Study of Grain-Level Stresses in CANDU Pressure Tubes

锆合金压力管由CANDU(CANDU)反应堆主压力边界的堆芯部分组成。这些管子很容易因从冷却剂中吸收氢而退化。即使是少量氢的吸收也可能导致断裂敏感性或由于脆性氢化物相的析出而降低断裂韧性。随着压力管的老化，工程师们需要不断开发更先进的评估程序。这些过程是基于对这些降解机制的本质的更好的理解，并通过实验数据进行了验证。显微镜下，压力管材料由原子以特定方向堆积的晶体组成。每个晶体也被称为颗粒。研究表明，不同制造历史的压力管具有不同的氢脆敏感性。虽然作用在压力管上的宏观载荷是众所周知的，但缺乏关于颗粒水平应力的数据，特别是接近氢化物的数据。由于氢化物和断裂在这个层面上是活跃的，理解这个长度尺度可能有助于解释氢化物脆化的变异性。本项目侧重于压力管中晶级应力的数值模拟。建模将由晶体塑性有限元程序完成，该程序可以模拟材料微结构的影响。探讨显微组织与氢化物脆化之间可能存在的关系。此外，还将探讨用现代衍射技术测量这种应力的可行性。该项目将与Kinectrics Inc.合作进行。其成果将支持工业对氢化物相性质的理解，并可供工业合作伙伴用来开发更先进的工程规范。

Zirconium alloy pressure tubes comprise the in-core portion of the primary pressure boundary of CANadianUranium Deuterium (CANDU) reactors. These tubes are susceptible to degradation associated with theabsorption of hydrogen from coolant. The absorption of even small amounts of hydrogen can causesusceptibility to fracture or reduction in fracture toughness due to the precipitation of brittle hydride phases. Aspressure tubes age, engineers are required to continually develop more advanced evaluation procedures. Theseprocedures are based upon improved understanding of the nature of these degradation mechanisms and arevalidated against experimental data.Microscopically, pressure tube material consists of crystals where atoms are stacked with specific orientations.Each crystal is also known as grain. It has been shown that pressure tubes with different manufacturinghistories have different susceptibilities to hydride embrittlement. Although the macroscopic loads acting on thepressure tubes are well understood, there is a lack of data on the grain-level stresses, particularly close tohydrides. As hydrides and fracture are active on this level, it is likely that understanding this length scale couldhelp explain variability in hydride embrittlement.This project focuses on numerical modelling of grain-level stresses in pressure tubes. The modelling will bedone by a Crystal plasticity finite element code that can simulate the effects of material microstructures. Theexistence of possible relationship between microstructure and hydride embrittlement will be explored. Also, thefeasibility of a modern diffraction technique for measuring such stresses will be explored. This project will beconducted in collaboration with Kinectrics Inc. The outputs will support industrial understanding of the natureof hydride phases, and can be used by industrial partners to develop more advanced engineering codes.