1. Atomic Scale Modelling of Zirconium Alloys and Hydrogen in Zirconium By Simon Lumley Supervised by Dr Mark Wenman, Prof. Robin Grimes and Dr Paul Chard-Tuckey

2. Modelling Zirconium Introduction: why model zirconium and hydrogen? Methods: density functional theory. Results: alloy solution energies. Results: lattice Strains. Future work.

3. Introduction: Zirconium The main component in the Zircaloy series of metals. Zircaloy is used in PWR, BWR and CANDU reactors. Its main use is as a fuel cladding material. A PWR fuel assembly being placed into storage.

4. Introduction: Why Zirconium? Adequate mechanical and thermal properties. Good corrosion resistance. Low thermal neutron capture cross-section. But...It is subject to hydrogen embrittlement. An optical micrograph of Zircaloy after heavy exposure to hydrogen. Kim YS, Ahn SB, Cheong YM. J. Alloys Cmpds. 2007;429:221-226.

5. Introduction: Zirconium Alloys

6. Methods: Density Functional Theory Kinetic Energy Potential Many Body Interaction Electron Density Interaction

7. Methods: Solution Energies The following cells were modelled in VASP: Done for niobium, tin and yttrium. Substitutional cells contained 54 atoms in total (1.85 at%).

8. Results: Solution Energies – Nb and Y 0.536 eV -0.135 eV 0.178 eV 0.287 eV

9. Results: Solution Energies – Sn -1.430 eV -1.229 eV

10. Methods: Solution Energies - Intermetallics

11. Results: Solution Energies – Sn 0.2909 eV 0.3817 eV

12. Results: Lattice Strains Y Sn Nb V Cr Fe

13. Future Work Extending solution energy calculations to other elements. Can we model hydrogen binding with intermetallic phases? Does the lattice strain play a role in this? Do intermetallic compounds provided a location for hydrogen to be absorbed. Thank you for your time. Any Questions?