Investigations on Catalyst Systems for Catalytic Recombiners

Abstract

Passive Autocatalytic Recombiners (PARs) are used for hydrogen removal in the containments of Light Water Reactors after a severe accident. These devices make use of the fact that hydrogen and oxygen react exothermally on catalytic surfaces already at low temperatures generating steam and heat. One major concern is the fact that existing recombiners bear the risk of ignition of the gaseous mixture by overheated catalytic substrates or parts of the casing, since the heat generated is not removed by cooling systems. Overheating may occur due to insufficient heat removal. Experimental investigations on existing systems show that the highest temperatures appear near the leading edges of the catalyst sheets. Furthermore, local conversion rates are too high not allowing sufficient reaction heat removal by convection. Possible countermeasures are additional cooling or limiting local conversion rates. At FZJ investigations are made on adapting the catalyst activity according to the requirements by using electro-plating technology instead of washcoat coatings, allowing well defined coating densities. Substrates with corresponding coatings have been tested, proving their ability in mixtures up to oxygen limitation. Different substrate materials and pre-treating measures are investigated for optimizing the surface properties. SEM-studies give insight in the surface structure and allow detailed analysis of the catalyst activity.

Studies on innovative hydrogen recombiners as safety devices in the containments of light water reactors

“…A washcoat coating offers far too high specific surfaces for such a task. More reasonable is e.g., the deposition of catalyst material directly on the substrate surface by means of galvanic techniques, as it was presented by Reinecke et al (2002). Fig.…”

“…7. With a set-up of three wire mesh elements e.g., conversion efficiencies around 70% have been reached at inlet hydrogen concentrations of up to 10 vol.% (Reinecke et al, 2002).…”