Graphite is a candidate material for Generation IV concepts and is used as a moderator in Advanced Gas-cooled Reactors (AGR) in the UK. Spatial material variability is present within billets causing different material property values between different components. Variations in material properties and irradiation effects can produce stress concentrations and diverse mechanical responses in a nuclear reactor graphite core. In order to characterise the material variability, geostatistical techniques called variography and random field theory were adapted for studying the density and Young's modulus of a billet of Gilsocarbon and NBG-18 graphite grades. Variography is a technique for estimating the distance over which material property values have significant spatial correlation, known as the scale of fluctuation or spatial correlation length. The paper uses random field theory to create models that mimic the original spatial and statistical distributions of the original data set. This study found different values of correlation length for density and Young's modulus around the edges of a Gilsocarbon billet, while in the case of NBG-18, similar correlation lengths where found across the billet. Examples of several random fields are given to reproduce the spatial patterns and values found in the original data.

石墨是第四代概念的候选材料，在英国的先进气冷堆（AGR）中用作缓和剂。坯料中存在空间材料变化性，从而导致不同组件之间的材料特性值不同。材料性能和辐照效果的变化会在核反应堆石墨芯中产生应力集中和多种机械响应。为了表征材料的变异性，采用了称为变异学和随机场理论的地统计学方法，以研究Gilsocarbon和NBG-18石墨等级的钢坯的密度和杨氏模量。变异函数学是一种用于估算距离的方法，材料属性值在该距离上具有显着的空间相关性，称为波动的标度或空间相关性长度。本文使用随机场理论来创建模拟原始数据集的原始空间和统计分布的模型。这项研究发现，在Gilsocarbon钢坯边缘附近的密度和杨氏模量的相关长度不同，而在NBG-18的情况下，整个钢坯的相关长度相似。给出了几个随机字段的示例，以重现原始数据中发现的空间模式和值。