Probabilistic Estimation for Rupture of a Pressurizer’s Welded Joint in a Nuclear Power Plant in the Presence of Metal Defects

The metal of the Pressurizer in Nuclear Powe Plant is subject to aging mechanisms caused temperature fatigue, temperature aging, vibration fatigue and corrosion. After decades of operation under these conditions, defects form in the metal structure. In addition to the well-known deterministic methods of testing and monitoring the metal, new approaches have been increasingly sought in recent years. This article examines the development of defects in the metal of the Pressurizer due to corrosion. Defects in the metal are detected and sized by ultrasonic non-destructive testing method. Their development is tracked over a period of time of 25 years. For such a long period of time, enough data for defects length is accumulated, a probability distribution can be applied. The statistical data represent the standardized defect sizes - the ratio of the measured length of the defect to the maximum permissible length, according to the normative documents. A Weibull distribution is applied for statistical processing of these data. The results show the Weibull distribution is suitable for data estimation. The probability of when defects in the Pressurizer’s metal will reach maximum length and the housing will be destroyed is estimated.