REACTION-KINETICS OF TELLURIUM AND SILVER AEROSOLS AT TEMPERATURES BELOW 1,232K

This paper describes a new model to quantify the chemical interaction of tellurium vapours with silver aerosols in the primary system of pre ssurized water reactors under severe accident conditions. The silver-t ellurium interaction alters the tellurium transport mechanisms through the primary system and could modify the source term. The model consid ers that the diffusion of tellurium in gaseous phase is the rate-contr olling step at temperatures higher than the melting point of the silve r-telluride formed (1,232K) and that the diffusion of silver ions thro ugh the product layer controls the reaction at temperatures lower than 1,232K. The main point of this article is the calculation of the reac tion rate at temperatures below 1,232K. The reaction rate equations ha ve been drawn based upon Wagner's theory of oxidation. The model has b een incorporated into the RAFT 1.1 transport code and it has been asse ssed by simulating the MARVIKEN Aerosol. Transport Test 4. The results show that the tellurium-silver interaction is the mechanism which con trols the transport in the first five volumes of the facility. The par tial pressure of tellurium is reduced and therefore tellurium condensa tion and chemisorption on walls are also reduced. The inclusion of the new model improves the agreement of the calculation results with the experimental data.