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NKS Programme Area:
Research Area:Severe accidents
Report Number:NKS-340
Report Title:Impact of Aerosols on the Transport of Ruthenium in the primary circuit of nuclear power plant
Activity Acronym:ATR
Authors:Ivan Kajan, Teemu Kärkelä, Unto Tapper, Leena-Sisko Johansson, Mélany Gouëllo, Henrik Ramebäck, Stina Holmgren, Ari Auvinen, Christian Ekberg,
Abstract:In the NKS-ATR activity (year 2014) by VTT Technical Research Centre of Finland and Chalmers University of Technology the aim was to study the effect of aerosols and air radiolysis products on the transport of gaseous and particulate ruthenium species through a model primary circuit. The radiotoxicity of ruthenium oxides is near that of iodine in the short term and near that of caesium in the long term. All experiments were conducted using VTT´s Ru transport facility at 1227 °C with dry or slightly humid air as the main carrier gas. The results show that the impact of additional NO2 gas feed (75 ppm volume) to the flow of ruthenium oxides (in humid air) was significant both on the transport of ruthenium through the facility and on the speciation of the transported ruthenium. Transport of gaseous RuO4 was increased significantly, whereas at the same time the amount of aerosols reaching the filter was decreased. However, the release of ruthenium from the crucible was similar as in an experiment without NO2 (in air atmosphere). This indicates that the molar ratio of RuO3/RuO4 in the gas flow had changed. A proposed explanation is based on the oxidation of RuO3 to RuO4 by NO2. On the other hand, when only pure silver particles (diameter 0.5-1.0 μm) were fed to the humid air flow, the transport of RuO4 decreased significantly. Most likely, gaseous RuO4 had reactively condensed on the surface of silver particles as RuO2. Addition of both silver particles and NOx in a form of , NO3 droplets (which decomposed to silver and NO3 when heated and further to NO2, NO and O2) to the flow of Ru oxides (in humid air) enhanced the transport of gaseous RuO4 as well, but not as much as in case of NO2 feed. In these experiments (with NO2 or AgNO3), the observed transport of gaseous ruthenium seemed to be several orders of magnitude higher than in the previous experiments with only pure ruthenium oxides in the air atmosphere. These results indicate that the composition of gaseous atmosphere in the primary circuit has a significant effect on the amount and chemical form of ruthenium transported to the containment during a SA.
Keywords:Ruthenium, Aerosol, Air radiolysis, Severe Accident, Source Term
Publication date:30 Jun 2015
ISBN:ISBN 978-87-7893-422-2
Number of downloads:605
Download:pdf NKS-340.pdf
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