SEGREGATION OF Sn IN Zr ALLOY AND ITS SURFACE OXIDES

摘要

The zirconium alloys used for nuclear reactor fuel cladding tubes are tested not only under serviceconditions but under the higher temperatures (up to melting point) to recognize the properties of thesealloys for the case of an accident stage, as well. This work is focused mainly on stage of Zr alloysexposed for various time in vapour under temperatures from interval 900 - 1200 deg.C.The X-ray photoelectron spectroscopy, Auger electron spectroscopy and confocal laser scanningmicroscope were used to characterize the exposed tubes, outer surfaces and fracture surfaces of metaland oxide layers.Main attention was given to Zr-Sn alloys and some tests for comparison were carried out with alloyZr-lNb.The samples of tubes were pre-oxidized under temperature 425 deg. C and after it exposed in 1200deg. C in vapour, and finally broken into small parts.Result shows that there is an intensive segregation process in oxide layer created on the surface ofZircalloy 4 where the very thin layer enriched up to 40 at. % Sn was identified by XPS. The inspectionof fracture surfaces needed the use of Auger spectroscopy with possibility to analyze small area(approx. 1 μm in diameter) on the intergranularly broken surface. Comparison of atomicconcentrations measured by XPS and data obtained from Auger spectroscopy enable us to describe thedistribution of Sn in the wall of exposed tube and, possibly, to start work on model of segregationprocesses of Sn in Zr alloys.