ML19291A018

Request for Relief I4R-07, Utilize Code Case N-513-4 - Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping of American Society of Mechanical Engineers Boiler and Pressure Code Section XI

ML19291A018
Person / Time
Site:	Wolf Creek
Issue date:	11/12/2019
From:	Jennifer Dixon-Herrity Plant Licensing Branch IV
To:	Reasoner C Wolf Creek
Singal B, NRR/DORL/LPL4-1
References
EPID L-2019-LLR-0075
Download: ML19291A018 (10)

Text

November 12, 2019 Mr. Cleveland Reasoner Chief Executive Officer and Chief Nuclear Officer Wolf Creek Nuclear Operating Corporation P.O. Box 411 Burlington, KS 66839

SUBJECT:

WOLF CREEK GENERATING STATION, UNIT 1 - REQUEST FOR RELIEF I4R-07 TO UTILIZE CODE CASE N-513-4, EVALUATION CRITERIA FOR TEMPORARY ACCEPTANCE OF FLAWS IN MODERATE ENERGY CLASS 2 OR 3 PIPING, SECTION XI, DIVISION 1, OF AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE (EPID L-2019-LLR-0075)

Dear Mr. Reasoner:

By letter dated August 15, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19232A139), Wolf Creek Nuclear Operating Corporation (licensee) submitted Relief Request I4R-07 for the fourth inservice inspection (ISI) interval of Wolf Creek Generating Station, Unit 1 (Wolf Creek). The licensee requested approval of a proposed alternative to the repair/replacement requirements in American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Rules for lnservice Inspection of Nuclear Power Plant Components. Specifically, the licensee proposed to apply the flaw evaluation methods of ASME 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 temporary acceptance of flaws. Pursuant to paragraph (z)(2) of Title 10 of Code of Federal Regulations (10 CFR) 50.55a, the licensee proposed the alternative in order to avoid additional radiation exposure and increased plant risk associated with a plant shutdown to comply with the ASME Code requirements. The licensee indicated that compliance with the ASME Code requirements results in hardship without a compensating increase in the level of quality and safety.

The NRC staff has reviewed the subject request and determines, as set forth in the enclosed safety evaluation, that the proposed alternative provides reasonable assurance of the integrity of the subject components and that complying with the applicable ASME Code,Section XI requirements 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) for the remainder of the fourth ISI interval. Therefore, the NRC staff authorizes the use of the proposed alternative at Wolf Creek for the remainder of the fourth ISI interval or until such time as the NRC approves Code Case N-513-4 in Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, or other document, whichever completes sooner.

C. Reasoner All other requirements of ASME Code,Section XI, for which relief has not been specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector.

If you have any questions concerning this matter, please contact the Project Manager, Mr. Balwant K. Singal at 301-415-3016 or via e-mail at Balwant.Singal@nrc.gov.

Sincerely,

/RA/

Jennifer L. Dixon-Herrity, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-482 Enclosure Safety Evaluation cc: Listserv

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF I4R-07 FOR USE OF CODE CASE N-513-4 WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STATION, UNIT 1 DOCKET NO. 50-482

1.0 INTRODUCTION

By letter dated August 15, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19232A139), Wolf Creek Nuclear Operating Corporation (the licensee) submitted Relief Request I4R-07 for the fourth inservice inspection (ISI) interval of Wolf Creek Generating Station, Unit 1 (Wolf Creek). The licensee requested approval of a proposed alternative to the repair/replacement requirements in American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Rules for lnservice Inspection of Nuclear Power Plant Components. Specifically, the licensee proposed to apply the flaw evaluation methods of ASME 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 temporary acceptance of flaws.

Pursuant to paragraph (z)(2) of Title 10 of Code of Federal Regulations (10 CFR) 50.55a, the licensee proposed the alternative in order to avoid additional radiation exposure and increased plant risk associated with a plant shutdown to comply with the ASME Code requirements. The licensee indicated that compliance with the ASME Code requirements results in hardship without a compensating increase in the level of quality and safety.

2.0 REGULATORY EVALUATION

The regulation under 10 CFR 50.55a(g)(4) requires that ASME Code Class 1, 2 and 3 components meet the ISI requirements, except the design and access provisions, set forth in Section XI of editions and addenda of the ASME Code, to the extent practical within the limitations of design, geometry, and materials of construction of the components.

