NLS2016076, 10 CFR 50.55a Request No. RR5-02 for Fifth Ten-Year Inservice Inspection Interval

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10 CFR 50.55a Request No. RR5-02 for Fifth Ten-Year Inservice Inspection Interval
ML16351A245
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Site: Cooper Entergy icon.png
Issue date: 12/14/2016
From: Limpias O
Nebraska Public Power District (NPPD)
To:
Document Control Desk, Office of Nuclear Reactor Regulation
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NLS2016076
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Nebraska Public Power District Always there w_hen you need us 10 CFR 50.55a NLS2016076 December 14, 2016 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001

Subject:

10 CFR 50.55a Request No. RR5-02 for Fifth Ten-Year Inservice Inspection Interval _

Cooper Nuclear Station, Docket No. 50-298, DPR-46

Dear Sir or Madam:

Pursuant to 10 CPR 50.55a(z)(2), Nebraska Public Power District requests relief from certain inservice inspection code requirements for Cooper Nuclear Station (CNS). This relief request is applicable to the fifth ten-year inservice inspection interval, which began April 1, 2016.

This request is associated with deferral of the repair of degraded Service Water piping. The details of the 10 CPR 50.55a request are contained in the attachment to this letter.

This request applies to wall thinning in Service Water piping that was discovered on September 13 and 15, 2016. Repairs were completed during the CNS fall 2016 refueling outage, thus restoring compliance with Code requirements on November 1, 2016. This request is being submitted to satisfy requirements of 10 CPR 50.55a for the time period the noncompliance existed. As the condition no longer exists, CNS has no specific deadline for approval.

This letter contains no commitments.

If you have any questions or require additional information, please contact Jim Shaw, Licensing Manager, at 402-825-2788.

""'""~<J\L-A. Limpias Vice President-Nuclear and Chief Nuclear officer

/lb COOPER NUCLEAR STATION P.O. Box 98 /Brownville, NE 68321*0098 Telephone: (402) 825-3811 /Fax: (402) 825-5211 www.nppd ..com

NLS2016076 Page 2 of2

Attachment:

10 CFR 50.55a Request No. RRS-02, Relief Request Associated with Deferral of Service Water System Repair cc: Regional Administrator w/attachment USNRC - Region IV Cooper Project Manager w/attachment USNRC- NRR Plant Licensing Branch IV Senior Resident Inspector w/attachment USNRC-CNS NPG Distribution w/attachment CNS Records w/attachment

NLS2016076 Attachment Page 1 of39 10 CFR 50.55a Request No. RRS-02 Relief Request Associated with Deferral of Service Water System Repair Proposed Alternative in Accordance with 10 CFR 50.55a(z)(2)

Hardship without a Compensating Increase in Quality and Safety

1. American Society of Mechanical Engineers (ASME) Code Components Affected ASME Section XI Code Class: 3 Examination Category: D-B Item Number: D2.10 Component Numbers:

Construction Code: USAS B31.1 - 1967 Design Pressure: 490 psig (Operating pressure assumed at the maximum design pressure)

Design Temperature: 145°F Piping Specification: 18 inch ferritic steel schedule 30, 0.437 inch nominal wall thickness

2. Applicable Code Edition and Addenda The applicable ASME Section XI Code Edition and Addenda for Cooper Nuclear Station (CNS) is the 2007 Edition, through 2008 Addenda. This fifth ten-year inservice inspection interval began April 1, 2016, and ends February 28, 2026.
3. Applicable Code Requirement In accordance with ASME Code Section XI, 2007 Edition, through 2008 Addenda, subparagraph IWD-3120(b) requires that existing flaws in ASME Code Class components which are unacceptable for continued service be subjected to supplemental examination, or to a repair/replacement activity and analytical evaluation, to the extent necessary to meet the acceptance standards in ASME Code

NLS2016076 Attachment Page 2 of39 Section XI, Article IWC-3000. In regard to the flaw analysis, IWD-3500, "Acceptance Standards" for Class 3 components, states that the requirements of IWC-3500, "Acceptance Standards" for Class 2 components, may be used.

Additionally, IWA-4000 describes the repair/replacement activities to correct an unacceptable flaw. Detection of a minimum wall thickness in the structural portion of an ASME Code Class 1, 2, or 3 component is direct evidence of a defect in the component.

