Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The service degradation and life assessment of key components in light water reactor nuclear power plants (NPPs) mainly depend on the accumulation of service property data of component materials, understanding of environmental degradation mechanism, and construction of evaluation models or methods. The current ASME design fatigue code does not take full account of the interactions of environmental, loading and material's factors. In the present work, based on the corrosion fatigue tests in simulated NPPs' high temperature pressurized water, the environmental fatigue behavior and dominant mechanism of nuclear-grade low alloy steel have been investigated. A design fatigue model was constructed by taking environmentally assisted fatigue effects into account and the corresponding design curves were given for the convenience of engineering applications. The process for environmental fatigue safety assessment of NPPs' components was proposed, based on which some tentative assessment cases have been given.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The dissimilar metal weld joint (DMWJ) in primary water system of pressurized water reactors (PWRs) has been proven to be a vulnerable component owing to its proneness to different type of flaws. Thus, maintaining integrity of such joint in case of defect presence is of great importance to the design and safe management of nuclear power plants (NPPs). For a reliable integrity analysis of DMWJ, it is essential to understand the microscopic characteristics in all regions of the joint. In this work, OM, TEM, SEM, durometer, AFM, MFM and SKPFM were utilized to investigate the microstructure, micro-hardness and the distribution of main elements, grain boundary characteristic and residual strain in the A508/52M/316L DMWJ that used for connecting the pipe safeend and the nozzle of reactor pressure vessel in PWRs, and a comparative analysis about the microstructure and property along the radical direction of the DMWJ was obtained. The results showed that there was no region that differed from the other part of the weldment in terms of the microstructure and micro-hardness dramatically. A layer of fine grain resulting from unmelted filler metal was found in the backing weld part of the joint. The residual strain in the heat affected zone (HAZ) of 316L was higher than that in other regions. Meanwhile, drastic variations in the microstructure, chemical composition distribution and grain boundary character distribution (GBCD) in both the 316L/52Mw and the 52Mb/A508 interface regions were observed. The analyses using TEM and MFM test showed that a large number of chromium and molybdenum-rich precipitates particles distributed both along the grain boundaries and inside grains in the 316L base metal, which were identified to be precipitates with complex elementary composition rather than the normal string delta ferrite in 316L austenitic stainless steel. The SKPFM test result indicated that these precipitates were more prone to be corroded than the base metal. Therefore, further investigation about the cause of deformation and the impacts to the corrosion resistance, particularly the stress corrosion cracking (SCC) sensitivity of the precipitates needs to be carried out.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The electropolished (EP) alloy 690TT samples were first oxidized in the simulated B and Li containing primary water with 2.5 mg/L H2 at 325 ℃ and 15.6 MPa for 720 h, and then half of the samples were continuously immersed in this solution with 2.0 mg/L O2 for another 720 h. The microstructures and chemical composition of the oxide films formed under the above two conditions were analyzed. The results show that the dual layered oxide film formed under the single hydrogen water chemistry is mainly composed of spinel oxides. The outer layer is composed of big oxide particles rich in Ni and Fe and the underlying loose needle-like oxides rich in Ni. The inner layer is continuous Cr-rich oxides. The oxide film formed on EP alloy 690TT under the hydrogen/oxygen water chemistry also shows a dual layered structure. The surface morphology and chemical composition of the outer layer are similar to the oxide film formed under the hydrogen water chemistry. However, the inner layer is changed to the nano-sized NiO. The stable phase region in the potential-pH diagram for the Ni oxides is enlarged by the later dissolved oxygen. As a result, the oxygen promotes the fast growth of the outer needle-like oxides rich in Ni. Further, the oxygen promotes the dissolution of the inner Cr-rich oxides formed under the hydrogen water chemistry and increases the corrosion rate of the EP alloy 690TT. Electropolishing treatment can not reduce the corrosion rate of alloy 690TT in the simulated primary water with sequentially dissolved hydrogen and oxygen.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：轻水堆核电站关键设备的服役损伤与寿命评价主要基于其材料性能数据的积累、环境失效机制的理解和评价模型或方法的构建。目前广泛应用的ASME疲劳设计曲线并未充分考虑环境、载荷、材料交互作用的影响。本文通过模拟核电高温高压循环水腐蚀疲劳试验，研究了核级低合金钢环境疲劳损伤规律与控制机理，构建了一个植入环境效应的疲劳设计模型，给出了便于工程应用的环境疲劳设计曲线，并建立了核电站实际构件的环境疲劳安全评估流程，给出了尝试实施例。
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