Study And Application On Soft Soldering For Vacuum Valve Used In Nuclear Fuel System

This study is based on the development of national nuclear power plants, every relevant industry is benefit from this. Nuclear vacuum valves used in nuclear fuel purification equipments are indispensable, and the market is huge. Soft soldering of vacuum valve used in nuclear fuel system is a key technology. Production still depends on workers’ manual operation according to experience up to now. When the bulk order is coming, technology and production capacity bottleneck will affect the delivery time.According to the existing product design, manufacturing, inspection and acceptance standards, theoretical analysis and experimental verification are carried out in this paper. The soft soldering process of nuclear vacuum valve is studied. Strength and sealability of the bellows combination are tested by pressure gauges, helium mass spectrometer leak detector and so on. The soft soldering process of nuclear vacuum valve bellows combination has been researched. The qualified rate of the soldering alloy composition inspection, welding quality inspection and assembly test are 95 percent or more. The results indicate that reach the purpose of saving energy and reducing consumption. Are as follows:1. According to the chemical compositions of S-Sn60 PbB and S-Sn60 PbSbB used in the soft soldering of vacuum valve, preparation tests of solder have been completed. Analyzed the influence of raw material, process, tools and temperature on the compositions, and determined that the ratio of tin(Sn99.90AA)and lead(Pb99.990) is 6:4,the tools’ material is improved to ultra-low carbon austenitic stainless steel, the problem of excessive impurities is solved through the test, and the preparation process of tin lead solder has been researched.2. By analyzing the composition and function of different fluxes, the selection and preparation of flux have been researched. The main flux is refined rosin. Rosin alcohol solution is used with zinc chloride solution. Zinc chloride solution is prepared from zinc metal and hydrochloric acid which concentration is 37 percent, rosin alcohol solution is prepared from refined rosin powder and ethylene alcohol(CH3CH2OH) which concentration is equal to 99.7 percent or more.3. According to the structure of the bellows combination and practice, two soldering solder specifications have been researched. Their dimensions are 3×16×R1.5 and 6×6×R2, the both specifications can meet the requirements of nuclear vacuum valve from DN3~DN100. The solder mold material and structure are both improved. The quality and efficiency of the soft soldering have been improved too.4. According to theoretical analysis and experimental verification, the machining process of bellows combination is studied, the best clearance is in the range of 30~50 μ m. Analyzed the influence of process on the quality, the soft soldering process and tools of nuclear vacuum valve bellows combination has been researched. The qualified rate of assembly test has been increased to 95 percent or more from 70 to 80 percent.5. Typical quality questions of soft soldering have been arranged and analyzed to how to deal with, precautions have been formulated too.