Modeling and Validation of Irradiation Damage in Ni-based Alloys for Long-Term LWR Applications (US/UK)

随着压水堆(PWR)工厂运行寿命的延长，越来越需要预测建模工具来描述材料退化，以确保安全、可靠的运行以及部件更换计划。目前存在一些模型，但它们的适用性有限，并且无法预测压水堆系统中使用的所有合金的退化。具体地说，能够预测核电站使用的镍基合金的任何退化是很重要的，因此，该计划代表了一种综合方法，以解决压水堆、690和625合金中使用的重要镍基材料的热和辐射诱导转变机制。与600合金相比，690合金具有更好的抗应力腐蚀性能，因此在现有压水堆核电站中得到了广泛的应用。625合金目前用于更有限的应用，但同时具有高强度(在老化条件下)和耐腐蚀/SCC的优点，正在考虑在未来的反应堆系统中使用。研究表明，这两种合金都可以由于热或辐射暴露而发生相变。在析出硬化条件下，625合金在中子辐照过程中，随着强化相的分解和亚稳态析出相的形成而“软化”。然而，这些转变的性质和速度作为暴露条件的函数还没有被很好地理解。同样，这些热和辐射引起的微结构变化对机械性能的影响也需要评估。拟议的计划结合了热和辐射实验、机械测试以及使用最先进的分析技术的先进微结构表征，其结果将与可用于预测材料性能的原子、微观和宏观模型相结合。这种能力还将极大地帮助研究为未来的核电站开发优化的现有合金或新合金。

As pressurised water reactor (PWR) plant operating lives are extended, there is an increased need for predictive modeling tools to describe materials degradation in order to ensure safe, reliable operation as well as plan for component replacements. Some models presently exist, but are limited in their applicability, and are not able to predict degradation of all alloys used in PWR systems. Specifically, it is important to be able to predict any degradation in Ni-based alloys used in nuclear power plants, thus, this program represents an integrated approach to address thermal and irradiation-induced transformations mechanisms of to important Ni-base materials used in PWRs, Alloys 690 and 625. Alloy 690 is widely used in existing PWR plants due to its superior SCC resistance compared to Alloy 600. Alloy 625 is currently used in more limited applications but offers the benefits of both high strength (in the aged condition) and corrosion/SCC resistance, and is being considered for use in future reactor systems. Research has shown that both alloys can undergo phase changes due to thermal or irradiation exposure. In the precipitation-hardened condition, Alloy 625 "softens" during neutron irradiation as the strengthening precipitates decompose and metastable precipitates form. However, the nature and rates of these transformations as a function of exposure conditions are not well understood. Similarly, the effects of these thermal and irradiation-induced microstructural changes on mechanical properties require evaluation. The proposed program combines thermal and irradiation experiments, mechanical testing, and advanced microstructural characterization using state-of-the art analytical techniques, the results of which will be combined with atomistic, micro-and macro-scale modelling that can be used to predict materials performance. Such a capability will also greatly aid in research to develop optimised existing alloys or new alloys for future nuclear power plants.