The geometry of cracked pipe, loading condition and crack size all can have a strong effect on its resistance against crack-tip plastic deformation and crack growth. Usually, specimens listed in test standards (e.g. CT specimen) are applied to evaluate the fracture resistance (J-R) curves, which may cause excessive safety margin in leak-before-break (LBB) design of nuclear pipes. In this study, standard (CT) specimen and constraint designed specimens, including curved CT and compact pipe (CP) specimens were applied to measure the J-R curves of nuclear pipes. Finite element analysis (FEA) was applied to derive J-equations to calculate J-R curves for newly designed specimens. Constraint effects in these specimens and full-scale pipes under various loading conditions were compared according to crack-tip plastic deformation level. Then, safety margins in LBB design using these specimens were quantitatively analyzed by constructing the critical crack length lines. Both the tests and FEA results verified the validity of these constraint designed specimens for reducing conservatism.

裂纹管的几何形状，加载条件和裂纹尺寸均对其抗裂纹尖端塑性变形和裂纹扩展的能力有很大影响。通常，使用测试标准中列出的样品（例如CT样品）来评估抗断裂强度（JR）曲线，这可能会导致核管的先裂后泄漏（LBB）设计中存在过多的安全裕度。在这项研究中，使用标准（CT）标本和约束设计标本，包括弯曲CT和紧凑管（CP）标本来测量核管的JR曲线。应用有限元分析（FEA）得出J方程来计算JR新设计标本的曲线。根据裂纹尖端塑性变形水平，比较了这些试样和全尺寸管道在各种载荷条件下的约束效果。然后，通过构建临界裂纹长度线，对使用这些样本的LBB设计的安全裕度进行了定量分析。测试和有限元分析结果都验证了这些约束设计的样本在降低保守性方面的有效性。