Investigation of zirconium oxide growth in nuclear fuel element claddings by micro-Raman, ellipsometry, and Laser-Induced Breakdown Spectroscopy

Abstract

The composition and structure of zirconium oxide layers formed in zirconium metal alloys represent an essential factor in the performance of the fuel rods used in nuclear pressurized water reactors (PWR). In this sense, zirconium claddings samples were subjected to a temperature of 350 °C and a pressure of 170 bar during distinct oxidation times. Laser-Induced Breakdown Spectroscopy (LIBS) analysis confirmed the composition of the cladding. Micro-Raman imaging was used to characterize the oxide phases and associated with spectroscopic ellipsometry technique, estimated the composition and thickness of the layers. The results reveal that a natural layer of tetragonal phase predominates on the metallic surface, and the intensity of the monoclinic phase spectra increases with increasing layer thickness. The detection of different phases concerning thickness is important information to model the film structure in the ellipsometry technique. The rupture process in thicker layers was identified by micro-Raman spectra, by the exposure of the innermost tetragonal phase. The relation between thickness and oxidation time was used to estimate the kinetics of the oxidation reaction. Therefore, LIBS, spectroscopic ellipsometry (SE), along with micro-Raman spectroscopy successfully proved the phase transition as the ZrO2 layer grows, and the rupture process of the monoclinic layer at oxidation times greater than 96 h (average thickness of 1.1 μm).