Mass spectrometric study of the laser-evaporated Fe-Zr-O system up to 3300 K

Material systems such as U-Zr-O, Fe-Zr-O, and Zr-O have been recognized as fundamental for the analysis of in-vessel nuclear fuel debris behavior during a severe meltdown accident. In the present work, the evaporation behavior of ZrO2 and Zr-Fe-O systems are investigated using heating with laser pulses of millisecond duration and time-of-flight mass spectrometry. The relative partial pressures of main species of vapor over ZrO2 and ZrO2-FeO systems were measured at temperatures above 2750 K. The temperature dependence of O/Zr atomic ratio in vapor over zirconia was analyzed: it turned out that evaporation occurs in a noncongruent mode at temperatures above 3000 K. Evaporation of the Zr-Fe-O system was greatly affected by the fast evaporation of FeO, implying that the atomic Zr/Fe ratio, less than 0.1 below 3000 K, significantly increased with temperature. Moreover, the ratios of main vapor components were defined only by the surface temperature, independent of the zirconia sample origin.