Cluster Dynamics Model for the Hydride Precipitation Kinetics in Zirconium Cladding

Abstract

Hydride precipitation in zirconium cladding is known to cause severe loss of toughness and greatly increase the risk of mechanical failure and fuel leakage. Modeling hydride formation kinetics is critical to the safety assessment of the fuel-cladding system and the entire reactor system. Existing reduced order models do not provide such details as number density and size distribution of hydride precipitates. We have recently developed a cross-scale cluster dynamics model with increased physical details and enhanced predictive capability for the hydride formation kinetics in zirconium. Our model takes information from atomistic simulations, such as migration energy of interstitial hydrogen and formation/binding energy of hydride embryos/clusters, as input, and establishes and solves a system of rate equations that describe the evolution of concentrations of freely migrating hydrogen as well as sessile hydride clusters of all different sizes. Used here to simulate an in situ hydride growth experiment on a TEM, our model is able to reproduce the linear growth behavior of pre-existing hydrides under hydrogen ion implantation and provide possible explanations for the estimated growth rate.