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

摘要

This paper describes a new model to quantify the chemical interaction of tellurium vapours with silver aerosols in the primary system of pressurized water reactors under severe accident conditions. The silver-tellurium interaction alters the tellurium transport mechanisms through the primary system and could modify the source term. The model considers that the diffusion of tellurium in gaseous phase is the rate-controlling step at temperatures higher than the melting point of the silver-telluride formed (1,232K) and that the diffusion of silver ions through the product layer controls the reaction at temperatures lower than 1,232K. The main point of this article is the calculation of the reaction rate at temperatures below 1,232K. The reaction rate equations have been drawn based upon Wagner's theory of oxidation. The model has been incorporated into the RAFT 1.1 transport code and it has been assessed by simulating the MARVIKEN Aerosol. Transport Test 4. The results show that the tellurium-silver interaction is the mechanism which controls the transport in the first five volumes of the facility. The partial pressure of tellurium is reduced and therefore tellurium condensation and chemisorption on walls are also reduced. The inclusion of the new model improves the agreement of the calculation results with the experimental data. [References: 33]