ML072220228

Relief Requests CMP-022 and CMP-023 Regarding Use of Weld Overlays as an Alternative Repair Technique

ML072220228
Person / Time
Site:	North Anna
Issue date:	12/19/2007
From:	Marinos E NRC/NRR/ADRO/DORL/LPLII-1
To:	Christian D Virginia Electric & Power Co (VEPCO)
Lingam, Siva NRR/DORL 415-1564
References
CMP-022, Rev 1, CMP-023, Rev 1, TAC MD3903, TAC MD3904
Download: ML072220228 (23)

Text

December 19, 2007 Mr. David A. Christian President and Chief Nuclear Officer Virginia Electric and Power Company Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711

SUBJECT:

NORTH ANNA POWER STATION, UNIT NOS. 1 AND 2 - RELIEF REQUESTS CMP-022 AND CMP-023 REGARDING USE OF WELD OVERLAYS AS AN ALTERNATIVE REPAIR TECHNIQUE (TAC NOS. MD3903 AND MD3904)

Dear Mr. Christian:

By letter dated January 3, 2007, and as supplemented by letters dated March 13, May 16, June 15, July 25 and October 1, 2007, Virginia Electric and Power Company (the licensee) submitted Alternative Relief Requests CMP-022, Revision 1, and CMP-023, Revision 1, concerning the preemptive weld overlay and inspection of pressurizer dissimilar and similar metal welds at North Anna Power Station, Unit Nos. 1 and 2 (North Anna 1 and 2), respectively.

The licensee proposed the use of full structural preemptive weld overlay with temper bead welding for repair and the Performance Demonstration Initiative program for inspection as alternatives to the requirements of American Society of Mechanical Engineers, Boiler and Pressure Vessel Code,Section XI.

The Nuclear Regulatory Commission (NRC) staff has reviewed and evaluated the licensees submittal and concludes that the proposed alternatives provide an acceptable level of quality and safety. Therefore, pursuant to Title 10 of the Code of Federal Regulations, Part 50, Section 50.55a(a)(3)(i), the proposed alternatives are authorized for the repair and examination of the subject welds for each units third 10-year inservice inspection (ISI) interval, which ends April 30, 2009, for North Anna 1 and December 13, 2010, for North Anna 2.

The NRC staff provided verbal authorization for the subject relief request for North Anna 1 and 2 during a teleconference with the licensee on March 29, 2007. The alternative was authorized for each units third 10-year ISI, which ends April 30, 2009, for North Anna 1 and December 13, 2010, for North Anna 2.

Sincerely,

/RA/

Evangelos C. Marinos, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-338 and 50-339

Enclosure:

Safety Evaluation cc w/encl: See next page

December 19, 2007 Mr. David A. Christian President and Chief Nuclear Officer Virginia Electric and Power Company Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711

SUBJECT:

NORTH ANNA POWER STATION, UNIT NOS. 1 AND 2 - RELIEF REQUESTS CMP-022 AND CMP-023 REGARDING USE OF WELD OVERLAYS AS AN ALTERNATIVE REPAIR TECHNIQUE (TAC NOS. MD3903 AND MD3904)

Dear Mr. Christian:

By letter dated January 3, 2007, and as supplemented by letters dated March 13, May 16, June 15, July 25 and October 1, 2007, Virginia Electric and Power Company (the licensee) submitted Alternative Relief Requests CMP-022, Revision 1, and CMP-023, Revision 1, concerning the preemptive weld overlay and inspection of pressurizer dissimilar and similar metal welds at North Anna Power Station, Unit Nos. 1 and 2 (North Anna 1 and 2), respectively.

The licensee proposed the use of full structural preemptive weld overlay with temper bead welding for repair and the Performance Demonstration Initiative program for inspection as alternatives to the requirements of American Society of Mechanical Engineers, Boiler and Pressure Vessel Code,Section XI.

The Nuclear Regulatory Commission (NRC) staff has reviewed and evaluated the licensees submittal and concludes that the proposed alternatives provide an acceptable level of quality and safety. Therefore, pursuant to Title 10 of the Code of Federal Regulations, Part 50, Section 50.55a(a)(3)(i), the proposed alternatives are authorized for the repair and examination of the subject welds for each units third 10-year inservice inspection (ISI) interval, which ends April 30, 2009, for North Anna 1 and December 13, 2010, for North Anna 2.

