ML23080A254
| ML23080A254 | |
| Person / Time | |
|---|---|
| Issue date: | 04/10/2023 |
| From: | Jeffrey Poehler NRC/RES/DE |
| To: | Steve Ruffin NRC/RES/DE/MEEB |
| Jeffrey Poehler 301-415-8353 | |
| Shared Package | |
| ML23068A021 | List: |
| References | |
| Download: ML23080A254 (6) | |
Text
April 10, 2023 MEMORANDUM TO: Steve Ruffin, Chief Materials Engineering Branch Division of Engineering Office of Nuclear Regulatory Research FROM: Jeffrey Poehler, Sr. Materials Engineer Reactor Engineering Branch Jeffrey C. Digitally signed by Jeffrey C.
Poehler Poehler Date: 2023.04.10 10:48:02 Division of Engineering -04'00' Office of Nuclear Regulatory Research
SUBJECT:
SUMMARY
OF MARCH 7, 2023 PUBLIC MEETING WITH ELECTRIC POWER RESEARCH INSTITUTE WELDING AND REPAIR TECHNOLOGY CENTER On March 7, 2023, the Nuclear Regulatory Commission (NRC) staff held a public meeting with the Electric Power Research Institutes Welding and Repair Technology Center (EPRI-WRTC).
The purpose of the meeting was to have a technical exchange focusing on several American Society of Mechanical Engineers (ASME) code cases that either have been conditionally approved by the NRC, disapproved by the NRC, or for which EPRI-WRTC is planning to make changes. All the presentations from the meeting, as well as the meeting notice, are contained in Agencywide Document Access and Management Systems (ADAMS) package number ML23068A021. Discussion with the industry participants took place during the presentations. A list of the meeting participants is enclosed.
Opening Remarks EPRI-WRTC indicated in its opening remarks that it had been over ten years since the EPRI-WRTC and the Nuclear Regulatory Commission (NRC) staff had held a public meeting. EPRI-WRTC indicated they saw the purpose of the meeting was to discuss code cases that are listed as disapproved in Regulatory Guide (RG) 1.193, ASME Code Cases Not Approved for Use, Revision 7, and conditionally approved RG 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, Revision 20, and also to discuss new code cases under development. EPRI-WRTC wanted to gain a better understanding of the NRCs basis for some of the conditions, so that it might be able to modify the code cases in the future to eliminate some of the conditions.
The NRC staff indicated in its opening remarks that it welcomed the opportunity to engage in meaningful technical discussions with the EPRI-WRTC on ASME code issues.
CONTACT: Jeffrey Poehler, RES/DE/REB (301) 415-8353
S. Ruffin Presentations The first presentation by the EPRI-WRTC (Steve McCracken) concerned Code Case N-847-1, Partial Excavation and Deposition of Weld Metal for Mitigation of Class 1 ItemsSection XI, Division 1, which provides a method for excavation and weld repair of welds with defects.
EPRI indicated that N-847-1 was intended to provide another method in the toolbox to repair or mitigate welds that are susceptible to stress corrosion cracking in both boiling water reactors (BWRs) and pressurized water reactors (PWRs). The excavate and weld repair method of N-847-1 may be designed to provide stress improvement to the weld being repaired and is applicable to both similar metal and dissimilar metal welds. During the presentation, EPRI and the NRC discussed some of the conditions currently included in RG 1.147 for N-847-1. The condition resulting in the most hardship for the industry is the one prohibiting partial arc repairs.
The NRC staff indicated that it could potentially approve to use partial arc repairs on a case-by-case basis, but imposed the condition so that licensees would have to submit a request for alternative to use this type of repair, thus providing the staff an opportunity to perform a review of the licensees technical basis for the partial arc repair.
With regard to the third NRC condition on Code Case N-847-1, which states that growth into Alloy 690 must be considered in the flaw growth analysis, EPRI (Steve McCracken) asked if there are any instances where the NRC doesnt require a flaw-growth analysis into primary water stress corrosion cracking (PWSCC)-resistant material. The NRC staff indicated it does not know of any such instances.
With regard to the fourth condition on N-847-1 which states that weld residual stress analyses must use the methods of NUREG-2228, EPRI asked for more background on this condition.
The NRC staff (Michael Benson) indicated that NUREG-2228 focuses on two aspects, 1.
Modeling guidelines; and 2) Method of validating a weld residual stress analysis. The NRC staff also clarified that the fourth condition applies to all types of repairs in N-847-1, not just partial arc repairs. EPRI asked if the NUREG-2228 guidelines must be applied if the repair is of the type that does not provide stress improvement. The staff clarified that model validation is needed when the user is required to perform a stress analysis as part of applying the code case.
