Validation of fracture toughness characteristics of nuclear plant piping and safety margin analysis by using CP specimen

Abstract

Generally, due to the limited sizes of the pressure piping in a nuclear power plant, it is difficult to obtain valid data from fracture resistance tests examining on the real pipe. Thus, the leak-before-break (LBB) concept which is widely used for design and estimation of pressure piping system is determined based on the fracture resistance (J-R) curves of fracture resistance tests on various types of specimens. However, the fracture resistance tests show that the specimen geometry and loading configuration have a strong effect on the J-R measurement. Thus, a fracture test using a pipe specimen of real scale needs to be carried out to obtain accurate fracture behavior for the exact integrity evaluation of a piping system. Therefore, to estimate the integrity of real pipes based on elastic-plastic fracture mechanics, we have to first establish the new test method for fracture resistance evaluation of nuclear piping using the real pipe.In this paper, we present the current state of a fracture resistance evaluation using a compact pipe (CP) specimen and the validity of the test method was reviewed by comparing the fracture resistance test results from the CP specimens and real pipes. In addition, the safety margin of the piping was evaluated by using a crack driving force diagram and the results were analyzed.