The NRC staff provided verbal authorization for the subject relief request for North Anna 1 and 2 during a teleconference with the licensee on March 29, 2007. The alternative was authorized for each units third 10-year ISI, which ends April 30, 2009, for North Anna 1 and December 13, 2010, for North Anna 2.

Sincerely,

/RA/

Evangelos C. Marinos, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-338 and 50-339

Enclosure:

Safety Evaluation cc w/encl: See next page Distribution: RidsAcrsAcnwMailCenter RidsRgn2MailCenter(EGuthrie)

PUBLIC RidsNrrPMSLingam (hard copy) RidsNrrCpnb(TChan)

LPL2-1 R/F RidsNrrLAMOBrien (hard copy) RidsNrrCpnb(DTarantino)

RidsOgcRp RidsNrrLpl2-1 (EMarinos) SCampbell, EDO Rgn II RidsNrrCpnb(JTsao) RidsNrrPMRJervey (hard copy)

ADAMS ACCESSION NO.: ML072220228 *Per SE dated 11/26/07 ML0733100851 OFFICE NRR/LPL2-1/PM NRR/LPL2-1/PM NRR/LPL2-1/LA NRR/CPNB/BC OGC NRR/LPL2-1/BC NAME SLingam RJervey MOBrien TChan* JAdler NLO EMarinos

DATE 12/10 /07 12/10 /07 12/10 /07 11/26 /07 12/14/07 12 /19/07 OFFICIAL RECORD COPY SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUESTS CMP-022 AND CMP-023 NORTH ANNA POWER STATION, UNIT NOS. 1 AND 2 VIRGINIA ELECTRIC AND POWER COMPANY DOCKET NOS. 50-338 AND 50-339

1.0 INTRODUCTION

By letter dated January 3, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML070040490), Virginia Electric and Power Company (the licensee) submitted Alternative Relief Requests (RR) CMP-022 and CMP-023 for North Anna Power Station, Unit Nos. 1 and 2 (North Anna 1 and 2), respectively, to the repair requirements of American Society of Mechanical Engineers (ASME), Boiler and Pressure Vessel Code (Code),

Section XI. The licensees January 3, 2007, alternative repair was based on Code Case N-740, Dissimilar Metal Weld Overlay for Repair of Class 1, 2, and 3 Items,Section XI, Division 1, modified by Appendix VIII, Supplement 11, Qualification Requirements for Full Structural Overlaid Wrought Austenitic Piping Welds.

The licensee submitted revised Alternative RR CMP-022, Revision 1(CMP-022R1), and CMP-023, Revision 1 (CMP-023R1), for North Anna 1 and 2, respectively, by letter dated March 13, 2007 (ADAMS Accession No. ML070730563). The licensee responded to the Nuclear Regulatory Commission (NRC) staffs request for additional information (RAI) by letters dated May 16, 2007 (ADAMS Accession No. ML071410300), June 15, 2007 (ADAMS Accession No. ML071700268) and July 25, 2007 (ADAMS Accession No. ML072070356). The revised RR added additional information to address the NRC staffs review questions. In addition, the licensee submitted a change to the CMP-022R1 proposal as a result of physical inspection of the affected welds in North Anna 1 on October 1, 2007 (ADAMS Accession No.

ML072750064).

This alternative will be used in lieu of the requirements contained in the 1989 edition of the ASME Code for North Anna 1 and the 1995 edition through 1996 addenda for North Anna 2 of ASME Code,Section XI, IWA-4000, and in the 1998 edition through 2000 addenda for North Anna 1 and 2 of Section XI, Appendix VIII, Supplement 11.

The revised RR references Code Case N-740-1 with modifications. It is described in of the letter to the NRC dated March 13, 2007, under Enclosure 1, Alternative Requirements for Dissimilar Metal Weld Overlays, as modified by the licensees October 1, 2007 letter.

Enclosure

The RR would be used to perform full structural preemptive weld overlays (PWOL) on pressurizer spray, relief, safety, and surge nozzle safe ends. This request was verbally approved on March 29, 2007. Industry issues with the PWOL technique and North Anna 2 results were discussed in the context of this review during development of this safety evaluation which postponed its completion. Subsequent in-plant work during the North Anna Unit 1 fall outage led to the discovery of a weld configuation which also affected the request. The NRC staff has completed the review of Alternative RRs CMP-022R1 and CMP-023R1 (CMP-022R1/023R1), for North Anna 1 and 2, respectively, and it is addressed as follows.

