ML18296A111

Relief Request (RR-4-15) for Use of ASME Code Case N-513-4

ML18296A111
Person / Time
Site:	Summer
Issue date:	11/08/2018
From:	Markley M Plant Licensing Branch II
To:	Lippard G South Carolina Electric & Gas Co
Williams S, 415-1009
References
EPID L-2018-LLR-0098
Download: ML18296A111 (12)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 8, 2018 Mr. George A. Lippard, Ill Vice President, Nuclear Operations South Carolina Electric & Gas Company Virgil C. Summer Nuclear Station P.O. Box 88, Mail Code 800 Jenkinsville, SC 29065

SUBJECT:

VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1 - RELIEF REQUEST (RR-4-15) FOR USE OF ASME CODE CASE N-513-4 (EPID L-2018-LLR-0098)

Dear Mr. Lippard:

By letter dated July 3, 2018, as supplemented by a second letter dated July 3, 2018, the South Carolina Electric & Gas Company (SCE&G, the licensee) submitted a relief request to the U.S.

Nuclear Regulatory Commission (NRC) for relief from certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (B&PV code),Section XI, IWA-4000 requirements at Virgil C. Summer Nuclear Station (VCSNS), Unit 1. SCE&G requested authorization to use Code Case N-513-4, "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1" for the temporary acceptance of a through-wall leak identified in a Class 3 service water (SW) branch tee located in the downstream piping of the 'B' component cooling water heat exchanger SW return valve.

The licensee submitted the proposed alternative pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Section 50.55a(z)(2) on the basis that the ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality or safety.

On July 3, 2018, the NRG staff verbally authorized the use of relief request RR-4-15 until the conclusion of the Unit 1 Fall 2018 refuleing outage (RF24), or until the temporary acceptance criteria of Code Case N-513-4 are exceeded, or until the leak rate exceeds 50.3 gallons per minute, whichever event occurs first.

The NRC staff has reviewed the proposed alternative and concludes, as set forth in the enclosed safety evaluation, that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, the NRG staff authorizes the use of alternative request RR-4-15 for VCSNS, Unit 1.

All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRG staff remain applicable, including the third party review by the Authorized Nuclear lnservice Inspector.

If you have any questions, please contact the Project Manager, Shawn Williams, at 301-415-1009 or by e-mail at Shawn.Williams@nrc.gov.

Docket No. 50-395

Enclosure:

Safety Evaluation cc: Listserv Sincerely, Michael T. Markley, Chief Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST RR-4-15 USE OF ASME CODE CASE N-513-4 RENEWED FACILITY OPERATING LICENSE NO. NPF-12 SOUTH CAROLINA ELECTRIC & GAS COMPANY SOUTH CAROLINA PUBLIC SERVICE AUTHORITY VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1 DOCKET NO. 50-395

1.0 INTRODUCTION

By letter dated July 3, 2018 (Agencywide Document Access and Management System (ADAMS) Accession No. ML18184A560), as supplemented by a second letter dated July 3, 2018 (ADAMS Accession No. ML18186A574), South Carolina Electric & Gas Company (SCE&G, the licensee), requested approval from the U.S. Nuclear Regulatory Commission (NRC) for relief from certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (B&PV code),Section XI, IWA-4000 requirements at Virgil C. Summer Nuclear Station (VCSNS), Unit 1. SCE&G requested authorization to use Code Case N-513, Revision 4 (Code Case N-513-4), "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1" for the temporary acceptance of a through-wall leak identified in a Class 3 service water (SW) branch tee located in the downstream piping of the B component cooling water heat exchanger B SW return valve.

The licensee submitted the proposed alternative pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Section 50.55a(z)(2) on the basis that the ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality or safety.

On July 3, 2018 (ADAMS Accession No. ML18190A404 ), the NRC staff verbally authorized the use of relief request RR-4-15 until the conclusion of the Unit 1 Fall 2018 refuleing outage (RF24), or until the temporary acceptance criteria of Code Case N-513-4 are exceeded, or until the leak rate exceeds 50.3 gallons per minute, whichever event occurs first.

Enclosure

2.0 REGULATORY EVALUATION

Paragraph 10 CFR 50.55a(g)( 4 ), lnservice inspection standards requirement for operating plants, states, in part:

Throughout the service life of a boiling or pressurized water-cooled nuclear power facility, components (including supports) that are classified as ASME Code Class 1, Class 2, and Class 3 must meet the requirements, except design and access provisions and preservice examination requirements, set forth in Section XI,... to the extent practical within the limitations of design, geometry, and materials of construction of the components.

