Nuclear waste repositories could be safer places thanks to UK chemists, who have revealed the likely structure of a contaminant in reprocessed nuclear fuel. 

Nuclear fuel is generally reprocessed by extracting out the actinide metals uranium and plutonium. However, this extracted material is often contaminated with another radioactive metal, technetium, which can catalyse unwanted side reactions and complicate waste storage. Now, Iain May, David Collinson and colleagues at the University of Manchester have discovered how technetium, in the form of pertechnate [TcO₄]^-, is extracted during reprocessing.

'Pertechnate would traditionally be classed as a weakly coordinating anion,' said May, 'and we were very interested in why pertechnate so effectively co-extracted.' Pertechnate contaminates the extracted material by forming a complex with uranium, said May. Studying perrhenate, [ReO₄]^-, a non-radioactive analogue of pertechnate, the team showed that perrhenate can act as a bridge between two uranium ions, as well as a simple, singly bonding ligand. 

'The demonstration of perrhenate as an inner-sphere ligand in these uranyl complexes serves as a good model for how pertechnate may coordinate actinyl compounds in general,' said Thomas Albrecht-Schmitt, an expert in actinide complexes at Auburn University, Alabama, US. 

'A better molecular understanding of the behaviour of pertechnate in this waste could ultimately aid safe and cost-effective treatment and disposal,' said May. 'Nuclear power is now being seriously considered by many countries as a key component of a secure "carbon neutral" energy policy. Future fuel processing technology will require a sound fundamental understanding of actinide and fission product coordination chemistry.' 

James Mitchell Crow