Thermophysical properties of U, Zr-oxides as prototypic corium materials

Abstract Simulated corium samples were prepared using a sol-gel process to yield U-Zr-oxide materials representative of a molten core covering the whole range of compositions in the U-Zr series. Discs of U-Zr-oxide were compacted by Spark Plasma Sintering (SPS). The materials were characterised by XRD and optical/electron microscopy techniques as well as SEM-EDX. The thermal diffusivity of all samples has been measured between 500 and 1600 K by the laser-flash technique and thermal conductivity was calculated. For comparison, a sample extracted from the fully melted core of the Three Mile Island reactor Unit 2 (TMI-2) was also investigated. The results for the simulated and real corium were analysed and compared to literature data. A substantial decrease of the thermal diffusivity occurred as the fraction of ZrO 2 increased up to 18 mol% in the simulated corium. In the range 18–74 mol% ZrO 2 only a weak composition dependence was observed. In this range the thermal conductivity at 500 K is between 2.5 and 3 W m −1 K −1 , in agreement with other experimental data.