Pursuant to 10 CFR 50.55a(z), alternatives to the requirements of paragraphs (b) through (h) of this section may be used when authorized by the Director, Office of Nuclear Reactor Regulation.

A proposed alternative must be submitted and authorized prior to implementation. The licensee must demonstrate (1) the proposed alternative would provide an acceptable level of quality and safety; or (2) compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

ASME Code Case N-513, Revision 3 (Code Case N-513-3) is approved for generic use by licensees in NRC Regulatory Guide (RG) 1.147, "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1," Revision 18 (ADAMS Accession No. ML16321A336), with one condition. This RG is incorporated into NRC regulations by reference in 10 CFR 50.55a. Code Case N-513 provides criteria, which allows licensees to temporarily accept flaws, including through-wall flaws, in moderate energy Class 2 or 3 piping without performing repair or replacement activities. Code Case N-513-4 contains several revisions including expanding the applicability of the code case beyond straight pipe to include elbows, bent pipe, reducers, expanders, and branch tees. Code Case N-513-4 has not been approved by the NRC for generic use by licensees.

Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request and the NRC to authorize the alternative requested by the licensee.

3.0 TECHNICAL EVALUATION

3.1 The Licensee's Request for Alternative 3.1.1 ASME Code Components Affected The affected component is an ASME Code Section Ill, Class 3, SW system 20-inch diameter piping branch tee.

3.1.2 Applicable Code Editions and Addenda The applicable ASME Code,Section XI, Edition and Addenda for the 4th 10-year lnservice Inspection Interval (ISi) at VCSNS, Unit 1, is the 2007 Edition through 2008 Addenda. The 4th ISi interval at VCSNS, Unit 1, began on January 1, 2014, and is scheduled to end on December 31, 2023.

3.1.3

Applicable Code Requirement

ASME Code Section XI, Article IWA-4000 provides requirements for welding, brazing, metal removal, and installation of repair/replacement activities.

3.1.4

Reason for Request

On July 2, 2018, the licensee discovered a pinhole leak in the SW system on the branch tee connection below field weld (FW-1 ), down stream of XVB03123B-SW component cooling water (CCW) heat exchanger B SW return valve. The leakage rate was estimated to be approximately 0.092 gallons per minute (gpm). The leaking branch tee cannot be isolated for repair. The licensee stated that as a result of the leak, a number of limiting conditions for operation (LCOs) of the plant technical specifications were not met, including, but not limited to, LCO 3.7.4, "Service Water System". The action statement requires that with only one service water loop OPERABLE, restore at least two loops to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

• ASME Code Case N-513-3 is approved by the NRC for generic use and provides criteria to allow temporary acceptance of flaws, including through-wall flaws in moderate energy Class 2 or 3 piping without performing repair or replacement activities in accordance with ASME Code Section XI, Article IWA-4000. However, it does not address the evaluation of flaws in branch tees. The licensee proposes to use Code Case N-513-4 which contains revisions that include the evaluation of flaws, including through-wall flaws, in elbows, bent pipe, reducers and branch tees.

The licensee stated that plant shutdown activities result in additional plant risk that would be inappropriate when a degraded condition is demonstrated to retain adequate margin to complete the component's function. Thus, the licensee contends that compliance with the current code requirements results in a hardship without a compensating increase in the level of quality and safety.

3.1.5

Licensee's Proposed Alternative and Basis for Use

The licensee's proposed alternative is to use ASME Code Case N-513-4 for the evaluation and temporary acceptance of a degraded SW system piping branch tee fitting with a through-wall flaw. The licensee stated that it will follow all requirements of the code case and will take no exceptions. The licensee also imposed a maximum allowable leakage rate of 50.3 gpm. The licensee will perform a permanent repair/replacement activity at the next scheduled outage which is fall 2018.

The licensee stated that the limitations in Code Case N-513-3 related to its use on piping components, such as elbows, bent pipe, reducers, expanders, branch tees, and external tubing or piping attached to heat exchangers, have been addressed in Code Case N-513-4. The licensee provided a high level overview of the differences between Code Case N-513-3 and Code Case N-513-4 in its application, as listed below:

1. Revised the maximum allowable time of use from no longer than 26 months to the next refueling outage.

2. Added applicability to piping elbows, bent pipe, reducers, expanders, and branch tees where the flaw is located more than (Rot)112 from the centerline of the attaching circumferential piping weld (Ro is the outside pipe radius and 't' is the evaluation wall thickness surrounding the degraded area).

