ML24101A008
| ML24101A008 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 04/10/2024 |
| From: | Byrd T NRC/NRR/DORL/LPL4 |
| To: | Brost W, Richards D South Texas |
| Byrd T | |
| References | |
| L-2024-LLR-0027 | |
| Download: ML24101A008 (5) | |
Text
From: Thomas Byrd (They/Them)
Sent: Wednesday, April 10, 2024 6:08 AM To: Brost, Wendy; Richards, Drew Cc: Warren, Christopher
Subject:
STP - Verbal Relief Request - - 50.55a(z)2 - ASME Code Case N-729-6 RV Head Penetration 75 (EPID - L-2024-LLR-0027)
Attachments: South Texas U2 script (EPID L-2024-LLR-0027).docx
In accordance with NRR Office Instruction LIC-102, Review of Relief Requests, Proposed Alternatives, and Requests to Use Later Code Editions and Addenda, Agencywide Documents and Management System (ADAMS) Accession No. ML18351A218), the NRR staff provided verbal authorization on September 14, 2024 for South Texas Project (STP), Unit 2, for the alternative relief request RR-ENG-4-07, as described in your letter dated April 6, 2024 (ML24097A007).
The script read that provides verbal authorization is attached. The NRC staff intends to follow-up this verbal authorization with a written safety evaluation within 150 days.
A copy of this email and attached verbal authorization will be made publicly available in ADAMS, and I will provide the accession number to you.
Please let me know if you have any questions.
The following personnel from the NRC and STP participated in the call:
NRC Jennie Rankin - Branch Chief, Licensing Branch IV (LPL4), Division of Operating Reactor Licensing (DORL), Office of Nuclear Reactor Regulation (NRR)
Matthew Mitchell - Branch Chief, Piping and Head Penetrations Branch (NPHP), Division of New and Renewed Licenses (DNRL), NRR Jay Collins - Senior Materials Engineer (NRR/DNRL/NPHP)
Thomas Byrd - Project Manager (NRR/DORL/LPL4)
Leanne Flores - Resident Inspector South Texas Project (Region IV)
Nicholas Taylor - Branch Chief, Engineering Branch 2 (Region IV)
Sam Graves - Senior Reactor Inspector (Region IV)
STP Drew Richards - Regulatory Affairs Manager Wendy Brost - Licensing Supervisor Walter Fulton - Licensing Specialist Michael Garner - Testing and Programs Principal Engineer Christopher Georgeson - Engineering General Manager Kellie Harris - Testing and Programs Engineering Supervisor Derrick Johnson - Licensing Specialist Mike Khanpour - Design Engineering Manager Matthew King - Design Engineering Supervisor Jon Konchak - Quality Assurance Oversight Jonah Morgan - Radiation Protection Manager Charles Spraggon Jr. - Quality Assurance Oversight Christopher Warren - Licensing Engineer Respectfully,
Thomas Byrd Project Manager - Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Office: (301) 415-3719
Hearing Identifier: NRR_DRMA Email Number: 2462
Mail Envelope Properties (BLAPR09MB63392286AB3E52B5777B7DDEFA062)
Subject:
STP - Verbal Relief Request - - 50.55a(z)2 - ASME Code Case N-729-6 RV Head Penetration 75 (EPID - L-2024-LLR-0027)
Sent Date: 4/10/2024 6:08:05 AM Received Date: 4/10/2024 6:08:00 AM From: Thomas Byrd (They/Them)
Created By: Thomas.Byrd@nrc.gov
Recipients:
"Warren, Christopher" <cwwarren@STPEGS.COM>
Tracking Status: None "Brost, Wendy" <webrost@STPEGS.COM>
Tracking Status: None "Richards, Drew" <amrichards@STPEGS.COM>
Tracking Status: None
Post Office: BLAPR09MB6339.namprd09.prod.outlook.com
Files Size Date & Time MESSAGE 2353 4/10/2024 6:08:00 AM South Texas U2 script (EPID L-2024-LLR-0027).docx 37039
Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:
VERBAL AUTHORIZATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FOR RELIEF REQUEST NUMBER RR-ENG-4-07 REQUEST FOR AN ALTERNATE TO ASME CODE CASE N -729-6 FOR REACTOR VESSEL HEAD PENETRATION 75 STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT, UNIT NO. 2 DOCKET NO. 50-499
Technical Evaluation read by Matthew Mitchell, Chief of the Piping and Head Penetrations Branch, Office of Nuclear Reactor Regulation
By letter dated April 6, 2024, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24097A007), STP Nuclear Operating Company (the licensee) requested relief from Paragraphs -3142.2 and -3200 of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Case N-729-6, Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1, as required by Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(g)(6)(ii)(D), related to supplemental examinations of reactor vessel head (RVH) penetration number 75 at the South Texas Project, Unit No. 2 (STP, Unit 2). The licensee submitted RR-ENG-4-07 for the proposed alternative during the current spring 2024 refueling outage, 2RE23.