2.0 REGULATORY EVALUATION

Pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(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, Rules for In-service Inspection (ISI) of Nuclear Power Plant Components, to the extent practical within the limitations of design, geometry, and materials of construction of the components.

The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) twelve months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The ASME Codes of Record for the current, third 10-year ISI interval at North Anna 1 and 2, are the 1989 edition and the 1995 edition through 1996 addenda, respectively.

Pursuant to 10 CFR 50.55a(a)(3)(i), alternatives to requirements may be authorized by the NRC if the licensee demonstrates that the proposed alternatives provide an acceptable level of quality and safety.

The licensee submitted RRs CMP-022R1/023R1, pursuant to 10 CFR 50.55a(a)(3)(i), which proposes alternatives to the implementation of ASME Code,Section XI, IWA-4000 and Appendix VIII, Supplement 11. The licensees alternative is based on Enclosure 1 to their March 13, 2007, letter, Alternative Requirements for Dissimilar Metal Weld Overlays, (Code Case N-740-1, with modifications) for the deposition of full structural preemptive weld overlay (PWOL) and the Performance Demonstration Initiative (PDI) program implementation of Appendix VIII, Supplement 11, as modified by the licensees October 1, 2007, letter which addressed weld inspection limitations found in Unit 1.

3.0 PROPOSED ALTERNATIVE REQUEST CMP-022R1/023R1 3.1 Licensees Reason for Requesting the Alternative Dissimilar metal welds (DMWs) primarily consisting of nickel based Alloy 82/182 weld metal are frequently used in pressurized water reactors (PWR) construction to connect stainless steel pipe and safe ends to vessel nozzles, generally constructed of carbon or low alloy ferritic steel.

These welds have shown a propensity for primary water stress corrosion cracking (PWSCC)

degradation, especially in components subjected to higher operating temperatures, such as the pressurizer.

This relief request includes six Class 1 DMWs located on the pressurizer for North Anna 1 and 2 which will have full structural PWOL applied. During the recent spring 2007 outage at North Anna 2, verbal approval was granted for the use of the alternative to address PWOL technique.

This RR covers the verbal approval and includes North Anna 1 and 2.

Repair/replacement activities associated with PWOL repairs are required to address the materials, welding parameters, as low as reasonably achievable (ALARA) concerns, operational constraints, examination techniques and procedure requirements for repairs. Comprehensive and generic NRC-approved criteria are not currently available for application of PWOL repairs to DMWs constructed of Alloy 82/182 weld material for mitigation of potential PWSCC.

The welding will be performed using a remote machine gas tungsten-arc welding (GTAW) process and using the ambient-temperature temper-bead method with ERNiCrFe-7A (Alloy 52M) weld metal. Manual GTAW, using ERNiCrFe-7 (Alloy 52) or Alloy 52M will be used if local repairs of weld defects are necessary or additional weld metal is required locally to form the final PWOL contour in locations at least 3/16 inch away from the low alloy steel (LAS) nozzles.

3.2 System/Components for Which the Alternative Is Requested The licensee states that ASME Code components associated with this request are the high safety significant (HSS) Class 1 DMWs with Alloy 82/182 weld metal believed to be susceptible to PWSCC. There are six welds intended to have full structural PWOL applied. The application of this alternative to apply PWOL on the six potentially PWSCC susceptible safe end-to-pressurizer nozzle welds will also involve extending the weld overlay across the adjacent stainless steel (SS) safe end-to-reactor coolant system (RCS) piping similar metal welds (SMWs).

The examination categories are R-A and the welds are included in the Risk-Informed Inservice Inspection (RI-ISI) Program. The six DM and SM welds scheduled for full structural PWOL at North Anna 1 and 2 are listed as follows:

NORTH ANNA - UNIT 1 Apply PWOL on six safe end-to-pressurizer nozzle DMW extending across the adjacent SS pipe/fitting/elbow-to-safe end SMW.

