Hydrogen recombiners, recently introduced in the French nuclear reactor buildings, display high temperature (up to ca. 900°C) and several thousands square meters of a very reactive surface when operating during a severe accident scenario. Small scale analytical experiments show that cesium and cadmium iodides are unstable, and generate volatile iodine, when heated in an oven that reproduces most physico-chemical parameters of recombiner operation. Based on these results, and due to its potential with regard to the environmental source term of a severe accident, iodine chemistry in hydrogen recombiners deserves close and careful scrutiny.
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