Advances in NDE of DM Welds From RPV ID

In Pressurized Water Reactors (PWRs), the similar and dissimilar welds joining the reactor pressure vessel (RPV) nozzles to the main coolant piping have normally been volumetrically examined as part of the full 10-year RPV inspection. Generally due to access challenges to the outside diameter (OD) surface, these examinations have been performed from the component inside diameter (ID) surface. In the US and for many plants around the world, these welds fall under the requirements of the ASME B&PV Code Section XI, Appendix VIII performance demonstration as mandated by the applicable safety authority, requiring blind demonstration of detection and sizing accuracy on known defects. Many in-service inspection (ISI) vendors have qualified themselves for ID these examinations under the EPRI Appendix VIII Performance Demonstration (PD) program since it’s initiation in the early 2000s, but examination of the wavy surface DM welds and field welds (closure welds) has been a challenge for virtually all vendors to achieve the target 0.125″ RMS depth sizing error. This has been managed by assuming a larger depth sizing error corresponding to whatever the vendor’s PD assessed error was should an indication be found that required accurate sizing to justify continued plant operation. Moreover, vendors have been reluctant to re-qualify their systems as new tools have immerged due to the high associated cost.Equipment obsolescence and an interest to apply the latest technology prompted AREVA to undertake a re-qualification for these welds. This has allowed use of more advanced phased array techniques with 3-D wavy surface compensation. In addition, a new nozzle examination tool, NEMO has been developed. Such a tool is particularly suitable for plants where the nozzles must be examined on their 10 year or shorter interval schedule but where the vessel examination can be deferred to 20 years. This paper discusses the detection and sizing advances for these wavy surface DM welds as well as the first deployment of the NEMO tool.© 2014 ASME