The regulation under 10 CFR 50.55a(z)(2) states, in part, that alternatives to the requirements of 10 CFR 50.55a(g) may be used when authorized by the U.S. Nuclear Regulatory Commission (NRC), if the licensee demonstrates 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 proposed an alternative to the requirements of ASME Code,Section XI, Articles IWC-3000 and IWD-3000 due to a hardship without a compensating increase in the level of quality and safety.

Enclosure

Based on the foregoing discussion and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request the use of an alternative and the NRC to authorize the proposed alternative.

3.0 TECHNICAL EVALUATION

3.1 ASME Code Components Affected

The affected components are the ASME Code Class 2 and 3 components within the scope of Code Case N-513-4. The subject components are moderate energy Class 2 or 3 components in liquid systems, which have a maximum operating temperature not exceeding 200 degrees Fahrenheit (F) and a maximum operating pressure not exceeding 275 pounds per square in gauge (psig).

3.2 Applicable ASME Code Edition and Addenda The applicable ASME Code edition and addenda for the fourth ISI interval of Wolf Creek is the 2007 Edition with the 2008 Addenda of the ASME Code,Section XI.

3.3 Applicable Code Requirements For Class 2 components, ASME Code,Section XI, IWC-3120 and IWC-3130 require that flaws exceeding the specified acceptance criteria be corrected by repair/replacement activities or evaluated for continued service by analytical evaluation. For Class 3 components, ASME Code Section XI, Subsection IWD-3120(b), requires that components exceeding the acceptance standards of IWD-3400 be subject to supplemental examination or a repair/replacement activity.

3.4 Reason for Request The licensee stated that ASME Code Case N-513-3, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1, does not allow evaluation of flaws located away from attaching circumferential piping welds that are in elbows, bent pipe, reducers, expanders, and branch tees. Code Case N-513-3 does not allow evaluation of flaws located in heat exchanger external tubing or piping. Code Case N-513-4 provides guidance for evaluation of flaws in these locations. Moderately degraded piping could require a plant shutdown within the required action statement timeframes to repair observed degradation. The licensee stated that plant shutdown activities result in additional dose and plant risk that would be inappropriate when a degraded condition is demonstrated to retain adequate margin to complete the component's function.

As discussed above, the licensees determination of hardship and level of quality and safety considered radiological dose and plant safety concerns and acceptable alternative flaw evaluation methods described in Code Case N-513-4 for temporary acceptance of flaws in the subject Class 2 and 3 components.

3.5 Proposed Alternative and its Basis The licensee proposed to use the methods in Code Case N-513-4 for moderate energy Class 2 or 3 components as an alternative to the ASME Code requirements for flaw evaluations and repair/replacement activities. The proposed alternative request intends to use the Code Case provisions for temporary acceptance of flaws in the subject components. The licensees request

also intends to avoid additional personnel radiation exposures and increases in plant risk associated with a plant shutdown to comply with the Code requirements. The licensees basis for the proposed alternative is further summarized below.

NRC has approved different versions of Code Case N-513 as described in Regulatory Guide (RG) 1.147, Revision 18, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, March 2017 (ADAMS Accession No. ML16321A336). The latest version of Code Case N-513-3 listed in RG 1.147, Revision 18, is Code Case N-513-3. Code Case N-513-3, as conditioned in RG 1.147, allows temporary acceptance of partial through-wall or through-wall leaks, at maximum, until the next refueling outage. Code Case N-513-3, in part, requires a licensee to demonstrate system operability considering the effects of leakage.

Limitations in Code Case N-513-3, related to its use on piping components such as elbows, bent pipe, reducers, expanders, and 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 Code Case N-513-4 changes, as follows:

Revised the maximum allowed time of temporary use from no longer than 26 months to the next scheduled refueling outage Added applicability to piping elbows, bent pipe, reducers, expanders, and branch tees Expanded use to external tubing or piping attached to heat exchangers Revised to limit the use to liquid systems Revised to clarify treatment of service level load combinations Revised to address treatment of flaws in austenitic pipe flux welds Revised to require minimum wall thickness acceptance criteria to consider longitudinal stress in addition to hoop stress Other minor editorial changes to improve the clarity of the Code Case Code Case N-513-4 utilizes flaw evaluation approaches based on principals that are accepted in other ASME Code documents already acceptable to the NRC. The application of this Code Case will maintain acceptable structural integrity while minimizing personnel radiation exposure and plant risk by minimizing the number of plant transients that could be incurred if degradation is required to be evaluated and repaired only based on ASME Code,Section XI, criteria.

