ML13087A517

Relief Request RR-ENG-3-09, Request for Relief from ASME Code Requirements; Deferral of Code Repair of Essential Cooling Water System Piping Until April 2013 Refueling Outage

ML13087A517
Person / Time
Site:	South Texas
Issue date:	04/12/2013
From:	Markley M Plant Licensing Branch IV
To:	Koehl D South Texas
Singal B
References
TAC ME9806
Download: ML13087A517 (9)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 12, 2013 Mr. Dennis L. Koehl President and CEO/CNO STP Nuclear Operating Company South Texas Project P.O. Box 289 VVadsworth,TX 77483

SUBJECT:

SOUTH TEXAS PROJECT, UNIT 2 - REQUEST FOR RELIEF FROM THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE, SECTION XI, REQUIREMENTS FOR THE ESSENTIAL COOLING VVATER SYSTEM PIPING (TAC NO. ME9806)

Dear Mr. Koehl:

By letter dated October 16, 2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12299A287), as supplemented by letters dated November 14, 2012, and January 31, 2013 (ADAMS Accession Nos. ML12341A229 and ML13045A309, respectively), STP Nuclear Operating Company (the licensee) submitted for U.S. Nuclear Regulatory Commission (NRC) review and approval Relief Request RR-ENG-3-09 for South Texas Project (STP), Unit 2. The licensee requested relief from Article IVVA-5250 of Section XI of the American SOciety of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) to permit the continued use of a Code Class 3 aluminum-bronze weld neck flange in the essential cooling water (ECVV) system with an identified flaw until the end of the refueling outage currently scheduled for April 2013. The licensee has proposed to replace the flange at the first opportunity after parts are available, but no later than the refueling outage scheduled for April 2013. The licensee submitted the relief request pursuant to Title 10 of the Code of Federal Regulations (10 CFR), paragraph 50.55a(a)(3)(ii).

The NRC staff has completed its review and, as set forth in the enclosed safety evaluation, determined that the proposed alternative provides reasonable assurance of structural integrity or leak tightness of the subject components and that complying with the specified 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(a)(3)(ii). Therefore, the NRC staff authorizes the proposed alternative at STP, Unit 2, for a period not to extend beyond the end of the refueling outage scheduled to begin in April 2013.

All other ASME Code,Section XI, requirements for which relief has not been specifically requested, remain applicable, including a third-party review by the Authorized Nuclear Inservice Inspector.

D. Koehl -2 If you have any questions, please contact Balwant K. Singal at 301-415-3016 or bye-mail at Balwant.Singal@nrc.gov.

Sincerely,

~.~

Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-499

Enclosure:

Safety Evaluation 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 REQUEST FOR RELIEF RR-ENG-3-009 FROM AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE. SECTION XI, REQUIREMENTS FOR ESSENTIAL COOLING WATER SYSTEM PIPING STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT, UNIT 2 DOCKET NO. 50-499

1.0 INTRODUCTION

By letter dated October 16, 2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12299A287), as supplemented by letters dated November 14, 2012, and January 31, 2013 (ADAMS Accession Nos. ML12341A229 and ML13045A309, respectively), STP Nuclear Operating Company (STPNOC, the licensee) submitted for U.S.

Nuclear Regulatory Commission (NRC) review and approval Relief Request RR-ENG-3-09 for South Texas Project (STP), Unit 2. The licensee requested relief from Article IWA-5250 of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) to permit the continued use of a Code Class 3 aluminum-bronze weld neck flange in the essential cooling water (ECW) system with an identified flaw until the end of the refueling outage currently scheduled to begin in April 2013. The licensee has proposed to replace the flange at the first opportunity after parts are available, but no later than the refueling outage scheduled for April 2013. The licensee submitted the relief request pursuant to Title 10 of the Code of Federal Regulations (10 CFR), paragraph 50.55a(a)(3)(ii).

2.0 REGULATORY EVALUATION

In this relief request, the licensee requested authorization of an alternative to the requirements of Article IWA-5250 of Section XI of the ASME Code pursuant to 10 CFR 50.55a(a)(3)(ii).

Adherence to Article IWA-5250 of Section XI of the ASME Code is mandated by 10 CFR 50.55a(g)(4) which states, in part, that throughout the service life of a bOiling or pressurized water-cooled nuclear power facility, components (including supports) which are Enclosure

-2 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 of editions and addenda of the ASME Code.

The regulations in 10 CFR 50.55a(a)(3) state, in part, that alternatives to the requirements of paragraph (g) of 10 CFR 50.55a may be used, when authorized by the NRC, if the licensee demonstrates (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Based on the above, the NRC staff concludes that regulatory authority to authorize an alternative to Article IWA-5250 of Section XI of the ASME Code, as requested by the licensee, exists.

3.0 TECHNICAL EVALUATION

3.1 Applicable Code Edition and Addenda ASME Code,Section XI, 2004 Edition.

3.2 Components for Which Relief is Requested Weld neck flange located in the ESW system line EW2283WT3; cross-tie piping, between Trains 2A and 2B near valve 2-EW-0274.

