Study on Sodium Nanofluid for Fast Reactor (1)Concept of Sodium Nanofluid

J.-I. Saito, K. Nagai, K. Ara
Japan Atomic Energy Agency,
Japan

Keywords: nanofluid, liquid sodium, nanoparticle, fast reactor, coolant, physical property

Summary:

Liquid sodium is used for a coolant of fast reactor (FR), because it has superior properties. For example, there are high heat conductivity, high melting temperature and excellent compatibility with structural materials. However high reactivity of sodium with water or oxygen is its only shortage. Plant design has to consider taking account of countermeasures against high reactivity of sodium. If the high chemical reactivity of sodium can be suppressed by new technology, an innovative design for the FR plant which possesses higher safety will be proposed. We obtained the suppression of reactivity of sodium with suspended nanoparticles in previous studies. Sodium with suspended nanoparticles is called sodium nanofluid. Higher safety of the nuclear plant is required at present. In this study, we investigate an effect for the reactivity suppression of sodium nanofluid. In this paper, we report a concept and its property of sodium nanofluid. Nanoparticles are suspended in liquid sodium, then, the atomic interaction forms between nanoparticles and sodium atoms. Nanoparticles bond strongly with surrounding sodium atoms. The chemical reaction of sodium nanofluid would be suppressed by the atomic interaction. A feature of this nanofluid is as follows. The magnitude of suppression effect depends on the interaction surface between nanoparticle and the surrounding sodium atoms. Hence a smaller diameter of nanoparticle has a large interaction surface. Therefore the excellent thermal hydraulics of sodium is kept, and only the chemical reactivity is suppressed. Surface tension is one of iesitlarg From our previous study, the surface tension of sodium nanofluid was larger than that of sodium. It means the atomic interaction became larger due to the suspension of nanoparticles in liquid sodium. the surface tension. snanofluid and 600eseThe decrease of evaporation rate of sodium nanofluid was caused by the increase of surface tension. Reaction heat of sodium and sodium nanofluid with oxygen was measured at 500. From the experimental results the reaction heat of sodium nanofluid decreased than that of sodium. It suggests that the atomic interaction effects the chemical reaction of sodium. The suspended nanoparticle and sodium atoms formed the strong atomic interaction in liquid sodium. Compared to the surface tension and the evaporation rate of sodium these of sodium nanofluid changed by the atomic interaction. Furthermore the decrease of reaction heat with oxygen was obtained experimentally. It means that there is a possibility of reactivity suppression by the application of sodium nanofluid.