| Nuclear energy is a green,low-carbon,safe and reliable clean energy.At present,nuclear power occupies a large proportion in the global power supply industry and it is an indispensable energy industry.With the goal of carbon peaking and carbon neutralization,the nuclear power industry is also a power industry that China vigorously supports and focuses on.In recent years,China’s nuclear energy industry has developed rapidly,and the requirements for the autonomy of nuclear power equipment are higher and higher,but there are some bottlenecks in key technologies that are difficult to break through.For example,some key nuclear power equipment and materials still need to be imported.In terms of nuclear fuel rod cladding welding technology,weld quality inspection technology still can’t meet the needs of rapid and efficient production.Tungsten inert gas welding is a common welding process in the production of nuclear fuel rods.The process is mature and can obtain high-quality welds,but it is easy to produce tungsten inclusion defects.In nuclear grade welding materials,the existence of tungsten inclusion defect has a great impact on the damage of weld toughness and strength.Because the nuclear fuel rod cladding is in a harsh working environment,it is more likely to be damaged if there are tungsten inclusion defects in the welds.The damage of nuclear fuel rods may lead to the leakage of radioactive materials,resulting in immeasurable consequences.At present,the inspection methods of nuclear fuel rod welds stipulated in national standards are metallographic inspection and X-ray film photography.Metallographic examination can’t be used for real-time quality inspection in the production process of nuclear fuel rods because of its destructiveness,while X-ray film photography has serious lag.At present,the popular digital radiographic testing technology can be used for real-time quality inspection in the production process,but its detection accuracy is not high enough,which is easy to cause misjudgment and missed judgment.Based on the actual quality inspection requirements of a nuclear fuel element production company for the production process of nuclear fuel rods,this paper takes a certain type of nuclear fuel rods as an example,and uses energy dispersive X-ray fluorescence(EDXRF)analysis to detect the tungsten inclusion in the weld of the nuclear fuel rod end plug.Through theoretical analysis,Monte Carlo simulation and experimental methods,the key technologies of tungsten inclusion detection by EDXRF are studied to realize the rapid and accurate detection of tungsten inclusion defects in welds.The main achievements and innovations are as follows:(1)The mathematical model of X-ray fluorescence analysis which suitable for special-shaped samples of nuclear fuel rod end plug weld was established,which laid a good foundation for theoretical analysis;(2)The excitation detection device for detecting tungsten inclusion by EDXRF based on tungsten K-series characteristic fluorescence is designed,and the detection depth is more than 0.5 mm.At the same time,the best working conditions of the experimental device are obtained by Monte Carlo simulation and experimental method: The detector angle is 15° ～ 20°;The diameter of X-ray outlet collimation hole is 1.8 mm;"Source outlet-Sample" distance is 6 mm;The "Sample-Detector" distance is 15 mm;The working voltage of the X-ray tube is 150 k V and the tube current is 0.5 m A;(3)The filter and conversion target in EDXRF analysis device were analyzed and studied.The simulation and experimental results show that the best detection conditions are: The primary filter is 600 μm thick tin sheet;The secondary filter is350 μm thick copper sheet;The conversion target is 500 μm ～ 600 μm thick lead sheet.In the simulation experiment,when the primary filter(600 μm thick tin sheet)is used,the detection limit of tungsten was the lowest,which is 30.4 μg/g;(4)The simulation experimental results of the minimum detectable scale of tungsten particles with different buried depths in zirconium matrix show that: With the increase of the buried distance of tungsten particles in zirconium matrix,the minimum diameter of detectable tungsten particles increases exponentially;When the buried distance of tungsten particles is 0(distributed on the surface),the minimum detectable tungsten particle diameter is 0.05 mm;When the buried distance of tungsten particles is 0.7 mm,the smallest detectable tungsten particle diameter is 0.24mm;(5)Zirconia reagent(powder)and tungsten powder were used to prepare powder samples with different tungsten content,and the spot samples with the shape of weld of nuclear fuel rod end plug were made.The detection limit of tungsten in the spot sample is 80.0 μg/g;(6)The tungsten inclusion detection test was carried out on the end plug of nuclear fuel rod of production samples.The results were consistent with the X-ray imaging detection results,and the EDXRF analysis results were more precise.The results show that the method of detecting tungsten inclusion by EDXRF with tungsten K-series characteristic fluorescence as excitation detection target can meet the actual needs of production,and the results have been applied in the on-line detection of nuclear fuel rod production process. |
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