Code Class: Class 3 3.3 Reason for Request In its request, the licensee stated that Code compliant repairs to the weld neck flange could not be completed immediately due to the need to replace the flange and the current unavailability of the necessary parts. The licensee also stated that, because the flange is located in cross connect piping, a multiple train outage may be required to complete repairs.

3.4 Proposed Alternative In its letter dated October 16, 2012, the licensee stated that ASME Code,Section XI, IWA-5250, requires that leakage be evaluated for corrective action and implies that any component with through-wall leakage must be repaired or replaced at the time of discovery regardless of the leakage rate. As an alternative to the ASME Code requirements, the licensee proposed to allow the component to remain in service until parts are available and has proposed to make the repair prior to the end of the refueling outage currently scheduled for April 2013. The licensee has committed to perform monthly visual inspections to detect changes in size of the discolored area or leakage until a code repair is performed. The licensee also committed to re-evaluate structural integrity and the monitoring frequency if significant changes in the condition of the developed area are found.

-3 3.5 Licensee's Technical Basis In its letter dated October 16, 2012, the licensee provided information which is based substantially on guidance provided by NRC Generic Letter 90-05, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,2, and 3 Piping," dated June 15,1990 (ADAMS Accession No. ML031140590), as a basis for the acceptability of its proposed alternative. This information is summarized below:

a. The ECW system is a low-pressure system with normal operating pressure of approximately 50 pounds per square inch gauge (psig) and a design pressure of 120 psig.

b. Under normal operating conditions, three ECW loops are available in Modes 1, 2, 3, and 4. Technical specification limits on plant operation are imposed if any of these loops are not operational. At the present time, engineering analysis has determined that the ECW piping is operational but degraded.

c. Components adjacent to ECW piping which may be impacted by spray from a leak in this piping are either designed to operate in a spray environment or are protected from spray.

d. Flooding from a leak in the ECW piping is bounded by the worst-case flooding analysis for this part of the plant. Since the component under consideration is in a cross-tie line behind locked valves, the actual flooding which could result from a failure of the weld neck flange is far lower than the bounding flooding case.

e. Leakage from ECW piping in this location flows to the Mechanical Auxiliary Building (MAB) ECW sump. Sump level alarms are available to warn operators if leakage exceeds the sump pump capacity. The MAB sumps have two sump pumps, each rated at 390 gallons per minute (gpm) for 110-ft of head.

f. The ECW pumps and the cooling reservoir have adequate design margin and make-up capability to account for postulated leakage and are therefore fully capable of fulfilling the design-basis functions and mission times during a design basis accident.

g. Plant experience with other aluminum-bronze fittings indicates that degradation progresses slowly. The degraded area is not currently leaking. Walkdown inspections on a monthly basis and VT-2 examinations on a 6-month basis will provide adequate notice of changes in the size of the degraded area.

h. During normal operations and accident conditions, cross-connect line 10"EW2283WT3 between ECW trains 2A and 2B is isolated by locked closed cross-tie valves and serves no purpose that is within the design basis assumptions of the ECW system.

i. The cross-tie piping is cited in several plant procedures; none of these procedures direct that the valves be opened.

-4

j. The cross-tie piping is not credited in the plant's probabilistic risk assessment.

k. The structural integrity of the aluminum-bronze flange under consideration was demonstrated to be adequate using the flaw evaluation approach in Section C-3.a of the NRC Generic Letter 90-0S.

4.0 NRC Staff Evaluation As stated in Section 2.0 of this safety evaluation, prior to authorizing the proposed alternative under 10 CFR SO.SSa{a)(3)(ii), the NRC staff must conclude that the technical information provided in support of the proposed alternative is sufficient to demonstrate that compliance with ASME Code,Section XI, IWA-S2S0 (1) would result in a hardship or unusual difficulty and (2) would not provide a compensating increase in the level of quality and safety when compared to the proposed alternative.

The NRC staff concludes that the licensee's interpretation of the ASME Code based on the fact that the Code contains no provisions for the continued service of components which do not meet the requirements of the Code. The licensee has indicated that a replacement flange is not currently available and will not be available until mid-December 2012. Given that the flange is made from aluminum bronze, the staff believes that the licensee's assertion that the flange is not currently available is reasonable. Given that the flange is not available and that, in the licensee's words, the ASME Code requires "leaks to be repaired at the time of discovery," it is reasonable to infer that, in absence of authorization of an alternative to the ASME Code requirement, the plant would be required to shut down. The NRC staff concludes that a plant shutdown constitutes a hardship. This satisfies the first condition of 10 CFR SO.SSa{a){3){ii).

In considering the second condition of 10 CFR SO.SSa(a){3){ii), whether adherence to the ASME Code requirement would provide an increase in quality and safety commensurate with the hardship or unusual difficulty imposed by meeting the Code requirement, the NRC staff considered the technical basis for the alternative as proposed by the licensee and summarized in items a-k in Section 3.S of this safety evaluation. While the staff finds no reason to object to the technical accuracy and/or sufficiency of items a-j, the staff does not concur with item k. The staff also does not believe that items a-j adequately address the seismic qualification of the piping system under consideration given the observed degradation.

