The Corrosion Behavior Of Zirconium Alloys In Oxygenated Water At 360?/20MPa

In order to satisfy the demands of higher fuel duty and increased cycle length,great efforts have been made to improve the comprehensive properties of zirconium alloys.Development of high-performance zirconium alloys with improved corrosion resistance is vital to meet the demand of servicing in more aggressive water chemical,such as potential dissolved oxygen?DO?in some advanced boil water reactor's?ABWR?and small module reactor's?SMR?environment.The advanced boiling water reactors?ABWRs?have a good application prospect in the future,due to their lower construction cost and more compact structure.Because the effect of hydrogenating deoxygenation in boiling water reactors?BWR?is not good,the dissolved oxygen?DO?content in BWR coolant circuit is significantly higher than that in typical PWR.So evaluating the performance of cladding materials in oxygenated water is very important to determine their suitability in BWR.Therefore,the corrosion behavior of zirconium alloys in oxygenated water should be studied.In this work,the corrosion behaviors of four commercial alloys Zr-4,M5,E110 and ZIRLO and two new-designed alloys SZA-4 and SZA-6 in oxygenated water at 360?/20MPa were studied by using a high resolution TEM?HRTEM?and an energy dispersive X-ray spectrometer?EDS?to clarify the corrosion behavior of zirconium alloys in oxygenated water.The main experimental results and conclusions can be given as follows:?1?The oxidation of Nb element is sensitive to dissolved oxygen,the corrosion behavior of zirconium alloys in oxygenated water is influenced by content of Nb.The weight gain tend to increase with Nb content in these alloys.?2?The?-Nb phase nearby the oxide/metal?O/M?is oxidized partially.DO can increase the initial oxidation rate of?-Nb phase.The?-Nb phase near the O/M interface is oxidized due to sufficient O atom in high content DO water condition.In the early stage,the?-Nb phase is oxidized but keeps crystalline structure,and this crystalline oxide gradually transform to amorphous structure as the oxidation proceeding.This amorphous structure will keep in the outer oxide film,that is,the full corroded?-Nb phase cannot totally dissolve into the surrounding oxide film.The reason for rapid corrosion rate of Nb-containing Zr alloy in DO water lies in the accelerated oxidation of?-Nb phase and the stability of the amorphous structure in the oxidized?-Nb.?3?The oxide film O/M interface of the most zirconium alloys have a transition layer identified as ZrO.This layer has restriction on the diffusion of O^2-though oxide film.It indicates that the existence of transition layer is related to the better corrosion resistance of Zr alloys.Alloys with better corrosion resistance have more formation of suboxide and the combined Zr-O region.?4?In Zr-Nb-Fe-Cr alloys,Cr tends to"bind"Fe into Zr?Fe,Cr?₂ phase for in-situ oxidation,while in Zr-Nb-Fe alloys,Fe is readily to diffuse into the surrounding oxide from the Zr?Nb,Fe?₂ phase on its onset of oxidation.The existence of Cr which may impose restriction on the diffusion of Fe is more possibly responsible for the difference in corrosion behaviors of these two Zr alloys in the process of corrosion.