3.6 Duration of the Proposed Alternative The duration of the proposed alternative is for the fourth lSI interval (scheduled to end on September 2, 2025) or until the NRC approves Code Case N-513-4 in RG 1.147 or another document, whichever completes sooner. The NRC staff noted that the fourth ISI interval has already started in 2015. Since 10 CFR 50.55a(z) specifies that NRC approval is necessary prior to implementation of a proposed alternative, the NRC staffs review of the licensees request is focused on the use of Code Case N-513-4 for the remainder of the fourth ISI interval.

3.7 NRC Staff Evaluation RG 1.147 identifies ASME Code,Section XI Code Cases that are acceptable to the NRC staff with conditions as necessary. The current revision of RG 1.147, Revision 18, as of August 2019, addresses the NRC staffs acceptance of Code Case N-513-3 with a condition that the repair or replacement activity temporarily deferred under the provisions of the Code Case shall be performed during the next scheduled outage.

Code Case N-513-4 has adequately addressed this condition in paragraph 2(h) of the Code Case. Therefore, such condition is not necessary for Code Case N-513-4. Specifically, the procedure in Code Case N-513-4, paragraph 2(h) specifies that the deferred repair/replacement activities shall not be performed later than the next refueling outage.

In August 2018, the NRC staff issued Draft Regulatory Guide DG-1342, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, as proposed RG 1.147, Revision 19 (ADAMS Accession No. ML18114A225). The NRCs intent to incorporate by reference RG 1.147, Revision 19, is documented in Approval of American Society of Mechanical Engineers Code Cases, published in the Federal Register on August 16, 2018 (83 FR 40685; August 16, 2018).

Table 1 of the proposed RG 1.147 (Revision 19) identifies Code Case N-513-4 as an acceptable Code Case with no condition. Even though the proposed RG has not been published as a final RG as of the NRCs review of this request, the use of Code Case N-513-4 is aligned with the NRC-proposed RG 1.147, Revision 19.

The NRC staffs evaluation of the changes from Code Case N-513-3 to Code Case N-513-4 is further documented below. The NRC staff notes that PVP2014-28355, Technical Basis for Proposed Fourth Revision to ASME Code Case N-513, Proceedings of the ASME 2014 Pressure Vessels & Piping Conference, discusses the changes between Code Case N-513-3 and Code Case N-513-4 and the associated technical basis. The evaluation described below does not constitute a generic approval for use of Code Case N-513-4.

3.7.1 Temporary Acceptance Period As discussed in Section 3.7 of this safety evaluation, the maximum temporary acceptance period for flaws was changed from 26 months to until the next scheduled refueling outage. This change adequately addresses the condition on Code Case N-513-3 that is imposed in RG 1.147, Revision 18, and is therefore acceptable.

3.7.2 Expanded Criteria for Flaw Evaluations Additional flaw evaluation and acceptance criteria are added to Code Case N-513-4 to address flaws in elbows, bent pipe, reducers, expanders and branch tees. The flaw evaluations for non-straight piping components are conducted based on the methodology for straight pipes.

The evaluations also use the hoop and axial stresses as scaled with stress indices and stress intensification factors. The use of the stress indices and intensification factors is to account for the effect of non-straight geometric configurations (e.g., those of elbows and branch tees) on the stresses and structural integrity. The equations used in Code Case N-514-3 are also consistent with the design-by-rule approach for piping in ASME Code,Section III, Subsection NC/ND-3600.

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 are consistent with the design-by-rule approach in ASME Code,Section III and are, therefore, acceptable.

3.7.3 Flaw Evaluation in Heat Exchanger Tubing or Piping Code Case N-513-4 is revised to include heat exchanger external tubing or piping if the flaw is characterized in accordance with paragraph 2(a) of the Code Case and leakage is monitored.

Paragraph 2(a) requires that the flaw geometry be characterized by volumetric inspection or physical measurement.

The methods for evaluating flaws in straight pipes are allowed in Code Case N-513-3. For bent pipes, the acceptability of the flaw evaluation methods is described in Section 3.7.2 above. The NRC staff finds that the flaw evaluation criteria in Code Case N-513-4 for straight or bent piping, as appropriate, can be applied to the external tubing or piping of heat exchangers.

