TARGET – Development of Submersible ROV System for BMN Inspection

Most PWRs have penetrations in the RPV lower heads for in-core nuclear instrumentation. These generally are made of nickel-based Inconel Alloy 600. Weld materials typically 82/182. Operating conditions PWR plants causing alloys cracking through a process called primary water stress corrosion (PWSCC). In 2003, licensee South Texas Project Unit 1 (STP-1) identified apparent boron deposits on head near two bottom mounted nozzles (BMNs). The NRC issued Bulletin 2003-02 to obtain information inspection activities and plans head. EPRI MRP-206 report that provides evaluation guidelines BMNs plants, including periodic bare metal visual examination evidence coolant leakage, or non-visual nondestructive examinations indications service-induced cracking. inspections (ultrasonic testing examination) may detect degradation before through-wall cracking, circumferential below J-groove weld, release loose parts, incipient boric acid wastage low-alloy steel reactor vessel material occurs. Therefore, will adequately manage potential by PWSCC preserve structural integrity. INETEC developed TARGET system inspection, consisted submersible ROV specially designed probe, composed several UT probes. technique detect, length depth size BMN volume is developed. NDE Center performed technical review validated INETEC’s ultrasonic BMNs. Aforementioned validation was done according requirements defined by: 1) MRP-206, 2) MRP-411.