Plutonium(IV) oxide

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Plutonium(IV) oxide is the chemical compound with the formula PuO₂. This high melting point, yellow-brown, solid is a principal compound of plutonium.

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Structure

PuO₂ crystallizes in the fluorite motif, with the Pu⁴⁺ centers organized in a face-centered cubic array. Oxide ions occupying tetrahedral holes. PuO₂ owes utility as a nuclear fuel to the fact that vacancies in the octahedral holes allows room for fissile 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 PuO₂ monolith to retain its structural integrity.

Synthesis

Plutonium metal spontaneously oxidizes to PuO₂ in an atmosphere of oxygen. Plutonium dioxide is mainly produced by calcination of plutonium(IV) oxalate, Pu(C₂O₄)₂.6H₂O, at 300 °C. Plutonium oxalate is obtained during the reprocessing of nuclear fuel.

Applications

PuO₂ is used in mixed oxide (MOX) fuels for nuclear reactors. Plutonium-238 dioxide is used as fuel for several deep-space spacecraft such as the 'New Horizons' Pluto probe. The isotope decays by emitting α-particles which then generate heat (see Radioisotope thermoelectric generator). There has been some safety concerns, as an accidental orbital earth re-entry may lead to the break-up and/or burn-up of the spacecraft, resulting in the dispersal of the plutonium either, over a large tract of the planetary surface, or within the upper atmosphere.

Safety

As with all plutonium compounds, it is subject to control under the Nuclear Non-Proliferation Treaty. Due to the radioactivity of plutonium, all of its compounds, PuO₂ included, are warm to the touch, although touching the material may result in serious injury.

See also

• International Atomic Energy Agency

Sources

• Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. 
• Space Radioisotope Power Systems Safety