3.7.4 Limited Use to Liquid Systems Use of Code Case N-513-4 is specifically limited to liquid systems. The NRC staff finds this change adequate since Code Case N-513-4 is not intended to apply to air or other compressible fluid systems.

3.7.5 Treatment of Service Load Combinations Code Case N-513-4 clarifies that all service load combinations must be considered in flaw evaluations to determine the most limiting condition although Code Case N-513-3 previously implied the same approach. Therefore, the NRC staff finds this clarification adequate.

3.7.6 Treatment of Flaws in Austenitic Pipe Flux Welds Paragraph 3.1(b) of Code Case 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. The NRC staff finds this acceptable because it is consistent with the ASME Code sections referenced above.

3.7.7 Minimum Wall Thickness Acceptance Criteria Considering Axial Stresses Previous versions of the Code Case only required the use of hoop stresses. Although it is unlikely that the minimum wall thickness based on axial stresses would be more limiting than that based on hoop stresses, Code Case N-513-4 requires consideration of axial stresses in the calculation of minimum wall thickness. The NRC staff finds this change acceptable because the revised approach is more conservative.

3.7.8 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 flaw evaluation remain valid. In comparison, Code Case N-513-4 continues to require that leakage be monitored daily, but also allows other

monitoring techniques to be used such as visual equipment or leakage detection systems. The NRC staff finds this change acceptable because the other allowed techniques are as effective as daily walkdowns. The Code Case continues to require through-wall leaks to be monitored on a daily basis and inspected at least every 30 days.

3.7.9 Consideration of Leakage Effects in the Operability Determination Paragraph 1(d) of Code Case N-513-3 states it is the responsibility of the [plant] owner to demonstrate system operability considering effects of leakage. Code Case N-513-4 slightly modified the last sentence, as located in paragraph (f), to state that it is the responsibility of the owner to consider effects of leakage in demonstrating system operability and performing plant flooding analyses. The NRC staff finds that Code Case N-513-4 adequately clarifies the licensees responsibility to ensure that the effect of leakage is properly considered in the system operability determination and plant flooding analyses.

3.7.10 Hardship Justification The licensee identified personnel radiological dose and plant safety concerns as the basis for hardship associated with the ASME Code requirements. Specifically, the licensee indicated that plant shutdown activities for Code-required repair/replacement activities would result in additional personnel dose and plant risk. The licensee also explained that the removal of a degraded component from service could have a detrimental overall risk impact since these actions may require the plant shutdown, use of a system in standby during normal operation and additional plant transients.

The NRC staff finds that a plant shutdown to repair/replace the degraded component during an operating cycle can increase the radiological dose and plant risk without an increase in safety and therefore the licensee adequately identified the hardship associated with the ASME Code requirements for repair/replacement activities without temporary acceptance of flaws.

3.8 Summary The NRC staff finds that the proposed alternative provides reasonable assurance of the structural integrity for the subject Class 2 and 3 components 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 in the components added to Code Case N-513-4 are based on acceptable methodologies; and (3) leakage monitoring performed on a daily basis is adequate to provide early identification of a significant increase in leakage. In addition, compliance 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

The NRC staff determines that the proposed alternative provides reasonable assurance of the integrity of the subject components and that complying with the applicable ASME Code Section XI requirement 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) for the remainder of the fourth ISI interval. Therefore, the NRC staff authorizes the use of the proposed alternative at Wolf Creek for the remainder of the fourth lSI

interval or until such time as the NRC approves Code Case N-513-4 in RG 1.147 or other document, whichever completes sooner.

Since 10 CFR 50.55a(z) specifies that NRC approval is necessary prior to implementation of a proposed alternative, the NRC staffs review of the licensees request is focused on the use of Code Case N-513-4 for the remainder of the fourth ISI interval only.

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 Inservice Inspector.

Principal Contributor: S. Min, NRR/DNRL/NPHB Date: November 12, 2019

ML19291A018 **via email *Memo dated OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA** NRR/DNRL/NPHP/BC(A)* NRR/DORL/LPL4/BC NAME BSingal PBlechman (JBurkhardt for) ABuford JDixon-Herrity DATE 11/5/19 10/31/19 10/15/19 11/12/19