Probability of Detection (POD) determination using ultrasound phased array for considering NDT in probabilistic damage assessments

NDT is an essential part during construction and maintenance of nuclear power plants. In Germany, type and extent of inspection are specified in Safety Standards of the Nuclear Safety Standards Commission (KTA). Only certified inspections are allowed in the nuclear industry. The qualification of NDT is carried out in form of performance demonstrations of the inspection teams and the equipment, witnessed by an authorized inspector. The results of these tests are mainly statements regarding the detection capabilities of certain artificial flaws. In other countries, e.g. the U.S., additional blind tests on test blocks with hidden and unknown flaws may be required, in which a certain percentage of these flaws has to be detected. The knowledge of the probability of detection (POD) curves of specific flaws in specific testing conditions using defined inspection methods is often not present. This contribution will present the results of a research project designed for POD determination of ultrasound phased array inspections of real cracks. The continuative objective of this project is to generate quantitative POD results and to integrate these results in a probabilistic damage assessment concept. Different POD applications will be shown. The distribution of the crack sizes of the specimens, the inspection planning and the designed inspection instruction will be discussed, and results of the ultrasound inspections will be presented. Furthermore, additional considerations for POD determination of phased array inspections will be discussed. In the context of the results, the remaining uncertainty of the inspections has to be taken into consideration for failure analysis.