Effect of Sn and Nb on generalized stacking fault energy surfaces in zirconium and gamma hydride habit planes

Abstract

We have investigated the effects of Sn and Nb on dislocation properties in a Zr lattice to elucidate the role of these alloying elements in hydride nucleation processes. According to experimental observations, γ-hydride habit planes are close to the prismatic plane in pure Zr and close to the basal plane in Zircaloy. Dislocation loops are observed around hydride precipitates, implying they play a part in hydride formation. Our ab initio generalized stacking-fault energy calculations showed remarkable effects of Sn on unstable-stacking energy and stacking-fault energy: these parameters for basal slip were considerably reduced while those for prismatic slip were increased in the presence of Sn. These results suggest selective stabilization and enhancement of dislocation spreading in the basal plane, promoting possible elementary processes of hydride precipitation with basal habit plane, i.e. screw-dislocation spreading and edge-dislocation emission in the basal plane.

Keywords:

• cladding
• zircaloy
• zirconium
• tin
• niobium
• hydride
• first principle

Acknowledgements

The present ab initio calculations have been performed on the JAEA supercomputers Altix3700Bx2, Altix350, Primergy and Prism. The authors are indebted to the efforts and assistance of technicians and researchers at the Center for Computational Science & e-Systems (CCSE). Part of this work is the result of a “Study on hydrogenation and radiation effects in advanced nuclear fuel cladding materials”, carried out under the Strategic Promotion Program for Basic Nuclear Research by the Ministry of Education, Culture, Sports, Science and Technology of Japan.