W3F1-2024-0039, Response to Request for Additional Information - Proposed Alternative WF3-RR-24-02 for Examinations of Steam Generator Pressure-Retaining Welds and Full Penetration Welded Nozzles
| ML24268A296 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 09/24/2024 |
| From: | Pyle S Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| W3F1-2024-0039 | |
| Download: ML24268A296 (1) | |
Text
Stephenie Pyle Director Regulatory Compliance 601-368-5516
Entergy Operations, Inc., 1340 Echelon Parkway, Jackson, MS 39213 W3F1-2024-0039 10 CFR 50.55a September 24, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Response to Request for Additional Information - Proposed Alternative WF3-RR-24-02 for Examinations of Steam Generator Pressure-Retaining Welds and Full Penetration Welded Nozzles Waterford Steam Electric Station, Unit 3 NRC Docket No. 50-382 Renewed Facility Operating License No. NPF-38 In accordance with 10 CFR 50.55a(z)(1), Entergy Operations, Inc. (Entergy) requested Nuclear Regulatory Commission (NRC) approval of a proposed alternative for Waterford Steam Electric Station, Unit 3 (WF3) (Reference 1). Specifically, the proposed alternative concerns American Society of Mechanical Engineers (ASME) Class 1, Examination Category B-B, Pressure-Retaining Welds in Vessels Other Than Reactor Vessels, Item Number B2.40, Steam Generators (Primary Side), Tubesheet-to-Head Weld, Class 2, Examination Category C-A, Pressure-Retaining Welds in Pressure Vessels, Item Number C1.20, Head Circumferential Welds, Class 2, Examination Category C-A, Item Number C1.30, Tubesheet-to-Shell Welds, Class 2, Examination Category C-B, (Pressure Retaining Nozzle Welds in Pressure Vessels,Section XI, Division 1), Item Number C2.21, Nozzle-to-Shell (Nozzle-to-Head or Nozzle-to-Nozzle) Welds, and Class 2, Examination Category C-B, Item Number C2.22, Nozzle Inside Radius Sections.
Entergy received a Request for Additional Information (RAI) from the NRC (Reference 2). The Enclosure to this letter provides Entergy's response to the RAI.
This letter contains no new regulatory commitments.
W3F1-2024-0039 Page 2 of 2 Should you have any questions or require additional information, please contact Phil Couture at 601-368-5102.
Respectfully, Stephenie Pyle SP/chm
Enclosure:
Response to Request for Information
References:
- 1) Entergy letter to NRC, "Proposed Alternative WF3-RR-24-02 for Examinations of Steam Generator Pressure-Retaining Welds and Full Penetration Welded Nozzles," ML24078A376, dated March 18, 2024
- 2) NRC email to Entergy, "Request for Additional Information Proposed Alternative WF3-RR-24-02 Examinations of Steam Generator Welds and Nozzles Waterford Steam Electric Station, Unit 3 Entergy Operations, Inc. Docket No. 50-382," ML24236A162, dated August 26, 2024 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - WF3 NRC Project Manager - WF3 Digitally signed by Stephenie Pyle DN: cn=Stephenie Pyle, c=US, o=Entergy, ou=Director, Fleet Regulatory Assurance, email=spyle@entergy.com Date: 2024.09.24 10:40:09 -05'00' Stephenie Pyle
Enclosure W3F1-2024-0039 Response to Request for Information
W3F1-2024-0039 Enclosure Page 1 of 6 TABLE OF CONTENTS
1.0 BACKGROUND
................................................................................................................. 2 2.0 REGULATORY BASIS....................................................................................................... 2 3.0 ISSUES.............................................................................................................................. 2 4.0 NRC REQUEST AND ENTERGY RESPONSE................................................................. 3 4.1 Request for Additional Information - 1........................................................................... 3 4.1.1 NRC Request.......................................................................................................... 3 4.1.2 Entergy Response................................................................................................... 3 4.2 Request for Additional Information - 2........................................................................... 4 4.2.1 NRC Request.......................................................................................................... 4 4.2.2 Entergy Response................................................................................................... 4 4.3 Request for Additional Information - 3........................................................................... 5 4.3.1 NRC Request.......................................................................................................... 5 4.3.2 Entergy Response................................................................................................... 5 4.4 Request for Additional Information - 4........................................................................... 5 4.4.1 NRC Request.......................................................................................................... 5 4.4.2 Entergy Response................................................................................................... 5
W3F1-2024-0039 Enclosure Page 2 of 6 RESPONSE TO REQUEST FOR INFORMATION
1.0 BACKGROUND
By letter dated March 18, 2024 (Agencywide Document Access and Management System Accession Number ML24078A376), Entergy Operations, Inc. (Entergy and the licensee) submitted to the United States Nuclear Regulatory Commission (NRC), a proposed alternative to the inservice inspection (ISI) requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, for the examination of steam generator (SG) welds at Waterford Steam Electric Station, Unit 3 (WF3).
