A further study on fracture resistance evaluation of nuclear pipes using CP specimens

Abstract

The leak-before-break (LBB) concept has been widely used to design the piping system in nuclear power plant, which is based on the fracture resistance (J-R) curves of cracked nuclear pipes. However, accurate fracture resistance evaluation of nuclear pipe is always a tough task. Full-scale nuclear pipe tests are costly and difficulty, and the specimens listed in test standards (e.g. ASTM E1820) are usually too conservative. Thus, compact pipe (CP) specimen has been developed to evaluate the J-R curves of nuclear pipes with high accuracy but much lower cost than full-scale pipe tests. But, the practical application of CP specimen still asks for more theoretical and experimental research. In this study, the assembly of CP specimen was modified to improve the assembly convenience and ensure a more uniform loading condition. Instead of load-line displacement (LLD), crack mouth opening displacement (CMOD) based J-formulation was proposed to determine the J-R curves of modified CP specimens considering more reliable evaluation of CMOD. In addition, the differences of constraint effect among CT specimen, CP specimens and full-scale pipes are distinguished using equivalent plastic strain (εp) isoline regions, which agrees quite well with the results of fracture resistance tests.