High Fidelity Ion Beam Simulation of High Dose Neutron Irradiation

开发新的、先进的核反应堆概念和延长现有轻水核反应堆寿命的希望，在很大程度上取决于对辐射如何降解反应堆堆芯结构部件材料的理解。在高剂量裂变反应堆概念（GEN-4）中，结构材料必须在超过400摄氏度的温度下承受200dpa的损伤。在如此高的损伤水平下，主要的降解模式可能是由空洞膨胀和相稳定性驱动的。由于辐照引起的材料降解既是一种限制寿命的现象，也是一种验证概念的现象，因此它确实是对全世界核能发展和活力的重大挑战。传统上，了解辐射引起的材料变化的研究是通过在试验堆中进行辐射效应实验，然后进行全面的辐照后表征计划。然而，试验反应堆产生辐射损伤的速度不会比商业反应堆快得多，这意味着辐射损伤研究往往无法“走在”运行过程中发现的问题之前。一个很有希望的解决方案是使用离子辐照，它可以产生高的损伤率，很少或没有残余放射性。离子辐照的优点很多。剂量率（通常为10-3至10- 4dpa /s）远高于中子辐照（10-7至10- 8dpa /s），这意味着200 dpa可在几天或几周内达到，而不是几十年。因为几乎没有活化，所以样品没有放射性。离子辐照实验的控制要比反应堆实验好得多。在反应堆中，温度、损伤率和损伤程度的测量是困难的，导致依靠计算来确定总剂量和估计辐照温度。相比之下，离子辐照已经发展到可以很好地控制和监测温度，并且可以在整个辐照过程中连续测量损伤率和总损伤，并且精度很高。然而，离子辐照有几个潜在的缺点；辐照材料的体积，高损伤率对所得微观结构的影响，以及考虑反应堆中发生的重要嬗变反应的需要，例如He和h的产生。理解和建模微结构-性能关系，以及微样品制造和测试的发展，虽然不能取代整体性能测定，但有望最大限度地减少有限辐照体积的缺点。高损伤率能在多大程度上产生与反应堆条件相关的微结构是一项重大挑战，但在解决这一问题方面正在取得重大进展。解释嬗变反应的策略是同时用重离子照射目标，同时用He和/或h轰击目标。这样的过程需要在双束或三束设备中耦合多个加速器。最近，英国已经开始制定一项计划，在其道尔顿坎布里亚设施建立这样一个双梁设施，拟议的项目将支持这一活动。为了使离子辐照合格，必须尽可能地再现中子辐照后的微观结构和中子引起的宏观性质变化。这项任务最好是使用与建模紧密结合的最先进的实验技术的组合来解决，这可以产生对缺陷发展过程的机制理解，同时在实验设计和理论建模中考虑到上述可能的混淆因素。

The promise for developing new, advanced nuclear reactor concepts and the extension of life of existing light water nuclear reactors rests heavily on understanding how radiation degrades materials that serve as the structural components in reactor cores. In high dose fission reactor concepts (GEN-4) structural materials must survive up to 200 dpa of damage at temperatures in excess of 400C. At such high damage levels, the major degradation modes are likely to be driven by void swelling and phase stability. As materials degradation due to irradiation is both a life-limiting and a concept-validating phenomenon, it is truly the grand challenge for the growth and vitality of nuclear energy world-wide. Traditionally, research to understand radiation-induced changes in materials is conducted via radiation effects experiments in test reactors, followed by a comprehensive post-irradiation characterization plan. However, test reactors cannot create radiation damage significantly faster than that in commercial reactors, meaning that radiation damage research often cannot "get ahead" of problems discovered during operation. A promising solution to the problem is to use ion irradiation that can produce high damage rates with little or no residual radioactivity. The advantages of ion irradiation are many. Dose rates (typically 10-3 to 10-4 dpa/s) are much higher than under neutron irradiation (10-7 to 10-8 dpa/s) which means that 200 dpa can be reached in days or weeks instead of decades. Because there is little activation the samples are not radioactive. Control of ion irradiation experiments is much better than experiments in reactor. Measurement of temperature, damage rate and damage level is difficult in reactor, resulting in reliance on calculations to determine the total dose, and estimate irradiation temperature. By contrast, ion irradiations have been developed to the point where temperature is extremely well controlled and monitored, and damage rate and total damage are also measured continuously throughout the irradiation and with great accuracy. However, ion irradiation has several potential drawbacks; the volume of irradiated material, the effect of high damage rate on the resulting microstructure, and the need to account for important transmutation reactions that occur in reactor, such as the production of He and H. Understanding and modeling the microstructure-property relationship, and the development of micro-sample fabrication and testing, while not a replacement for bulk property determination, hold the promise for minimizing the drawback of limited irradiated volume. The extent to which high damage rates can produce microstructures relevant to reactor conditions is a major challenge, but significant progress is being made to address this issue.The strategy to account for transmutation reactions is to simultaneously irradiate a target with heavy ions while also bombarding it with He and/or H. Such a process requires multiple accelerators coupled in a double or triple beam facility. Recently, the UK has begun development of a plan to create such a double beam facility at its Dalton Cumbrian Facility and the proposed project will underpin this activity.To qualify ion irradiation it is necessary to reproduce as best as possible both the neutron irradiated microstructure and the neutron-induced macroscopic property changes using ion irradiation. This task is best addressed using a combination of state of the art experimental techniques closely coupled to modeling, which can yield mechanistic understanding of the defect development process, while taking into account in the experimental design and theoretical modeling the possible confounding factors mentioned above.