ML19140A473

Relief Request (RR-4-23) to Utilize Code Case N-513-4

ML19140A473
Person / Time
Site:	Summer
Issue date:	06/04/2019
From:	Markley M Plant Licensing Branch II
To:	Lippard G South Carolina Electric & Gas Co
Williams S, NRR/DORL/LPLLPL
References
EPID L-2019-LLR-0034
Download: ML19140A473 (11)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 June 4, 2019 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-4-23) TO UTILIZE CODE CASE N-513-4 (EPID L-2019-LLR-0034)

Dear Mr. Lippard:

By letter dated April 30, 2019, the South Carolina Electric & Gas Company (SCE&G, the licensee) requested approval from the U.S. Nuclear Regulatory Commission (NRC) for relief from certain requirements of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI, at Virgil C. Summer Nuclear Station (Summer), Unit 1.

SCE&G requested authorization to use the alternative 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" to Class 2 and 3 moderate energy piping in lieu of specified ASME Code requirements.

The licensee submitted the proposed alternative pursuant to Title 1O 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.

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 NRC staff authorizes the use of the licensee's proposed alternative request RR-4-23 for Summer, Unit 1, for the remainder of the fourth 10-year ISi interval, scheduled to end December 31, 2023, or until such time as the NRC approves Code Case N-513-4 for general use through revision of NRC Regulatory Guide 1.147 "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1." If the proposed alternative is applied to a flaw near the end of the authorized fourth 10-year ISi interval, and the next refueling outage is in the subsequent interval, the licensee is authorized to continue to apply the proposed alternative to the flaw until the next refueling outage.

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

G. Lippard 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.

Sincerely, Michael T. Markley, Chief Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-395

Enclosure:

Safety Evaluation cc: Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST RR-4-23 USE OF ASME CODE CASE N-513-4 RENEWED FACILITY OPERATING LICENSE NO. NPF-12 SOUTH CAROLINA ELECTRIC & GAS COMPANY VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1 DOCKET NO. 50-395

1.0 INTRODUCTION

By letter dated April 30, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19120A514), the South Carolina Electric & Gas Company (SCE&G, the licensee) requested approval from the U.S. Nuclear Regulatory Commission (NRC) for relief from certain requirements of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI, at Virgil C. Summer Nuclear Station (Summer), Unit 1.

SCE&G requested authorization to use the alternative 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" to Class 2 and 3 moderate energy piping in lieu of specified ASME Code requirements.

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.

2.0 REGULATORY EVALUATION

The licensee proposes an alternative to the requirement of ASME Code, Section XI, Articles IWC-3000 and IWD-3000.

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 Enclosure

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 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-513-3 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 components are ASME Code Class 2 and 3 moderate energy piping systems, as described in Code Case N-513-4, paragraphs 1(a), 1(b), 1(c), and 1(d), whose maximum operating temperature does not exceed 200 degrees Fahrenheit (°F) and whose operating pressure does not exceed 275 pounds per square inch gauge (psig).

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

3.1.3 Applicable Code Requirement For ASME Code Class 2 components, Subarticles IWC-3120 and IWC-3130 of ASME Code, Section XI, require that flaws exceeding the specified acceptance standards be corrected by repair or replacement activities or determined to be acceptable by analytical evaluation. For ASME Code Class 3 components, Paragraph IWD-3120(b) of ASME Code, Section XI, requires that components containing flaws exceeding the acceptance standards of IWD-3400 be subject to supplemental examination, or to a repair or replacement activity.

3.1.4 Reason for Request The licensee stated that performing an ASME Code repair of moderately degraded piping could require a plant shutdown within the required technical specification action statement timeframes.

In addition, the licensee stated that plant shutdown activities result in additional radiological dose and plant risk that would be inappropriate when a degraded condition is demonstrated to retain adequate margin to complete the component's function. 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.

The licensee's proposed alternative, to use Code Case N-513-4, would allow temporary acceptance of flaws in components currently not addressed in Code Case N-513-3, such as elbows, bent pipe, reducers, expanders, branch tees, and heat exchanger tubing.

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 flaws, including through-wall flaws, in moderate energy Class 2 and 3 piping in lieu of specified ASME Code, Section XI requirements. The licensee's proposed alternative permits the temporary acceptance of flaws, meeting the requirements of the code case, until the next scheduled refueling outage or prior to exceeding the allowable flaw size (whichever comes first), at which time an ASME Code, Section XI compliant repair or replacement will be completed. In addition, the licensee's proposed alternative includes the determination of an allowable leakage rate by dividing the critical leakage rate by a safety factor of four.

