高温反应堆核燃料陶瓷涂层的基础研究

High temperature reactors (HTR) is a new generation nuclear reactors, which attracts increasing attention from nuclear industry mainly due to intrinsic safty nature of HTR.The safe operation of HTR even during accident scenarios is mainly due to the containment of nuclear fuels inside multilayer pyrolytic carbon and silicon carbide layers, i.e. spherical nuclear fule particles of 0.5 mm diameter are fully enclosed within successive layers of pyrolytic carbon and silicon carbide (SiC) forming the tristructural-isotropic (TRISO) fuel particle. Since failure of individual fuel particle will inevitably lead to fission product release into the primary circuit, a comprehensive understanding of possible failure mechanisms during regular operation and possible accident scenarios is of immediate safety concern. In TRISO particles, SiC plays a key role in maintaining integrity of TRISO particles, and containment of fission products. Therefore, study of mechanical properties and fission product diffusion through SiC is essential in development of TRISO particles for HTR. In this proposal, our research objectives are: 1.To establish optimum condition for manufacture of TRISO particle coatings with use of fluidized bed chemical vapour deposition, and ensure reproducibility of TRISO particles. 2.To produce SiC and ZrC with the maximum mechanical properties and high temeprature stability and effective barrier to the fission product release in TRISO particles. 3.To provide reliable data of mechanical property of SiC and ZrC for performance modelling of TRISO particles. 4.To establish a fission product Ag release rate model. To achieve these objectives, we will address scientific issues as follows: 1. Study of fluidized bed chemical vapour deposition for manufacture of PyC, SiC and ZrC. 2. To study high temperature mechanical properties of SiC and ZrC. 3. Deformation of SiC and ZrC under mechanical load. 4. Fission product Ag reaction with SiC and ZrC. The ultimatum goal is to establish manufacture condition for production of the most safe TRISO for use in HTR.

高温气冷反应堆是新一代的先进、安全的核能系统，其燃料为氧化铀小球（直径约0.5mm)，被包裹在热解碳PyC层和碳化硅层组成的多层球壳内，因此被称为TRISO(Tri-layered isotropic)型燃料颗粒。与传统压水堆相比，这种燃料颗粒可大幅提高反应堆的安全性。一般来讲，SiC层是保证燃料颗粒结构完整性的关键，同时也是保证核反应裂变产物不泄漏的关键。因此，对SiC层力学性能，以及裂变产物如何在SiC层中扩散机制的研究是发展高温气冷堆用TRISO颗粒的基础。 本研究将解决以下关键科学问题： 1. 研究流化床化学气相沉积制备热解PyC层、SiC层以及ZrC层的制备工艺。 2. 研究SiC和ZrC涂层的高温力学性能。 3. 研究SiC和ZrC涂层在力学载荷下的变形机制。 4. 裂变产物银与SiC和ZrC的反应机制。 目标是为新一代高温气冷堆开发出安全可靠的燃料颗粒。

TRISO包覆型燃料颗粒因在中子辐射下具有优异的高温耐受性和稳定性，使其在高温气冷堆中的应用备受关注。SiC层作为TRISO 燃料颗粒体系的核心，是控制TRISO 燃料颗粒热传导和失效的关键因素。由此，课题组通过改变工艺参数，制备了四种不同的TRISO包覆型燃料颗粒，系统分析了TRISO颗粒的微观组织（如SiC层结构、晶粒大小）及其对整个包覆燃料颗粒力学性能的影响，获得了最佳的TRISO包覆燃料颗粒沉积工艺。同时，课题组开发了采用拉曼光谱仪技术测量TRISO颗粒各层的热导率的实验方法，并建立了激光测量燃料颗粒各层热导率的物理模型，该技术突破传统技术对样品尺寸的限制，能够测量微区的热导率，适合在TRISO颗粒中应用。此外，课题组通过模拟压水堆正常工况条件，系统研究了TRISO颗粒的水热腐蚀行为，揭示了TRISO颗粒在水热环境下的腐蚀机制。并对其力学性能（断裂强度）进行表征。揭示了影响TRISO颗粒断裂强度的原因。依托本项目经费资助，已在J.Am.Ceram.Soc、J.Eur.Ceram.Soc等国际知名期刊发表文章3篇，待发表文章1篇。