ML15056A405
| ML15056A405 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 01/22/2015 |
| From: | Hacker K Electric Power Research Institute, NDE |
| To: | David Alley Division of Engineering |
| Alley D | |
| References | |
| 20150122-01 | |
| Download: ML15056A405 (6) | |
Text
Nondestructive Evaluation (NDE) _____________________________________________20150122-001 Mr. Dave Alley, Chief Component Performance NDE and Testing Branch Division of Engineering Office of Nuclear Reactor Regulation United States Nuclear Regulatory Commission One White Flint N 11555 Rockville Pike Rockville, MD 20852-2739
Subject:
Industry response to U.S. Nuclear Regulatory Commission (NRC) Staff Concerns with Performance Demonstration Initiative, Site Specific Configuration Mockup Requirements for Dissimilar Metal Welds, Revision C, June 9, 2014 [ML14099A291]
Dear Mr. Alley:
In response to the five large stress corrosion cracks discovered in the inlet hot leg steam generator nozzle dissimilar metal weld (DMW) at North Anna Power Station Unit 1, the industry formed the nondestructive evaluation (NDE) Improvement Focus Group (NIFG). The NIFG efforts focused on DMWs where site-specific mockups have been used and non-encoded examinations conducted.
In 2013, the Electric Power Research Institute (EPRI) published the following reports to provide guidance for nuclear power plant owners with respect to improving the reliability of NDE:
- 1) Report 300200091, Nondestructive Evaluation: Guideline for Conducting Ultrasonic Examinations of Dissimilar Metal Welds, Revision 1
- 2) Report 3002000204, Nondestructive Evaluation: Performance Demonstration Initiative (PDI)
Guidance for Improved Reliability in Ultrasonic Examinations These reports include:
- 1) Performance Demonstration Initiative (PDI), Site Specific Configuration Mockup Requirements for Dissimilar Metal Welds, Revision C
- 2) Guidelines for the Application of Team Scanning for Ultrasonic Examination of Dissimilar Metal Welds (DMW)
The subject letter requests further information on several NRC comments on these reports. Industry responses follow.
Mr. Dave Alley, U.S. Nuclear Regulatory Commission (NRC)
January 22, 2015 Page 2.
U.S. Nuclear Regulatory Commission (NRC) Staff Concerns with Performance Demonstration Initiative, Site Specific Configuration Mockup Requirements for Dissimilar Metal Welds, Revision C:
[These comments were given at the Public Meeting held on February 28, 2013 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML13071A165)]
NRC comment:
Requirements with respect to quantity, size, type, and locations of implanted flaws in the mockups need to be well-defined. One flaw in each orientation is insufficient as one flaw cannot cover a range of sizes, angles, or locations. Using only small flaws or one flaw location does not cover the range of possibilities in the field.
Response
The number of flaws and sizes is dictated by the complexity of the site configuration and is required to be justified by the technical basis document (TBD). The site specific mockup process is intended to use the qualified procedure and demonstrate its effectiveness for the subject configuration. It relies and expands upon the initial Appendix VIII qualification and is not purposed to include in itself the entire range of possibilities. This may be as simple as one flaw in each direction but the TBD will evaluate the complexity and justify the number of flaws.
NRC comment:
Designing robust acceptance criteria for open testing is challenging, it is possible that blind testing is simpler than open testing. Predetermined and quantitative acceptance criteria need to be developed prior to testing.
Response
The flaw detection and characterization requirements in the procedure are qualified during blind Appendix VIII qualification. The site-specific demonstration process requires that the mockup flaws must meet the procedures qualified criteria in order to show effectiveness for this configuration.
The site-specific demonstration is not intended to be a new, Appendix VIII-compliant qualification.
NRC comment:
Modeling of the ultrasonic search unit should be mandatory.
