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超高温反应堆（VHTR）设计，并已在中国的超高温- pm反应堆中部署。首先在英国进行概念和测试，TRISO燃料已被证明是一种非常坚固的燃料类型，能够承受高达1600-1800摄氏度的温度，而最小的故障。这种行为使得超低温堆在冷却剂损失事故的情况下是安全的。然而，不可避免的是，有些领域的理解不足，或者可以在设计上进行改进。目前，大多数三iso燃料故障是由有缺陷的燃料颗粒引起的。缺陷可能以多种形式出现，当层沉积具有不同/不均匀的厚度或形状为椭圆形或包含平坦区域时。所有这些缺陷都可能影响颗粒失效的可能性。也有许多不同设计的三iso燃料与不同的尺寸和确实燃料核材料（UO2， UCO等）。帝国理工学院最近的工作开发了一个有限元模型，该模型包含了制造TRISO燃料[1]的残余应力；我们已经开发了事故条件下全TRISO粒子的周动力学二维模型[2]，最近我们进一步将这些模型开发为3D[3]。这些高保真模型可以用来更好地理解燃料故障的原因，从而改进更实用的燃料性能代码，如STRESS3 （NNL TRISO燃料性能代码）或更广泛使用的代码，如美国代码BISON。该项目将探索我们的周动力学模型的发展和使用，通过断裂行为的威布尔模型[4-5]和几何缺陷来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A. battistiini， T. A. Haynes, Daniel Shepherd， M. R. Wenman。制备三iso包覆颗粒燃料残余应力的有限元分析。j .诊断。板牙。（2023）正在审查中。[10] A.海恩斯，A.巴蒂斯蒂尼，A. j .莱德，D.刘，L.琼斯，D.谢泼德，文曼。高温反应器中TRISO颗粒裂解的动力学模拟。j .诊断。Mater. 576（2023）。[15] A. battistiini， T. A. Haynes， L. D. Jones， M. R. Wenman.三iso燃料颗粒中碳化硅和缓冲层裂纹的三维动力学模型（未发表的作品）L.D. Jones， L.J. Vandeperre， T.A. Haynes， M.R. Wenman。基于二维周动力学的脆性固体威布尔分布建模。工程机械学报，（2020）：444 - 444L.D. Jones， L.J. Vandeperre， T.A. Haynes， G. Rossiter, m.r. Wenman。威布尔分布对核燃料断裂围动力学模拟的影响。j .诊断。Mater. 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.