K. Nagai, J. Saito, K. Ara
Japan Atomic Energy Agency, Japan
pp. 214 - 217
Keywords: nanofluid, liquid sodium, nanoparticle, fast reactor, coolant, reactivity suppression
Liquid sodium is used for a coolant of fast reactor, because of its superior thermal properties and high melting temperature etc. However liquid sodium has high chemical reactivity with oxygen or water. This is the only fault of liquid sodium. Plant design has to consider taking account of countermeasures against high reactivity of sodium. We have developed sodium which possesses suppressed chemical reactivity in previous studies. The idea of the reactivity suppression is suspension of metallic nanoparticles in liquid sodium. We call it sodium nanofluid. Recently more safety of a nuclear plant is demanded. The purpose of this study is to investigate experimentally the chemical reactivity suppression of sodium nanofluid in severe environment. In fast reactor accidents which are caused by the high chemical reactivity of liquid sodium are sodium fire and sodium-water reaction. Therefore the reaction behavior of sodium combustion and sodium-water reaction were investigated using sodium and sodium nanofluid. Sodium combustion assumed at high temperature, and the combustion behavior of sodium and sodium nanofluid were observed experimentally. We took into account the thermal damage by sodium combustion, then we compared temperature of structure (floor steel plate). From the experimental results temperature of the floor steel plate of sodium nanofluid decreased compared to that of sodium. It means the soundness of structural materials was maintained even if high temperature. Furthermore sodium combustion of sodium nanofluid stopped in the middle of combustion. This particular behavior appeared on only sodium nanofluid. We call it “self-extinguishing effect”. We have already understood its mechanis. From these results, the reactivity suppression effect of sodium nanofluid appeared at the high temperature. And the thermal damage of floor steel plate will be prevented by the application of sodium nanofluid. Reaction heat of sodium and sodium nanofluid with water was measured at solid state (30°C) and liquid state (110°C). If the atomic interaction of sodium nanofluid is stronger than sodium, it is expected that the reaction heat is smaller. From the experimental results the reaction heat of sodium nanofluid at both temperature decreased than that of sodium. These results means that temperature of sodium-water reaction jet around a tube in steam generator of fast reactor certainly decrease. In fact, temperature of reaction jet of sodium nanofluid decreased greatly compared to that of sodium. From this result the rupture propagation of the tube of steam generator will be prevented by the application of sodium nanofluid. In this study the differences of the reaction behavior of sodium and sodium nanofluid were understood. As results, the reactivity suppression of sodium nanofluid appeared dominantly in sodium combustion and sodium-water reaction. In particular, the self-extinguishing effect of sodium combustion and the decrease of reaction heat of sodium-water reaction are specific effects of sodium nanofluid. It was obtained from these experiments that sodium nanofluid showed the excellent reaction suppression than that of sodium.