There was also discussion of the background for the fifth condition, which requires the first inservice inspection (ISI) of the repair at the second refueling outage following the repair (versus the code case which would allow the first inspection to be between the first and third refueling outage). The NRC staff indicated the condition to require ISI at the second refueling outage was included because the staff felt that the second refueling outage would provide more meaningful results since more operating time would be accumulated and cracking would be more likely to have initiated in the repair than at the first refueling outage. The NRC staff indicated it considered the third refueling outage was too long to wait for the first ISI. The NRC staff also indicated that it had tried to structure the condition such that the inspection frequencies would be consistent between N-847-1 and Code Case N-770-5, Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated With UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation ActivitiesSection XI, Division 1.
The second presentation by Westinghouse (Steve Marlette) concerned Code Case N-894, a new code case for repair of piping with thermal fatigue cracking, which has not yet been approved by the ASME Section XI Standards Committee. N-894 also covers growth of cracks by SCC. N-894 focuses on the base metal as well as the weld, and requires the use of stress
S. Ruffin corrosion cracking (SCC) resistant material in the environment. N-894 requires a full structural weld overlay (FSWOL). Westinghouse noted that the code case has some unique aspects related to the required examination volume for the FSWOL, which will be reviewed by the Section XI Subgroup on Nondestructive Examination. One of the unique aspects of the post-welding acceptance examination is the requirement for an ultrasonic examination of the base metal adjacent to the weld overlay on the inner one-third of the pipe thickness, which is intended to verify flaws were not opened after the application of the weld overlay. This area is also required to be examined during subsequent inservice examination.
The NRC staff (Jay Collins) expressed that it is supportive of the examination requirements for the base metal that are included in N-894. Westinghouse also noted that a group of NRC staff had reviewed N-894 and indicated that it was one of the bigger plus values in the ASME Code lately.
The third presentation, by EPRI-WRTC (Steve McCracken) addressed Code Case N-818-1, Use of NDE and Fracture Mechanics for acceptance of Full Penetration Butt Welds in Lieu of Weld Repair, Class 1 and 2,Section III, Division 1. This code case would allow leaving fabrication flaws in place and accept using UT examination plus fracture mechanics. N-818-1 is on the list of disapproved code cases in RG 1.193. The intent of N-818-1 is to allow fabricators to avoid performing repairs that could limit component life later. Weld repairs during fabrication are known to increase residual stresses in components which can contribute to SCC during the operational life of the component. UT is also better at detecting cracklike defects that are harmful to component service life.
The NRC staff had nine concerns related to N-818-1 detailed in RG 1.193. One concern is that N-818-1 applies to ferritic, stainless steel and dissimilar metal welds, while Code Case N-831 for UT in lieu of RT is only applicable to ferritic materials. EPRI-WRTC asked the NRC staff if this concern is still applicable given that N-831-1 is now approved by ASME, which now covers both ferritic and austenitic pipe. Another one of the seven concerns that is a sticking point for the staff is the maximum flaw depth of 20% permitted by N-818-1. The NRC staff (John Honcharik) noted that a 20% throughwall flaw may be acceptable on a case-by-case basis but is difficult to accept on a generic basis. EPRI-WRTC also requested clarification regarding the basis of two of the concerns, specifically the fifth concern about a calibration block versus a qualification block, and the sixth concern about the root mean square error in I-3.2(d) not being appropriate for fabrication flaws. However, it was noted that a major concern with the generic approval of the code case could leave significant flaws in place for an unlimited number of welds in a system which could compromise the systems ability to perform its intended function.
Additional discussion of N-818-1 included the observation that fabricators usually want to do things as quickly as possible, and likely wouldnt use N-818-1 unless pushed to do so by the owner. Therefore, EPRI-WRTC questioned the need to move forward with a revision to N-818-
- 1. EPRI-WRTC also mentioned the possibility of making N-818 a Section XI code case.
The fourth presentation concerned Code Case N-853-1, PWR Class 1 Primary Piping Alloy 600 Full Penetration Branch Connection Weld Metal Buildup for Material Susceptible to Primary Water Stress Corrosion Cracking,Section XI, Division 1. This code case provides a method to modify branch connections that have a PWSCC-susceptible nozzle that is welded to a larger pipe or vessel via a full-penetration weld, by application of a PWSCC-resistant weld metal buildup and new nozzle. These type of branch connections are found in only a few PWR plants constructed by Babcock & Wilcox or Combustion Engineering. Code Case N-853 was endorsed as an acceptable code case in RG 1.147, Revision 19. Code Case N-853-1 is approved by
S. Ruffin ASME but not yet included in RG 1.147 by NRC. A revision of the code case (N-853-2) is under development that would make changes to the UT examination requirements to allow the use of ASME Section XI acceptance criteria and bring the code case into alignment with Non-mandatory Appendix Q, Code Case N-740-3, and Draft Code Case N-894. The revision also includes changes to the examination volume, specifically to not require examination of portions of the weld buildup that are not credited in the structural integrity analysis. The NRC staff stated it generally supports N-853 because it would like to see these type of branch connections mitigated, since they are a safety concern.