Specifically, pursuant to Title 10 of the Code of Federal Regulations, Part 50, Section 55a, Paragraph (z)(1) (10 CFR 50.55a(z)(1)), the licensee is proposing to defer the ISI examinations for the SGs at WF3 from the current ASME Code,Section XI, 10-year requirement to the end of currently licensed operating life, which is scheduled to end on December 18, 2044 as discussed in Proposed Alternative WF3-RR-24-02. The licensee referred to the results of the probabilistic fracture mechanics (PFM) analyses in the following Electric Power Research Institute (EPRI) nonproprietary reports as the primary basis for the deferral of the ISI examinations:
EPRI Technical Report 3002015906. "Technical Bases for Inspection Requirements for PWR Steam Generator Class 1 Nozzle-to-Vessel Welds and Class 1 and Class 2 Vessel Head, Shell. Tubesheet-to-Head and Tubesheet-to-Shell Welds," 2019 (hereinafter referred to as "EPRI report 15906," ML20225A141).
EPRI Technical Report 3002014590, "Technical Bases for Inspection Requirements for PWR Steam Generator Class 1 Feedwater and Main Steam Nozzle-to-Shell Welds and Nozzle Inside Radius Sections," 2019 (hereinafter referred to as "EPRI report 14590,"
To complete its review, the NRC staff requests for the additional information as discussed below.
2.0 REGULATORY BASIS The NRC has established requirements in 10 CFR Part 50 to protect the structural integrity of structures and components in nuclear power plants. Among these requirements are the ISI requirements of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a to ensure that adequate structural integrity SG vessels (including their welds) is maintained through the service life of the vessels. Therefore, the regulatory basis for the following request for additional information (RAl) has to do with demonstrating that the proposed alternative ISI requirements would ensure structural integrity of the SG welds of WF3, and thereby would provide an acceptable level of quality and safety per 10 CFR 50.55a(z)(1) for the welds.
3.0 ISSUES The licensee referenced probabilistic and deterministic analyses in the above EPRI reports to estimate potential fatigue crack growth in the subject SG welds and to justify application of these analyses to the proposed examination elimination for the welds and nozzle inner radius locations. The licensee presented plant-specific information to demonstrate that the referenced
W3F1-2024-0039 Enclosure Page 3 of 6 analyses in the EPRI reports would bound the subject SG welds, including the ISI history of the welds.
Leveraging PFM analyses to define the basis for risk-informing inspection requirements requires knowledge of both the current and future behavior of the material degradation and the associated uncertainties applicable to the subject SG welds. Confidence in the results of these analyses hinges on the assurance that the PFM model adequately represents, and will continue to represent, the degradation behavior in the subject SG welds. The NRC staff has determined that, when considering proposed elimination of examinations, adequate performance monitoring through inspections is needed to ensure that the assumptions of the PFM model remain valid, and that novel or unexpected degradation is detected and dispositioned in a timely fashion.
