Zirconium-Applied Anisotropic Cluster Dynamics for Irradiation-Induced Defect Modeling in Presence of Hydrogen

Abstract

Under irradiation, zirconium (Zr) alloys experience free growth, following a three-step kinetic: a transitioning phase with fast growth, followed by a stabilization phase, and finally an acceleration phase (fluence 6 to 10 × 1021 n/cm2). While the initial growth kinetics are related to the <a> dislocation loops, the acceleration phase is driven by the nucleation and growth of <c> dislocation loops. Corrosion of zirconium alloys in a pressurized water reactor environment leads to an increase in their hydrogen content, with hydrogen being a subproduct of the oxidation reaction. Experiments have evidenced that increasing hydrogen content in zirconium alloys leads to higher <c> loop linear density. Atomistic modeling also shows that increasing the hydrogen concentration lowers the stacking fault energy of the <c> loops and thus stabilizes them. Using cluster dynamics calculations, this study attempts to simulate the microstructural evolution observed in zirconium alloys under irradiation, based on the diffusional anisotropy difference model, which is well adapted for zirconium. The hydrogen effect is included in this model by means of its influence on the stacking fault energy of <c> loops. After neutron irradiation in the research reactor, the microstructure of prehydrided Zr alloy samples has been characterized. A correlation between the hydrogen content in the samples and the nucleation and growth of <c> dislocation loops is highlighted. The modeling results are then compared to the experimental observations and a good agreement is obtained.