Improving fuel performance modelling of TRISO fuel failure

三结构各向同性（TRISO）颗粒燃料将用于下一代甚高温堆（VHTR）设计，并已在中国HTR-PM反应堆中部署。TRISO燃料首先在英国进行概念化和测试，已被证明是一种非常坚固的燃料类型，能够承受高达1600- 1800 C的温度，故障最少。这种特性使得VHTR反应堆在冷却剂丧失事故的情况下是安全的。然而，不可避免地存在着一些领域，在这些领域中，人们几乎没有什么了解，或者可以在设计上做出改进。目前，大多数TRISO燃料故障是由有缺陷的燃料颗粒引起的。缺陷可以以许多形式出现，其中层以不同/不均匀的厚度沉积，或者形状是椭圆形的或包含平坦的区域。所有这些缺陷都可能影响颗粒失效的可能性。还有许多不同设计的TRISO燃料，具有不同的尺寸和实际上的燃料核材料（UO 2、UCO和其他）。帝国理工学院最近的工作已经开发了一个有限元模型，该模型包含了TRISO燃料制造过程中的残余应力[1];我们已经开发了事故条件下完整TRISO颗粒的周向2D模型[2]，最近我们将这些模型进一步开发为3D模型[3]。这些高保真度模型可用于更好地了解燃料故障的原因，从而改进更实用的燃料性能代码，如STRESS 3（NNL TRISO燃料性能代码）或更广泛使用的代码，如美国代码野牛。该项目将探索开发和使用我们的周波模型，以通过断裂行为[4-5]和几何缺陷的Weibull模型纳入更多的材料统计行为。从这些模型中，我们将寻求改进工业使用的燃料性能代码中使用的参数和参数误差。[1]A. Battistini，T. A.作者声明：丹尼尔·谢泼德R.文曼TRISO包覆颗粒燃料残余应力的有限元分析。核材料杂志（2023）回顾。[2]T.A. Haynes，A. Battistini，A.J. Leide，D.柳湖，加-地琼斯，D. Shepherd，M.R.文曼高温反应堆TRISO颗粒裂纹的周向模拟。核材料杂志576（2023）.154283[3] A. Battistini，T. A.海恩斯湖D.琼斯，M。R.文曼TRISO燃料颗粒的SiC和缓冲层中的裂纹的3D周向模型（未发表的工作）。[4]L.D.作者声明：John，T.海恩斯，M.R.文曼脆性固体中威布尔分布的二维周波模拟。Procedia Structural Integrity 28，（2020）1856-1874. [5]L.D.作者声明：John，T.海恩斯湾罗西特，M. R.文曼威布尔分布对用周波法模拟核燃料断裂的影响。核材料杂志572（2022）154087。

Tri-structural isotropic (TRISO) particle fuel will be used in the next generation of very high temperature reactor (VHTR) designs and is already deployed in the Chinese HTR-PM reactor. First conceptualised and tested in the UK, TRISO fuel has proven to be a very robust fuel type able to withstand temperatures up to 1600-1800C with minimal failure. This behaviour allows VHTR reactors to be walk-away safe in the case of a loss of coolant accident. However, there are inevitably areas where there is little understanding or where design improvements could be made. At present the majority of TRISO fuel failures arise from defective fuel particles. Defects can occur in many forms where layers are deposited with different/non-uniform thicknesses or the shape is oval or contains regions that are flat. All of these defects are likely to impact on the likelihood of a particle failing. There are also many different designs of TRISO fuel with different dimensions and indeed fuel kernel materials (UO2, UCO and others). Recent work at Imperial College has developed a finite element model that incorporates the residual stresses from manufacture of TRISO fuel [1]; we have developed Peridynamic 2D models of full TRISO particles under accident conditions [2] and most recently we have further developed these models into 3D [3]. These high fidelity models can be used to understand the causes of fuel failures better and therefore improve the more practical fuel performance codes such as STRESS3 (NNL TRISO fuel performance code) or indeed more widely used codes such as the US code BISON. The project will explore the development and use of our peridynamics models to incorporate more statistical behaviour of materials through Weibull models of fracture behaviour [4-5] and geometric defects. From these models we will look to refine both the parameters, and errors on the parameters, used in the fuel performance codes used by industry.[1] A. Battistini, T. A. Haynes, Daniel Shepherd, M. R. Wenman. A finite element analysis of the residual stresses in as-fabricated TRISO coated particle fuel. J. Nucl. Mater. (2023) in review. [2] T.A. Haynes, A. Battistini, A.J. Leide, D. Liu, L. Jones, D. Shepherd, M.R. Wenman. Peridynamic modelling of cracking in TRISO particles for high temperature reactors. J. Nucl. Mater. 576 (2023).154283[3] A. Battistini, T. A. Haynes, L. D. Jones, M. R. Wenman. 3D Peridynamics models of cracking in SiC and buffer layers of TRISO fuel particles (unpublished work).[4] L.D. Jones, L.J. Vandeperre, T.A. Haynes, M.R. Wenman. Modelling of Weibull Distributions in Brittle Solids Using 2-Dimensional Peridynamics. Procedia Structural Integrity 28, (2020) 1856-1874.[5] L.D. Jones, L.J. Vandeperre, T.A. Haynes, G. Rossiter, M. R. Wenman. The Effect of Weibull Distributions on Modelling Nuclear Fuel Fracture Using Peridynamics. J. Nucl. Mater. 572 (2022) 154087.