ZIRCONIUM ALLOYS OXIDATION IN HIGH-TEMPERATURE AND HIGH-PRESSURE STEAM

The zirconium alloys (zircaloy-2 and zircaloy-4) are submitted to a no dular oxidation in steam at high pressure (10,5-11 MPa) in the tempera ture range of 450 divided by 500 degrees C, oxidation characterized by the occurrence of some white zirconium oxide nodules. The nodular oxi dation tests were performed in static autoclaves, in overheated steam at 450 divided by 500 degrees C (11 MPa) on samples from zircaloy-2 sh eet, zircaloy-4 tube and zirconium bar. The nodular oxidation behaviou r in overheated steam is influenced by: the chemical composition, the initial state of surface and the thermal treatment and also by the tes ting temperature. The evaluation of the oxidation behaviour in overhea ted steam of zirconium alloys, function of several factors, is made by gravimetric method and through metallographic and scanning electron m icroscopy examinations.