Pu-240. 

 

Weapons grade plutonium is different from reactor grade plutonium. For plutonium to be considered ‘weapons grade,’ it must consist of a much higher percentage of Pu-239 (approximately 93%) and less than eight percent of Pu-240.
 

Plutonium is widely known for its role in nuclear energy, although it is also relevant to other scientific applications outside the realm of commercial nuclear power. For example, the Pu-238 isotope is used to power spacecraft. This isotope fuels radioisotope thermoelectric generators (RTGs) which provide heat and electricity for space shuttles on deep space missions. The Transit 4A space satellite was launched in 1961 and was the first satellite equipped with an RTG. Spacecraft are still fueled by RTGs today. In the U.S., Pu-238 is produced through the collaboration of three Department of Energy (DOE) laboratories: Los Alamos National Laboratory (LANL), Idaho National Laboratory (INL), and Oak Ridge National Laboratory (ORNL).

Additionally, Pu-238 has been used in the medical field. Beginning in the 1960s, this isotope was used to power cardiac pacemakers. These nuclear-powered devices had remarkable longevity and lasted for over 30 years. Despite discontinued use of Pu-238 as a power source for pacemakers in the 1980s, patients with these nuclear-powered devices reported that they were still functional through the early 2000s.
 

Plutonium’s use in nuclear energy spans a wide array of scientific applications. It's employment in the commercial nuclear energy industry, space exploration, and medicine demonstrates its potential for peaceful use.