Response
Industry concurs that mathematical modeling is potentially a useful and powerful tool for enhancing NDE reliability. EPRI and NRCs Office of Nuclear Regulatory Research are engaged in a multi-year collaborative effort to identify and benchmark models that will be useful for these tasks, and to establish modeling best practices to ensure that modeling results are reliable and repeatable. The scope and requirements for modeling should not be established until such benchmarking and best practices are available.
Mr. Dave Alley, U.S. Nuclear Regulatory Commission (NRC)
January 22, 2015 Page 3.
NRC comment:
Paragraph 10.2 should be struck from the document as it is unnecessary and the language is open to abuse.
Response
The paragraph states: If the results of the demonstration do not meet the above criteria the licensee shall consider alternative examination processes or methods. Industry feels that if the Section XI examination requirement cannot be met, an alternative process or method may provide a useful result and should be considered. Can the nature of the potential abuse be clarified?
NRC comment:
In addition to the Authorized Nuclear Inservice Inspector (ANII), the staff would like the performance demonstration administrator (PDA) to review and approve the procedure and technical basis document as the new procedure would be considered qualified.
Response
PDA should not be involved because essential variables arent changed. As changes in the essential variables are not allowed, the Licensee can perform this work. If they wish to get the PDA involved that is at their discretion. There are no Appendix VIII qualification requirements for the PDA to review. The grading of PDI qualifications involves comparing results to the mockup key; the site-specific demonstration process requires a qualified UT Level III to perform this task and evaluate the demonstration.
NRC comment:
The staff believes that the Technical Basis Document should be sent to the PDA and that it becomes part of the record for equipment, procedure and personnel.
Response
The licensee is responsible for retaining these records; the PDA is responsible for retaining Appendix VIII qualification records.
U.S. Nuclear Regulatory Commission Staff Concerns with the Concept of Team Scanning:
[These comments were given at the public meeting held on June 4, 2013 (ADAMS Accession No. ML13159A012) in the context of the proposed testing of team scanning that was conducted in July 2013, after these comments were provided. The testing described in the presentation has been completed and represented a proof of concept of team scanning under ideal conditions.
NRC comment:
The implementation of team scanning in the field is performed under a wide range of conditions.
For example, inspectors may or may not be able to see each other, inspectors may or may not have worked together before, and the training levels of inspectors can vary greatly. There has been
Mr. Dave Alley, U.S. Nuclear Regulatory Commission (NRC)
January 22, 2015 Page 4.
no work done to date to determine the important variables in team scanning or the effects of these variables on the effectiveness of the scanning. How can the NRC staff be assured that team scanning is effective in the field if the effects of these variables are not known?
Response
The relation between the lab environment and the field environment is the same for PDI qualifications and for the team scanning demo1. The lab conditions used for Appendix VIII qualifications and for the team scanning demo are not intended to capture every possible field condition that the examination personnel must work in. Rather, they are intended to support an evaluation of whether the demonstrated procedures and processes work, and whether the examiners are capable; if so, then we should have confidence that, applied properly, the examinations should be effective in the field. The lab conditions are more stressful than most field conditions, as the examiners know that if they don't pass they may not get the raise or additional work that they depend on.
Regarding the specific items in the comment:
Inspectors may or may not be able to see each other The guidance published in Appendix B of document 300200091 requires, with the authority of an NEI 03-08 Needed requirement:
- 6. When performing the examination, the scanner and the qualified examiner shall be in direct communication. The qualified examiner shall maintain the ability to monitor the scanners technique.
- 7. The scanner shall have the ability to monitor the instrument display that the qualified examiner is viewing to assist in performing a proper scan. This may be accomplished by viewing the same instrument as the qualified examiner or a remote display.
During the demonstration the individuals were able to see each other.
Inspectors may or may not have worked together before The demonstration included four teams with various levels of experience with team scanning. Each team included a Level II or Level III examiner and a Level I or Trainee scanner. One team had performed team scanning together in the past; individuals from two teams had performed team scanning in the past but not together; and individuals from one team had never performed team scanning. All teams were successful.