WELD SIZE (OD) DESCRIPTION COMMENT(1-5)

NUMBER SW-51 Surge Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS Reducer safe end 14-Inch Safe End Reducer-to-Pipe (14-39 SS safe end/SS weld/SS pipe RC-10-2501R-Q1)

SW-30 Safety Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS safe end 6-Inch Safe End-to-Elbow (6-RC SS safe end/SS weld/SS pipe 21 1502-Q1) (elbow)

SW-31 Safety Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS safe end 6-Inch Safe End-to-Elbow (6-RC SS safe end/SS weld/SS pipe 17 1502-Q1) (elbow)

SW-38 Safety Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS safe end 6-Inch Safe End-to-Elbow (6-RC SS safe end/SS weld/SS pipe 25 1502-Q1) (elbow)

SW-64 Relief Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS 6-Inch safe end Safe End-to-Concentric SS safe end/SS weld/SS pipe (6 x 4 30 4-Inch Reducer (4-RC-34-1502-Q1) concentric reducer)

SW-71 Spray Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS safe end 4-Inch Safe End-to-Pipe (4-RC 11 SS safe end/SS weld/SS pipe 1502-Q1)

NORTH ANNA - UNIT 2 Apply PWOL on six safe end-to-pressurizer nozzle DMW extending across the adjacent SS pipe/fitting/elbow-to-safe end SMW.

WELD SIZE (OD) DESCRIPTION COMMENT(1-5)

NUMBER SW-5 Surge Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS Reducer safe end 14-Inch Safe End Reducer-to-Pipe (14-1 SS safe end/SS weld/SS pipe RC-410-2501R-Q1)

SW-6 Safety Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS safe end 6-Inch Safe End-to-Elbow (6-RC-437- SS safe end/SS weld/SS pipe 1

1502-Q1) (elbow)

SW-9 Safety Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS safe end 6-Inch Safe End-to-Elbow (6-RC-438- SS safe end/SS weld/SS pipe 1

1502-Q1) (elbow)

SW-17 Safety Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS safe end 6-Inch Safe End-to-Elbow (6-RC-439- SS safe end/SS weld/SS pipe 1

1502-Q1) (elbow)

SW-40 Relief Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS 6-Inch safe end Safe End-to-Concentric SS safe end/SS weld/SS pipe (6 x 4 1 4-Inch Reducer (6-RC-434-1502-Q1) concentric reducer)

SW-62 Spray Nozzle-to-Safe End LAS nozzle/Alloy 82-182 weld/SS safe end 4-Inch Safe End-to-Pipe (6-RC-415-42 SS safe end/SS weld/SS pipe 1502-Q1)

(1) LAS Nozzle = Low Alloy Steel, SA-508 Class 2, (P-3, Group 3)

(2) Alloy 82/182 = Safe End-to-Nozzle weld and buttering, (F-43)

(3) SS Safe End = Wrought Stainless Steel, SA-182 GR F316L, (P-8)

(4) SS Surge Line Pipe, Safety Line Elbows, Relief Line Reducer and Spray Line Pipe = Wrought Seamless SS, (P-8)

(5) SS welds = Stainless Steel (A-8) 3.3 Code Requirements North Anna 1 is currently in the third 10-year ISI interval (May 1, 1999 through April 30, 2009).

The ASME Code of record for the current 10-year ISI interval isSection XI, 1989 edition. This is also the version used for the Repair/Replacement Program.

North Anna 2 is currently in the third 10-year ISI interval (December 14, 2001 through December 13, 2010). The ASME B&PV Code of record for the current 10-year ISI interval isSection XI, 1995 edition, including addenda through 1996. This is also the version used for the Repair/Replacement Program.

The alternative described in Section 3.4 below is proposed to permit the implementation of PWOL at North Anna 1, as an alternative for the repair/replacement requirements of the ASME Code,Section XI, 1989 edition, IWA-4000 and at North Anna 2, as an alternative for the repair/replacement requirements of the ASME Code,Section XI, 1995 edition, including addenda through 1996, IWA-4000.

The alternative proposed by this RR is required because IWA-4000 for the year and addenda in use at North Anna 1 and 2 does not address all the necessary requirements to adequately implement this type of repair. In the proposed alternative, the ultrasonic (UT) examination of the completed PWOL will be accomplished based on the ASME Code,Section XI, 1998 edition including addenda through 2000 for North Anna 1 and for North Anna 2, Appendix VIII, Supplement 11, as modified to comply with the PDI program as listed in Attachment 2, of the letter to the NRC dated March 13, 2007, and further explained by the RAI response dated July 25, 2007.

