QUALIFICATION OF INVESSEL VISUAL EXAMINATION FOR KERNKRAFTWERK LEIBSTADT (KKL) AND KERNKRAFTWERK (KKM) MÜHLEBERG PLANTS

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1 More Info at Open Access Database QUALIFICATION OF INVESSEL VISUAL EXAMINATION FOR KERNKRAFTWERK LEIBSTADT (KKL) AND KERNKRAFTWERK (KKM) MÜHLEBERG PLANTS BACKGROUND J. Lindberg, EPRI, USA R. Schwammberger, Kernkraftwerk Leibstadt, Switzerland P. Graedel, BKW FMB Energie, Switzerland In 2008, Swiss regulators implemented a requirement that all safety related inspections at nuclear power plants must be performed using qualified personnel and procedures. Prior to 2008, several inspection techniques were demonstrated on open mockups and personnel were not required to be qualified to perform data analysis. In 2009, a qualification project was started in support of the Kernkraftwerk Leibstadt AG (KKL) and Kernkraftwerk Mühleberg (KKM) In-Vessel Visual Inspection (IVVI) programs to detect stress corrosion cracking (SCC) using visual inspection techniques. To meet the regulation, KKL and KKM plant personnel initiated and coordinated a complex project to work with the Swiss qualification body, QSt; KKL and KKM s inspection vendor, GE-Hitachi; and the Electric Power Research Institute (EPRI) for qualification technical support. The scope of this project was to develop and implement a qualification program as described by guideline HSK-B07[1], where the Swiss Federal Nuclear Safety Inspectorate, ENSI, requires all inservice inspection (ISI) to be performed by means of qualified inspection systems (procedure, equipment, and personnel). In compliance with ENSI, all IVVIs for detection of structurally significant cracking on reactor pressure vessel (RPV) internals shall be performed solely with qualified inspection systems, procedures, and personnel beginning with the 2011 outage. The 2011 outage time requirement was later revised to QUALIFICATION REQUIREMENT AND SCOPE The Swiss ENSI-B07 guideline requires all inservice inspection (ISI) to be perfromed by means of qualified inspection systems, which includes procedures, equipment and personnel. In Switzerland, every NDE qualification project is assessed by the Qualification Body (QB) consisting of representatives from the Swiss Association of Technical Inspection (SVTI/ASIT). According to the qualification requirements, the qualification will ensure that the IVVI to be performed provide reliable and reproducible results that allows comparison with past and future inspections. The qualification process included VT-1 visual examinations as referred in Swiss regulatory document, SVTI - Festlegung NE-14. Revision 6 [2]; and enhanced visual examination, EVT-1, as referred in the Boiling Water Reactor Vessel and Internals Project, BWRVIP-03, Reactor Pressure Vessel and Internals Examination Guidelines, EPRI Report TR , dated October 1995[3]. The overall scope of qualification included the following elements: the Invessel Visual Inspection (IVVI) procedures and related techniques, all remote visual examination equipment underwater camera systems, and examination personnel all Level II and Level III visual examiners. The goal of qualifying IVVI is to detect flaws that have potential to affect public safety or the integrity of the component and are considered significant. IVVI should be focused on reliably detecting significant flaws rather than all possible flaws. Intergranular stress corrosion cracking (IGSCC) is considered the predominant damage mechanism in reactor internals (austenitic) components and this is the defect type selected for the qualification. 70

2 The qualification flaw was selected as a stress corrosion cracking (SCC) type defect with a crack opening dimension (COD) of 30 µm (microns) and a length of 25mm (0.984 inches). The 30 µm COD target was based on the median value for IGSCC taken from SKI report 2006:24[4], and remote visual examination testing results taken from a U.S. Nuclear Regulatory Commission report, NUREG 6943 [5]. The 25 mm long flaw was based on the minimum flaw length allowed per reactor internals flaw handbooks. The flaw detection capability for this target flaw and size were proven through parametric studies and verified via the successful qualification results. TEST SPECIMEN DESIGN AND FABRICATION Remote visual examination (RVT) test specimens had to be designed and fabricated to support the IVVI qualification project. Using recent research in RVT flaw fabrication, and their expertise in test specimen fabrication; EPRI designed and fabricated test specimens for parametric and qualification testing. In addition, they developed and issued the Technical Justification (TJ) for the KKL/KKM remote visual qualification test specimens, that was approved by QSt for the qualification program. The test specimen fabrication process was a complex process that was implemented under ERPI s Test Specimen Fabrication Quality program; consisting of the following steps: 1. Design of flaws and test specimens; including qualification defect sizes, materials, surface finish/texture, color, and surface features, such as grinding marks, scratches, other anomalies. 2. Fabrication of the blank stainless steel and ceramic test specimens. 3. Laser micromachining of the surface of the test specimens to simulate SCC type flaws. 4. Addition of surface features, such as grinding marks, and scratches 5. Fingerprinting of the test specimens using metallurgical microscopy. 6. Completion of the test specimen fabrication documentation packages. 7. Development, issuance and approval of the Technical Justification for use of the test specimens for the KKL/KKM IVVI Qualification program. The TJ identifies the essential parameters and shows that the test specimens have sound technical basis and are suitable for the planned qualification including parametric studies. The TJ validates that the test specimens, as designed, fabricated and described in TJ satisfy the procedure and personnel qualification based on a minimum targeted simulated SCC 0.98 inch (25 mm) in length and a crack opening dimension (COD) of 30 microns. Justification was provided for the use of qualification specimens using flat plate fabricated from both 304 stainless steel and colored ceramic plates to represent both the original metallic and colored (oxidized surface) component conditions. The test specimens contained both weld crowns and a ground flush surface and were populated with non-flaw features such as tooling marks, grinding marks, and weld undercut. The flaw production method used a laser micromachining process where light energy is used to machine narrow grooves in the surface of the material to simulate surface cracks with varying COD. The images in Figure 1 show that the laser machining technique is capable of simulating some characteristics associated with SCC. 71

