Simulation of Initiation and Development of Corrosion Cracks in Zirconium Fuel Claddings Under Conditions of Stress Corrosion Cracking in Environment of Iodine

Abstract

KeywordsThe process models of iodine corrosion cracking of zirconium fuel claddings, used to calculate the durability of the cladding (time for loss of tightness) are considered. A method for determining the corrosion crack propagation rate in claddings made of E110 alloy Ø 9.1 0.65 mm and the results of corresponding studies (estimation of corrosion crack propagation rate and stress intensity factor K ISCC ) are given at a temperature of 380 C in iodine environment at a concentration of ~ 0.2 mg/cm 2 . Studies were performed using tubular samples with a fatigue crack. A fatigue crack on the inner surface of cladding made of E110 Ø 9.1 × 0.65 mm alloy is the initiator of a corrosion crack emergence (nucleation). The results of corresponding studies are consistent with data from the literature. The proposed study of the corrosion cracking process of fuel claddings in accordance with the results of fracture mechanics is of practical importance for substantiation of the regulation of reactor operating conditions E110 zirconium alloy, Introduction. The experience of operating nuclear power plants (NPP) with thermal neutron reactors made it possible, based on fuel elements failure cause analysis, to determine that the interaction between the fuel and the cladding during non-stationary (transient) operating conditions may lead to burst of the fuel claddings. The most probable mechanism for such burst is cracking of zirconium claddings due to stress corrosion (SCC) at iodine exposure [1], which is released from the fuel during uranium fission. The release of atomic iodine in a fuel element can occur both as a result of chemical reactions involving oxygen and uranium fission products, and as a result of cesium iodide radiolysis [2], that determines the actual possibility of iodine corrosion of the claddings made from zirconium alloys in the presence of tensile stresses in them.