Experiments on silver-indium-cadmium control rod failure during severe nuclear accidents

Highlights: • Ag-In-Cd control rod failure occurred at temperatures between 1470 and 1600 K. • Inner oxidation of the zircaloy guide tube retards control rod failure. • After failure of the CR first Cd burst release occurs before discharge of In and Ag. • No ballooning of the stainless steel cladding takes place before failure. • Solidus and liquidus temperatures of 80Ag15In5Cd alloy were determined by DSC. - Abstract: A large-scale bundle experiment with silver-indium-cadmium absorber rod in the QUENCH facility as well as a series of small-scale single absorber rod tests with prototypical materials have been conducted. A variety of parameters like temperature history, initial contact between cladding and guide tube and possibility of inner oxidation of the guide tube was investigated in the single-rod tests. Different failure modes from local melt-through to explosive failure were observed depending on the sample type. No interaction between Ag-In-Cd melt and stainless steel was seen up to 1750 K, near to the melting temperature of the steel. The cladding did not balloon before failure. Metallographic post-test analysis identified various phases formed during the high-temperature interactions between the involved materials. Furthermore, solidus and liquidus temperatures of the Ag-In-Cd alloy were determined accurately by DSC.