In situ high temperature oxidation analysis of Zircaloy-4 using acoustic emission coupled with thermogravimetry

• Published in: Journal of nuclear materials Vol. 461; pp. 365 - 375
• Main Authors: Omar, Al Haj, Véronique, Peres, Eric, Serris, François, Grosjean, Jean, Kittel, François, Ropital, Michel, Cournil
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2015; Elsevier
• Subjects: Acceleration; Acoustic emission; Chemical and Process Engineering; Cooling; Cracks; Engineering Sciences; Helium; Oxidation; Thermogravimetry; Zirconium dioxide; Zircaloy-4; Acoustic Emission; AE; Thermogravimetric analysis; AE Burst; High temperature corrosion; TGA
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2015.03.014

•Thermogravimetry associated to acoustic emission (AE) improves knowledge on the corrosion of metals at high temperature.•Kinetic transition is detected under air oxidation tests at 900°C of Zircaloy-4 by a change in the rate of mass gain and by the AE activity.•AE analysis is complementary to characterizations of post mortem oxidized samples.•AE allows us to distinguish the cracks which occur during the Zircaloy-4 oxidation from the cracks which arise during the cooling of the samples. Zircaloy-4 oxidation behavior at high temperature (900°C), which can be reached in case of severe accidental situations in nuclear pressurised water reactor, was studied using acoustic emission analysis coupled with thermogravimetry. Two different atmospheres were used to study the oxidation of Zircaloy-4: (a) helium and pure oxygen, (b) helium and oxygen combined with slight addition of air. The experiments with 20% of oxygen confirm the dependence on oxygen anions diffusion in the oxide scale. Under a mixture of oxygen and air in helium, an acceleration of the corrosion was observed due to the detrimental effect of nitrogen. The kinetic rate increased significantly after a kinetic transition (breakaway). This acceleration was accompanied by an acoustic emission activity. Most of the acoustic emission bursts were recorded after the kinetic transition (post-transition) or during the cooling of the sample. The characteristic features of the acoustic emission signals appear to be correlated with the different populations of cracks and their occurrence in the ZrO2 layer or in the α-Zr(O) layer. Acoustic events were recorded during the isothermal dwell time at high temperature under air. They were associated with large cracks in the zirconia porous layer. Acoustic events were also recorded during cooling after oxidation tests both under air or oxygen. For the latter, cracks were observed in the oxygen enriched zirconium metal phase and not in the dense zirconia layer after 5h of oxidation.