Irradiation damage and recovery of zirconium-based alloys

在轻水反应堆(LWR)核燃料中，锆基合金被用作结构部件。更好地理解辐射引起的变化，以及从这些变化中恢复的可能性，是继续发展燃料棒性能模拟的核心。大部分辐射损伤是由中子造成的。裂变产生的中子能量最高可达10 MeV。从正常晶格位置置换一个Zr原子所需的能量约为40 eV，任何快中子(E&gt；1 MeV)都可以很容易地转移足够的能量来置换一个Zr原子(初级碰撞)，而这个原子又可以置换额外的原子。直接的结果是空位的小簇、单个空位、单个空位，而在短时间之后，空位和空位循环。这统称为辐射损伤。辐射损伤的恢复和辐射硬化的软化可能是由于反应堆运行期间的短期温度漂移或由于长期储存排放的燃料期间的温度略有升高而发生的。正确地理解辐照损伤以及潜在的恢复对于进一步完善燃料棒在反应堆运行期间和之后的性能模型是至关重要的。为了正确地理解辐照损伤以及相关的辐照诱导生长背后的机制，我们需要更好地理解位错环群体的形成和演化。机制存在看似合理的假设，但我们目前缺乏一些详细的实验数据，这些数据将使我们能够检验这些假设。特别是，我们需要开发能够定量测量辐照材料中具有统计代表性的体积中的位错环数量的技术。在过去的四年中，曼彻斯特大学的锆组一直在开发使用x射线衍射线轮廓分析来量化位错环。这需要实验、模拟和理论的共同努力，我们现在正在接近这样一个点，我们已经有了一套可以在系统研究中部署的表征工具。这个博士研究生的目标是帮助这些工具从开发阶段过渡到可以广泛传播的阶段，供一般社区使用。同样，这将需要模拟、理论和实验工作的结合，以对我们开发的技术进行基准测试和验证。在实现这一目标的过程中，学生还将研究作为温度函数的回路种群的演变，以了解锆中辐射损伤结构的发展，以及在短期温度瞬变和长期储存中，温度诱导辐射损伤恢复的机制。这将使我们能够测试假设的生长机制，并解开时间、温度、剂量和剂量率对辐射损伤和恢复的影响。学生尤其将：-进行精心设计的辐照和退火实验，以研究线圈群对时间和温度的响应；-创建典型线圈群的原子模型，并根据它们生成模拟的x射线衍射线轮廓；-结合上述结果，进一步开发CMWP线形轮廓分析软件，以量化线圈群。目的：-提高我们对温度时间对辐照损伤的影响的理解，在缺陷退火和损伤产生的背景下都是如此。更好地理解辐射温度和剂量率的相互作用。-基于辐射实验实验，为使用x射线衍射线轮廓分析来计数回路的校准提供基准数据

Zirconium-based alloys are used for structural components in Light Water Reactor (LWR) nuclear fuel. Improved understanding of irradiation-induced changes, as well as potential recovery from these changes, are central in the continued development of fuel rod performance modelling. Most of the irradiation damage is caused by neutrons. The energy of neutrons produced by fission ranges up to about 10 MeV. The amount of energy required to displace an atom of Zr from its normal lattice position is about 40 eV, and any fast neutron (E>1 MeV) can easily transfer enough energy to displace a Zr atom (the primary knock-on), which in turn can displace additional atoms. The immediate results are small clusters of vacancies, individual vacancies, individual interstitials, and after a short time, vacancy and interstitial loops. Collectively this is termed irradiation damage.Recovery from irradiation damage, and softening of irradiation hardening, may occur due to short-term temperature excursions during in-reactor operation or due to slightly elevated temperatures during long-term storage of discharged fuel. A proper understanding of irradiation damage as well as the potential recovery is essential for further refining the modelling of fuel rod performance during and after in-reactor operation.To properly understand the mechanisms behind irradiation damage, and the associated irradiation induced growth, in zirconium alloys we need a better understanding of the formation and evolution of populations of dislocation loops. Plausible hypotheses for mechanisms exist, but we currently lack some of the detailed experimental data that will enable us to test these hypotheses. In particular we need to develop techniques that can quantitatively measure the dislocation loop populations in statistically representative volumes of irradiated material.Over the last four years, the Zirconium Group at the University of Manchester has been developing the use of x-ray diffraction line profile analysis for the quantification of dislocation loops. This has required a concerted effort employing experiment, simulation and theory and we are now approaching the point where we have a set of characterisation tools ready to deploy in systematic studies.This PhD studentship aims to assist in taking these tools through the transition from the development stage to one in which they can be disseminated widely for use by the community in general. Again, this will require a combination of simulation, theoretical and experimental work to benchmark and validate the techniques that we have developed. In the course of achieving this, the student will also study the evolution of loop populations as a function of temperature, in order to understand the development of irradiation damage structures in zirconium as well as the mechanisms involved in temperature induced recovery from irradiation damage, both in short-term temperature transients and long-term storage. This will allow us to test the hypothesised growth mechanisms and to disentangle the effects of time, temperature, dose and dose rate on irradiation damage and recovery. In particular the student will:- Undertake carefully designed irradiation and annealing experiments, to study the response of loop populations to time and temperature;- Create atomistic models of representative loop populations and generate simulated x-ray diffraction line profiles from them;- Combine the results of the above to further develop the CMWP line profile analysis software for the purpose of quantifying loop populations.Aims:- Improve our understanding of the effects of time-at-temperature on irradiation damage, both in the context of defect annealing and the production of damage. Develop an improved understanding of the interplay of irradiation temperature and dose rate.- Provide benchmark data for calibration of the use of x-ray diffraction line profile analysis to count loops, based on irradiation experiments experiments