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NKS Programme Area:NKS-R
Research Area:Severe accidents and Reactor Physics
Report Number:NKS-161
Report Title:Analysis of flow fields, temperatures and ruthenium transport in the test facility
Activity Acronym:Ruthenium Releases
Authors:Teemu Kärkelä, Jouni Pyykönen, Ari Auvinen, Joonas Jokiniemi
Abstract:Ruthenium transport experiments were conducted at VTT during years 2002-2006. Experiments gave information about ruthenium behaviour in air ingress accident conditions. This study complements those experiments with an analysis of the flows and thermal fields in the test system. Temperature profiles were measured at the walls of the experimental facility. Computational fluid dynamics (CFD) simulations used the measured profiles and provided predictions of flows and temperatures inside the furnace. Ruthenium transport was also modelled with CFD Thermal characterisation of the reactor demonstrated that buoyancy has a significant role during the cooling after the furnace. A hypothesis of the dominant role of RuO2 and RuO3 condensation on reactor walls gave simulation results that are in accordance with radiotracer measurements of deposition in experiments conducted with furnace at 1500K. Actually, RuO3 does not condensate, but it thermal decomposes to RuO2. This does not seem to have effect on result. Particle formation around the furnace exit could be detected from the comparison of modelling results with the measured profiles. In several other experiments ruthenium behaviour is dominated by other issues. These are related to the complex ruthenium chemistry that includes various surface reactions. Thermal equilibrium indicates significant gaseous RuO4 concentration around 1300 K. It seems that seed particles decreased the catalytic decomposition activity of RuO4 to RuO2 around this temperature pushing the gas concentration towards the equilibrium, and further give rise to gaseous RuO4 transport to low temperatures. At higher temperature increasing mass flow rate of RuO2 particles is likely to catalyse (decomposition) reaction of RuO4 to RuO2
Keywords:Ruthenium; nuclear safety; temperature; CFD
Publication date:01 Mar 2008
ISBN:ISBN: 978-87-7893-226-2
Number of downloads:903
Download:pdf NKS-161.pdf
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