3.4 Licensees Proposed Alternatives and Basis As described in the revised RR, the mitigative weld overlay shall be applied by deposition of weld reinforcement (weld overlay) on the outside surface of the piping, component, or associated weld, including ferritic materials when necessary, provided the requirements as stated in Enclosure 1, Alternative Requirements for DMW Overlays, are met. This alternative is the result of the industrys experience with mitigative weld overlay repairs for flaws suspected or confirmed to be from PWSCC and for the first time directly applies to the Alloy 52 or 52M weld material primarily being used for these overlay repairs.

A full structural PWOL (designed for the worst case flaw) will be applied in accordance with the requirements of Enclosure 1 followed by a UT examination upon completion. This proposed alternative is requested for implementing the six scheduled full structural PWOL for the potentially PWSCC susceptible safe end-to-nozzle welds of the pressurizer. The PWOL will include the adjacent stainless steel elbow/pipe/reducer-to-safe-end welds. The request applies to each of the welds listed in Section 2.2 and generically depicted in Figure 1 of the revised RR.

3.4.1 Full Structural PWOL Assembly The ferritic materials of the nozzles are P-3, Group 3, material; the safe ends and pipe/elbow/reducers are wrought SS, P-8 material. The existing weld filler material is Alloy 82/182 (F-43).

The ASME Committee has indicated that the inside diameter (ID) compressive stress levels remain essentially the same between 100 square inches and 500 square inches in relation to weld overlay applications. The RR allows for the installation of the PWOL using temper-bead welding for up to 500 square inches over the ferritic material. The justification entitled, Bases for 500 Sq. In. Weld Overlay Over ferritic Material, was provided to the NRC staff in the January 10, 2007, meeting (ADAMS Accession No. ML070470565). Additional justification is provided in Electric Power Research Institute (EPRI) Report 1014351, Repair and Replacement Applications Center: Topical Report Supporting Expedited NRC Review of Code Cases for DMW Overlay Repairs, December 2006.

The full structural weld overlay satisfies all the structural design requirements of the pipe assuming no strength is contributed by the original safe end-to-nozzle DMWs or the elbow/pipe/reducer-to-safe-end SMWs. The mitigative weld overlay is designed to meet structural requirements as if the original welds were removed. As shown in Figure 1 of the alternate request, this structural weld overlay (weld reinforcement) will completely cover the existing Alloy 82/182 DMWs extending onto the ferritic and austenitic SS material on each end of the weld, including the adjacent pipe/elbow/reducer-to-safe-end SMWs. The weld overlay extends the full 360-degrees around the nozzle.

The Procedure Qualification Reports (PQR) for qualification of the temper-bead portion of the welds and for overlay of the buttered P3 nozzle material were performed using ERNiCrFe-7 (Alloy 52) or ERNiCrFe-7A (Alloy 52M) filler metal. Both filler materials have 28.0 to 31.5%

chromium (Cr) and the Alloy 52M filler metal will be used for the production overlays.

Furthermore, paragraph 1(e) of the revised RR (Enclosure 1), states that a diluted first layer may be credited toward the required thickness, provided the portion of the layer over the austenitic base material, austenitic filler material weld and the associated dilution zone from an adjacent ferritic base material contains at least 24% Cr and the Cr content of the deposited weld metal is determined by chemical analysis of the production weld or of a representative coupon taken from a mock-up prepared in accordance with the Weld Procedure Specification (WPS) for the production weld. The licensees PWOL vendor has prepared representative coupons taken from mock-ups prepared in accordance with the WPS (including use of Alloy 52M filler metal) for the production weld. Where the representative coupons provide a first layer Cr content less than 24%, the production weld overlay procedure will deposit a sacrificial layer of Alloy 52M filler metal over the material responsible for the excessive dilution. The sacrificial layer will not count as a structural layer of the PWOL; the layer covering the sacrificial layer will be the first layer credited as a structural PWOL layer. Where the representative coupons provide a first layer Cr content equal to or greater than 24%, a sacrificial layer of Alloy 52M will not be used and the weld layer will count as a structural layer of the PWOL.