Further, the staff has communicated concepts that licensees can implement on a fleet-wide basis to develop a performance monitoring plan and bolster the technical basis for alternative requests (see slide packages dated January 30, 2023, and April 27, 2023, at ML23033A667 and ML23114A034, respectively).
In Section 5.1.10 of the submittal, the licensee stated that SG welds04-068, 04-073,04-074, and 04-076 were last examined during the third 10-year ASME Section XI interval and proposed performing the required ASME Code,Section XI examinations prior to the end of currently licensed operating life, which is scheduled to end on December 18, 2044. To provide additional defense in depth to the alternative request, the licensee stated that they will adopt a performance monitoring plan during the requested deferral period. Given this inspection scenario, the WF3 inspection history in Attachment 1 to the submittal, and the licensee's proposed extended examination intervals, the staff noted that all subject SG welds will be in operation for more than 20 years past their last inspection. This inspection plan would not meet the threshold the staff have adopted for performance monitoring because 20 years is too long without validating data.
4.0 NRC REQUEST AND ENTERGY RESPONSE 4.1 Request for Additional Information - 1 4.1.1 NRC Request Describe the performance monitoring that will be implemented with this proposed alternative to ensure that the PFM model adequately represents, and will continue to represent, the degradation behavior in the subject components commensurate with the duration of the requested alternative.
4.1.2 Entergy Response From WF3-RR-24-02 (Reference 1), Section 5.1.10, WF3 requested to utilize a performance monitoring plan for the following components: 04-076,04-068, 04-073,04-074 as these exams have not been completed in the current 4th inspection interval.04-075 has been examined in the current interval and will be inspected in the future as shown below.
This monitoring plan will be implemented as stated in the table below. As seen in this table, all five steam generator (SG) welds (100% of the required ASME section examinations) for WF3 will be inspected in less than 20 years. This is considerably more than the 25% required by the NRC using the binomial distribution model in ML23033A667 (Reference 5) and ML23114A034 (Reference 6) for adequate performance monitoring.
W3F1-2024-0039 Enclosure Page 4 of 6 Table 1 - Inspection History - Monitoring Plan Item No.
Comp ID Exam Date Interval/Period/Outage Future Exam Schedule Outage Current Schedule Approximate Years Between Exams C2.21 04-073 4/30/2017 3rd / 3rd / 1RF21 5th Int / 3rd Per 2035 18 C2.22 04-074 4/28/2017 3rd / 3rd / 1RF21 5th Int / 3rd Per 2035 18 C1.30 04-075 10/6/2020 4th / 1st / 1RF23 6th Int / 1st Per 2039 19 C1.20 04-068 4/29/2017 3rd / 3rd / 1RF21 5th Int / 3rd Per 2035 18 B2.40 04-076 5/4/2017 3rd / 3rd / 1RF21 5th Int / 3rd Per 2035 18 As shown in the Inspection History Table above, all these exams have been performed since 2017 with ASME Section XI approved techniques. Also, future exams are scheduled to be performed in less than 20 years.
4.2 Request for Additional Information - 2 4.2.1 NRC Request Explain how this performance monitoring will provide, over the extended examination interval, (1) direct evidence of the presence and extent of degradation, (2) validation and confirmation of the continued adequacy of the PFM model; and (3) timely detection of novel or unexpected degradation.
4.2.2 Entergy Response
- 1) The performance monitoring plan provided above includes sampled inspections using ASME Section XI exam methods that will provide direct evidence of the presence and extent of any degradation over the extended examination interval for these welds.
- 2) The WF3 operating history is validation and confirmation of the conservative nature of the PFM and deterministic fracture mechanics (DFM) models used in the EPRI Technical Reports 3002015906 (Reference 3) and 3002014590 (Reference 4) which were referenced in WF3-RR-24-02 (Reference 1). This also shows that the models will predict future behavior conservatively. The proposed performance monitoring plan includes sampling of examinations across the remainder of the WF3 current operating license.
