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1. PARTITIONING
1.1 Aqueous separation techniques
This section briefly describes aqueous separation techniques currently used on industrial scale
and research activities in the field of new separation methods for more effective separation of minor
actinides and fission products. There has been a large number of reports published until now and a
selection of the important ones is listed in Annex D.
1.1.1 PUREX process
The PUREX process, see Figure II.1, which is universally employed in the irradiated fuel
reprocessing industry, is a wet chemical process based on the use of TBP, a solvent containing
phosphorus. As shown in Table II.1 this solvent displays the property of extracting actinide cations in
even oxidation states IV and VI, in the form of a neutral complex of the type M•A n •2TBP (where M is
the metallic cation and A an anion, generally nitrate ion), from an acidic aqueous medium. Conversely,
the actinide cations with odd oxidation state are not significantly extracted, at least in the high acidity
conditions prevailing during reprocessing operations.
Uranium and plutonium, whose stable oxidation states in nitric medium are VI and IV,
respectively, are co-extracted by TBP and thus separated from the bulk of the fission products which
remain in the aqueous phase. This is the basic principle of the PUREX process.
Table II.1 Extractability of actinide nitrates in 3 M nitric acid by TBP
Oxidation state
III IV V VI
U (m) (•) m
Np (m) • m
Pu (•) m (•) (m)
Am • (m)
Cm
•
m: extractable by TBP, •: not extractable by TBP, ( ): unstable in the media
Uranium and plutonium are recovered with an industrial yield close to 99.9% (including losses
in secondary wastes).
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