3 a) Core Shroud Crack b) Simulated Crack Figure 1 - Photographs of a Core Shroud Crack at KKM (a) and a Similar Simulated Crack on an EPRI Sample Viewed through Remote IVVI Inspection System with Sample Immersed in Water (b) Additional discussion in the TJ addressed the conservative approach of specimen design as it relates to reactor component stress corrosion cracks. The purpose of this discussion was to document that the intent of specimen design was to provide a robust test of inspection capabilities. The methods used for the fabrication of test specimens that are described in detail in the TJ resulted in the production of specimens that have an appearance that closely simulates color, texture, surface features (weld crown, grinding marks, scratches, and weld undercut), and crack morphology of the actual components and SCC type flaws. 72

4 QUALFICATION PLAN At the beginning of this qualification project it was recognized this project was a complex mission. There were several organizations and personnel with varying responsibilities, many first-of-a-kind and interrelated tasks, and a hard date for the successful completion of the qualification. A detailed project plan and schedule was prepared, reviewed, and approved by the project team. Because personnel and organizations were functioning separately and across the ocean; weekly telephone calls were implemented, detailed action item lists were maintained, and periodic face-to face meetings in Switzerland were held to drive progress and accountability to the project plan and schedule. The plan and schedule was discussed and revised on a frequent basis to update progress, address arising issues, and develop recovery plans, as needed. The main qualification program activities were as follows: Test specimen design, fabrication and fingerprinting Lead by EPRI, Charlotte, NC o Development and issuance of test specimen technical justification EPRI o Performed in parallel with most of the other key activities IVVI Procedural development and parametric studies Lead by GE-Hitachi, Wilmington, NC Guided Practice to test procedure parameter and qualification methodology GE-Hitachi, San Jose; QSt, KKL/KKM and EPRI personnel Procedure refinements, additional parametric studies Lead by GE-Hitachi, Wilmington, NC o Development, review, and issuance of equipment and procedure technical justifications Finalize and issue IVVI procedure/techniques o Development, review, and issuance of final equipment and procedure technical justifications Finalize and issue IVVI Qualification methodology protocol Lead by QSt, EPRI technical support Implement qualifications procedure and personnel Performed at EPRI Charlotte; Lead by QSt, EPRI technical and qualification support, KKL/KKM support, GE-Hitachi The qualification program took about two and a half years from beginning through the successful completion of the personnel qualification. The bulletized list of activities above oversimplifies the intricacies and challenges encountered in the implementation of the overall program. Each of the above activities was multi-faceted and interrelated, and required constant coordination. For example, test specimen fabrication activities were being performed in parallel with procedural development and refinement, parametric studies, preparation of technical justifications, and the development of the final qualification protocol. Periodically, test specimens were released to support parametric studies, prior to final approval of the test specimen technical justification. Also, there were challenges with resources. The inspection vendor encountered resource limitations during refueling outage seasons. While these interruptions were taken into account in the schedule; stopping and restarting vendor tasks caused schedule inefficiencies and apprehension with maintaining the schedule and goals. Ultimately, the teams perseverance in meeting the schedule and achieving the goal resulted in success. 73

