Mechanical and Chemical Indicators for SCC in Alloy 800 Steam Generator Tubing

600合金蒸汽发生器(SG)管子的应力腐蚀开裂(SCC)是CANDU和压水堆核反应堆面临的主要问题。更换合金800(A800)卡套管也不能幸免于应力腐蚀；欧洲最近出现了开裂报告。为了改进对800合金在使用条件下开始开裂的预测，需要彻底了解这种材料的机械和化学行为之间的相互作用。化学环境的影响是众所周知的；对微观尺度上的机械应力的影响还不是很清楚，因此它们的综合影响还没有得到很好的表征。目前一个由行业赞助的研究项目集中在这方面对合金600 SG油管材料的应力腐蚀开裂进行研究，该项目团队已经开发出确定出现晶间开裂的样品的微观应变、晶界析出和微观结构的方法。更重要的是，在理解这些参数如何影响裂纹扩展过程方面也取得了一些进展。因此，下一步是应用这些方法中的一些方法来研究合金800 SG管材的SCC行为，该材料是当前CANDU反应堆的材料选择和先进CANDU反应堆(ACR)的指定材料。 该研究计划提出了三项任务。第一个任务是确定以受控方式引起晶间开裂的条件。第二项任务的结果将帮助我们确定控制合金800 SG油管开裂的因素，并将用于解释与合金600相比，合金800具有更高的抗应力腐蚀能力。第三项任务是对已退役的SG油管材料进行检查。这项任务对CANDU动力反应堆生命周期管理(LCM)计划中所载的退化评估至关重要。 拟议的研究将在多所大学/行业研究联盟内进行，该联盟已作为当前研究计划的一部分成立。

Stress corrosion cracking (SCC) of Alloy 600 steam generator (SG) tubing is a major issue for both CANDU and PWR nuclear reactors. Replacement Alloy 800 (A800) tubing is also not immune to SCC; cracking has recently been reported in Europe. To improve the prediction of the onset of cracking in Alloy 800 under service conditions, the interplay of mechanical and chemical behaviour of this material needs to be thoroughly understood. The effects of chemical environments are well known; the effects on mechanical stress on a microscopic scale are less well understood and their combined effects therefore have not been well characterized. A current industry-sponsored research project has focused on this aspect for the stress corrosion cracking of Alloy 600 SG tubing materials and the project team has developed methodologies for determining the microstrain, grain boundary precipitation and microstructure of the samples exhibiting intergranular cracking. More importantly, some progress has also been made in understanding how these parameters contribute to the crack growth process. Thus, the next step is to apply some of these methodologies to study the SCC behaviour of Alloy 800 SG tubing material, the current material choice for CANDU reactors and the specified material for Advanced CANDU reactors (ACRs). Three tasks have been proposed for the research program. The first task is to determine the conditions that would induce intergranular cracking in a controlled manner. Outcome from the second task would help us to determine the factors that control the cracking of Alloy 800 SG tubing and would also be used to explain the enhanced SCC resistance of Alloy 800 compared to Alloy 600. The third task focuses on the examination of SG tubing material removed from service. This task is of central importance to degradation assessments contained in the Life-Cycle Management (LCM) plans of CANDU power reactors. The proposed research would take place within the multi-university/industry research consortium that has already been established as part of the current research program.