A study on the hydrogen recombination rates of catalytic recombiners and deliberate ignition

A study is being carried out by the Department of Nuclear and Mechanical Constructions at the University of Pisa on catalytic recombiners and on deliberately induced weak deflagration. These are the most practical methods for recombining hydrogen released into large nuclear containments during severe accidents. The recombination rates of different types of catalytic device were obtained from a thorough analysis of published experimental data. The main parameter that affects the effectiveness of these devices seems to be the molar density of the deficiency reactant rather than its volumetric concentration. The recombination rate of weak deflagrations in vented compartments has been assessed with experimental tests carried out in a small-scale glass vessel. Through a computerized system of analysis of video recordings of the deflagrations, the flame surface and the burnt gas volume were obtained as functions of time. These values of flame surface and burnt gas volume were used as inputs for a computer code to calculate the recombining rate, the burning velocity and the pressure transient in the experimental test. The code is being validated with a methodology principally based on a comparison of the measurements of pressure with the calculated values.