An improved method for hydrogen deflagration to detonation transition prediction under severe accidents in nuclear power plants

Abstract

This work proposed a new method for prediction of hydrogen Deflagration to Detonation Transition (DDT) on the basis of oxygen concentration in the presence of inerting diluents. Whereas previously, the traditional criterion for deflagration to detonation transition hypothesized an unchanged air composition, it now seems appropriate to question the assumption and consider possible situations in which the presence of inerting gas components incapacitates the old criterion for applications. Under some circumstances (severe accidents in nuclear power plants), hydrogen may be massively generated by intense chemical reactions between zirconium cladding and overheated coolant in the nuclear reactor vessel. In order to prevent hydrogen explosions, Passive Autocatalytic Recombiners (PARs) that mitigate hydrogen risk by hydrogen oxidations have been implemented in the nuclear energy industry worldwide. It consumes a large amount of oxygen as the reactant and gives rise to an increased ratio of inert gas nitrogen to oxygen in the air, the product of which, water mist, also alleviates explosion hazards. The new method addressed on the variation of oxidant volume fraction and proposed new parameters: the equivalent air and the equivalent inert gases concentrations in deflagration to detonation transition criterion. The HYDRAGON code, that has been specially developed for hydrogen analysis in nuclear power plants, implemented both new and original criteria and has been applied to assessments. Close agreements between numerical simulations and a large number of experimental data sets: a wide variety of fuel gases and inert diluents, suggested that such new technique was viable and applicable to predict deflagration to detonation transition for various combustible gases. A hydrogen risk analysis of an advanced pressurized water reactor using the new method was also demonstrated in this paper.