Characterization of transient deformation of Zircaloy fuel cladding for LOCA conditions

Evaluation of the transient deformation behavior of nuclear fuel during a loss of coolant accident (LOCA) is currently the subject of intensive research at many laboratories in both the United States and Europe. In response to the licensing requirements in the United States a series of tests on Zircaloy cladding material were performed at elevated temperatures to provide transient deformation information with the emphasis on predicting the behavior as a function of time. Basic transient deformation data for Zircaloy were obtained by biaxial stress tests using a step application of a constant pressure and by uniaxial stress tests using a step application of a constant load. The transient deformation results were characterized by using least squares two dimensional cubic spline surface fitting techniques. The procedure uses a product of two orthogonal cubic splines to describe the strain over a cell or subspace. Different cubics are used for each subspace with forced continuity of change in strain with stress and time as well as the strain at the interface of each subspace. The results were evaluated by comparing predicted deformations with experimental results from ramp load, ramp pressure, and ramp temperature tests. Oxidation effects were also included in the experiment which provided the opportunity to show how numerical analysis techniques coupled with specialized creep/creep rupture test data can be used to predict behavior under variable stress and temperature conditions. (orig.)