5 EXAMINATION TECHNIQUES Standard distance based IVVI examination techniques were utilized during the first phase of the parametric studies to determine the effective limits for flaw detection. Surface illumination, lens-toobject distance and camera angle to the surface were significant factors to demonstrate repeatable examination results. The consequences of distance based examinations were realized when 3D models were developed based on the qualified distance. Many components had restricted access due to various configurations of piping and brackets. During the 2 nd phase of the parametric study, a field-of-view (FoV) examination technique was developed by GE-Hitachi. This technique allowed the use of camera s optical zoom to essentially duplicate the field-of-view obtained during the distance based calibration. With the use of the FoV technique, examiners were allowed to increase the lens-to-object distance up to 400 mm for improved access. The combination of the two techniques increases the examination coverage for many components that have configuration limitations. QUALIFCATION METHODOLOGY A critical element in the qualification process is the development and issuance of the qualification methodology or qualification protocol. In this case, the responsibility for the qualification protocol was with the qualification agency, QSt; with input from KKL/KKM and EPRI. Since the remote visual examination was a first-of-a-kind qualification for Switzerland there were a lot of technical challenges to address and resolve before a protocol document could be produced. Often, there were more questions and opinions than definitive answers. Questions like the use of live data versus recorded data for qualification; recording criteria, false call criteria, were discussed often and finally resolved. While certain aspects of the qualification process were well established, the options for implementing the actual qualification testing were flexible to some degree. The use of guided practice/trial qualification was an important activity in addressing many of the qualification implementation and protocol questions and challenges. The guided practice was performed at GE-Hitachi s BWR test facility in San Jose, CA. The intent of this activity was to exercise the current version of the IVV procedure under simulated qualification test conditions, to assess readiness and procedure adequacy and evaluate the qualification testing methodology. The guided practice was very beneficial; as it was determined that additional parametric studies were needed to support the procedure technical justification, and aided in finalizing the qualification test protocol. The result was improved examination techniques and IVVI procedure; an implementable testing methodology, and finally an approved qualification protocol. 74

6 QUALIFICATION Following the guided practice, it was decided to perform the procedure and personnel qualification testing at EPRI qualification test facilities in Charlotte, NC. EPRI had recently built a remote visual examination test tank and scanner, which was set-up in a light controlled and secure test area (See figure 2). QSt personnel had overall responsibility for conducting, monitoring, and grading the procedure and personnel qualification testing. EPRI provided technical support during the testing, and assisted in preparation and transfer of the test specimens in and out of the test area. KKL/KKM witnessed portions of the procedure and personnel testing. The procedure qualification activity was performed in January and February This testing was performed in a blind manner, using live data; and exercised all examination techniques and camera systems. At the end of this testing, the IVVI procedure, with all techniques and camera systems, and four examination personnel were successfully qualified. Due to resource constraints to support spring outages, the personnel qualification testing started in late April 2012 and was completed by mid-may The personnel qualification was a more challenging task that the procedure qualification, because a total of 28 qualified visual examiners were needed to support the upcoming KKL/KKM IVVI workscopes. A two shift operation was established for the qualification. In addition, inspection vendor personnel (qualification candidates) were scheduled to complete procedure indoctrination training for two days prior to performing qualification testing. The personnel qualification testing was performed in a blind manner, using live data; and the candidate had to successfully demonstrate proficiency of 10 techniques from the procedure using both a color and black and white camera systems. Twenty eight examination personnel (Level II and III) were successfully qualified during personnel qualifications. Figure 2 Photo (top left) shows remote visual examination test tank and scanner in secure test area; photo (bottom) shows close up of scanner with test specimen mounted on right side of scannner; photo (right) shows controlled area for examination personnel and test monitors 75

7 LESSONS LEARNED This qualification was a challenging and complex task that resulted in the successful qualification of an IVVI procedure, three camera systems, and twenty eight remote visual examination personnel. The project took over two and half years to complete, and required a high level of management, coordination, technical support, and attention to detail. The following in a synopsis of key lessons learned that came out of this project: Do not underestimate the scope and complexity of qualifying remote visual examination Development of credible test samples with field representative surface color, texture, and realistic flaws (size, contrast etc) is complex and can be improved in the future Take your time with all involved parties to set ambitious, but realistic goals Do not rush the design of experiment for the Parametric study, because it may result in a lot of unnecessary work Camera handling with poles/ropes provides a lot of flexibility, but has its inherent limitations, which are difficult to simulate in a qualification Communication and teamwork is paramount to success; listen carefully to each other s deviating opinions before defending your own opinion SUMMARY This complex and challenging remote visual examination qualification program consisted of planning and implementing a multifaceted, multi-year plan that involved several global orgnaizations. The project included the simulataneous development of qualification acceptance criteria and test protocol; design, fabrication and technical justification of remote visual examination test specimens; and the performance of parametric studies and testing to develop and refine the examination procedure and determine capabilities of equipment. The culmination of the program was the implementation and successful qualification of examination procedure and associated techniques, equipment (3 camera systems), and 28 Level II and III visual examination personnel. More importanly, the qualfied procedure, equipment and personnel were succesfully implemented during KKL and KKM s 2012 outages with noted improved quality over previous examinations. REFERENCES [1] HSK-B07(ENSI-B07), Sicherheitstechnisch klassierte Behälter und Rohrleitungen: Qualifizierung der zerstörungsfreien Prüfungen, September 2008 [2] Swiss regulatory document, SVTI - Festlegung NE-14. Revision 6, Dated January 01, 2005 [3] Boiling Water Reactor Vessel and Internals Project, BWRVIP-03, Reactor Pressure Vessel and Internals Examination Guidelines, EPRI Report TR , dated October 1995[2]. [4] Swedish Nuclear Power Inspectorate. Crack Characterization for In-Service Inspection Planning, SKI Report 2006:24, Stockholm, Sweden. May [5] U.S. Nuclear Regulatory Commission. A Study of Remote Visual Methods to Detect Cracking in Reactor Components, Pacific Northwest National Laboratory. NUREG/CR Washington, D.C