中文摘要：

随着核电站的老化，核管道安全评估变得更为重要。以往核管道的损伤容限评定通常只考虑单一裂纹问题，或只局限于研究一个主裂纹的问题，或主要集中于考虑两个裂纹满足何条件时，二者方可合并为一个裂纹的问题，对多裂纹情况下应力强度因子变化规律的研究较粗糙。在理论与方法方面，多裂纹问题一直是断裂力学不够完善的部分。本文以核管道的内表面裂纹为对象，采用有限元法分析核管道两个裂纹情况下的应力强度因子，得到其随裂纹间距、裂纹长度、裂纹深度变化的规律。又两个裂纹的现象为多裂纹现象中最基本的情况，即本研究工作可为存在多裂纹的核管道的安全评估提供方法依据。

英文摘要：

With the aging of nuclear power plants, safety assessment for nuclear pipeline becomes more important. In the past, the assessment of nuclear piping only consider a single crack problem; or confined to the issue of a main crack~ or focused on considering two cracks meeting any condition to he merged into one crack, namely, detailed study on multiple cracks under the stress intensity factor variation is rough. It is not a perfect part of fracture mechanics for multiple crack problems. In order to improve the content of fracture mechanics, fracture mechanics applied to increase the value and improve the safety and reliability of nuclear piping, inner surface cracks is determined as the major flaws of nuclear piping, the role of nuclear piping two cracks stress intensity factor and its general form are obtained by analysis of the actual variation with the finite element method. Two crack phenomenon is the basic situation of multiple cracks. Thus, this work provides a method to assess the basis for the existence of multiple cracks in nuclear safety pipeline.