ABSTRACT
Although it is generally accepted that fission-product attenuation in the reactor coolant system will be relatively small in comparison to attenuation in the main containment building, specific chemical reactions in the primary circuit may significantly alter the chemical forms of the radioactive release into the containment. An adequate understanding of fission-product behaviour in the primary system is required, and any important chemical changes and resuspension of material need to be identified to assist in a more confident assessment of the consequences. Fission-product vapour species can undergo physicochemical reactions with primary circuit surfaces, resulting in the initial attenuation and possible resuspension of material in different chemical forms after an ill-defined period of time.
Experiments have been undertaken to identify and characterise the important interactions between fission-product vapours and primary circuit materials. Preliminary studies have focussed on the behaviour of iodine, caesium and tellurium species. First-order rate constants have been derived for the caesium hydroxide vapour reaction with 304L stainless steel, and the reaction of elemental tellurium with Zircaloy. Mass spectrometry has also been used to determine the chemical species formed in these systems. The new compounds generated under these conditions alter the ultimate volatility and transport properties of fission-product caesium and tellurium. The implications of the caesium iodide-boric acid reaction will also be discussed in terms of the formation of hydrogen iodide in the reactor coolant system and the potential attenuation of this species by interaction with bulk surfaces.
