25 years QUENCH program. Highlights of separate-effects tests

The main objective of the QUENCH program at KIT is the investigation of the hydrogen source term and materials interactions during LOCA and the early phase of severe accidents including reflood. Bundle experiments as well as separate-effects tests are conducted to provide data for the development of models and the validation of severe fuel damage code systems. In the framework of the QUENCH jubilee session highlights of 25 years separate-effects tests were presented in this talk. The focus of the QUENCH SETs are clearly on high-temperature (> 600°C) oxidation and materials interactions of zirconium alloys (cladding), absorber materials, and structure materials in well-defined atmospheres. In this context, hydrogen release and uptake by the Zr alloy cladding materials was investigated as well. More recent experiments concentrated on the high-temperature behavior of new ATF cladding materials. The main takeaways from this presentation were: • Zirconium oxidation at high temperatures is a source of significant release of hydrogen and heat affecting nuclear accident progression. • Oxidation is not always of parabolic kinetics and may be strongly dependent on experimental boundary conditions. • Eutectic interactions may lead to melt formation far below the melting points of the individual materials. These melts may slowly relocate and severely oxidize. • ATF claddings could strongly decrease the risk of temperature escalation and hydrogen detonation during BDB accidents as well as significantly increase the coping time for AMMs. • Most experimental results were used to improve models, especially in cooperation with IBRAE, GRS, and IRSN as well as internally by H. Steiner and M. Grose.