3. Expanded use to external tubing or piping attached to heat exchangers.

4. Revised to limit the use to liquid systems.

5. Revised to clarify treatment of service level load combinations.

6. Revised to address treatment of flaws in austenitic pipe flux welds.

7. Revised to require minimum wall thickness acceptance criteria to consider longitudinal stress in addition to hoop stress.

8. Daily walkdown requirement for through-wall leaks was changed to allow other techniques to be used to monitor leakage.

9. Other minor editorial changes to improve the clarity of the Code Case.

The licensee stated that significant changes in Code Case N-513-4 when compared to NRC approved Code Case N-513-3 are discussed in Reference 6 of the July 3, 2018, application, "Technical Basis for Proposed Fourth Revision to ASME Code Case N-513," from the Proceedings of the ASME 2014 Pressure Vessels & Piping Conference, July 20-24, 2014, Anaheim, California.

The licensee performed ultrasonic testing (UT) of the degraded area and used the "Through-Wall Flaws in Branch Tees" approach from Code Case N-513-4 to perform a flaw evaluation. The results of the flaw evaluation determined that the flaw is acceptable in the configuration evaluated, in accordance with Code Case N-513-4. The flaw evaluation is provided in Enclosure 2 of the licensee's July 3, 2018, application.

During the UT examination of the area surrounding the through-wall leak, the licensee discovered a gouged area on the external surface of the subject piping. The gouged area has a 2.5-inch long linear portion that is below the calculated minimum wall thickness of 0.162 inches.

The licensee stated that there is no approved ASME Code Case or ASME Section XI or Section Ill methods to evaluate the external surface gouge. The licensee determined the most conservative evaluation of the flaw would be to analyze the gouge as a separate through-wall flaw, in which it would be bounded by the flaw calculation performed for the leaking flaw.

A previously identified pinhole leak, in field weld FW-1, located 3.75 inches above the branch tee leak which is the subject of this proposed alternative, was evaluated in accordance with Code Case N-513-3. No relief is requested for this degraded area. However, as part of determining the effects of leakage on operability and the flooding analysis, the licensee combined the previously identified leak in FW-1 with the current branch tee leak and calculated a combined total leakage of approximately 0.16 gpm. Taking SW system flow margin, spray effects, and building flooding into consideration, the licensee determined that there is 271 gpm margin for leakage in the SW system. The licensee stated that the 50.3 gpm maximum allowable leakage in the proposed alternative is within the limits of the 271 gpm margin that it calculated for the SW system.

3.1.6 Hardship Justification The licensee stated the following hardship justification:

Code repair is considered a hardship without a compensating increase in the level of quality and safety. A Code repair would require a plant shutdown to replace the branch tee. The branch tee is located between valve XVB03123B-SW and the service water pond. The piping cannot be isolated from other portions of the service water system.

Plant shutdown activities result in additional plant risk. Such a shutdown would be inappropriate when an affected ASME Code component in a degraded condition is demonstrated to retain adequate margin to fulfill the component's function. Accordingly, compliance with the current code requirements results in a hardship without a compensating increase in the level of quality and safety.

3.1. 7 Duration of Proposed Alternative The licensee requested use of the proposed alternative until the conclusion of the Unit 1 Fall 2018 refuleing outage (RF24).

3.2

NRC Staff Evaluation

The NRC staff evaluated the adequacy of the proposed alternative in maintaining the structural integrity of the branch tee located on the SW piping between valve XVB03123B-SW and the service water pond. The NRC staff also evaluated the hardship or unusual difficulty without a compensating increase in the level of quality and safety if the licensee performed an ASME Code repair in accordance with ASME Code Section XI, IWA-4000.

Code Case N-513-3, which is conditionally approved for use in RG 1.147, Revision 18, provides alternative evaluation criteria for temporary acceptance of flaws, including through-wall flaws, in moderate energy Class 2 and 3 piping. However, Code Case N-513-3 is limited to straight pipe with provisions for flaws that extend for a short distance into the fitting at the pipe to the fitting weld. Evaluation criteria for flaws in elbows, bent pipe, reducers, expanders, branch tees and heat exchanger tubing and piping are not included within the scope of N-513-3. Code Case N-513-4 addresses these aforementioned limitations. Given that the previous revision of this code case ( Code Case N-513-3) is conditionally approved for use in RG 1.14 7, Revision 18, which is incorporated by reference in 10 CFR 50.55a, the NRC staff focused its review on the differences between Code Cases N-513-3 and N-513-4 as they apply to the evaluation of the subject SW branch tee.

