Until the UK Government arrives at a decision regarding the final treatment and disposition of Pu, the NDA remain responsible for the “safe and secure storage”. However, ageing mechanisms associated with the storage of PuO2 are poorly understood. The generation, stability and mobility of fission products in addition to the role of the surface oxide layer being key factors. Atomistic computer simulation techniques remain complementary to experimental methods and are ideally suited to provide fundamental insight into the defect chemistry.
The scope of this study is to focus on investigating the defect chemistry of PuO2 associated with ageing phenomena, in particular the incorporation and entrapment of helium. Radiogenic helium gas generation naturally occurs in the ageing of PuO2 due to the spontaneous alpha decay of Pu isotopes, creating self-radiation damage to the lattice. Helium gas bubbles can form in the matrix, causing swelling and accumulation along grain boundaries can cause embrittlement.
Computational modelling techniques would employ robust interatomic potentials derived from empirical fitting to experimental data to predict bulk and surface structures and their defect chemistry. Relative thermodynamic stabilities of fission products and Helium atom incorporation/aggregation would be calculated and compared with bulk and surface sites in order to predict migration pathways and mechanisms. Extended defects such as grain boundaries and their role in fission product/helium migration would be simulated using surface simulation techniques. These simulations would be extended through the application of molecular dynamic techniques to model the effect of radiation damage on the lattice structure and subsequent effect on fission product and trapped helium atom mobility. The combination of these modelling techniques would provide valuable insight into furthering the understanding of ageing mechanisms associated with PuO2 at the atomic scale relevant to storage.
Academic Lead: Mark Read
Researcher: Elanor Murray
Location: University of Birmingham