The Code does not include analytical evaluation criteria for acceptance ofthrough-wall flaws in pressure retaining base material of ferritic pipe or fittings. Code Case N-513-3, "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1," which has been conditionally approved by the U.S. Nuclear Regulatory Commission (NRC) in Regulatory Guide 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," Revision 17, provides analytical evaluation rules for temporary acceptance of flaws in piping. Code Case N-513-3, however, does not apply to piping whose maximum operating pressure exceeds 275 psig.

Relief is requested so that code repair of the nonplanar flaws at these locations may be deferred until the conclusion of the CNS refueling outage (RE29) which was completed during the fall of 2016.

4. Reason for Request In accordance with the provisions of 10 CFR 50.55a(z)(2), Nebraska Public Power District (NPPD) is requesting an alternative from the requirement to perform repair/replacement activities for degraded RHRSW piping which has a maximum operating pressure in excess of 275 psig. Paragraph l(b) provision of Code Case N-513-3, "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1", prohibits its application to Class 2 or 3 piping whose maximum operating pressure exceeds 275 psig. The ASME Section XI Class 3 RHRSW piping at CNS has a maximum design pressure of 490 psig.

Operating pressure at these locations is conservatively assumed to be 490 psig for evaluation under this Code Case which assures that the degraded piping areas would have retained structural and leakage integrity until a permanent Code repair was completed.

Technical Specification 3.7.1, "Residual Heat Removal Service Water Booster (RHRSWB) System," Limiting Condition for Operation, requires "two RHRSWB subsystems shall be OPERABLE." Declaring one RHRSW subsystem inoperable would require the unit to shut down if the subsystem is not restored to operable status in 7 days. This would have required CNS to shut down on Tuesday, September 20, 2016, prior to the scheduled shutdown on Saturday, September 24, 2016.

NLS2016076 Attachment Page 3 of39 Without approval of this relief request, CNS would be required to enter MODE 3 resulting in undue hardship without a compensating increase in safety. Moving to a shutdown condition unnecessarily cycles the unit and increases the potential of an unnecessary transient which can be avoided through the use of the N-513-3 analysis.

No compensating increase in the level of quality and safety would be gained by immediate repair of the flaw. The RHRSW system continued to be capable of performing its required safety functions and is not susceptible to sudden or catastrophic failure.

The RHRSW system is a Technical Specification required system that is designed to provide an adequate supply of cooling water to the RHR system under all accident and transient conditions. The RHRSW system has sufficient capacity and redundancy so that no single active component failure can prevent the system from achieving its safety objective.

The RHRSW System consists of two mechanically and electrically independent loops each with two pumps taking suction from the station SW System headers and providing coolant to the RHR heat exchangers. Final discharge is to the circulating water discharge canal. Both loops are designed to Class I Seismic criteria. The RHRSW Booster Pumps are each rated 4000 gpm at 840 feet TDH, maintaining the SW side of the RHR exchangers at a higher pressure than the RHR System side to prevent out-leakage of_

radioactive water into the SW System.

Class: The RHRSW piping is classified as safety related, ASME Section XI Code Class 3, and of high energy (piping design rating of 490 psig@ 145°F).

Flaw Characterization and Root Cause Determination:

Component SW-Z4-2851-7 is defined as a straight section of piping downstream of support SW-H92 (see Figure 1). During ultrasonic thickness examinations of the component on September 13, 2016, four localized areas associated with this component were identified that are below the design minimum wall thickness, tmin of 0.255 inches.

The thinnest location identified (limiting) has a low of 0.127 inch and is contained within a localized area of 1 1/2 x 1 1/ 4 inches (see Enclosure 7.b.l).

NLS2016076 Attachment Page 4 of39

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Figure 1: Location of SW-Z4-2851-7 Component SW-E-3-2851-3 is defined as a 90-degree elbow with corresponding upstream and downstream pipe extensions near support SW-S51A (see Figure 2). During ultrasonic thickness examinations of the component on September 15, 2016, two localized areas were identified that are below the design tmin of 0.255 inches. The thinnest location identified has a low of 0.200 inches and is contained within a localized area of 1 1/4 x 1 inch (see Enclosure 7.b.2). Both thin areas are located in the straight run of piping downstream of the 90 degree elbow.

