Determination of critical material damage parameter for Indian clad tube burst behavior under severe accident scenario

Abstract

During loss of coolant accident scenario in PHWRs, heat removal from clad tubes containing the uranium oxides fuel may get severely impaired. This results in increase in temperature of the fuel clad and subsequent increase in the clad tube internal pressure. This causes the clad tube to deform and balloon leading to the increase in diameter of the fuel clad. After a critical value of deformation is reached, the clad tube gets burst. The burst process is due to initiation of crack in the clad due to creep deformation process in the presence of internal pressure and high temperature environment. In this work, experimental data of fuel clad bursts from literature have been used to evaluate a critical damage parameter that can be used to predict the onset of burst phenomenon of clad tubes. Finite element modelling of the fuel clad has been carried out to simulate the ballooning deformation of the fuel clad tubes due to creep. Norton’s creep model has been used in the simulation. The critical damage parameter evaluated, using analysis and experimental data, has been used subsequently to predict burst time of Zircaloy-4 fuel clad when subjected to different types of loading environments. An exponential decay type correlation has been obtained from the finite element analysis results which can be used by safety analysts to predict burst pressure of Zircaloy-4 fuel clad of Indian PHWR as a function of burst temperature or vice-versa.