Investigation of thermo-catalytic decomposition of metal-iodide aerosols due to passage through hydrogen recombiners Original Research Article

Passive autocatalytic recombiners (PARs) are a means of preventing hydrogen accumulation in the containment building of a water-cooled nuclear reactor during an accident. A potential problem exists concerning suspended radioactive aerosols: particles passing through the catalytic elements are heated up with significant evaporation of more volatile chemical species. The aerosols, vapours and carrier-gas mixture may chemically react resulting potentially in conversion of easily-retained aerosol material into more troublesome vapours and gases. An experimental programme, RECI, demonstrated that potential exists for PARs to generate volatile forms of iodine, namely molecular iodine, by thermo-catalytic decomposition of metal-iodide aerosols. Here, analysis of RECI results aided by two computer codes, one a field code the other a lumped-parameter approach, provides significant insight into the iodide-iodine phenomenology where, in particular, the rapid cooling of the reacting mixture explains the persistence of volatile species downstream at ambient conditions. While understanding of the phenomenology has progressed, the current results cannot be extrapolated to the reactor case since further experiments are needed reproducing more closely expected accident conditions.