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Hydrogen removal from LWR containments by catalytic coated thermal insulation elements


In the THINCAT project, an alternative concept for hydrogen mitigation in a LWR containment has been developed and investigated. Based on catalytic coated thermal insulation elements of the main coolant loop components, it could be considered either as an alternative to back fitting passive autocatalytic recombiner devices, or as a reinforcement of their preventive effect. Potential advantages of catalytic thermal insulation studied in the project are -Reduced risk of unintended ignition, -Improved start-up behaviour of recombination reaction, -No workspace obstruction in the containment, -No need for seismic qualification of additional equipment. The work programme to develop the innovative concept included -Development of suitable materials and procedures to manufacture catalytic coated surfaces for thermal insulation elements, -Experimental qualification of the coatings with respect to recombination efficiency, -Experimental qualification of coated insulation elements under containment-typical conditions, including natural convection conditions, -Numerical prediction of hydrogen concentration transients in the containment for selected scenarios, -Analysis of cost/benefit ratio and safety for the innovative concept, comparison with conventional recombiner concept. Efforts to develop a suitable catalytic layer resulted in the identification of a coating procedure that ensures high chemical reactivity and mechanical stability. Test samples for use in experiments with this coating were produced. Models to predict the catalytic rates were developed, validated and applied in a safety analysis study. Results show that an overall hydrogen concentration reduction can be achieved which is comparable to the reduction obtained using conventional recombiners. Existing experimental information supports the argument of a reduced ignition risk. Depending on the construction of the insulation system, the installation of the new concept in an existing plant may become time consuming and costly, as conventional mattress systems require considerable work time for mounting. Recent cassette type insulation systems are equipped with quick release fasteners and thus more suitable for the THINCAT concept as installation times are significantly lower. After the bankruptcy of the previous co-ordinating organisation Battelle Ingenieurtechnik GmbH it was withdrawn from the project in October 2001. As Battelle was a project key partner because of the planned integral experiments to be performed at the THAI facility, the project could not achieve all initial objectives and was terminated untimely. As a consequence some work-packages were skipped and some activities were not performed. This concerns especially the large-scale experiments and some of the small-scale tests, which were intended to demonstrate the performance of the new concept under relevant conditions.

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