The LMFBRs (Liquid Metal Cooled Fast Breading Reactors) is a key technology for the future electricity demand. Therefore, the establishment of safety of LMFBRs is deeply desired. To evaluate the safety of LMFBR steam generators, empirical studies have been performed for the ruptures of heat transfer tube caused by the overheat due to sodium-water reaction in case of a practical scale conditions. But few systematical experiments have been performed for the clarification of phenomena from the viewpoint of thermal hydraulics and physical chemistry. The absence of such studies is derived from the fact that sodium is chemically active and is not feasible for visualized experiments. To evaluate the safety against the secondary failure of heat transfer tubes by an analytical code, which has been tried in JAEA, it is required to understand the heat transfer phenomena around the tube. In this study, we investigated experimentally the thermal hydraulics behavior around a single heated rod with sodium-water reaction as an essential study for the clarification of raptures phenomena of heat transfer tube. The experimental apparatus was consisted of a sodium pool tank, an electrically heated test rod, a gas jet nozzle of argon-water mixture. We set horizontally in the sodium pool the test rod that is heated with the constant heat flux, and to which a gas jet of argon-water mixture was supplied for the sodium-water reaction from its lower side. The temperature of sodium pool was kept to be 420K so that a product of sodium-water reaction, NaOH (melting point is 591K), may exist as a solid phase. Gas jet velocity was set to be 17.3m/s, and the amount of water vapor in the gas mixture was 3% in mass. Just after the introduction of gas mixture, the temperature of sodium pool increased by the heat of chemical reaction. At the same time, the heat transfer to the rod surface decreased rapidly. By the observation after the experiment, it was confirmed that coarse reaction products deposited thickly at the upper side of the rod and finely granular products adhered to the lower ones. Thus, at low-sodium temperature conditions, the products of sodium-water reaction on the rod surface cause the decrease of heat transfer rate between the rod and sodium pool, which depends on the local distribution of deposits. The present authors therefore obtained experimentally the phenomena important for the development of an analytical code of JAEA.

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