ML12313A111

Relief Request RI-07 from ASME Code Requirements for Residual Heat Removal Shell Circumferential and Nozzle to Head Welds, Fourth 4th 10-Year Inservice Inspection Interval

ML12313A111
Person / Time
Site:	Cooper
Issue date:	01/22/2013
From:	Lynnea Wilkins, Markley M Plant Licensing Branch IV
To:	Limpias O Nebraska Public Power District (NPPD)
Wilkins L
References
TAC ME7875
Download: ML12313A111 (8)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 January 22, 2013 Mr. Oscar A Limpias Vice President-Nuclear and CNO Nebraska Public Power District 72676 648A Avenue Brownville, NE 68321

SUBJECT:

COOPER NUCLEAR STATION - RELIEF REQUEST NO. RI-07 FOR THE FOURTH 10-YEAR INSERVICE INSPECTION INTERVAL REGARDING WELD EXAMINATIONS (TAC NO. ME7875)

Dear Mr. Limpias:

By letter dated January 16, 2012, as supplemented by letter dated June 22,2012 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML12023A005 and ML12181A195, respectively), Nebraska Public Power District (NPPD, the licensee), submitted Relief Request RI-07 to the Nuclear Regulatory Commission (NRC). Request RI-07 is applicable to the fourth 1O-year inservice inspection (lSI) interval at the Cooper Nuclear Station (CNS). Approval of this request would allow the licensee to achieve less than the examination coverage required by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) for the residual heat removal (RHR) heat exchanger shell to distributor ring-end top weld RHR-CA-2A and nozzle-to-head top weld RHR-CB-1A. Both of these weld examinations fall under the requirements of the 2001 Edition of the ASME Code with 2003 Addenda.

Specifically, pursuant to paragraph 50.55a{g)(5)(iii) of Title 10 of the Code of Federal Regulations (10CFR), the licensee requested to use the proposed alternative in RI-07 on the basis compliance with the code requirements is impractical for CNS.

The NRC staff has reviewed the licensee's submittal, as supplemented. Pursuant to 10 CFR 50.55a(g)(6)(i), the NRC grants the licensee's request for relief for the CNS's fourth 10-year lSI interval, which ends on February 29,2016. The NRC staff has determined that granting RI-07 is authorized by law and will not endanger life, or property, or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed All other ASME Code,Section XI, requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

O. Limpias - 2 The detailed results of the NRC staff review are provided in the enclosed safety evaluation. If you have any questions concerning this matter, please contact Ms. L Wilkins of my staff at (301) 415-1377 or via e-mail at Lynnea.Wilkins@nrc.gov.

Sincerely,

),J~ j ---c ~'"U'(r Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-298

Enclosure:

As stated cc w/encl: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FOURTH 10-YEAR INSERVICE INSPECTION INTERVAL REQUEST FOR RELIEF NO. RI-07 NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION DOCKET NO. SO-298

1.0 INTRODUCTION

By letter dated January 16, 2012, as supplemented by letter dated June 22, 2012 (Agencywide Documents Access and Management System (as stated by the licensee) ML 12023AOOS and ML 12181A19S, respectively), Nebraska Public Power District (NPPD, the licensee), submitted Relief Request RI-07 to the Nuclear Regulatory Commission (NRC). Relief Request RI-07 is applicable to the fourth 10-year inservice inspection (lSI) interval at the Cooper Nuclear Station (CNS). Approval of this request would allow the licensee to achieve less than the examination coverage required by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) for the residual heat removal (RHR) heat exchanger shell-to distributor ring end top weld RHR-CA-2A and nozzle-to-head top weld RHR-CB-1A. Both of these weld examinations fall under the requirements of the 2001 Edition of the ASME Code with 2003 Addenda.

Specifically, pursuant to paragraph SO.SSa(g)(S)(iii) of Title 10 of the Code of Federal Regulations (10 CFR), the licensee requested to use the proposed alternative in RI-07 on the basis compliance with the code requirements is impractical for CNS.

2.0 REGULATORY EVALUATION

Pursuant to 10 CFR SO.SSa(g)(4), ASME Code Class 1,2, and 3 components (including supports) must meet the requirements, except the design and access prOVisions and the pre service examination requirements, set forth in the ASME Code,Section XI to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that lSI of components and system pressure tests conducted during the 1O-year intervals be in compliance with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR SO.SSa(b), 12 months prior to the start of the 120-month interval. The ASME Code of record for CNS is the 2001 Edition of the ASME Code,Section XI with 2003 Addenda. Pertinently, ASME Code Case N-460, which has been approved unconditionally in NRC Regulatory Guide 1.147, Revision 16, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," allows that "a reduction in Enclosure

-2 examination coverage for any Class 1 or Class 2 weld may be acceptable provided that the reduction in coverage for that weld is less than 10%."

The regulations in 10 CFR 50.55a(g)(5)(iii) state, in part, that "if the licensee has determined that conformance with certain code requirements is impractical for its facility, the licensee shall notify the Commission and submit, as specified in [10 CFR] §50.4, information to support the determinations."

The regulations in 10 CFR 50.55a(g)(6)(i) state that "the Commission will evaluate determinations [submitted by the licensee] under paragraphs (g)(5) of this section [10 CFR 50.55a] that code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility."

3.0 TECHNICAL EVALUATION

3.1 Applicable ASME Code Components Affected (as stated by the licensee)

Code Class: 2

References:

IWC-2500, Table IWC-2500-1 Examination Category: C-A - Pressure Retaining Welds in Pressure Vessels C Pressure Retaining Nozzle Welds in Vessels Item Number: C1.10, C2.21

Description:

Shell Circumferential Weld, Nozzle to Head Weld Component Numbers: RHR-CA-2A (Shell to Distributor Ring End Top)

RHR-C8-1A (Nozzle to Head Top) 3.2 Applicable Code Edition and Addenda (as stated by the licensee)

American Society of Mechanical Engineers (ASME) Code Section XI, 2001 Edition, 2003 Addenda.

