Influence of minor materials on iodine behavior

Besides the materials normally considered in ex-vessel phenomena during hypothetical severe nuclear reactor accidents, several other important materials are also present in a real nuclear power station. In a typical Swedish BWR containment there are large amounts of aluminium, copper, zinc and various synthetic rubbers around and below the vessel. The atmosphere in the containments of these reactors is inerted during operation and consists of nitrogen and steam. When a core melt situation arises with molten corium exiting through the bottom of the pressure vessel, much of these secondary materials are subjected to high temperatures by direct contact with the melt or by thermal radiation from the melt during its downwards flow into the pedestal. This will pyrolyze the organic materials and may even melt some of the aluminium and zinc present near the melt passage. Such processes and their effect on the source term have seldom been considered up till now. This paper points out the possible effects these materials may have on the chemical environment in the containment and the possible effects on iodine chemistry