Raman spectroscopy coupled to principal component analysis for studying UO2 nuclear fuels with different grain sizes due to the chromia addition

Abstract

Current necessities of nuclear power plants have led to increase burn-up of the fuel during operation. In this context, some undesirable processes, such as a higher release of gaseous fission products, may occur. New UO2-based fuels are being developed by adding doping agents. Chromia (Cr2O3) has proved to considerably enhance grain growth during sintering, and thus promote the retention of these fission products. The study of these Cr-doped UO2 fuels at in situ conditions would allow testing the real performance of the fuel in operating conditions. The existence of Raman portable instruments makes this scenario feasible. But first, the measurement protocols need to be developed. Therefore, in this paper, we explore the use of Raman spectroscopy as an approach for the analysis of the effect of Cr2O3 addition in a set of UO2Cr2O3 sintered pellets. The validity of Raman is demonstrated by using Principal Component Analysis (PCA). Three Principal Components describe 98.8% of the total variance of the data, and they are related to the main Raman modes of the samples. In addition, SEM images have shown the presence of bigger precipitates of Cr2O3 not only when the solubility limit of Cr3+ is exceeded, but also when it is not reached. By XRD, the well-known Vegard behavior is observed, and a solubility limit of Cr3+dissolved into the UO2 matrix is found to be (748±16) ppm for the particular sintering conditions used.