Use of plutonium in PWRs

Plutonium fuel developed for light water reactors is now an industrial product used by power plant operators in Belgium, Germany, Switzerland and France.

MOX ("Mixed Oxides") is the name commonly used to designate this fuel. It takes the form of a ceramic in which plutonium oxide (PuO ₂ ) is intimately mixed with a matrix of uranium oxide (UO ₂ ), which may be natural, depleted or reprocessed.

Plutonium does not exist in nature. It is formed in reactors by neutron capture. Some is consumed by in situ fission, while the rest is present in spent fuel discharged from the reactor.

Plutonium is a fissile material with high energy potential. One gram of plutonium in MOX produces the same amount of electricity as one tonne of oil.

Originally intended for use in fast-neutron reactors, plutonium can be substituted for uranium 235 in water reactors. This use, which requires the reprocessing of irradiated fuel, contributes to the closure of the fuel cycle and valorizes recoverable fissile materials.

The aim of this article is not to cover every aspect of plutonium use in light water reactors, but only to highlight the key facts.

After a review of the process that led to the current situation, the main technical areas specific to MOX are developed, and avenues for development are discussed.

For obvious reasons, the studies and developments presented here are largely based on achievements in France. At national level, effective coordination between the main players - research laboratories, nuclear industry and operator EDF - has enabled the use of plutonium in reactors to become an industrial reality.