Modelling long timescale effects of irradiation damage of nuclear graphite

模拟核石墨辐照损伤的长期效应

基本信息

批准号：
EP/V050281/1
负责人：
Kenny Jolley
金额：
$ 48.38万
依托单位：
Loughborough University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2021
资助国家：
英国
起止时间：
2021 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FV050281%2F1
关键词：
Modelling long timescale effects irradiation

项目摘要

There are currently 14 Advanced Gas-cooled Reactors (AGRs) in the UK which are operated by EDF. The reactor cores in these AGRs are composed of several tonnes of a synthetic form of graphite, commonly called nuclear graphite. This nuclear graphite serves two purposes: to moderate (slow down) neutrons to enhance nuclear fission, and to form the main structure of the reactor core.Nuclear graphite is not a single crystal but is instead composed of a highly complex microstructure consisting of many mis-orientated graphite grains. This microstructure can be tailored by the manufacturing conditions.A key problem is that the high temperature and high irradiation conditions of a nuclear reactor core causes the graphite bricks to swell considerably (dimensional change). This induces stress in the bricks which eventually results in cracks. Cracked and crumbling bricks would eventually lead to blocked channels in the reactor core which would prevent the insertion or removal of fuel rods and control rods. Therefore, materials (and particular microstructures) that are resistant to radiation damage and do not readily swell or crack under irradiation are desirable since they would lead to longer run times of future generation 4 nuclear reactors.The key aim of this project is to develop understanding of how the microstructure of a graphite brick influences its properties (such as dimensional change) in the high temperature and high irradiation conditions of a reactor core.This understanding will be gained by the following project objectives:(1) Model the interaction of small and large atomic defect structures with a view to understanding the main causes of dimensional change in graphite. Uncover the key mechanisms for dimensional change by studying the motion of vacancy and interstitial atoms within graphite as well as the buckling of the graphene layers. We will use advanced computer simulation techniques that can model these graphite structures with atomic level detail. Long timescale techniques will be used to extend the simulation time of our atomistic simulations.(2) Model the mechanical properties of micrometre sized thin graphite wafer structures containing realistic densities of defects in graphite. Computer simulations of indentation and scratching processes will be performed and compared with experimental results.(3) Investigation of the thermal properties of graphite structures containing realistic distributions of defects and grain boundaries. Non-equilibrium molecular dynamics simulations will be performed on a range of these structures to determine the effect of the microstructure upon the thermal conductivity of the graphite. The coefficient of thermal expansion will also be simulated for a range of representative graphite structures. These results will also be compared to experimental results.(4) Computer simulations are only ever as good as the underlying approximations made in fitting a usually limited data set in the model. The data generated in this project will be used to assess the suitability of existing models for graphite available in the literature. These existing models will be improved upon by identifying the best components of each model and combining them into a new hybrid model capable of accurately predicting a wide range of graphite material properties.

目前英国有 14 座先进气冷反应堆 (AGR) 由 EDF 运营。这些 AGR 中的反应堆堆芯由数吨合成石墨（通常称为核石墨）组成。这种核石墨有两个用途：缓和（减慢）中子以增强核裂变，以及形成反应堆堆芯的主要结构。核石墨不是单晶，而是由高度复杂的微观结构组成，该微观结构由许多金属组成。定向石墨晶粒。这种微观结构可以根据制造条件进行定制。一个关键问题是核反应堆堆芯的高温和高辐照条件导致石墨砖大幅膨胀（尺寸变化）。这会在砖块中产生应力，最终导致裂缝。破裂和破碎的砖块最终会导致反应堆堆芯通道堵塞，从而阻止燃料棒和控制棒的插入或移除。因此，需要能够抵抗辐射损伤并且在辐照下不易膨胀或破裂的材料（以及特定的微观结构），因为它们将延长未来第四代核反应堆的运行时间。该项目的主要目的是加深理解石墨砖的微观结构如何影响其在反应堆堆芯的高温和高辐照条件下的性能（例如尺寸变化）。这种理解将通过以下项目目标获得：（1）模拟小和小粒子的相互作用大原子缺陷结构，以期了解石墨尺寸变化的主要原因。通过研究石墨内空位和间隙原子的运动以及石墨烯层的屈曲，揭示尺寸变化的关键机制。我们将使用先进的计算机模拟技术，可以用原子级细节对这些石墨结构进行建模。长时标技术将用于延长原子模拟的模拟时间。(2) 对包含实际石墨缺陷密度的微米级薄石墨晶片结构的机械性能进行建模。对压痕和划痕过程进行计算机模拟，并与实验结果进行比较。(3)研究含有真实缺陷和晶界分布的石墨结构的热性能。将对一系列这些结构进行非平衡分子动力学模拟，以确定微观结构对石墨导热率的影响。还将模拟一系列代表性石墨结构的热膨胀系数。这些结果还将与实验结果进行比较。(4) 计算机模拟的效果取决于在模型中拟合通常有限的数据集时所做出的基本近似值。该项目生成的数据将用于评估文献中现有石墨模型的适用性。这些现有模型将通过识别每个模型的最佳组件并将它们组合成能够准确预测各种石墨材料特性的新混合模型来改进。