- 3) The performance monitoring schedule described above will provide timely detection of any novel or unexpected degradation in these components.
W3F1-2024-0039 Enclosure Page 5 of 6 4.3 Request for Additional Information - 3 4.3.1 NRC Request If through this performance monitoring indications are detected that exceed the acceptance standards of ASME Code,Section XI, IWB-3500, confirm that they will be evaluated as required by ASME Code,Section XI (which includes requirements for successive inspections and additional examinations) and describe other actions (if any) specified in the plants corrective action program to ensure that the integrity of the component is adequately maintained.
4.3.2 Entergy Response If during the performance monitoring schedule described above, indications are detected that exceed the applicable ASME Code,Section XI acceptance standards of IWB-3500 or IWC-3500, then the indications will be addressed as required by ASME Code Section XI, and the WF3 Corrective Action Program. The additional examination and successive inspection requirements of ASME Code,Section XI, also apply during the current outage. The number of additional exams shall be the number required by ASME Section XI, IWB-2430/IWC-2430.
4.4 Request for Additional Information - 4 4.4.1 NRC Request If through this performance monitoring indications are detected that exceed the acceptance standards of ASME Code,Section XI, IWB-3500, then scope expansion may be appropriate to assess extent of condition. Furthermore, if this performance monitoring plan or industry-wide operating experience indicates that a new or novel degradation mechanism is possible in SG welds or nozzle inner radii, scope expansion may be appropriate to ensure that no such mechanism is occurring in the subject plants.
Discuss the detailed scope expansion plans for these scenarios.
4.4.2 Entergy Response As stated above, if indications are detected that exceed the applicable ASME Code,Section XI acceptance standards of IWB-3500 or IWC-3500, then the indications will be addressed as required by ASME Code Section XI, and the WF3 Corrective Action Program. The additional examination and successive inspection requirements of ASME Code,Section XI, also apply during the current outage. The number of additional exams shall be the number required by ASME Section XI, IWB-2430/IWC-2430.
In addition to ASME Section XI, Entergy utilizes the Corrective Action Program to review and evaluate industry Operating Experience (OE) to determine the appropriate actions required based upon the specific OE. If the OE indicates that a new or novel degradation mechanism is possible in SG welds or nozzle inner radii, the appropriate examinations will be performed or considered to ensure that no such mechanism is occurring in the subject plants.
5.0 REFERENCES
- 1.
Entergy letter to NRC, "Proposed Alternative WF3-RR-24-02 for Examinations of Steam Generator Pressure-Retaining Welds and Full Penetration Welded Nozzles,"
ML24078A376, dated March 18, 2024
W3F1-2024-0039 Enclosure Page 6 of 6
- 2.
NRC email to Entergy, "Request for Additional Information Proposed Alternative WF3-RR-24-02 Examinations of Steam Generator Welds and Nozzles Waterford Steam Electric Station, Unit 3 Entergy Operations, Inc. Docket No. 50-382," ML24236A162, dated August 26, 2024
- 3.
EPRI Technical Report 3002015906, "Technical Bases for Inspection Requirements for PWR Steam Generator Class 1 Nozzle-to-Vessel Welds and Class 1 and Class 2 Vessel Head, Shell, Tubesheet-to-Head and Tubesheet-to-Shell Welds," ML20225A141, EPRI, Palo Alto, CA: 2019
- 4.
EPRI Technical Report 3002014590, "Technical Bases for Inspection Requirements for PWR Steam Generator Feedwater and Main Steam Nozzle-to-Shell Welds and Inside Radius Sections," ML19347B107, EPRI, Palo Alto, CA: 2019
- 5.
Constellation slides on Performance Monitoring from NRC Meeting, ML23033A667, January 30, 2023
- 6.
NRC slides, "Probabilistic Fracture Mechanics and Performance Monitoring,"
ML23114A034, April 27, 2023