Decommissioning, Immobilisation and Storage
soluTIons for NuClear wasTe InVEntories

PuO2 and Fuel Residues

DISTINCTIVE is a multi-disciplinary collaboration of 10 universities and 3 key industry partners from across the UK’s civil nuclear sector. 

Understanding the Interfacial Interactions of Plutonium Dioxide with Water

Understanding the Interfacial Interactions of Plutonium Dioxide with Water


Academic Lead – Simon Pimblott

Researcher – Jamie Southworth

University – The University of Manchester

More than 100 tonnes of Pu are stored at Sellafield as PuO2 powder in sealed steel storage cans. Under certain circumstances, gas generation may occur within the can with consequent can pressurisation. This comprises one of the most serious fault scenarios to be considered in the safety cases for PuO2 storage and avoided in practice. 5 routes to gas production having been suggested:

  • Helium accumulation from alpha decay;
  • Decomposition of polymeric packing material;
  • Steam produced by H2O desorption from hygroscopic PuO2 due to self-heating
  • Radiolysis of adsorbed water;
  • Generation of H2 by chemical reaction of PuO2 with H2O, producing a postulated PuO2+x phase.

The last 3 mechanisms, all involving the interaction of PuO2 with H2O, are complex and poorly understood, not least because of the interplay between them. An additional challenge to the safe storage and eventual disposition of Pu is that a substantial portion of the inventory is “out-of-specification” because of impurities (specifically chlorine or carbon) or unfavourable powder properties (moisture content, unusually high/low specific surface area). These must be treated to stabilise them for storage in welded cans in new stores.

Thus, within the DISTINCTIVE theme of PuO2 behaviour during extended storage, this programme, a collaboration between the universities of Lancaster and Manchester, and UCL, will seek to:

  • Understand how the structure and properties of PuO2 change with time in the presence of H2O
  • Attribute these to the fundamental chemical, physical & radiation driven processes at the PuO2 surface;
  • Understand the roles these processes play in gaseous product evolution at Pu oxide surfaces;
  • Understand how the overall ‘system’ as well as the specific processes are affected by the ageing of the Pu including variations in Pu isotopics;
  • Generate data sets for the better underpinning of the Pu storage safety cases.

Back to Top