Zirconium alloy getter bed air-ingress thermal failure analysis

Abstract

In the event of an unexpected inrush of air into a packed St-909 getter bed, the exothermic reaction of oxygen and pellet material pushes temperatures within the bed to extremely high levels. This failure mode, which could be caused by a line rupture, was modeled, analyzed, and a full-scale experiment was performed in the Tritium Science and Engineering group at Los Alamos National Laboratory to confirm the results that the primary bed container will not fail from overheating. The oxidation of St-909 pellets was modeled and determined to be limited by the oxide diffusing into the pellet material. An effective diffusivity of the oxide into the pellet and its variance with temperature was determined. In the full-scale experiment, air was pumped through the bed at 15 standard liters per minute. Oxygen breaking through the bed was gradual and began after almost one hour of air flow. Maximum temperatures along the centerline of the bed reached 1280°C, primary container temperatures reached 840°C, and the primary container maintained structural integrity throughout the experiment.