The NRC staff also evaluated the licensee's proposed limitation on the leakage rate and its hardship justification.

3.2.1 Temporary Acceptance Period Code Case N-513-3 specifies a temporary acceptance period of a maximum of 26 months.

Code Case N-513-3 is accepted for use in RG 1.147, Revision 18, with the following condition:

The repair or replacement activity temporarily deferred under the provisions of this Code Case shall be performed during the next scheduled outage.

Code Case N-513-4 includes wording that limits the use of the code case to the next refueling outage and the licensee confirmed in its proposed alternative that it will repair the degraded branch tee at the next refueling outage. Thus, the NRC staff finds that Code Case N-513-4 and the proposed alternative appropriately address the NRC condition on Code Case N-513-3, and, therefore, is acceptable.

3.2.2 Flaw Evaluation Criteria for Elbows, Bent Pipe, Reducers/Expanders and Branch Tees.

Evaluation and acceptance criteria have been added to Code Case N-513-4 for flaws in elbows, bent pipe, reducers, expanders and branch tees using a simplified approach, which is based on the Second International Piping Integrity Research Group (IPIRG-2) program reported in NUREG/CR-6444, BMl-2192, "Fracture Behavior of Circumferentially Surface-Cracked Elbows,"

published December 1996.

The flaw evaluation methodology approach in Code Case N-513-4 for piping components is conducted as if in straight pipe by scaling hoop and axial stresses using ASME piping design code stress indices and stress intensification factors to account for the stress variations caused by the geometric differences. Equations used in the Code Case are consistent with the piping design by rule approach in ASME Code Section Ill, NC/ND-3600. NUREG/CR-6444 shows that this approach is conservative for calculating stresses used in flaw evaluations in piping elbows and bent pipe. The Code Case also applies this methodology to reducers, expanders and branch tees.

The NRC staff finds that the flaw evaluation and acceptance criteria in Code Case N-513-4 for elbows, bent pipe, reducers, expanders and branch tees is acceptable because the flaw evaluation methods in the code case are consistent with ASME Code Section XI, ASME Code Section Ill design by rule approach and provides a conservative approach as confirmed by comparing the failure moments predicted using this approach to the measured failure moments from the elbow tests for through-wall circumferential flaws conducted as part of the IPIRG-2 program.

The NRC staff reviewed the licensee's evaluation of the through-wall flaw and verified that it was performed in accordance Code Case N-513-4, Paragraph 3.3, 'Through-Wall Flaws in Branch Tees," and, therefore, is acceptable. In addition, the staff reviewed the UT data used to determine the size and dimensions of the gouged area on the outside surface of the branch tee.

Based on the size and dimensions of the flaw and the lack of expected flaw growth, the staff finds that the licensee's approach to analyze the gouged area as a through-wall flaw to be acceptable because the gouged area dimensions are within the dimensions of the degraded leaking area and the licensee's assumption that the gouged area is a through-wall flaw is conservative.

3.2.3 Flaw Evaluation in Heat Exchanger Tubing or Piping Code Case N-513-4 has been revised to include heat exchanger external tubing or piping, provided that the flaw is characterized in accordance with Section 2(a) of the Code Case and leakage is monitored. Section 2(a) requires that the flaw geometry be characterized by volumetric inspection or physical measurement.

The NRC staff finds the proposed alternative does not involve heat exchanger piping or tubing.

Therefore, this change is not applicable to the current proposed alternative.

3.2.4 Limit Use to Liquid Systems Use of Code Case N-513-4 is specifically limited to liquid systems.

The NRC staff finds the proposed alternative is limited to a liquid system and, thus, is consistent with Code Case N-513-4.

3.2.5 Treatment of Service Load Combinations Modifications in Code Case N-513-4 now make clear that all service load combinations must be considered in flaw evaluations to determine the most limiting condition. Although previously implied in Code Case N-513-3, Code Case N-513-4 makes this requirement clear.

Therefore, the NRC staff finds this change acceptable. In addition, the NRC staff verified that the licensee considered all service load combinations in its evaluation of the branch tee flaws.

3.2.6 Treatment of Flaws in Austenitic Pipe Flux Welds The proposed alternative does not involve austenitic pipe flux welds. Therefore, this change is not applicable to the current proposed alternative.