Thermocouples will be used to monitor welding preheat and interpass temperatures during application of the weld overlay. After completion of the overlay, the thermocouples will be removed, the thermocouple attachment areas will be ground, and the ground areas will be subjected to a surface examination.

3.4.2 Weld Overlay Design The PWOL will be designed as mitigating full structural overlays (assumed worst-case flaw) in accordance with Enclosure 1, Section 2 of the letter to the NRC dated March 13, 2007. Crack growth calculations will be performed to demonstrate that the crack growth in the weld overlay or base metal is acceptable and that residual stress distribution in the weld overlay and original weld result in a favorable stress distribution. This is true for all nozzle structural mitigation weld overlay analyses except the portion of the ASME Code,Section III analysis for the surge line weld overlay that addresses the insurge/outsurge transients. This portion of the analysis will be addressed with an engineering evaluation of insurge/outsurge transients that will use data from a D.C. Cook, ASME Code,Section III analysis that will qualify the design for seven heat-ups and cool-downs with thirty insurge/outsurge cycles. (This is an excerpt from the licensees letter of March 13, 2007, and is understood to frame conservative engineering judgement in evaluation of stress caused by transient cycles). The D.C. Cook analysis is representative of

the North Anna situation since the nozzles are very similar in configuration and the worst case transient severity is bounded (i.e., the D.C. Cook transient is considered more severe than the North Anna 1 and 2 transient).

The seven heat-ups and cool-downs with thirty insurge/outsurge cycles represent a very conservative limit placed on interim operation and are associated with the interim analysis.

Interim measures are not meant to correlate with a specific operating cycle. These limiting insurge/outsurges are not expected to occur in the next seven operating cycles based on one heat-up and one cool-down per cycle. The North Anna 1 and 2 specific ASME Code,Section III analysis will be completed by December 31, 2007, at which time the seven heat-ups and cool-downs with thirty insurge/outsurge cycle restrictions will be resolved. The number of heat-ups and cool-downs are currently monitored and recorded by procedure. The North Anna 1 and 2 ASME Code,Section III analysis will be an elastic-plastic analysis based on the defined number for life of plant transients.

A weld shrinkage evaluation will be performed to ensure the effect of weld shrinkage on other components or supports is acceptable. This evaluation will also address increased stiffness at the joint due to increased thickness in the localized area, increased weight due to the increased thickness in the localized area, and the impact on the piping due to thermal contraction caused by the weld cooling process. In addition to the weld shrinkage evaluation, mock-up testing will be used to demonstrate piping movements as a result of the weld overlay application.

After final installation of the pressurizer weld overlays, the actual shrinkage will be compared to the value assumed in the evaluation to ensure consistency.

The North Anna 1 and 2 pressurizer surge line nozzle-to-safe-end and safe end-to-pipe welds are not included as part of the approved leak-before-break analysis.

3.4.3 Examinations As stated in the licensees July 25, 2007, letter, the examinations will meet the requirements of of the revised RR. The UT examination of the completed full structural PWOL will be performed based on ASME Code,Section XI, 1998 edition including addenda through 2000 for North Anna 1 and for North Anna 2, Appendix VIII, Supplement 11. This conforms to the modified PDI program as listed in Table 1 of Enclosure 1 to Attachment 2 of letter dated March 13, 2007.

UT examination requirements for the weld overlays are provided in Section 3 of Enclosure 1 of the revised RR, which specifies that UT examination is to be performed in accordance with Section XI of the ASME Code. Unlike ASME Code,Section III, the ASME Code,Section XI, UT examination is qualified for use based on PDI for both personnel and procedures, and it has been proven to be capable for this application. Therefore, for this application, UT examination in accordance with ASME Code,Section XI requirements for UT are more appropriate than UT examination using ASME Code,Section III requirements. Surface examination requirements of NB-5300 for the weld overlay and NB-2500 for the base material are required for this application. (ASME Code,Section III requirements are intended for construction activity and Section XI is intended for repair.)

The current configuration and geometric limitations of these welds does not permit an effective UT examination that will obtain the coverage (examination volume) as required by ASME Code,

Section XI, Appendix VIII, Supplement 10. As documented in the licensees January 31, 2007, letter, four of the six DM welds on each unit have examination coverage estimates of significantly less than the required examination volume (50% - 65%). The remaining two DM welds are estimated as capable of achieving approximately 75% to 80% of the required examination coverage. It is estimated that approximately 0.6 Rem per unit would be expended to perform the UT examinations for these two welds for a total of 1.2 Rem.

