ML12313A415

Relief from the Requirements of the ASME Code

ML12313A415
Person / Time
Site:	Saint Lucie
Issue date:	11/09/2012
From:	Jessie Quichocho Plant Licensing Branch II
To:	Nazar M Florida Power & Light Co
Orf, T J
References
TAC ME8874
Download: ML12313A415 (11)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 9,2012 Mr. Mano Nazar Executive Vice President and Chief Nuclear Officer Florida Power and Light Company P.O. Box 14000 Juno Beach, Florida 33408-0420

SUBJECT:

ST. LUCIE PLANT, UNIT 2 - RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS CODE (TAC NO. ME8874)

Dear Mr. Nazar:

By letter dated June 11, 2012 (Agencywide Documents Access and Management System Accession No. ML12172A142) and revised by letter dated September 1, 2012 {ML122S0A667},

Florida Power and Light Company{the licensee) submitted Relief Request No. 13 to the U.S.

Nuclear Regulatory Commission (NRC) for relief from certain requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code Case N-770-1, as conditioned by Title 10 of the Code of Federal Regulations (10 CFR), Section SO.SSa{g){6){ii){F){3) at St. Lucie, Unit No.2.

Specifically, pursuant to 10 CFR SO.SSa{a){3)(ii), the licensee requested to use an alternative to the specified inspection requirement on the basis that complying with the requirement would result in hardship or unusual difficulty.

As set forth in the enclosed safety evaluation, the NRC staff has determined that the proposed alternative to the specified inspection requirement provides reasonable assurance of structural integrity of the subject components and that complying with the 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).

M. Nazar -2 If you have any questions, please contact the Project Manager, Tracy Orf at 301-415-2788 or by e-mail at tracy.orf@nrc.gov.

