Preliminary Development of a Simulation Capability for Zircaloy Clad Ballooning in LOCA

Zircaloy clad is widely known to be vulnerable to ballooning and burst in a loss-of-coolant accident (LOCA) typical of high-temperature steam environment, due to internal and external pressure difference and degraded strength. Ballooning can be detrimental in light of nuclear reactor safety. Due to the large deformation and complex constitute models in the ballooning process, detailed numerical simulation of Zircaloy clad ballooning has long been a challenge. This paper presented a preliminary Finite-Element-Method (FEM) implementation for analyzing Zircaloy clad ballooning. The developed capability can be used to predict progressive clad ballooning up to failure determined by empirical burst limit. Included physic models are currently phase transformation and high-temperature creep. Especially, anisotropic creep was considered for the α phase Zircaloy. The stress update algorithm is implicit in time integration, which ensures relatively large time increment during the simulation. The PUZRY separate effect tests were used to validate the FEM capability. The predicted time to failure (burst) is acceptable when compared with the experimental data. Besides, it was found that the effect of anisotropic coefficients is significant on the prediction of ballooning.