NLS2016076 Attachment Page 5 of39

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Figure 2: Location of SW-E-3-2851-3 Augmented Examination:

The nonplanar indications are a result of isolated pitting of carbon steel materials resulting from under deposit corrosion influenced by microbial activity and intermittent flow in raw water piping and is independent of operating pressure. Such corrosion indications are limited to localized areas under these conditions at CNS and do not manifest in general thinning, cracking, or other prompt structural failure precursors.

The RHRSW system is a portion of the SW system and CNS operating experience has shown that this damage mechanism occurs throughout the entire SW system.

This known damage mechanism is independent of system operating pressure. CNS monitors this damage mechanism by selecting a sample based on operating experience and previous inspections. Prior to RE29, CNS selected eighteen (18) other SW components that could be credited in meeting the Augmented Examination

NLS2016076 Attachment Page 6 of39 requirements of Section 5 of Code Case N-513-3. During RE29, five (5) additional locations were examined in the RHRSW with no areas below required thickness requirements.

5. Proposed Alternative and Basis for Use NPPD is requesting approval to apply the evaluation methods of 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," to the RHRSW system piping having a maximum operating pressure of 490 psig in order to avoid accruing additional personnel radiation exposure and increased plant risk associated with an early plant shutdown to comply with the cited Code requirements.

The NRC issued Generic Letter 90-05, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping (Generic Letter 90-05)," to address the acceptability of limited degradation in Moderate Energy Piping. The generic letter defines conditions that would be acceptable to utilize temporary non-code repairs with NRC approval. The ASME recognized that relatively small flaws could remain in service without risk to the structural integrity of a piping system and developed Code Case N-513. The Generic Letter 90-05 moderate energy limitations of200°F and 275 psig were retained in the Code Case to maintain consistency with service conditions previously acceptable to the NRC as defined in Generic Letter 90-05. NRC approval of Code Case N-513 versions in Regulatory Guide 1.147, "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1," allows acceptance of partial through-wall or through-wall leaks for an operating cycle provided all conditions of the Code Case and NRC conditions are met.

Code Case N-513-3 provides analytical methods to be used for evaluating degraded piping conditions for determining structural integrity. The analytical methods provided in the Code Case are based on ASME Section XI, Appendix C, "Evaluation of Flaws in Piping," with supplemental guidance given in the Code Case specific to through-wall flaws. Linear Elastic Fracture Mechanics principles for evaluation of flaws in ferritic piping are normally employed. The ASME Section XI piping flaw evaluation methods do not place pressure or temperature limits for evaluating flaws in piping. The Code Case also allows evaluation by the branch reinforcement approach to allow evaluation of nonplanar through-wall flaws. The Code Case analytical methods account for flaw length, depth, pipe material toughness, applied stresses, and use of safety factors. These a

analytical methods do not have technical basis for limiting use to 275 psig, and would, in fact, be technically appropriate without a pressure limitation.

CNS conducted a Code Case N-513-3 evaluation of the thinned areas to demonstrate structural stability by using the higher design pressure (see Enclosure 7.a). The evaluation concluded the most limiting allowable flaw length is 2.2 inches in the axial direction and 3 .9 inches in the circumferential direction. The conservatively characterized through-wall flaw is 1.5 inches in the axial and circumferential directions.

NLS2016076 Attachment Page 7 of39 Since the allowable flaw size is larger than the conservatively characterized flaw, the structural evaluation of Code Case N-513-3 was met.

In conclusion, all flaws meet the N-513-3 separation requirements and are evaluated independently. The evaluation in accordance with ASME Section XI Code Case N-513-3 demonstrates that the allowable through-wall flaw lengths bound the conservatively characterized flaws.

6. Duration of Proposed Alternative NPPD requests approval of this relief request for the duration of time from identification of the initial nonplanar flaw (September 13, 2016) until the repairs were completed during the fall 2016 refueling outage (November 1, 2016). The CNS fall 2016 refueling outage started on September 24, 2016, and ended on November 8, 2016.
7. Enclosures
a. Engineering Report 2016-53, Revision 0, Review of SIA Calculation 1601004.301, Cooper High Pressure RHRSW Thinning Evaluation per Code Case N-513-3, Revision 0
b. Examination Data Sheets:

(1) SW-Z4-2851-7 (2) SW-E-3-2851-3

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