Event Timeslots (1)

Day 1 – June 20
With efforts being made to prolong the burnup of nuclear fuels and increase efficiency of pressurised water reactors (PWRs), there is a focus on extended residence times of fuel within reactors. In addition, there are potentially significant cost benefits through plant simplification if a soluble boron-free lithiated primary water chemistry can be demonstrated to be a viable route for PWR-based small modular reactor operation. However, the corrosion behaviour of the zirconium alloy clad material under lithiated conditions remains a concern as the mechanisms that underpin this have yet to be fully identified. The mechanism by which Li accelerates zirconium alloy corrosion will allow new alloying additions to be considered and new water chemistry regimes to be investigated, improving the efficiency and performance of future nuclear power reactors.

Density functional theory (DFT) and targeted experiments were used to identify the most stable accommodation mechanisms for Li in ZrO2. Atomic scale modelling was used to produce Brouwer diagrams that predict the nature of the defect structures and their competing species concentrations as Li is accommodated in ZrO2. This was then combined with experimental data to corroborate the predictions.

The solubility of Li in bulk ZrO2 is predicted to be low, however, solubility in amorphous structures has been found which comprise complex grain boundaries. An increase of Li results in an increase in vacant oxygen defects which may aid transport of oxygen to the metal surface, accelerating corrosion. Further experiments using differential scanning calorimetry have shown that in Li stabilises the amorphous structure to higher temperatures before crystallisation compared to the undoped amorphous ZrO2 samples.