The next topic was a revision to Code Case N-888, Similar and Dissimilar Metal Welding Using Ambient Temperature SMAW or Machine GTAW Temper Bead Technique Section XI, Division
- 1. A verbal presentation was given by Joe Weicks, consultant. Code Case N-888 replaced Code Cases N-638 and N-839 and combined the two. Mr. Weicks stated that historically, N-638 and N-839 required all NDE to be in accordance with the construction code, ASME Boiler and Pressure Vessel Code,Section III (Section III). For all applications of ambient temperature temper bead welding, volumetric examination has been used, with anything cracklike being rejected. However, many of these flaws could be accepted using fracture mechanics.
Therefore, the revision would provide an alternative use Section XI acceptance standards instead of Section III acceptance standards. The NRC staff requested that a white paper be developed detailing the technical basis of the revision. The white paper would address leaving flaws in service with no further volumetric inservice inspection to monitor the flaw. Other code cases that reference N-888 would only rely on the welding requirements not the NDE requirements of N-888. The NRC commented that this should be specifically stated in the code case.
The last presentation by EPRI (Jon Tatman) concerned a new code case for cold spray mitigation of spent fuel canisters. The code case is being developed by a new ASME Section XI Task Group for Mitigation and Repair of Spent Nuclear Fuel Canisters. The scope of the code case is mitigation by applying a corrosion-resistant barrier, not repair, although cold spray can also be used for repair. Cold spray would mainly be applied to the outside of the canisters since that is where the corrosion is likely to occur. The NRC staff (John Honcharik) asked if this code case would be reviewed by the ASME Section XI Subgroup on Repair and Replacement Activities (SG-RRA). Mr. Tatman indicated that the code case may need to be reviewed by SG-RRA because the task group reports directly to the Section XI standards committee.
Public Comments There were no comments made by the public at the end of the meeting.
Closing Remarks EPRI-WRTC thanked NRC for the opportunity to engage in meaningful discussion of code cases. The NRC staff also expressed its appreciation for the opportunity for technical discussions on these topics. Both the NRC staff and EPRI-WRTC agreed that it would be useful to have periodic meetings of this type, perhaps yearly.
Enclosure As stated
S Ruffin Enclosure - List of Attendees March 7, 2023 Public Meeting, Technical Exchange with Electric Power Research Institute Welding and Repair Technology Center Last Name First Name Affiliation Anchondo-Lopez Isaac NRC Baborak Darren EPRI Basie Mekonen NRC Bass Joseph NRC Bass Ryann NRC Benson Michael NRC Bergman Jana Curtiss Wright Bloom Steve NRC Bowers Steven Constellation Nuclear Buford Angie NRC Burton Mat NRC Carlson Jesse NRC Cirilli Jim EPRI Collins Jay NRC Cruz Ramon Constellation Nuclear Cumblidge Stephen NRC Daniel Jason NRC Davis Bob NRC Dijamco David NRC Fairbanks Carolyn NRC Focht Eric NRC Frederick Greg EPRI Friant Carl Constellation Nuclear Graham Jacqueline Constellation Nuclear Hall Marc Dominion Energy Haywood Emma NRC Honcharik John NRC Hull Amy NRC Iyengar Raj NRC Jenkins Joel NRC Kalikian Varoujan NRC Khan Omar NRC Lin Bruce NRC Malik Shah NRC Marlette Steve Westinghouse McCracken Steve EPRI Min Seung NRC Mitchell Matthew NRC Mohr Nick EPRI Moyer Carol NRC Nove Carol NRC Olson Travis Framatome Parker Cory NRC Poehler Jeff NRC Reichelt Eric NRC Rezai Ali NRC Rudland Dave NRC Ruffin Steve NRC
S. Ruffin Last Name First Name Affiliation Sida Karen NRC Steve Marlette Westinghouse Tate Stephen EPRI Tatman Jon EPRI Tsao John NRC Ulmer Christopher NRC Weicks Joe consultant Widrevitz Dan NRC Young Kemper Constellation Nuclear Young Austin NRC
S. Ruffin
SUBJECT:
SUMMARY
OF MARCH 7, 2023 PUBLIC MEETING WITH ELECTRIC POWER RESEARCH INSTITUTE WELDING AND REPAIR TECHNOLOGY CENTER DISTRIBUTION:
Steve Bloom Matthew Mitchell Angela Buford David Rudland Jay Collins Eric Reichelt Carol Nove Bruce Lin John Tsao Michael Benson Robert Davis James Gavula Brian Allik Joel Jenkins John Honcharik Ali Rezai RES_DE_REB Distribution RES_DE_MEB Distribution Karen Sida Stephen Cumblidge Omar Khan Varoujan Kalikian Mat Burton Bart Fu Seung Min Louise Lund John McKirgan Raj Iyengar Steve Ruffin Austin Young Ryann Bass Shah Malik Mekonen Bayssie Matthew Homiack ADAMS Accession Number: ML23080A254 *via email OFFICE RES/DE/REB RES/DE/MEB NAME S. Ruffin J. Poehler DATE 4/4/23 3/23/23 OFFICIAL RECORD COPY