Training levels of inspectors can vary greatly The examiner must be at least a Level II and the scanner must be at least a Trainee.
1 The team scanning demonstration was published in Nondestructive Evaluation: 2013 Team Scanning Assessment Conducted on Behalf of the NDE Integration Committees NDE Improvement Focus Group, product ID 3002002048. Four teams performed demonstrations equivalent to Appendix VIII Supplement 10 or Supplement 12 qualifications. All were successful, except one team passed the austenitic portion of its Supplement 12 demonstration but failed the ferritic add-on.
Mr. Dave Alley, U.S. Nuclear Regulatory Commission (NRC)
January 22, 2015 Page 5.
During the demonstration the teams compositions were: Trainee with Level II; Trainee with Level III; Level I with Level II; Level I with Level III. All of the Level II and Level III examiners were highly experienced, though two of them were specialists in automated UT and had not performed manual, non-encoded field examinations in years. The scanners had a range of experience. One scanner was close to completing the experience and training requirements to reach Level II, while another had only recently reached Trainee and had essentially no field experience.
NRC comment:
American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI, Appendix VIII, describes a minimum list of essential variables, but does not take team scanning variables in to account. Which variables in team scanning should be considered essential? Should procedures have to list the team design as an essential variable?
Response
Team scanning is not an essential variable, it is simply a style of scanning. Scanning styles are not controlled - for example, which hand is used preferentially, or the specific division of the examiners attention between the instrument screen and the scanning hand. In team scanning, the qualified examiner ensures that the examination is performed within the demonstration procedure requirements and essential variables are maintained.
NRC comment:
Many variables in team scanning can be eliminated by limiting the implementation of team scanning. Requiring line of sight, direct communication, and requiring both parties to have a view of the instrumentation would significantly reduce the uncertainties caused by team scanning. Other variables can be eliminated by establishing formal requirements such as minimum team-scanning training requirements and minimum team scanning experience requirements.
Response
The published requirements for implementation of team scanning address the technical points raised in the comment. From Appendix B of document 300200091:
- 4. During the pre-job brief, the qualified examiner, as well as the responsible utility representative, shall review the expectations for the examination with the person performing the scanning. The review shall include the procedure scanning requirements such as: scan speed, indexing, monitoring proper coupling, dimensioning of indication, etc.
- 5. The team shall demonstrate the scanning process on a mockup containing reflectors, if available. If no mockup is available a calibration block shall be used. The qualified examiner shall ensure correct scan speed, indexing, and adequate coupling, and the process for dimensioning of indications are demonstrated. The process for team communication to be used in the field shall also be practiced during the demonstration.
Mr. Dave Alley, U.S. Nuclear Regulatory Commission (NRC)
January 22, 2015 Page 6.
- 6. When performing the examination, the scanner and the qualified examiner shall be in direct communication. The qualified examiner shall maintain the ability to monitor the scanners technique.
- 7. The scanner shall have the ability to monitor the instrument display that the qualified examiner is viewing to assist in performing a proper scan. This may be accomplished by viewing the same instrument as the qualified examiner or a remote display.
The results of the demonstration show that specific minimum requirements for team scanning training or experience are not needed. Industry also believes that team scanning provides an important benefit that would be mitigated by excessive limitation of the practice. Team scanning is a good learning experience for the person who is scanning, and also provides valuable in-plant opportunities for Trainee and Level I personnel; these opportunities are less frequent today as utilities control their costs.
Thank you for the opportunity to respond to your comments. For further information I am available at kevin.j.hacker@dom.com.
Sincerely, Kevin Hacker, Dominion Generation Chairman, EPRI NDE Integration Committee cc:
Joe Donahue, Duke Energy Gary Lofthus, Southern Nuclear Steve Swilley, EPRI Damon Priestley, TVA Al Brooks, DTE Energy Chung Tran, Luminant