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, listed below:

1. Revised the maximum allowed 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. Other minor editorial changes to improve the clarity of the Code Case.

The licensee referenced technical basis document, "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. [This document is copyrighted and submitted to the NRC as part of another licensee's alternative to use Code Case N-513-4 (ADAMS Accession No. ML16029A003)].

The licensee stated that the effects of leakage may impact the operability determination or the plant flooding analyses specified in paragraph 1(f) of Code Case N-513-4. For a leaking flaw, the licensee will determine the allowable leakage rate by dividing the critical leakage rate by a safety factor of four (4). The critical leakage rate is determined as the lowest leakage rate that can be tolerated with respect to loss of inventory, room flooding, and other effects of leakage on operability. The licensee contends that the proposed allowable leakage rate provides quantitative measurable limits, which ensure the operability of the system and early identification of issues that could erode defense-in-depth and lead to adverse consequences.

The licensee stated that Code Case N-513-4 utilizes technical evaluation approaches that are based on principals that are accepted in other Code documents already acceptable to the NRC. The licensee contends that the application of Code Case N-513-4, in concert with safety factors on leakage limits, will maintain acceptable structural and leakage integrity while minimizing plant risk and personnel exposure by minimizing the number of plant transients that could be incurred if degradation is required to be repaired based on ASME Section XI acceptance criteria only.

3.1.6 Hardship Justification The licensee stated that performing an ASME Code repair of moderately degraded piping could require a plant shutdown within the required technical specification action statement timeframes. Plant shutdown activities result in additional radiological dose and plant risk that would be inappropriate when degraded piping is demonstrated to retain adequate margin to complete the piping's function. The licensee stated that the use of an acceptable alternative analysis method in lieu of immediate action for a degraded condition will allow it to perform additional extent of condition examinations on the affected piping while allowing time for safe and orderly long-term repair actions if necessary. Actions to remove degraded piping from service could have a detrimental overall risk impact by requiring a plant shutdown, thus requiring use of a system that is in standby during normal operation. 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. 7 Duration of Proposed Alternative The licensee requested use of the proposed alternative for the reminder of the fourth 10-year ISi interval, or until the NRC approves Code Case N-513-4 in Regulatory Guide (RG), RG 1.147 or other document. The licensee stated that when using its proposed alternative, a Section XI compliant repair or replacement will be completed prior to exceeding the next refueling outage or the allowable flaw size, whichever comes first. The licensee will also apply a maximum allowable leakage rate as part of the proposed alternative. The licensee stated that if a flaw is

evaluated near the end of an ISi interval, and the next refueling outage is in the subsequent interval, the flaw may remain in service until the next refueling outage.

3.2 NRC Staff Evaluation The NRC staff evaluated the adequacy of the proposed alternative in maintaining the structural integrity of piping components identified in Code Case N-513-4. Code Case N-513-3, which is conditionally approved for use in RG 1.147, 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 contains limitations that the licensee considers restrictive and could result in an ASME Code repair that leads to an unnecessary plant shutdown. Code Case N-513-3 is limited to straight pipe with provisions for flaws that extend for a short distance, at the pipe to fitting weld, into the fitting. Evaluation criteria for flaws in elbows, bent pipe, reducers, expanders, branch tees and heat exchangers are not included within the scope of N-513-3.

Code Case N-513-4 addresses these aforementioned limitations. Given that Code Case N-513-3 is conditionally approved for use in RG 1.147, Revision 18, the staff focused its review on the differences between Code Case N-513-3 and N-513-4. The significant changes in N-513-4 include: (1) revised temporary acceptance period; (2) added flaw evaluation criteria for elbows, bent pipe, reducers/expanders and branch tees; (3) expanded applicability to heat exchanger tubing or piping; (4) limited use to liquid systems; (5) clarified treatment of service load combinations; (6) revised treatment of flaws in austenitic pipe flux welds; (7) revised minimum wall thickness acceptance criteria to consider longitudinal stress in addition to hoop stress; and (8) revised leakage monitoring requirements. The NRC staff also evaluated the licensee's proposed limitation on the leakage rate and its hardship justification.

The NRC staff notes that many requirements specified in Code Case N-513-4 are not discussed in this safety evaluation, but they should not be considered as less important. As part of the NRG-approved proposed alternative, all requirements in the Code Case must be followed. Any exceptions or restrictions to the Code Case that are approved in this safety evaluation also need to be followed.

