The development of the crack growth model in zirconium claddings in iodine environment

The theoretical model of iodine induced stress corrosion cracking of zirconium claddings which takes into account the cladding texture has been developed. The process of quasistationary crack growth is considered. In the model the crack is described with the set of brittle and ductile regions which are alternating along the crack front. The cladding material has polycrystalline structure and mechanical behavior of the grains depends on their orientation relative to the applied stresses. Chemical potential of dissolved iodine has minimum in the places with maximum tensile stresses which occur in the brittle region of the crack tip. Iodine weakens interatomic bonds in the crack tip and leads to growth of the crack. The stresses in the brittle region relax and the redistribution of the stresses causes the crack growth in the ductile region. In the model the stresses in both regions are calculated self-consistently. Critical iodine concentration in the gaseous phase near the tip determines the condition of crack growth This criterion can be presented in the form that the stress intensity factor exceeds some threshold value. The value of iodine flux to the crack tip has been calculated. The comparison of calculated rate of crack growth with the experimental results has demonstrated a satisfactory agreement. The model predicts the decrease of the threshold SIF for the increase of the tangential component of texture factor that is in a good agreement with the experimental observations.