随着核能技术的快速发展，对于提供核反应堆安全参数的“最佳估计预测值+不确定性”的需求日益增长。同时为了提高核反应堆安全参数的可信度并寻找影响安全参数最重要的不确定性参数，以达到改善核反应堆安全分析的保守裕度、优化工程设计，需要开展核反应堆计算不确定性研究。而球床式高温气冷堆是中子物理、热工水力及燃耗计算强烈耦合的复杂系统，不确定性因素天然存在并且很多，国际上系统性开展高温气冷堆不确定性分析刚刚起步，尚缺乏经验和分析方案，因此开展球床式高温气冷堆不确定性研究既迫切又存在挑战。 本文针对球床式高温气冷堆计算模型和特殊设计，建立了一套不确定性分析的框架。在此框架基础上，研究了各个环节的特点及明确了各环节不确定性输入、输出和传播不确定性，同时研究了基于微扰理论和抽样统计的不确定性分析方法的适用范围，在抽样统计不确定性分析方法的基础上开发了不确定性和敏感性分析程序包CUSA，为开展高温气冷堆计算不确定性分析建立了理论方法体系。 基于本文建立的球床式高温气冷堆不确定性分析框架，以HTR-PM示范工程为研究对象，重点分析了球床高温气冷堆几个关键特点和环节，如VSOP程序球流模型、球流混流效应、球床填充率、燃料球装铀量、核截面数据等的不确定性。针对不同环节，本文建立了不同的不确定性分析模型并明确不确定性根据，以CUSA-VSOP程序、CUSA-THERMIX程序和SCALE程序为计算工具，定量分析了各个环节的不确定性及传播不确定性。 依据本文建立的不确定性分析框架，HTR-PM事故工况下燃料最高温度不确定性视为各不确定性输入参数在燃料最高温度计算过程所有模块中的传播终点。本文在初步敏感性分析的基础上选取了堆芯功率水平、余热空间分布、球床等效导热系数等八个参数作为不确定性输入参数，基于本文对于各个特殊环节不确定性分析的结果明确了燃料最高温度所在区域余热空间分布的不确定性，其他输入参数不确定性依据相关文献和实验结果确定。然后分别采用均方根和抽样统计不确定性分析方法定量地分析了HTR-PM示范工程燃料最高温度的不确定性结果。不确定性分析结果不仅验证了HTR-PM的固有安全性，同时对示范工程具有参考价值。

There has been an increasing demand for the best estimate of nuclear reactor parameters to be provided plus their uncertainties with the rapid development of nuclear power technology. In addition to establish best-estimate calculations for nuclear reactor design and safety analysis, understanding uncertainties is important for improving the reliability of the results, identifying the importance of uncertainty parameters and ensuring appropriate design margins. The pebble bed HTGR is a complicated system in which neutronics, thermal hydraulics and burnup calculations are tightly coupled and there are many uncertain elements affecting the system. Recently uncertainty analysis of HTGR is just starting internationally and lacking of experience and systemic analysis methods. So carrying out uncertainty analysis of the pebble bed HTGR is urgent but full of challenges. Based on the calculation model and specific design of the pebble bed HTGR, a frame of uncertainty analysis was established in this paper. The features of different components of the frame were in-depth studied besides of input, output and propagated uncertain parameters. At the same time the application scope of two uncertainty analysis methods, such as deterministic method and statistical sampling method, was made clear. Then a software package CUSA for uncertainty and sensitivity analysis was developed, which is a powerful computational tool for carrying out uncertainty analysis in the pebble bed HTGR. HTR-PM was selected as the research object and uncertainty analysis of some key components of HTR-PM, such as the pebble flow model in VSOP code, mix flow, filling fraction of pebble bed, uranium quantity of fuel sphere and nuclear date cross section, were in-depth studied. Then different uncertainty analysis models and uncertain input parameters were established to quantify the uncertainties and propagated uncertainties of different components using CUSA-VSOP code, CUSA-THERMIX code and SCALE. Based on the frame of uncertainty analysis, the uncertainty in the calculated maximum fuel temperature under accident condition is the most important parameter of inherent safety of HTR-PM and considered as the end point of propagated uncertainty. In fact, many elements contribute to the total uncertainty in the maximum fuel temperature. Through the preliminary sensitivity analysis of these elements via the THERMIX simulation, eight parameters are selected for this study: total reactor power, spatial distribution of decay heat of the zone in which the fuel temperature rise to the maximum, decay heat production rate and so on. The uncertainty of spatial distribution of decay heat was determined through the uncertainties and propagated uncertainties of different components analyzed in this paper and the uncertainty of other parameters were determined through experimental data and literatures. In order to quantify the uncertainty of maximum fuel temperature, two uncertainty analysis method, Root Mean Square (RMS) method and sampling statistics method, have been used. In addition the inherent safety of HTR-PM being verified, the uncertainty results have an important reference value for HTR-PM.