ML20206K928
| ML20206K928 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 07/30/2020 |
| From: | Shawn Williams Plant Licensing Branch II |
| To: | Burchfield J Duke Energy Carolinas |
| Williams S | |
| References | |
| EPID L-2020-LLR-0036 | |
| Download: ML20206K928 (6) | |
Text
OCONEE NUCLEAR STATION, UNITS 1 AND 2 - AUTHORIZATION OF ALTERNATIVE (RA-20-0036) FROM CERTAIN REQUIREMENTS OF THE ASME CODE FOR REPAIR/REPLACEMENT ON LOW PRESSURE SERVICE WATER SYSTEM PIPING (EPID L-2020-LLR-0036)
LICENSEE INFORMATION Licensee: Duke Energy Carolinas, LLC Licensee Address: Mr. J. Ed Burchfield, Jr.
Site Vice President Oconee Nuclear Station Duke Energy Carolinas, LLC 7800 Rochester Highway Seneca, SC 29672-0752 Plant Name and Units: Oconee Nuclear Station (ONS), Units 1 and 2 Docket Nos.: 50-269, 50-270 APPLICATION INFORMATION Submittal Date: March 2, 2020 Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML20062G131 Supplement Date(s): June 16, 2020 Supplement ADAMS Accession No.: ML20168B026 Licensee Proposed Alternative No. or Identifier: Relief Request RA-20-0036 Applicable Inservice Inspection (ISI) Interval: Fifth ISI Interval began on July 15, 2014, and is scheduled to end on July 15, 2024.
Applicable Regulation: Title 10 of the Code of Federal Regulations (10 CFR),
Section 50.55a(z)(2).
Applicable Code Requirements: American Society of Mechanical Engineers (ASME) Code,Section XI, Paragraph IWA-4421 requires that defects be removed or mitigated in accordance with IWA-4340, IWA-4411, IWA-4461, or IWA-4462.
Applicable Code Edition and Addenda: ONS has adopted ASME Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2007 Edition with the 2008 Addenda as the code of record for the fifth 10-year ISI interval.
Brief Description of the Proposed Alternative:
On September 26, 2019, a thru-wall leak was discovered in a 3-inch branch connection weld, connected to the 12-inch Class 3 Low Pressure Service Water (LPSW) header. The 12-inch LPSW header is the common cooling water supply header to the Unit 1 and the Unit 2 component cooling system's heat exchangers.
The ASME Code,Section XI, IWA-4421, requires removing the defective portions of Class 3 LPSW system piping prior to performing repair/replacement activities to correct wall thickness loss by installing replacement pressure-retaining material that will fully encapsulate the degraded piping. In lieu of the requirement in ASME Code,Section XI, IWA-4421, the licensee proposed alternative requirements described in the Enclosure to the application, Sections 5.1.1 to 5.1.11.
The licensee stated that to perform the required ASME Code repair, removal of defective portions of the subject 3-inch piping would require that the LPSW system be isolated and depressurized requiring a dual Unit 1 and Unit 2 shutdown, and this creates a hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The proposed alternative is requested for the remaining life of ONS, Units 1 and 2.
For additional details on the licensees submittal, please refer to the documents located at the ADAMS Accession No(s) identified above.
REGULATORY EVALUATION Regulatory Basis: 10 CFR 50.55a(z)(2)
Adherence to Section XI of the ASME Code is mandated by 10 CFR 50.55a(g)(4), which states, in part, that ASME Code Class 1, 2, and 3 components must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI.
Paragraph 10 CFR 50.55a(z) states, in part, that alternatives to the requirements of 10 CFR 50.55a(b)-(h) or portions thereof may be used, when authorized by the Director, Office of Nuclear Reactor Regulation, if (1) the proposed alternatives would provide an acceptable level of quality and safety; or (2) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The licensee submitted the request under 10 CFR 50.55a(z)(2) on the basis that compliance with the specified requirements of 10 CFR 50.55a would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
TECHNICAL EVALUATION The NRC staff evaluated the pre-installation evaluation, design, installation, examination and pressure testing of the proposed alternative. The NRC staff also evaluated the licensee's determination that Code compliant repair/replacement of the leaking piping would represent a hardship. The goal of NRC's evaluation is to determine whether the proposed alternative will provide reasonable assurance of the structural integrity and leak tightness of the subject piping after encapsulation.
The licensee supplied previous wall thickness readings used to evaluate the structural integrity of the leak location that were also used in designing the proposed encapsulation. This information also showed where the proposed encapsulation would be attached to the existing piping. This information allowed the NRC staff to verify material thickness in the areas of attachment of the encapsulation to both the 3-inch and 12-inch pipe were adequate for the encapsulation design. The licensee stated the wall thickness examinations would be repeated prior to installation of the encapsulation to verify the thickness remains sufficient. Based on the above, the NRC staff finds the licensees pre-installation evaluation acceptable.
