High temperature oxidation of zircaloy

Our experimental program plus an extensive literature search on Zircaloy oxidation has led to the development of the full range oxidation model, FROM. The moving boundary diffusion problem has been reduced to an efficient algorithm for simple diffusion by use of a coordinate transformation. The resulting algorithm incorporates the growth/deletion of corrosion layers and non-equilibrium conditions at phase boundaries for arbitrary heating/cooling transients between room temperature and melting. The simulation also provides information on the formation of the duplex oxygen stabilized alpha-layer and the formation of alpha incursions. As the deformation and ductility of Zircaloy sheathing is markedly affected by the oxygen profile in the oxygen stabilized alpha-layer, accurate prediction of oxygen concentrations as well as corrosion layer thicknesses is required for fuel performance modelling. Comparison of FROM predictions to corrosion layer thicknesses during complex transients and to oxygen concentration profiles determined using a scanning Auger microscope show excellent agreement. (author)