Development of 2D Finite Element Module to Evaluate Cladding Mechanical Behavior During Off-normal Condition

Because the zirconium alloy cladding is the first and important barrier to prevent a fission product release, its integrity is the most important concern. In the view of a mechanical integrity, stress and strain are key factors which affect to cladding's performance during normal and or off-normal operation which induces force interaction between pellet and cladding. In order to evaluate stress and strain of cladding, one dimensional (1D) approach with various models have been proposed. In case of steady state and mild transient operation period, 1D model, which considers only radial direction of cladding, is able to calculate stress and strain of cladding efficiently. However, in case of fast transient such as an Anticipated Operational Occurrence (AOO) a Reactivity Initiated Accident (RIA), it is difficult for 1D model to simulate cladding's stress and strain accurately due to its modeling limitation. Moreover, for Loss of Coolant Accident (LOCA), cladding's large deformation, so called 'ballooning', has been observed. However, this large deformation cannot be understood by 1D modeling. Consequently, Finite Element (FE) modeling which can simulate a higher order deformation of structure is indispensable requirement to understand mechanical behavior of cladding during AOO, LOCA and RIA In this study, axisymmetric 2D FE module has been developed. The FE module employs effective-stress function algorithm which can be stable and accurate computations of stresses in finite element thermoelastic- plastic and creep analysis of metals. A brief description and verification results of newly developed 2D FE module are presented. To verify the developed module, commercial FE code ADINA was employed