XPS studies of the thermal behaviour of passivated Zircaloy‐4 surfaces

Abstract

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...

Synchrotron-based high-resolution photoemission spectroscopy study of ZIRLO cladding with H2O adsorption: Coverage and temperature dependence

“…Sequentially, we annealed a sample with H 2 O adsorbed on ZIRLO to check the temperature dependence. On annealing up to 100 °C, there were no significant changes, whereas after annealing beyond 300 °C, the relative proportion of zirconium metal increased, and the relative quantities of the total zirconium oxides reduced with the decrease in Zr 3+ and Zr 4+ because of the decomposition of Zr 2 O 3 and ZrO 2 accompanied by oxygen diffusion into the bulk, in agreement with literature 10,20 . To the best of our knowledge, the coverage and temperature dependence of ZIRLO cladding with H 2 O adsorption have not been systematically studied using synchrotron-based HRPES.…”

Chemical composition of ZrC thin films grown by pulsed laser deposition

“…The spectra collected from the as-received surface confirmed that the surface was strongly contaminated by adventitious carbon and a combination of Zr oxides-hydroxides. After the first sputtering cycles, the O 1s and Zr 3d signals corresponding to ZrO 2 oxide were the strongest, with almost no adventitious C. Continuing the sputtering one can note a shift in the binding energy of C 1s and Zr 3d peaks towards 281.6 eV and 179.2 eV, respectively, the values corresponding to ZrC [24]. An O 1s peak is barely visible, its intensity decreased markedly, corresponding to around 5-8% in bulk.…”

Angle‐resolved core‐level spectroscopy of Zr1Nb alloy oxidation by oxygen, water and hydrogen peroxide

“…5,6,9 The clean surfaces were prepared either by heating or by ion sputtering. Hoflund et al 2 studied the oxidation of a Zr surface cleaned by heating and observed that heating above 1135 K greatly reduces the uptake of oxygen whereas inert ion sputtering restores the high activity of Zr towards oxygen.…”