A Combined SIF and Temperature Model of Delayed Hydride Cracking in Zirconium Materials

In the last four decades several theoretical models have been developed to diagnose the DHC velocity in zirconium alloys. However, majority of the known models ignore a dependence of the crack-tip hydrides on stress intensity factor (SIF) and temperature. In this paper we first present the integrated model of DHC which combines two independent calculation models. The first calculation sub-model is designed to predict the critical characteristics of hydrides (their length and thickness) depending on both temperature and SIF. On this basis, the second calculation sub-model allows us to diagnose the DHC velocity. As a whole, the present model is based on the steadystate solution of diffusion equation, provides the improved description of the local stress in the process zone ahead of the crack and refines the location and critical characteristics of the crack-tip hydride platelets. To illustrate the efficacy of our model some of the recent experimental data are presented on DHC in Zr–2.5%Nb pressure tubes used in Canadian and Indian PHWR’s (Pressurized Heavy Water Reactors).