Sincerely,

~ F. ~iChOChO, Acting hi

~~~~t Licensing Branch 2-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-389

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 RELIEF REQUEST NO. 13 REGARDING ALTERNATIVES TO CODE CASE N-770-1 FLORIDA POWER AND LIGHT COMPANY, ET AL.

ST. LUCIE PLANT. UNIT 1 DOCKET NO. 50-389

1.0 INTRODUCTION

By letter dated June 11, 2012 (Agencywide Documents Access and Management System Accession No. ML12172A142) as revised by letter dated September 1, 2012 (ML12250A667),

Florida Power and Ught Company (the licensee) requested relief from certain requirements of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code)

Case N-770-1, as conditioned by Title 10 of the Code of Federal Regulations (10 CFR),

Section 50.55a(g)(6)(ii}(F)(3), for the third 10-year inspection interval at St Lucie, Unit 2 (SL2), in the examination of nickel-based Alloy 82/182 dissimilar metal butt welds (DMBWs).

Specifically, pursuant to 10 CFR 50.55a(a)(3)(ii), the licensee requested to use an alternative on the basis that complying with the specified requirement would result in hardship or unusual difficulty.

2.0 REGULATORY EVALUATION

In Relief Request 13, the licensee proposes to use alternatives to the requirements of ASME Code Case N-770-1.

Section 50.55a(g}(6){ii)(F)(1) of 10 CFR states "licensees of existing, operating pressurized water reactors as of July 21, 2011, shall implement the requirements of ASME Code Case N-770-1, subject to the conditions specified in paragraphs (g}(6)(ii}(F)(2) through (g}(6)(ii)(F)( 10) of this section, by the first refueling outage after August 22, 2011."

Section 50.55a(g}(6)(ii)(F)(3) of 10 CFR states that baseline examinations for welds in Code Case N-770-1, Table 1, Inspection Items A-1, A-2, and B, shall be completed by the end of the next refueling outage after January 20, 2012. Previous examination of these welds can be credited for baseline examinations if they were performed within the re-inspection period for the weld item in ASME Code Case N-770-1, Table 1 using Section XI, Appendix VIII requirements Enclosure

-2 and met the Code required examination volume of essentially 100 percent. Other previous examinations that do not meet these requirements can be used to meet the baseline examination requirement, provided U.S. Nuclear Regulatory Commission (NRC) approval of alternative inspection requirements in accordance with paragraphs (a)(3)(i) or (a)(3)(ii) of this section is granted prior to the end of the next refueling outage after January 20, 2012.

Section 50.55(a)(g}(6}(ii)(F)(4) of 10 CFR states that the axial examination coverage requirements of Code Case N-770-1, -2500(c) may not be considered to be satisfied unless essentially 100 percent coverage is achieved.

Section 50.55a(a)(3) of 10 CFR states, in part, that alternatives to the requirements of 10 CFR 50.55a(g) may be used when authorized by the NRC if the licensee demonstrates:

(i) the 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 staff finds that regulatory authority to authorize an alternative to the ASME Code, as requested by the licensee, exists.

3.0 TECHNICAL EVALUATION

3.1 Applicable Code edition and addenda The ASME Code, Rules for Inservice Inspection of Nuclear Power Plant Components,Section XI, 1998 Edition with Addenda through 2000 as conditioned by 10 CFR 50.55a is the code of record for the S1. Lucie Unit 2, third 10-year interval.

3.2 Code Requirements for Which Relief is Requested Relief is being requested from the baseline examination volume coverage requirements in Code Case N-770-1, "Alternate Examination Requirements and Acceptance Standards for Class 1 PWR [pressurized-water reactor] Piping and Vessel Nozzle Butt Welds Fabricated with UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities,Section XI, Division 1" as conditioned by 10 CFR 50.55a(g)(6)(II(F)(1),

10 CFR 50.55a(g)(6)(II(F)(3), and 10 CFR 50.55a(g)(6)(II(F)(4).

The subject welds are classified as Inspection Item "B," "Unmitigated butt weld at Cold Leg operating temperature ~ 525 of and < 580 of' for which visual and essentially 100 percent volumetric examinations are required.

3.3 Affected Systems and Components The licensee is requesting relief for Class 1 PWR pressure retaining piping and vessel nozzle DMBWs containing alloy 82/182, Inspection Item B for which 100 percent volumetric examination was not obtained, as shown in Table 1 below.

-3 Table 1: Inspection Coverages Component 10 Location Circ Scan for Axial Scan for Limitations Axial Flaws Circ Flaws (percent) (percent)

RC-112-1501-771-C Reactor Coolant 50 73 Cast Stainless Pump (RCP) 2A 1 Steel (CASS),

Inlet Elbow to Weld Taper Safe-end RC-112-11066-771 RCP 2A 1 Outlet 49 75 CASS, Weld Safe-end to Pipe Taper RC-115-1501-771-A RCP 2A2 Inlet 52 82 CASS, Weld Elbow to Safe-end Taper RC-115-701-771 RCP 2A2 Outlet 49 71 CASS, Weld Safe-end to Pipe Taper RC-121-1501-771-B RCP 2B1 Inlet 52 78 CASS, Weld Elbow to Safe-end Taper RC-121-901-771 RCP 2B1 Outlet 51 77.9 CASS, Weld Safe-end to Pipe Taper, Spray Nozzle RC-124-1501-771-D RCP 2B2 Inlet 49 72 __ , Weld Elbow to Safe-end Taper RC-124-1301-771 RCP 2B2 Outlet 50 77 CASS, Weld Safe-end to Pipe Taper, Spray Nozzle 3.4 Proposed Alternative As an alternative to the volumetric examination coverage requirements of ASME Code Case N-770-1, the licensee proposes to perform the following:

