Plutonium(IV) oxide or (plutonia) is the
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
Pu O2. This high melting-point solid is a principal compound of
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
. It can vary in color from yellow to olive green, depending on the particle size, temperature and method of production.
Structure
PuO
2 crystallizes in the
fluorite
Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.
The Mohs sca ...
motif, with the Pu
4+ centers organized in a
face-centered cubic
In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
There are three main varieties of ...
array and oxide ions occupying tetrahedral holes. PuO
2 owes its utility as a nuclear fuel to the fact that vacancies in the octahedral holes allows room for fission products. In nuclear fission, one atom of plutonium splits into two. The vacancy of the octahedral holes provides room for the new product and allows the PuO
2 monolith to retain its structural integrity.
Properties
Plutonium dioxide is a stable ceramic material with an extremely low solubility in water and with a high melting point (2,744 °C). The melting point was revised upwards in 2011 by several hundred degrees, based on evidence from rapid laser melting studies which avoid contamination by any container material.
Due to the radioactive
alpha decay
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...
of plutonium, PuO
2 is warm to the touch. As with all
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
compounds, it is subject to control under the
Nuclear Non-Proliferation Treaty
The Treaty on the Non-Proliferation of Nuclear Weapons, commonly known as the Non-Proliferation Treaty or NPT, is an international treaty whose objective is to prevent the spread of nuclear weapons and weapons technology, to promote cooperation ...
.
Synthesis
Plutonium spontaneously oxidizes to PuO
2 in an atmosphere of oxygen. Plutonium dioxide is mainly produced by
calcination
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), genera ...
of plutonium(IV) oxalate, Pu(C
2O
4)
2·6H
2O, at 300 °C. Plutonium oxalate is obtained during the
reprocessing of nuclear fuel as plutonium is dissolved in a solution of
nitric and
hydrofluoric acid
Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...
.
Plutonium dioxide can also be recovered from
molten-salt breeder reactors by adding sodium carbonate to the fuel salt after any remaining uranium is removed from the salt as its hexafluoride.
Applications
![Plutonium pellet](https://upload.wikimedia.org/wikipedia/commons/7/71/Plutonium_pellet.jpg)
PuO
2, along with
UO2, is used in
MOX fuel
Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alt ...
s for
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
s. Plutonium-238 dioxide is used as fuel for several deep-space spacecraft such as the
Cassini,
Voyager,
Galileo
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
and
New Horizons
''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research ...
probes as well as in the
Curiosity
Curiosity (from Latin '' cūriōsitās'', from ''cūriōsus'' "careful, diligent, curious", akin to ''cura'' "care") is a quality related to inquisitive thinking such as exploration, investigation, and learning, evident by observation in humans ...
and
Perseverance
Perseverance may refer to:
Behaviour
* Psychological resilience
* Perseverance of the saints, a Protestant Christian teaching
* Assurance (theology)
Geography
* Perseverance, Queensland, a locality in Australia
* Perseverance Island, Seychelles
...
rovers on
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
. The isotope decays by emitting α-particles, which then generate heat (see
radioisotope thermoelectric generator
A radioisotope thermoelectric generator (RTG, RITEG), sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioacti ...
). There have been concerns that an accidental re-entry into Earth's atmosphere from orbit might lead to the break-up and/or burn-up of a spacecraft, resulting in the dispersal of the plutonium, either over a large tract of the planetary surface or within the upper atmosphere. However, although at least two spacecraft carrying PuO
2 RTGs have reentered the Earth's atmosphere and burned up (
Nimbus B-1 in May 1968 and the
Apollo 13
Apollo 13 (April 1117, 1970) was the seventh crewed mission in the Apollo space program and the third meant to land on the Moon. The craft was launched from Kennedy Space Center on April 11, 1970, but the lunar landing was aborted aft ...
Lunar Module in April 1970), the RTGs from both spacecraft survived reentry and impact intact, and no environmental contamination was noted in either instance; in fact, the Nimbus RTG was recovered intact from the Pacific Ocean seafloor and launched aboard
Nimbus 3
Nimbus 3 (also called Nimbus-B2) was a meteorological satellite. It was the third in a series of the Nimbus program.
Launch
Nimbus 3 was launched on April 14, 1969, by a Thor-Agena rocket from Vandenberg Air Force Base, Lompoc, CA. The spacecr ...
one year later. In any case, RTGs since the mid-1960s have been designed to remain intact in the event of reentry and impact, following the 1964 launch failure of
Transit 5-BN-3 (the early-generation plutonium RTG on board disintegrated upon reentry and dispersed radioactive material into the atmosphere north of
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
, prompting a redesign of all U.S. RTGs then in use or under development).
Physicist Peter Zimmerman, following up a suggestion by
Ted Taylor, demonstrated that a low-yield (1-
kiloton
TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The is a unit of energy defined by that convention to be , which is the approximate energy released in the detonation of a t ...
)
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
could be made relatively easily from plutonium dioxide. Such bomb would require a considerably larger
critical mass
In nuclear engineering, a critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fissi ...
than one made from elemental plutonium (almost three times larger, even with the dioxide at maximum crystal density; if the dioxide were in powder form, as is often encountered, the critical mass would be much higher still), due both to the lower density of plutonium in dioxide compared with elemental plutonium and to the added inert mass of the air contained.
Toxicology
The behavior of plutonium dioxide in the body varies with the way in which it is taken. When ingested, most of it will be eliminated from the body quite rapidly in body wastes, but a small part will dissolve into ions in acidic gastric juice and cross the blood barrier, depositing itself in other chemical forms in other organs such as in phagocytic cells of lung, bone marrow and liver.
In particulate form, plutonium dioxide at a particle size less than 10 µm
[World Nuclear Society]
Plutonium
(accessed Nov 29 2013) is radiotoxic if inhaled due to its strong
alpha-emission.
See also
*
International Atomic Energy Agency
The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was established in 1957 ...
*
Uranium dioxide
Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear rea ...
References
External links
Space Radioisotope Power Systems Safety
{{Oxides
Plutonium compounds
Oxides
Nuclear materials