Comparison of safety margin in LBB design of nuclear pipes based on various types of fracture resistance test specimens

Abstract

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.