The licensee requested authorization for this alternative in accordance with the requirements of 10 CFR 50.55a(z)(2), on the basis that performing the supplemental examinations required by Paragraphs -3142.2 and -3200 represents a hardship or unusual difficulty without a compensating increase in the level of quality and safety.
In performance of the current refueling outage bare metal visual examination (VE) of the RVH, the licensee found a relevant condition on the head surface near RVH penetration number 75.
During light cleaning and evaluation, the licensee took actions to identify the source of the leakage. The licensee concluded that a source of the leakage was from the core exit thermocouple nozzle flange on penetration 75 above the RVH. However, due to some remaining corrosion products in the annulus region, the licensee was not able to preclude possible nozzle leakage as another source of the leakage. Therefore, the licensee considered the indication on the head surface to be a relevant condition of possible nozzle leakage in accordance with Paragraph -3142.1 of ASME Code Case N-729-6. As such, Paragraphs -3141.2 and -3200 of ASME Code Case N-729-6 require the licensee to perform either a repair/replacement activity or supplemental volumetric and surface examinations.
Instead of the supplemental examinations, the licensee stated that it would clean the remaining area of the RVH surface and verify the structural integrity of the RVH. During the upcoming cycle of operation, the licensee stated that it would monitor for leakage in a manner which will continue to ensure the structural integrity of the RVH. Finally, during the next scheduled refueling outage, 2R24, the licensee would perform an additional VE of the RVH near penetration 75 to ensure no leakage is occurring.
The U. S. Nuclear Regulatory Commission (NRC) staff reviewed the licensees identified hardship and found the licensees estimation of radiological dose to perform the supplemental volumetric and surface examinations during this outage was consistent with estimates at other facilities. The NRC staff finds that the radiological dose estimate of 9 person-REM for this work is a hardship on the licensee consistent with 10 CFR 50.55a(z)(2).
The NRC staff notes that the nozzle and weld material (alloy 690/52/152) of the RVH at STP, Unit 2 has been extensively tested by NRC contractors and demonstrated no cracking in service in pressurized water reactor environments, which supports the conclusion that it is unlikely that cracking is currently present. Further, if minor leakage of a RVH penetration was currently occurring, the resistance of alloy 690/52/152 to crack growth provides additional assurance that any cracking currently present would be unlikely to increase to the point of challenging the structural integrity of the RVH over one additional operating cycle. Finally, due to this slow crack growth rate, the licensees leakage monitoring actions would be able to identify leakage through RVH penetration 75 prior to it presenting a challenge to structural integrity of the RVH.
Hence, the NRC staff finds that the licensees proposed alternative provides reasonable assurance of the structural integrity of the RVH for the next operating cycle at STP, Unit 2 without requiring the licensee to perform supplemental volumetric and surface examinations during the current refueling outage.
Therefore, the NRC staff finds, given the actions of the licensees proposed alternative under RR-ENG-4-07, there would be limited value in quality and safety in requiring supplemental volumetric and surface examinations to verify no indications of cracking in these materials during the current refueling outage. Given the hardship, the NRC staff finds that (1) there is reasonable assurance that the licensees proposed alternative has a minimal impact on quality and safety; and (2) the licensees hardship justification is acceptable.
NRC Staff Conclusion read by Jennie Rankin, Branch Chief, Plant Licensing Branch IV, Office of Nuclear Reactor Regulation
As Chief of Plant Licensing Branch IV, I concur with the Piping and Head Penetration Branch's evaluation.
The NRC staff has determined that complying with the specified require ments described in the licensees alternative, RR-ENG-4-07, would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Further, the licensees proposed alternative provides reasonable assurance of structural integrity of the RVH and penetration number 75. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
Therefore, as of April 9, 2024, the NRC authorizes the use of RR-ENG-4-07 until the end of operating cycle 24 at STP, Unit 2, scheduled for Fall 2025.
All other requirements of ASME Code and 10 CFR 50.55a(g)(6)(ii)(D) for which relief was not specifically requested and authorized by the NRC staff remain applicable, including the third-party review by the Authorized Nuclear lnservice Inspector.