• Periodic system pressure tests in accordance with ASME Section XI Examination Category B-P, Table IWB-2500-1

• Conduct ultrasonic examinations to the maximum extent practical in accordance with Materials Reliability Program (MRP)-139 (Reference 1)

• Perform plant personnel walkdowns of Class 1 systems inside containment during refueling outages in accordance with plant procedures

• Perform bare metal visual examinations in accordance with ASME Code Case N-722-1 3.5 Licensee's Basis for Request The licensee is requesting permission to utilize the Ultrasonic examinations performed in accordance with MRP-139 during the 2011 (SL2-19) outage to satisfy the baseline examination requirements of 10 CFR 50.55a(g)(6)(ii)(F)(3). However, the welds listed within this request did

-4 not satisfy the required ASME Code Case N-770-1, as conditioned by 10 CFR 50.55a(g)(6)(ii)(F)(3), volume coverage due to their configuration. The scanning limitations prohibited essentially 100 percent ultrasonic examination coverage of the required examination volume.

Section 50.55a(g)(6)(ii)(F)(4) of 10 CFR provides the following exception to ASME Code Case N-770-1, "the axial examination coverage requirements of -2500(c) may not be considered to be satisfied unless essentially 100 percent coverage is achieved." Relief is requested from the 10 CFR 50.55a(g)(6)(ii)(F)(4) condition to ASME Code Case N-770-1 that essentially 100 percent coverage be achieved for the baseline volumetric examinations.

St. Lucie Unit 2 contains a 30-inch inside diameter (lD) inlet and a 30-inch ID outlet weld connected to each of the four RCPs. Each weld joins mill-clad SA-516, Grade 70 carbon steel pipe with SA-240-304L stainless steel cladding to an SA-351, Grade CF8M CASS safe end.

All of the welds covered by this relief request are found in cold leg temperature regions of the system. This means there is a lower probability of crack initiation, and a slower crack growth rate. These welds are also highly flaw tolerant, as demonstrated in the MRP-109 (Reference 2) report. No service-induced flaws have been found in these large diameter pipes, even though most of the plants in industry have been in service for over 25 years.

Examinations of the eight RCP inlet/outlet dissimilar metal (DM) welds were performed during previous intervals utilizing manual conventional ultrasonic techniques in accordance with the requirements of ASME Section XI, Category B-F. These examinations were performed prior to the requirement to implement ASME Section XI, Appendix VIII, Supplement 10 qualified equipment, procedures, and personnel. No indications were identified during the previous interval examinations.

During the 2011 (SL2-19) outage, examinations were performed of the eight RCP inlet/outlet DM welds utilizing a manual non-encoded phased array ultrasonic testing (UT) technique. In all cases, examination was performed from the carbon steel side of the weld. No indications were identified. The equipment, procedure, and personnel utilized for the performance of the examinations were qualified in accordance with the requirements of ASME Section XI, Appendix VIII, Supplement 10, as implemented through the Performance Demonstration Initiative (POI) program. Because the examination of the RCP inlet/outlet configuration is included in the POI sample set, a site specific mock-up was not applicable for these weld examinations.

The UT techniques proposed for each weld were reviewed to determine the amount of examination coverage that could be achieved. Extensive surface conditioning was performed to obtain the maximum amount of coverage. As a result, essentially 100 percent of the susceptible material in all eight welds was examined for circumferential flaws. However, due to the weld taper and no access for examination from the CASS safe-end side of the welds, limited examination volume coverage was noted for axial flaws.

The amount of coverage credited was determined in accordance with the qualified examination procedure utilizing field obtained contours. The qualified procedure provides the following for the determination of examination volume coverage:

- S-For axial beam directions (circumferential flaws), coverage of the examination volume is based on the minimum inner diameter (10) impingement angle of 40 to SO degrees. The sound beam was directed essentially perpendicular to the weld axis utilizing a raster scan pattern that provided a minimum of SO percent overlap of the transmitting element in the indexing direction. Procedurally, if the weld crown cannot be conditioned to an acceptable level, coverage of the non-cast or accessible portion of the examination volume can be claimed from the base material, without scanning on top of the weld provided the procedurally defined angles cover the required examination volume.

Scanning was performed from the carbon steel side only.

For circumferential beam directions (axiall'laws), coverage of the examination volume is based upon 10 impingement angles between 4S and 60 degrees. The sound beam was directed essentially parallel to the weld axis in both the clockwise and counterclockwise directions utilizing a raster scan pattern that provided a minimum of SO percent overlap of the transmitting element in the indexing direction. Additionally, the search unit was physically skewed into the weld centerline at angles between 0 and 30 degrees for both the clockwise and counterclockwise scan directions. Scanning was performed from the carbon steel side only. Procedurally, coverage could be claimed up to the weld centerline from the non-cast side provided the center point of the ultrasonic beam was capable of intersecting this area.