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. The NRC staff finds that Code Case N-513-4 appropriately addresses the NRC condition on Code Case N-513-3, and is, therefore, 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. The flaw evaluation 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.

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 determined that the flaw evaluation criteria in Code Case N-513-4 for straight or bent piping, as appropriate, can be applied to heat exchanger external tubing or piping. The staff determined the methods for evaluating flaws in straight pipe are acceptable since they are currently allowed in Code Case N-513-3. For bent pipe, the acceptability is described in Section 3.2.2 above. Therefore, the NRC staff finds inclusion of heat exchanger external tubing or piping in the code case to be acceptable because only heat exchanger tubing flaws that are accessible for characterization and leakage monitoring may be evaluated in accordance with the code case and the code case provides acceptable methods for the evaluation of flaws.

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 this change acceptable since Code Case N-513 is not intended to apply to air or other compressible fluid systems.

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.

3.2.6 Treatment of Flaws in Austenitic Pipe Flux Welds Paragraph 3.1(b) of N-513-4 contains modifications which include a reference to ASME Code Section XI, Appendix C, C-6320, to address flaws in austenitic stainless-steel pipe flux welds.

The ASME Code, Section XI, Appendix C, C-6000 permits the use of elastic plastic fracture mechanics criteria in lieu of limit load criteria to analyze flaws in stainless steel pipe flux welds.

Equation 1 of the code case was also revised to be consistent with ASME Code, Section XI, Appendix C, C-6320, so the equation can be used for flaws in austenitic stainless-steel pipe flux

welds. The NRC staff finds this acceptable because Code Case N-513-4 includes the appropriate methods for the evaluation of stainless steel pipe flux welds in accordance with ASME Code, Section XI.

3.2. 7 Minimum Wall Thickness Acceptance Criteria to Consider Longitudinal Stress Although it is unlikely that a longitudinal stress based minimum wall thickness would be limiting when compared to a hoop stress based minimum wall thickness, 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.

3.2.8 Leakage Monitoring for Through-Wall Flaws Code Case N-513-3 required through-wall leakage to be observed by 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 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 inspected every 30 days.

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."

In its application, the licensee stated that the allowable leakage rate will be determined by dividing the critical leakage rate by a safety factor of four. The licensee contends that applying a safety factor of four to the critical leakage rate provides quantitative measurable limits which ensure the operability of the system and early identification of issues that could erode defense-in-depth and lead to adverse consequences.

Code Cases N-513-3 and N-513-4 do not contain leakage limits for components with through-wall flaws. The NRC staff finds that the licensee's approach of applying a safety factor of four to the critical 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 would unnecessarily cycle the units, resulting in an increase in personnel exposure and plant risk.

Additionally, performing certain ASME Code repairs during normal operation may challenge a Technical Specification Completion Time and place the plant at higher safety risk than warranted. Therefore, the NRC staff determines 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 Summary The NRC staff finds that the proposed alternative will provide reasonable assurance of the structural integrity because: (1) Code Case N-513, Revision 4 addresses the NRC condition in RG 1.147, Revision 18, for Code Case N-513-3; (2) flaw evaluations in component types added to Revision 4 of Code Case N-513 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. In addition, 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 RR-4-23 provides reasonable assurance of structural integrity of the subject piping segments, and that complying with IWC-3120, IWC-3130, IWD-3120(b), and IWD-3400 of the 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 licensee's proposed alternative request RR-4-23, to use ASME Code Case N-513-4 at Summer, Unit 1, for the remainder of the fourth 10-year ISi interval, scheduled to end December 31, 2023, or until such time as the NRC approves Code Case N-513-4 for general use through revision of NRC RG 1.147. If the proposed alternative is applied to a flaw near the end of the authorized fourth 10-year ISi interval, and the next refueling outage is in the subsequent interval, the licensee is authorized to continue to apply the proposed alternative to the flaw until the next refueling outage.

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

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.

Principal Contributor: Robert Davis, NRR Da~: June 4, 2019

G. Lippard

SUBJECT:

VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1 - RELIEF REQUEST (RR-4-23) TO UTILIZE CODE CASE N-513-4 (EPID L-2019-LLR-0034)

DATED JUNE 4, 2019 DISTRIBUTION:

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NAME SWilliams KGoldstein SCumblidQe DATE 05/30/19 05/29/19 05/24/19 OFFICE DORL/LPL2-1/BC DORL/LPL2-1/PM NAME MMarkley SWilliams DATE 06/04/19 06/04/19 OFFICIAL RECORD COPY