3.3 ASME Code Requirements for which Relief is Requested (as stated by the licensee)

Table IWC-2500- 1, Examination Category C-A, Item C 1.10 requires 100%

volumetric examination of pressure vessel welds as defined by Figure IWC-2500-1.

Table IWC-2500-1, Examination Category C-8, Item C2.21 requires 100%

surface and volumetric examination of pressure retaining nozzle vessel head welds as defined by Figure IWC-2500-4(d).

- 3 3.4 Reason for Request By letter dated January 16, 2011, the licensee stated:

The CNS construction permit was issued before the effective date of implementation for ASME Section XI, thus the plant was not designed to fully meet the requirements of inservice inspection.

[... J A major modification to the RHR heat exchanger or replacement would be required in order to improve overall examination coverage. Therefore, obtaining essentially 100%

coverage is not feasible or practical.

In addition, the licensee included diagrams within the RR detailing the design limitations.

The licensee stated that it achieved 41.8 percent coverage for the RHR-CA-2A weld, and 65.1 percent coverage for the RHR-CB-1A weld due to component configuration.

Examinations conducted in the previous 10-year lSI interval had greater than 90 percent coverages reported, however, these coverages would not be deemed credible under current improved practices.

3.5 Proposed Alternative and Basis for Use (as stated by the licensee)

In lieu of performing the code-required examinations, CNS proposes to examine the accessible portions of the RHR heat exchanger welds to the extent practical.

The examinations were performed prior to CNS' last refueling outage in March 2011, and in accordance with ASME [Code] Section XI using qualified personnel, procedures, and equipment. The magnetic particle examination performed on RHR-CB-1A achieved greater than 90% coverage, however, based on the configurations of these welds, the volumetric examination coverages achieved were 65.1% for RHR-CB-1A (See Figure RI-07-1) and 48.1% for RHR-CA-2A (See Figure RI-07 -2). Volumetric examination coverages reported in the previous interval were both over 90% however, the reductions in coverages achieved this interval are attributed to more conservative examination techniques thus providing more reliable results. Using the provisions of this relief request as an alternative to the specific requirements of ASME Table IWC-2500- 1, identified above, will continue to provide reasonable assurance of structural integrity since the percent of examination coverage already obtained would have identified any pattern of service induced degradation that may have developed.

3.6 Duration of Proposed Alternative (as stated by the licensee)

Relief is requested for the fourth ten-year interval of the CNS Inservice Inspection Program ending on February 29,2016.

-4 3.7 NRC Staff Evaluation The ASME Code requirement for the subject welds requires a volumetric examination of "essentially 100%," however, due to design issues, the licensee only achieved 41.8 percent coverage for the RHR-CA-2A weld, and 65.1 percent coverage for the RHR-CB-1A weld. The NRC staff reviewed the diagrams detailing the examinations including those submitted by letter dated June 22,2012. The weld design itself precluded achieving ASME Code acceptable coverage since the welds were designed prior to the implementation of the ASME Code requirements.

By letter dated June 11, 2012 (ADAMS Accession No. ML12159A299), the NRC staff requested the licensee to clarify the difference in technique between the examinations conducted during the previous lSI interval and those conducted during the current interval. In addition, the NRC staff asked the licensee to explain why the coverage percentages differed so much between intervals.

By letter dated June 22,2012, the licensee clarified that for the RHR-CA-2A weld, the previous coverage values were achieved using Ita 'Full Vee Path' calibration using a 45° [degree]

transducer and the use of a 0° transducer from the face of a filet weld are not accepted techniques for circumferential angle beam inspection and therefore were not performed."

For the RHR-CB-1A weld, the previous circumferential coverage values were obtained using "a

'Full Vee Path' calibration using a 45° transducer is not an accepted technique for circumferential angle beam inspection and therefore was not performed."

The NRC staff concludes that, in both cases, it is doubtful that the previously applied techniques provided a significant increase in the certainty of the integrity of the welds.

Due to the design of the 1A RHR heat exchanger at CNS, the ASME Code requirements with respect to the subject welds discussed above are impractical. The subject welds were designed and constructed prior to the implementation of ASME Code Section XI and, therefore, preclude 100 percent coverage. No recordable indications of degradation were found within the examined volume. The NRC staff concludes that there is reasonable assurance that evidence of degradation would be detected by examinations performed by the licensee within the examined area. Redesigning the heat exchanger to increase coverage would present a significant burden and would not significantly increase assurance of structural integrity of the welds.

4.0 CONCLUSION

Based on the above, the NRC staff concludes that the proposed alternative provides reasonable assurance of structural integrity of the subject welds and that complying with the ASME Code requirement would result in significant hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Therefore, pursuant to 10 CFR 50.55a(g)(6)(i), the NRC grants the licensee's request for relief for the CNS fourth 10-year lSI interval, which ends on February 29, 2012. The staff has

- 5 determined that granting RI-07 pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life, or property, or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed.

All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in the subject request for relief remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Principal Contributors: C. Sydnor D. Widrevitz Date: January 22, 2013

ML12313A111 *memo dated II OFFICE NRR/LPL4/PM NRR/LPL4/LA N RR/DE/EVI B/BC NRR/LPL4/BC NRR/LPL4/PM IINAME LWilkins JBurkhardt SRosenberg* MMarkley LWilkins IlDATE 12110/12 12/10/12 10/11/12 1/22113 1/22/13