The Production Of Surface Iron Contamination During The Processing Of Nuclear Grade Austenitic Stainless Steel And The Detection

As a kind of clean, efficient, economic and sustainable energy, nuclear power is catching more and more worldwide attention. Long-term energy policy and development plan of nuclear power industry have also been established in china. It was pointed out that it is the only way for China to develop the localization of nuclear power equipment with the development of nuclear power on a large scale. Surface cleanliness and integrity manufacturing of nuclear power key parts is one core technology problem to achieve localization of nuclear power equipment, so the technology and theory of surface cleanliness and integrity will be a main direction and advanced topic of scientific research and technological development of nuclear power key equipments in the future.Austenitic stainless steel is widely used as an important structural material in nuclear power plant. The surfaces of austenitic stainless steel components are easily contaminated by iron during fabrication if they are in contact with ferritic steel, and that may affect the working stability of the components and water chemistry of nuclear power plant. Base on the nuclear grade 304L stainless steel, the production and transfer of surface iron contamination of stainless steel in different processing manufacturing rules were simulated. The influences of cutting tools and methods on the production of iron contamination were studied and the production and transfer law were then acknowledged.In this paper, base on nuclear standards and relevant industry standards, the rules of avoiding iron contamination on the surface of austenitic stainless steel during fabrication, handling, storage and transportation stages were introduced. A new test solution and test method for iron contamination was invented and was contrast to traditional test methods. The results show that phenanthroline test has a higher sensitivity in measuring passive film of stainless steel in comparison with ferroxyl test, and also has advantage of safety and stability, convenient operation and a small damage to material.The production and transfer of iron contamination caused by different grinding methods were particularly studied.and the influences of iron contamination on the corrosion resistance of 304 stainless steel were studied by FeCl3 pitting corrosion test and electrochemical test. Iron particles from 45 steel have been transferred to the surface of 304 stainless steel under the action of wheel in grinding process, which introduce a different extent of iron contamination, and iron contamination is in the form of inclusions. Iron contamination doesn't show obviously effect on the corrosion rate of 304 stainless steel immersed in 6% FeCl3 solution, while the pitting morphology have a different character; Iron contamination causes corrosion potentials and pitting potentials of 304 stainless steel shifted in negative direction in 3.5% NaCl solution, even influencing the passivation behavior of 304 stainless steel, and active dissolution happens in electrochemical corrosion process. Iron contamination damages the surface cleanliness of austenitic stainless steel, promotes the local or selective corrosion, and increases the release rate of metal. Iron contamination brings a serious threat to nuclear power equipment safety reliability and water chemical condition of nuclear power plant, and then affects working safe and stable operation of the nuclear power plant.