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

Modelling Zirconium

•Introduction: why model zirconium and hydrogen?

•Methods: density functional theory.

•Results: alloy solution energies.

•Results: lattice Strains.

•Future work.

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.

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.

Introduction: Zirconium Alloys

Methods: Density Functional Theory

Kinetic Energy

Potential

Many Body Interaction

Electron Density Interaction

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%).

Results: Solution Energies – Nb and Y

0.536 eV

-0.135 eV

0.178 eV

0.287 eV

Results: Solution Energies – Sn

-1.430 eV

-1.229 eV

Methods: Solution Energies - Intermetallics

Results: Solution Energies – Sn

0.2909 eV

0.3817 eV

Results: Lattice Strains

Y

SnNb

VCr

Fe

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?