Studies conducted at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington, focused on assessing the effectiveness of nondestructive examination (NDE) techniques for inspecting control rod drive mechanism (CRDM) nozzles and J-groove weldments. The primary objectives of this work are to provide information to the U.S. Nuclear Regulatory Commission (NRC) on the effectiveness of NDE methods as related to the in-service inspection of CRDM nozzles and J-groove weldments and to enhance the knowledge base of primary water stress corrosion cracking (PWSCC) through destructive characterization of the CRDM assemblies.Two CRDM assemblies were removed from service, decontaminated, and then used in a series of NDE and destructive examination (DE) measurements; this report addresses the following questions: 1) What did each NDE technique detect? 2) What did each NDE technique miss? 3) How accurately did each NDE technique characterize the detected flaws? 4) Why did the NDE techniques perform or not perform? Two CRDM assemblies including the CRDM nozzle, the J-groove weld, buttering, and a portion of the ferritic head material were selected for this study. This report focuses on a CRDM assembly that contained suspected PWSCC, based on in-service inspection data and through-wall leakage.The NDE measurements used to examine the CRDM assembly followed standard industry techniques for conducting in-service inspections of CRDM nozzles and the crown of the J-groove welds and buttering. These techniques included eddy current testing (ET), time-of-flight diffraction ultrasound, and penetrant testing. In addition, laboratory-based NDE methods were employed to conduct inspections of the CRDM assembly with particular emphasis on inspecting the J-groove weld and buttering. These techniques included volumetric ultrasonic inspection of the J-groove weld metal and visual testing via replicant material of the J-groove weld. The results from these NDE studies were used to guide the development of the destructive characterization plan.The NDE studies found several crack-like indications. The NDE and DE studies determined that one of these was a through-weld, radially oriented PWSCC crack in the wetted surface of the J-groove weld, located at the transition point between the weld and the buttering. The crack was 6 mm long on the surface and quickly grew to 25 mm long at a depth of 8 mm, covering the length of the weld between the penetration tube and the carbon steel.The NDE studies found that only ET was able to detect the through-weld crack. The crack was oriented poorly for the ultrasonic testing and was too tight for accurate dye penetrant testing or visual testing. The ET voltage response of the through-wall crack was 30% of the response from a deep electrical discharge machined notch.Destructive examination showed the crack is PWSCC and that it initiated on the wetted surface, grew and expanded through the weld metal, and exited into the annulus. The crack was branched and discontinuous along its length.iii iv Su...
). The results of the earlier work are being published because it was conducted semi-blind and will be a valuable source of information relative to performance demonstration assessments. In addition, there were some examinations of DMWs, and the number of studies published to date providing DMW examination results are limited.The early work demonstrated the potential for using low-frequency ultrasound coupled with synthetic aperture focusing technique (SAFT) signal processing to detect cracking in coarse-grained stainless steels. The follow-on efforts are detailed in NUREG/CR-6929 and NUREG/CR-6933. It should be noted that the inspection techniques have greatly improved since the initial work; in particular, the use of lowfrequency phased arrays which permits faster inspections, more flexible and precise scans, and better detectability.The technique discussed in this report uses a zone-focused, multi-incident angle, low-frequency (250-450 kHz) inspection protocol coupled with the synthetic aperture focusing technique (SAFT). The primary focus of this work is to provide information to the United States Nuclear Regulatory Commission on the utility, effectiveness and reliability of ultrasonic testing (UT) inspection techniques as related to the inservice ultrasonic inspection of coarse grained primary piping components in pressurized water reactors (PWRs).Experiments were conducted in order to assess the low-frequency (350 kHz) ultrasonic inspection technique for coarse-grained stainless steel components. Software was modified and experiments were performed for applying a noise reduction algorithm to the pre-and post-SAFT processed data sets. PNNL staff traveled to the EPRI NDE Center to examine samples from the inventory of Westinghouse Owner's Group (WOG) CASS and DMW sections. The results reported here do not represent data from a statistically large number of field-representative CASS samples. Approximately 20 CASS specimens (PNNL and EPRI specimens) were examined using this examination protocol. Results from this field test clearly show that the low-frequency/SAFT inspection technique is capable of providing quality detection and localization data, and accurate length sizing information. Office of Nuclear Regulatory Research FOREWORDThe low cost and relative corrosion-resistance of cast austenitic stainless steel (CASS) have resulted in its extensive use in the primary pressure boundary of pressurized-water reactors (PWRs). This is significant because Section XI of the Boiler and Pressure Vessel Code promulgated by the American Society of Mechanical Engineers (ASME) requires periodic inservice inspection of welds in the primary pressure boundary, including those that are fabricated using CASS.In most applications, ultrasonic testing (UT) techniques can reliably detect and accurately size flaws that may occur during service. However, this is not the case for CASS because its coarse-grained nonhomogeneous, anisotropic microstructure makes components constructed with CASS difficult to inspect. Anisotropic means ...
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