The encapsulation design proposed by the licensee is fabricated from a 6-inch pipe cap and 6-inch pipe. Both the cap and the pipe are schedule 40 carbon steel components. The encapsulation will have a 1/2 inch carbon steel coupling installed for pressure testing. The licensee stated the design of the encapsulation is compliant with B31.1, Power Piping - 2007 Edition. In the June 16, 2020, supplement, the licensee described the methods used to analyze the encapsulation and confirm its compliance with B31.1. The design of the encapsulation assumed a corrosion degradation rate of four times the estimated maximum corrosion rate (0.002 inches/year) based on actual measurements. This is more conservative than the requirements of the current condition in 10 CFR 50.55a(b)(2)(xxv) on the use of ASME Code,Section XI, IWA-4340. The licensees analysis estimated 160 years for the flaw to propagate from the 3-inch pipe into the portion of the 12-inch header where the proposed encapsulation device will attach and 125 years for the flaw to propagate into the line stop fitting. Based on this information, the NRC staff finds the licensees proposed design for the encapsulation acceptable.
The original Construction Code is B31.1 - 1967. The licensee stated the installation of the encapsulation would be performed in accordance with B31.1 - 2004 Edition. The NRC staff finds the licensees proposed installation plans acceptable because SME Code,Section XI, allows the use of later versions of the original construction code.
The licensee stated that after the installation of the encapsulation, a system leakage test will be conducted at normal operating pressure (approximately 80 psig [pounds per square inch above atmospheric pressure]), a fluid temperature 100°F, and a hold time of 10 minutes after attaining test pressure. The NRC staff finds the licensees proposed post-installation pressure test for the encapsulation acceptable.
The licensee stated that after the installation of the encapsulation, the repair will be subject to inservice inspection in accordance with Table IWD-2500-1, Category D-B, which requires a system leakage test and accompanying VT-2 examination each inspection period. Additionally, the licensee stated that the wall thickness measurements of the area immediately adjacent to the proposed encapsulation attachment at the line stop fitting will be taken to ensure propagation of the defect into the material credited for structural integrity does not occur during the design life of the modification. The licensee stated that these measurements will be taken at
least once per operating cycle and thickness data will be gathered in accordance with the ONS Service Water Piping Corrosion Program. The NRC staff finds the licensees proposed post-installation examinations for the encapsulation acceptable.
The NRC staff finds that the licensee has considered various options of performing the repair in accordance with the ASME Code,Section XI, and approved code cases, as provided in the application. The NRC staff finds that isolating and depressurizing the LPSW system, requiring a dual Unit 1 and Unit 2 shutdown, to perform a repair in compliance with ASME Code,Section XI, IWA-4421, would result in hardship without a compensating increase in the level of quality and safety.
NRC staff finds it is acceptable to authorize the alternative for the remaining life of ONS, Units 1 and 2, for the following reasons:
- 1. The design of the modification meets the original Construction Code B31.1;
- 2. The corrosion rates the licensee used in the design are based on four times the measured rates, and using these corrosion rates it is estimated the corrosion would not affect the material relied upon for structural integrity for 125-160 years; and,
- 3. The follow-on nondestructive examination and monitoring will ensure the corrosion does not impact the structural integrity.
CONCLUSION The NRC staff concludes that complying with the specified requirements described in the licensees request referenced above would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The proposed alternative provides reasonable assurance of structural integrity and leak tightness of the subject components.
The NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
The NRC staff authorizes the use of proposed alternative RA-20-0036 at ONS, for the remaining life of ONS, Unit 1 and Unit 2, as specified in the Renewed Facility Operating Licenses Nos.
DPR-38 and DPR-47, respectively.
All other ASME BPV Code,Section XI requirements for which an alternative was not specifically requested and authorized as part of this proposed alternative remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: Keith M. Hoffman, NRR Date: July 30, 2020 Michael T. Digitally signed by Michael T. Markley Markley Date: 2020.07.30 09:51:20 -04'00' Michael T. Markley, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
ML20206K928 *via e-mail OFFICE NRR/DORL/LPL2-1/PM* NRR/DORL/LPL2-1/LA* NRR/DNRL/NPHB/BC*
NAME SWilliams KGoldstein MMitchell DATE 07/27/2020 07/24/2020 07/23/2020 OFFICE NRR/DORL/LPL2-1/BC* NRR/DORL/LPL2-1/PM*
NAME MMarkley SWilliams DATE 07/30/2020 07/30/2020