A simulation of different clcctrical dischargcs nnder SF6 atmasphere with subscquent surfacc and depth profile analysis is employed to investigate Lhc cfftch that fhe fonned corrosivc byproducts have on gas-insulatcd system (GIS) clcctrodes. Cu, A1 and Ag electrodcs were freated with sparks (in the rangc of 0.15 JisparW in an SFb dischargc cell under various conditions at the Instihit fur Spektrochcmie und Angcwmdte Spektroskopie (ISAS) in Dortmund. Thc saint materials were cxposed to sF6 in a GIS test compartment in which partial discharge ( r d occurred (Itaipu, Brazil), The treatcd materials wele analyzed with encrgy dispersivc X-ray (LOX) jn a scanning clcctron microscope, X-ray photoelectron spcctroscopy and high frequency (HF) plasma secondary neutral mass spectrometry (sNMS). The SNMS depth profiles wcrc calibrated in ordcr to quantify that part of the corrosive gaseous products having reacted with thc solid material. The analysis of thc clcctrodes exposed to the stressed SFh atmuspherc show surface reaction only in the topmost nm, whereas with sparks, sulfiir (S) and especially fluorine (P) compounds are dctccted to N 40pm depths, A first coinparison betwccn surface analysis and Fourier transform infrared (FTIII) nieasuremcnts of the reactivc gaseous products indicates a correlation of SFb decomposition and thc extcnt of electrodc degradation,

The composition and the chemical states of components of Zircaloy-4 (zirconium alloy) surfaces were studied in the temperature range between room temperature and 500°C. Each sample was kept at constant temperature (25, 100, 200, 300, 400, 500°C) for up to 16 hours. The changes of composition and chemical states of the Zircaloy-4 surface during heating were monitored by x-ray photoelectron spectroscopy (XPS). Originally, the components form well-defined layers elucidated by angle-resolved x-ray photoelectron spectroscopy (ARXPS). In contrast to depth profiling using ion sputtering, ARXPS is nondestructive. However, it is applicable for layers of up to a few nanometres thickness only.The experiments showed a decomposition of the ZrO, coverage above 200 "C accompanied by oxygen diffusion into the bulk. These processes lead to the reduction of ZrO, to metallic zirconium on the surface at 300°C and higher temperatures. The oxygen diffusion into the bulk was indicated by A M depth profiles. The layered structure observed up to B heating temperature of 200°C could not be seen at higher temperatures. After Zr metal appears at the surface during the heating process, a reaction with the adsorbed hydrocarbons takes place, leading to the formation of zirconium carbide. Though the depth resolution of an AES depth profile does not permit identification of layers with thicknesses in the nanometre region, the temperature-depeadent behaviour of oxygen is reflected by its AES profiles, showing features in accordance with the results from ARXPS, especially with respect to the fact that well-defined layers vanish above 200 "C. INTRODUCTIONSurface processes between structural materials and fission products in a nuclear reactor are of importance in many fields of reactor safety considerations during normal operation as well as in the case of an accident.In particular, aggressive gaseous fission products, such as molecular iodine or volatile iodine compounds, may severely attack structural materials. In addition, although the quantity of gaseous iodine released in the case of an accident was found to be much less than had been previously adopted, it is of interest to get information on possible retention mechanisms for fission iodine in the (case of a core meltdown accident. '-Surface analytical methods have been widely applied to investigate such mechanisms as well as to study the resistivity of structural and fuel material in the presence of aggressive media under operational conditions. Observation of stress corrosion cracking of the fuel cladding material Zircaloy in the presence of gaseous iodine above a critical concentration at elevated temperatures, ' which may lead to reduced mechanical stability of the fuel cladding tubes, gave rise to the question of what the basic processes of this effect were.Since the attack of iodine on the Zircaloy starts from the surface, the surface analytical methods XPS and AES are suitable for use in the investigation of such processes because the information depths of these methods are only a fe...

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