Item k addresses structural integrity calculations concerning the component under consideration. The licensee proposed that these calculations are conducted in accordance with Section C-3.a of the NRC Generic Letter 90-0S and demonstrate that the component is structurally adequate. The NRC staff notes that, in performing these calculations, the licensee used material properties for the aluminum bronze flange under consideration which are typical of "as received" material. The staff believes that selective leaching of the aluminum bronze will degrade the material properties for some distance ahead of the crack. The NRC staff, therefore, concludes that the structural integrity calculations should have been performed using material properties consistent with the actual material properties in the vicinity of the crack (Le.,

degraded properties). The staff believes that the approach used by the licensee is non conservative and does not accept the premise that the structural integrity of the component under consideration has been demonstrated. Additional discussion of this topic may be found in

- 5 the NRC's safety evaluation "South Texas Project. Unit 2 -Request for Relief RR-ENG-3-08 from American Society of Mechanical Engineers Boiler and Pressure Vessel Code Section XI Requirements for Repairs to Class 3 Valves in Essential Cooling Water System Piping" dated August 16, 2012 (ADAMS Accession No. ML12201A256).

In its evaluation of the licensee's request, the NRC staff identified the potential that the observed degradation could affect the seismic qualification of the piping. This observation is based on the concept that selective leaching in these components is known to occur from the inside diameter and progress outward in a narrow, circumferential band at a location, which is generally near the ends of the component. Such degradation could be substantially through-wall, completely around the circumference of the component, prior to demonstrating any observable indications on the outside diameter of the component. Given the lack of knowledge regarding the material properties of the leached material and the lack of knowledge of the extent to which degradation has occurred, the NRC staff concludes that it is necessary to assume that, in the event of an intermittent load, such as a seismic load, a guillotine break will occur at the location of the degradation. By letter dated January 31, 2013, in response to the NRC staff's request for additional information (RAI) dated January 2, 2013 (ADAMS Accession No. ML13003A072), the licensee stated, in part, that STPI'JOC pipe stress (ME 101) analytical model was modified to introduce a guillotine break (separation) at the location of the existing flaw and then re-analyzed using design basis approach and stress limits. The results of this evaluation show that this piping system meets the ASME Code reqUirements and therefore remains seismically qualified.

The NRC staff reviewed the analytical approach taken by the licensee and concludes that the results of the analysis adequately demonstrate the seismic qualification of the piping system in the event of a guillotine break at the point of degradation.

The information provided in items a-j, the seismic analysis described above, and as stated by the licensee in its letter dated November 14, 2012 that this piping was not credited in the plant's probabilistic risk assessment, demonstrates that flow through the piping in which the flange under consideration is located is not relied upon under normal operating conditions or any design basis condition and that further degradation of the flange will not adversely affect adjacent piping. Based on this analysis, the NRC staff concludes that, while the presence of this piping may provide desirable options to the plant in beyond design basis events, it provides no safety benefit under normal operating conditions or design-basis accident events. The staff, therefore, concludes that adherence to the ASME Code requirement does not provide a compensating increase in the level of quality and safety when compared to the proposed alternative and, therefore, meets the second criterion in 10 CFR 50.55a(a)(3)(ii).

Based on the above, the NRC staff concludes that the technical requirements of 10 CFR 50.55a(a)(3)(ii) have been met and, therefore, the licensee's proposed alternative provides reasonable assurance of structural and leak-tight integrity of the subject components.

The staff, therefore, finds no technical basis that would preclude it from authorizing an alternative to Article IWA-5250, of Section XI, of the ASME Code as requested by the licensee.

-6 S.O REGULATORY COMMITMENTS In its letters dated October 16 and November 14, 2012, the licensee made the following regulatory commitment:

Commitment Expected i Condition Report Completion Date* Action No.

Perform monthly visual inspection of line 06/01/2013 12-22876-S 10"EW2283WT3 and valve 2-EW-0274 to detect changes in size of the discolored area or leakage until a code repair is performed.

Re-evaluate structural integrity and the monitoring frequency if significant changes in the

! condition of the developed area are found.

6.0 CONCLUSION

As set forth above, the NRC staff determines that the proposed alternative provides reasonable assurance of structural integrity or leak tightness of the subject components and that complying with the specified 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 SO.S5a(a)(3)(ii). Therefore, the NRC staff authorizes the alternative proposed by RR-ENG-3-09 at STP, Unit 2, for a period of time not to extend beyond the end of the refueling outage scheduled for April 2013.

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 the third-party review by the Authorized Nuclear In-service Inspector.

Principal Contributor: Dave Alley, NRR/EPNB Date: April 12, 2013

D. Koehl -2 If you have any questions, please contact Balwant K. Singal at 301-415-3016 or bye-mail at Balwant.Singal@nrc.gov.

Sincerely, IRA!

Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-499

Enclosure:

Safety Evaluation cc w/encl: Distribution via Listserv DISTRIBUTION:

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