[en] In case of a severe hypothetical accident in a pressurized water reactor, the reactor assembly melts partially or completely. The material formed, called corium, flows out and spreads at the bottom of the reactor. To limit and control the consequences of such an accident, the specifications of the O-U-Zr basic system must be known accurately. To achieve this goal, the corium mix was melted by electron bombardment at very high temperature (3000 K) followed by quenching of the ingot in the Isabel 1 evaporator. Metallographic analyses were then required to validate the thermodynamic databases set by the Thermo-Calc software. The study consists in defining an overall surface quantitative analysis method that is fast and reliable, in order to determine the overall corium composition. The analyzed ingot originated in a [U+Fe+Y+UO₂+ZrO₂) mix, with a total mass of 2253.7 grams. Several successive heating with average power were performed before a very brief plateau at very high temperature, so that the ingot was formed progressively and without any evaporation liable to modify its initial composition. The central zone of the ingot was then analyzed by qualitative and quantitative global surface methods, to yield the volume composition of the analyzed zone. Corium sample analysis happens to be very complex because of the variety and number of elements present, and also because of the presence of oxygen in a heavy element like the uranium based matrix. Three different global quantitative surface analysis methods were used: global EDS analysis (Energy Dispersive Spectrometry), with SEM, global WDS analysis (Wavelength Dispersive Spectrometry) with EPMA, and coupling of image analysis with EDS or WDS point spectroscopic analyses. The difficulties encountered during the study arose from sample preparation (corium is very sensitive to oxidation), and the choice of acquisition parameters of the images and analyses. The corium sample studied consisted of two zones displaying very different morphologies and compositions. The upper oxide zone is fairly homogeneous, with three distinct and well contrasted phases: U₆Fe (white), (U Zr)O_2-x (grey) and (Zr(O) (black). The lower metallic phase is very heterogeneous and composed of a large number of phases: U₆Fe, (U,Zr)O_2-x, (Zr(O), Fe₂(UZr) and many phases with different compositions of the (Fe, U,Zr) ternary. The EDS and WDS global analysis methods were compared with the coupling image analysis method and with point spectroscopic analysis, which is considered to be reliable and accurate, being based on accurate rules. Global EDS and WDS could be applied to both zones. However, the coupling of image analysis and point analyses could not be accurately applied to the metallic zone because of its many phases. To obtain a valid comparison, it was necessary for every method to employ similar conditions such as sample preparation, choice of analyzed zone and magnification and global analysis parameters. A corrective method was also applied to the global results to eliminate the influence of surface oxidation. A 10 % atomic oxygen content was in fact observed in the white phase, which turned out not to be a UaFebOc oxide, but an oxidized U₆Fe phase. (authors)