Hydrogen concentration variation and examination of PAR installation in reactor containment building during hydrogen release from different direction failure places

The structure of the catalyst used in a passive autocatalytic recombiner (PAR) is crucial for making the PAR reliably functional in environments of high humidity and for concentrations of hydrogen ...

Catalyst for Recombination of Hydrogen and Oxygen in Confined Spaces under High Concentrations of Hydrogen

The paper describes one of the variants of mathematical models of a fluid dynamics process inside the containment, which occurs in the conditions of operation of spray systems in severe accidents at nuclear power plant. The source of emergency emissions in this case is the leak of the coolant or rupture at full cross-section of the main circulating pipeline in a reactor building. Leak or rupture characteristics define the localization and the temporal law of functioning of a source of emergency emission (or accrued operating) of warmed up hydrogen and steam in the containment. Operation of this source at the course of analyzed accident models should be described by the assignment of the relevant Dirichlet boundary conditions. Functioning of the passive autocatalytic recombiners of hydrogen is described in the form of the complex Newton boundary conditions.

/pdf/modeling-of-spray-system-operation-under-hydrogen-and-steam-1ahlybw5x6.pdf

Modeling of Spray System Operation under Hydrogen and Steam Emissions in NPP Containment during Severe Accident

/pdf/pasywne-urzadzenia-do-usuwania-wodoru-z-obudowy-5815pfy840.pdf

Pasywne urządzenia do usuwania wodoru z obudowy bezpieczeństwa reaktora jądrowego

Simulation of gas mixing and transport in a multi-compartment geometry using the GOTHIC containment code and relatively coarse meshes

Summary In case of a severe accident in light water reactors, a large amount of hydrogen could be generated from the reaction between steam and zirconium at high fuel clad temperature and also from reactions of molten core debris with concrete. The hydrogen generated will be released in the containment atmosphere, mix with air and steam and possibly create local flammable conditions. In order to prevent loads resulting from a possible hydrogen combustion, French and German reactor containments are equipped with passive autocatalytic recombiners (PARs) which recombine hydrogen with oxygen already at concentrations below the flammability limit. In common PAR designs, catalytic materials (platinum and palladium on ceramic washcoat) are housed in a metallic structure whose purpose is to optimize the circulation of gases in contact with the catalyst. Numerous tests have been conducted in the past to investigate the PAR behaviour in situations representative of severe accidents (Battelle Model Containment in Germany, H2PAR and KALI H2 in France, AECL Whiteshell Laboratories in Canada, etc.). Furthermore, these tests demonstrated that, provided that special care is paid to the design and construction of the catalysts, catalyst poisoning by materials such as carbon monoxide, iodine and aerosols present in the containment atmosphere will not reduce fundamentally the effectiveness of the PARs. Some of the mentioned tests show also that PARs could ignite the flammable gas mixture at elevated hydrogen concentrations. These experimental results need however to be corroborated by more detailed experiments and by refined modelling of phenomena occurring in PARs. In order to better characterise the PARs induced ignition risk, a series of dedicated experiments has started at the REKO-3 facility located in Forschungszentrum Julich (FZJ). In parallel, a refined modelling of the recombiners has been developed by IRSN and will be used to have an insight of phenomena occurring at the PAR catalyst plates. Furthermore, previous tests indicated that the position of recombiners could have an impact on their overall efficiency. The installation of PARs in the reactor building is influenced by geometric and operational constraints; numerical models were developed from the experimental data for codes like COCOSYS or ASTEC in order to optimize the PAR location and to assess the efficiency of the PAR implementation in different scenarios. However, these models are usually simple (black-box type) and based on the manufacturer correlation to calculate the hydrogen depletion rate. Recently, enhanced CFD models have been developed at IRSN and FZJ in order to take into account phenomena such as PARs location effect, gas mixture ignition induced by PARs, and oxygen starvation effect. A new specific instrumented facility is also under construction at FZJ to investigate these phenomena in more detail.

Review of LP&CFD recombiner modelling and experiments: applicability to reactor simulations and open issues

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Review of LP&CFD recombiner modelling and experiments: applicability to reactor simulations and open issues