Qualification for the UT examination of the cast material is "in the course of preparation." No coverage is claimed in the cast material since access for scanning was not available from the cast side of the weld, and the qualified procedure specifically excludes cast materials in the coverage calculation. However, as shown in the figures, the theoretical beam path extends into the cast material for the examinations performed from the carbon steel side of the weld. While the coverage is not claimed, UT examinations conducted using Appendix VIII qualified procedures also provide reasonable assurance for the detection of flaws on the cast side of OM welds, even though there is presently no standardized process to qualify them.

In all cases, the 10 surface of the susceptible material was interrogated for circumferential flaws with the ultrasonic beam based upon 10 impingement angles between 40 to SO degrees. A small amount of the upper portion of the coverage box for welds RC-115-701-771 and RC-121-1S01-771-8 was not interrogated for circumferential flaws with the ultrasonic beam due to the weld taper. Additionally, portions of the carbon steel base material examination volume were not interrogated for circumferential flaws with the ultrasonic beam for a circumferential distance of 6.80 inches for weld RC-121-901-771 and S.70 inches for weld RC-124-1301-771 due to the proximity of the spray nozzles.

As identified in MRP-109, the axial flaw(s) that could result from a primary water stress corrosion cracking (PWSCC) mechanism in the susceptible alloy 82/182 butt weld are less safety significant than circumferential flaws. The critical axial flaw length for an RCP inlet and outlet alloy 82/182 butt weld is 38.2 inches (MRP-109 Table S-2), which exceeds the width of the St. Lucie Unit 2 RCP inlet and outlet alloy 82/182 butt weld material width of 1.75 inches 2.5 inches. Therefore a critical axial flaw in an RCP inlet or outlet alloy 82/182 butt resulting from a PWSCC mechanism is not credible and improving the exam axial flaw examination volume coverage would not result in an increase in safety with respect to pipe rupture.

-6 During the SL2 2011 refueling outage, examination volume coverage for the RCP inlet and outlet welds was extensively improved by grinding and contouring to meet the ASME Section XI, Appendix VIII, Supplement 10 qualified procedure scanning requirements for the search units.

Further contouring is limited by design minimum wall calculations for the piping. To obtain acceptable surface contour conditions for axial flaw examinations, weld build up of the DM weld, additional contouring, and a Construction Code radiologic testing examination would be required. This additional effort to improve axial flaw coverage would be a hardship that would not result in a compensating increase in the level of health and safety to the public.

As stated above, the initiation or growth of a safety significant flaw in a cold leg alloy 82/182 DMBW is extremely unlikely. However, as an added measure of safety, the industry imposed an Nuclear Energy Institute (NEI)-03-08 "needed" requirement, to improve their reactor coolant system (RCS) leak detection capability in part due to the concern with PWSCC (Reference 3).

St. Lucie Unit 2 has adopted the standardized approach to measuring RCS leak rate in WCAP 16423 (Reference 4) and has proceduralized the action levels in WCAP-16456 (Reference 5).

The enhanced leak rate monitoring and detection procedure monitors specific values of unidentified leakage, 7-day rolling average, and baseline means. Action levels are initiated as low as when the unidentified leak rate exceeds 0.1 gpm. The enhanced leak detection capability provides an increased level of safety so that if a flaw were to grow through wall, although unlikely, that it would be detected prior to growing to a safety-significant size.

Therefore, the examination coverage that was achieved, which includes essentially 100 percent of the susceptible material for the safety significant circumferential flaw and a significant percentage of the susceptible material for the nonsafety-significant axial flaw combined with the periodic system pressure tests and outage system walk downs, provides an acceptable level of quality and safety for identifying degradation from PWSCC prior to a safety significant flaw developing.

3.6 NRC Staffs Evaluation PWSCC of nickel-based pressure retaining boundary materials is a safety concern. Operational experience has shown that PWSCC can occur as the result of the combination of susceptible material, such as Alloy 182 (SFA-5.11 ENiCrFe-3) weld metal, corrosive environment, and tensile stresses resulting in leakage and the potential for loss of structural integrity. The examination requirements of AS ME Code Case N-770-1 are intended to ensure the structural integrity of DMBWs through nondestructive examination.

The staff reviewed the licensee's proposed alternative under the requirements of 10 CFR 50.55a(a)(3)(ii), such that:

Compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Without the proposed alternative, the licensee would need to modify each of the subject welds, which cannot be accomplished during the current outage without considerable hardship. Full coverage of the welds is unachievable due to the presence of CASS material, through which no ultrasonic examination coverage can be claimed. The staff is not aware of other options for

-7 attaining the required examination coverage and, therefore, finds that attaining the required ASME Code Case N-770-1 examination coverage would present a hardship.

The licensee states that all eight RCP inlet/outlet OMBWs had been examined during several previous intervals in accordance with the requirements of ASME Section XI, Category B-F prior to the implementation of MRP-139. In those examinations and in the 2011 outage, no indications were identified. When preparing for the MRP-139 required examinations, the licensee performed extensive surface conditioning to obtain the maximum amount of coverage.

As a result, the licensee was able to examine essentially 100 percent of the susceptible material for circumferential flaws. MRP-139 examination coverage volume did not include CASS material. The licensee is unable to claim essentially 100 percent coverage for ASME Code Case N-770-1 examinations because there is no qualified procedure for UT examination of CASS material. In two of the welds (RC-121-901-771 and RC-124-1301-771), portions of the carbon steel base material examination volume were unable to be examined for circumferential flaws due to the proximity of spray nozzles. However, the examinations in all welds were able to interrogate the entire root volume of the PWSCC-susceptible Alloy 182 weld material, which is the area where PWSCC flaws are most likely to form. Furthermore, the licensee states that no inside surface connected flaws were detected in any of the weld examinations.

The NRC staff notes that the current inspection requirements were recently imposed on the licensee. These inspections required the first volumetric examination of these welds during plant life. As these inspections are required to be performed by all licensees during the first refueling outage starting after January 20, 2012, the NRC expected licensees to complete these exams across the fleet by the spring 2014 refueling outage season. The licensee's best effort inspection coverage combined with surface examinations and system walkdowns conducted during this outage provides confidence in the structural integrity and leaktightness of these component welds. As these welds are located in the cold leg of the RCS loop, the average temperature significantly lowers the susceptibility of these welds to the initiation and crack growth rate of PWSCC. Further, the licensee has not identified any indications of PWSCC in any OM weld in the RCS.

In conclusion, the staff's review finds the licensee's proposed alternatives will provide reasonable assurance of structural integrity until the first non baseline examination required by Section XI Code Case N-770-1, when the licensee shall perform a permanent mitigation, repair or meet ASME Section XI Code Case N-770-1 baseline examinations for the OM welds.

4.0 CONCLUSION

As set forth above, the NRC staff determines that the proposed alternative provides reasonable assurance of structural integrity of the subject components and that complying with the 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 use of the proposed alternative to Code Case N-770-1 examination requirements for the duration of the third inservice inspection interval, which ends August 7, 2013. At which time, the licensee is expected to be able to meet the examination coverage requirements for these welds.

-8 All other requirements of ASME Code,Section XI, Code Case N-770-1, and 10 CFR 50.S5a{g)(6){ii){F) 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.

5.0 REFERENCES

1. Material Reliability Program: Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139, Revision 1), Electric Power Research Institute (EPRI), Palo Alto, CA:

2008. 1015009.

2. Material Reliability Program, Alloy 82/182 Pipe Butt Weld Safety Assessment for US PWR Plant Designs (MRP-109): Westinghouse and Combustion Engineering (CE) Design Plants, EPRI, Palo Alto CA: 2005. 1009804.

3. Guidance for Management of Materials Issues, Nuclear Energy Institute, Washington, DC:

May 2003. NEI, 03-08, and NEI Materials Guidelines Implementation Protocol, Revision 0, May 2004.

4. WCAP-16423-NP, Rev. 0, "Pressurized Water Reactor Owners Group Standard Process and Methods for Calculating RCS Leak Rate for Pressurized Water Reactors,"

Westinghouse Electric Co., September 2006.

5. WCAP-16456-NP, Rev. 0, "Pressurized Water Reactor Owners Group Standard RCS Leakage Action Levels and Response Guidelines for Pressurized Water Reactors,"

Westinghouse Electric Co., September 2006.

Principal Contributor: Margaret Audrain Date: November 9, 2012

M. Nazar - 2 If you have any questions, please contact the Project Manager, Tracy Ort at 301-415-2788 or by e-mail at tracy.ort@nrc.gov.

Sincerely, IRA!

Jessie F. Quichocho, Acting Chief Plant Licensing Branch 2-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-389

Enclosure:

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