| Accelerator driven sub-critical system (ADS) is a choice for future advanced nuclear reactor, because of its strong transmutation capability, good neutron economy and its inherent safety. Lead bismuth eutectic (Pb44.5Bi55.5, LBE) is a preferred material as coolant and spallation target of ADS, because of its low melting, high boiling, low saturated vapor pressure, small neutron cross section, low chemical activity with water and air, excellent neutron properties and good thermal conductivity, etc. Compared to pure lead, bismuth is rare metal, limited resource and expensive, also it can generate volatile210Po used for reactor. Compared to LBE, the performance of pure lead are better than that of LBE except melting, therefore the international nuclear scientists tend to use pure Pb instead of LBE, but the use of high melting point of the pure Pb will have some engineering problems. The melting rose slowly with content of Bi decreased Between LBE and pure Pb, and there is no sharp boundary. Thus combining the advantages of Pb and LBE, it can consider to reduce the content of Bi and to use hypoeutectic alloy as the coolant. As impurities will significantly reduce the thermal performance of the lead bismuth alloy, such as thermal conductivity and viscosity, and lots of impurities also plug channel of heat exchanger and piping systems, it can affect the safe operation of reactor and lead to reactor accident, so it is necessary to prepare high purity lead bismuth alloy and to study its thermophysical properties for its composition optimization, and in the mean time, to purify impurities by exploring on-line purification technology for reducing the accident rates and ensuring the safe operation of reactor. In this paper, preparation technology of high purity LBE and viscosity performance were studied, and also the compatibility with structural materials and thermal expansion performance for composition optimization of lead-bismuth alloy, meanwhile an on-line purification device named cold trap was designed and built for control component of LBE. The experimental results provide data support for design and operation of nuclear reactor.Firstly, according to demand of ADS, component requirement of lead bismuth eutectic was proposed in this paper, the preparation process of LBE was studied based on the requirement. To prevent impurities, surface treatment process which could passivate surface of crucible and ingot mould was obtained after many experiments. According to volatilization kinetics and thermodynamics, the ingot of lead bismuth eutectic was prepared in the vacuum induction furnace.The test composition test showed that the contents of single impurity element and the total content of impurity elements were less than10ppm and100ppm, respectively.Secondly, in this paper, the viscosity and thermal expansion performance of high purity lead-bismuth alloy were studied, and also the compatibility with structural material. Viscosities of different proportion lead-bismuth alloy which contained LBE, Pb6oBi4o, Pb7oBi3o, PbgoBi20and Pb were investigated in a certain temperature range above liquidus. The results showed that the viscosities of five melts decrease with the increase of temperature. Excepting for pure Pb, anomalous changes in the viscosity values were found in LBE, Pb6oBi4o, Pb7oBi3o and PbgoBi20in the test temperature range, it is presumed that melts structure occurred at the anomalous point of the viscosity. In the temperature range of350℃-650℃, viscosity value of Pb6oBi4o was obviously higher than that of the other proportion of lead bismuth alloy, and it increased with the decrease of bismuth content at temperature above750℃. In addition, the volume change of LBE and Pb with temperature was obtained with self-heating probe instrument, and the results showed that the volume of LBE increased0.80%and Pb decreased1.64%during the liquid-solid phase transition at the melting point. Aging effect on the volume of solid LBE at room temperature was also studied and the preliminary results showed the main reason of macroscopic volumetric expansion of solid LBE was the phase transition of LBE from β-phase to y-phase. At last, the role of pure Pb, pure Bi and LBE on the corrosion of T91and316L has been studied by static corrosion device at the temperature of600℃. The results showed that the corrosion rate of316L is about10times of T91in liquid metal. Loss of steels in liquid Bi, Pb or LBE occurs primarily through dissolution of steel components into the liquid. The solubility of Ni in liquid metal is much higher than that of Fe and Cr. Structural material corrosion is caused primarily by Bi, the liquid lead is less corrosive than LBE does at the same operation condition. The main reason is that solubility of Fe, Cr and Ni in Bi is always greater than that in liquid lead as shown in the figure.Finally, on-line purification technology of liquid metal was explored in this paper. On-line purification device named cold trap has been designed and built based on the properties of liquid lead bismuth alloy and heat transfer calculation check and design experiences of purification device at home and abroad.The experimental results provide data support for design and operation of nuclear reactor and the choice of lead-bismuth hypo eutectic applied in advanced nuclear reactor. |
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