US Approach to Dissimilar Metal Weld Inspection and Inspection Qualification in Light of Recent Field Events

摘要

Nondestructive examination of dissimilar metal (DM) welds in nuclear power plants has attracted considerable attention worldwide for many years. Service experience of discovery of various forms of stress corrosion cracking coupled with technical difficulties of examination of DM welds has been responsible for stimulating focused research into effective examination techniques and qualification approaches to demonstrate that inspection can be performed reliably. Until recently, service experience has indicated that DM weld degradation was to be expected primarily in BWR plants. Recent experience in the US and in other countries, however, has shown that PWR units can also expect potential degradation in DM welds. This has been realized with the recent discovery of PWSCC in CRDM head penetrations and in nozzle-to-safe end welds in domestic PWRs. The US nuclear industry in cooperation with international utility companies has organized a comprehensive program to develop, qualify, and apply effective NDE methods to detect and characterize PWSCC in PWR and BWR components. In particular, PWSCC in PWR CRDM head penetrations and main coolant piping components is a major focus. This paper will describe US approaches to DM weld inspection and inspection qualification for potentially affected materials and locations in the plant.