Understanding the behavior of corium, a molten mixture formed during nuclear severe accidents, is critical for enhancing nuclear safety. When core temperatures exceed 2000 K, materials such as U1-xZrxO2-y melt and form corium, whose thermophysical properties govern accident progression and mitigation strategies. This study investigates key parameters—surface tension and density—that play vital roles in corium fragmentation and stratification. By combining experimental measurements with theoretical modeling, this work provides essential insights to inform accident management systems and reactor safety designs.
Importance of Surface Tension in Steam Explosions
Surface tension of corium significantly affects jet fragmentation behavior during interaction with coolant, a precursor to steam explosions. A lower surface tension leads to finer fragmentation, which increases the interaction surface area and subsequently the explosive energy release. Understanding how composition and temperature influence this property helps in predicting and potentially mitigating steam explosion risks. This research highlights how variations in U/Zr ratios and zirconium oxidation alter surface tension, providing crucial input for simulation and safety evaluation.
Role of Corium Density in Stratification Phenomena
The density of corium determines how different phases separate in the reactor vessel during severe accidents. Stratification influences heat transfer, material interactions, and eventual solidification. Accurate density measurements are essential for predicting the distribution of fuel and fission products. This study examines how high temperatures and compositional changes affect corium density, contributing to more accurate modeling of accident scenarios and improved reactor containment strategies.
Experimental Measurement Using Maximum Bubble Pressure Method
Thermophysical property data were gathered using the maximum bubble pressure method, an effective technique for studying molten materials at extreme temperatures. This approach allows for direct measurement of surface tension and indirect estimation of other properties. In this work, tests conducted at temperatures exceeding 2723 K offer rare, high-quality data on U1-xZrxO2-y corium, aiding validation of theoretical models and filling existing experimental gaps in nuclear material science.
Post-Test Characterization with SEM-EDS
To ensure accuracy in thermophysical property determination, SEM-EDS analyses were performed after each test to identify compositional shifts during high-temperature experiments. This post-test characterization revealed significant sample alteration in the liquid state, enabling the estimation of actual composition during property measurements. Such correction ensures that the data reflect realistic in-situ conditions, improving the reliability of derived models and their application in safety analyses.
Modeling Surface Tension with Butler’s Equation
In addition to experimental data, a thermodynamic model based on Butler’s equation was employed to predict surface tension variations across different compositions and temperatures. This coupling of empirical results with theoretical frameworks enhances understanding beyond experimental limits and supports extrapolation to broader operational conditions. The correlation between experimental trends and model predictions offers a promising path to comprehensive databases needed for reactor safety simulation tools.
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