3.2. 7 Minimum Wall Thickness Acceptance Criteria to Consider Longitudinal Stress Although it is unlikely that a minimum wall thickness calculated based on the longitudinal stress would be limiting when compared to a minimum wall thickness calculated based on hoop stress, Code Case N-513-4 includes revisions that require consideration of longitudinal stress in the calculation of minimum wall thickness. Previous versions of the code case only required the use of hoop stress. The NRC staff finds this acceptable because it will ensure that the more limiting of the longitudinal or hoop stress is used to determine minimum wall thickness. In addition, the NRC staff verified that the licensee considered longitudinal stress to determine the minimum wall thickness of the subject branch tee.

3.2.8 Leakage Monitoring for Through-Wall Flaws Code Case N-513-3 required through-wall leakage to be observed via daily walkdowns to confirm the analysis conditions used in the evaluation remain valid. Code Case N-513-4 modifies this requirement by continuing to require that leakage be monitored daily, but now allows other techniques to be used to monitor leakage such as using visual equipment or leakage detection systems to determine if leakage rates are changing. The NRC staff finds this change acceptable because the Code Case continues to require through-wall leaks to be monitored daily and the expanded allowable monitoring methods should have no adverse impact. In addition, the licensee stated that it will perform daily walkdowns to quantify the leakage.

3.2.9 Leakage Rate Code Case N-513-3, Paragraph 1(d) states:

The provisions of this Case demonstrate the integrity of the item and not the consequences of leakage. It is the responsibility of the Owner to demonstrate system operability considering effects of leakage.

Code Case N-513-4 modified the last sentence, now located in paragraph (f), to state:

It is the responsibility of the Owner to consider effects of leakage in demonstrating system operability and performing plant flooding analyses.

The combined leakage of the previously identified pinhole leak, evaluated in accordance with Code Case N-513-3, and the pinhole leak that is the subject of the current proposed alternative is currently 0.16 gpm. The maximum allowable leakage rate under the proposed alternative is 50.3 gpm. The maximum leakage rate of 50.3 gpm provides a safety factor greater than 5 when compared to the 271 gpm margin calculated by the licensee. The staff notes that the leak is downstream of all cooling loads and throttle valves. Therefore, leakage at or below 50.3 gpm would have little or no effect on cooling load flow. The NRC staff finds that the licensee's proposed allowable leakage rate is acceptable because it will provide sufficient time for corrective measures to be taken before significant increases in leakage erodes defense-in-depth, which could lead to adverse consequences.

3.2.10 Hardship Justification The NRC staff finds that performing a plant shutdown to repair the subject piping branch tee would unnecessarily cycle the unit, resulting in an increase in personnel exposure and plant risk. Therefore, the NRC staff determined that compliance with the specified ASME Code repair requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

3.3 NRC Staff Conclusion

The NRC staff concludes that the proposed alternative will provide reasonable assurance of structural integrity of the subject branch tee because: ( 1) Code Case N-513-4, addresses the NRC condition in RG 1.147, Revision 18, for Code Case N-513-3; (2) flaw evaluations for branch tees are based on acceptable methodologies; and (3) the method for determining the allowable leakage rate is adequate to provide early identification of a significant increase in leakage.

The NRC staff concludes that complying with ASME Code,Section XI, requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

4.0 CONCLUSION

As set forth above, the NRC staff determined that the proposed alternative provides reasonable assurance of structural integrity of the subject branch tee, and that complying with ASME Code,Section XI, would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. 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, the NRC staff authorizes the use of the proposed alternative described in the licensee's application until the conclusion of the Unit 1 Fall 2018 refuleing outage (RF24 ), or until the temporary acceptance criteria of Code Case N-513-4 are exceeded, or until the leak rate exceeds 50.3 gallons per minute, whichever event occurs first.

All other requirements of the ASME Code,Section XI, for which relief has not been specifically requested and authorized by NRC staff remain applicable, including a third party review by the Authorized Nuclear In-service Inspector.

The NRC staff notes that approval of this alternative does not imply NRC approval of ASME Code Case N-513-4 for generic use.

Principal Contributor: Robert Davis, NRR Date: November 8, 2018

ML18296A111 OFFICE DORL/LPL2-1 /PM DORL/LPL2-1/LA NRR/DMLR/MPHB/BC*

NAME SWilliams KGoldstein SRuffin (KHoffman for)

DATE 10/29/18 10/24/18 10/15/18 OFFICE DORL/LPL2-1 /PM NAME SWilliams DATE 11/8/18