Interaction between silver and Zircaloy-4 at high temperatures

Interaction between silver-indium-cadmium control rod alloy and Zircaloy-4 is an important reaction in the analysis of a severe accident of a PWR, since it has a great influence on the fuel bundle degradation. The authors have reported the results of the experiments on the interaction between silver-indium-cadmium alloy and Zircaloy-4. To examine the mechanism of this complex reaction system, reaction couples of silver, the main component of silver-indium-cadmium alloy, and Zircaloy-4 were isothermally heated in argon at the temperatures ranging from 1273 to 1473 K. The dissolution behavior of Zircaloy-4 in silver/Zircaloy-4 reaction was compared with that in silver-indium-cadmium alloy/Zircaloy-4 reaction and the role of indium was discussed. The reaction rate of silver/Zircaloy-4 reaction increased with the temperature increase and was low compared to that of silver-indium-cadmium alloy/Zircaloy-4 reaction. This difference is larger at lower test temperatures and is believed to be caused by the difference of melting points between silver-indium-cadmium alloy and silver. Two reactions show comparable reaction rate at 1473K. Silver/Zircaloy-4 reaction approximately obeyed the parabolic rate law, thereby reaction rate constants and an apparent activation energy, 580.8kJ/mol, were determined. (author)