It is proposed that North Anna 1 and 2 will apply a full structural PWOL in accordance with of the alternate request designed for a worse-case through-wall flaw that is 360 degrees in circumference. Therefore, none of the identified welds will receive a pre-weld overlay UT examination. The NRC staff has determined that this provides an acceptable level of quality and safety and does not require the licensee to receive an additional dose from UT examination of these welds prior to application of the PWOL. In addition, if the welds are found with PWSCC or other unacceptable flaws during the post-weld overlay UT examination, no additional examination expansions will be performed because there are no remaining DM welds associated with the pressurizer environment not previously mitigated by application of a PWOL.

As described in the licensees letter to the NRC, dated October 1, 2007, during the North Anna Unit 1 refueling outage, fall 2007, a PWOL was applied to the pressurizer safety nozzle in accordance with RR CMP-022R1. However, less than 100% volumetric examination coverage was obtained following application of the PWOL, due to a localized fabrication repair in the original DMWs buttering region of A safety valve nozzle PWOL. In addition, the calculated composite coverage of the required examination volume is 99.8%. Therefore, a revision to the NDE requirements of RR CMP-022R1 is provided for the North Anna Unit 1 A safety valve nozzle PWOL. The revision modifies Sections 3(b) preservice and 3(c) inservice examination requirements of Enclosure 1 to Attachment 2 of the letter to the NRC, dated March 13, 2007, and provides a detailed basis for requesting the reduced examination volume.

i) The examination volume is extended 0.30 inches towards the nozzle taper for 114 degrees of the circumference of the weld. The interface of the alloy 600 to low alloy steel defining the examination boundary was confirmed by acid etching. The qualified UT examination procedure requires an examination of the volume to include an additional beam angle of 45 degrees to provide effective coverage of the outer 25% of the existing weld and base material for 1/2 inch on each side of the weld. This angle is required to provide coverage of 100% of this volume. In addition, the outer 25% of the existing weld and base material volume can be effectively examined in three of the required four beam directions. The downstream axial beam direction is limited to 99.2% of the required examination volume due to the restriction of the nozzle taper.

This does not allow access to scan the transducer the required distance from the weld to obtain coverage of the lower near corner of the examination volume. The limited examination volume is located at least 0.25 inches from the alloy 600 buttering material and is effectively examined in the three other required beam directions. The calculated composite coverage of the required examination volume is 99.8%.

ii) Several different options were considered to resolve the examination coverage issue. One option was to apply additional overlay material (approximately 1/2 inch) parallel to the PWOL.

However, the addition of material would require a considerable additional dose expenditure and new PDI qualified transducers that are not readily available. Another option was to apply an additional overlay at a 6-degree slope. Even though this option results in less weld material being added, it would still involve considerable dose expenditure (2 manrem) and an additional

qualified transducer that is not readily available. The final option was machining of the pressurizer nozzle to provide additional scan surface for the transducer. This option reduced the strength of the nozzle by increasing the cumulative usage factor by at least a factor of four.

The option also required a significant additional dose (0.750 manrem).

iii) The volume of material that will be un-inspectable by UT lies entirely in the low alloy steel, SA508 CL 2, of the pressurizer nozzle. This zone of material is 0.25 inches or more from the alloy 82/182 butter on the nozzle. There is no likelihood of primary water stress corrosion crack initiation or propagation in the low alloy steel material itself and no likelihood of propagation of a postulated primary water stress corrosion crack from the alloy 82/182 butter into the low alloy steel. Consequently, there is no likelihood of any undetectable cracking occurring in the small zone of material with no UT inspection coverage. Furthermore, the PWOL was designed to accommodate a 360-degree through-wall crack in the repaired area with no failure, which bounds the case of a crack that might be postulated to exist in the un-inspectable material.

Additionally, if the small volume of this base metal contained a flaw, the flaw would only potentially reduce the strength of the nozzle by an insignificant amount. However, cutting a transition in the nozzle in order to facilitate 100% inspection coverage will create a small but real reduction of strength of the nozzle. The reduction of strength for this small improvement in inspection coverage may be acceptable, but will constitute a deliberate reduction of strength in the nozzle to address a potential reduction of strength due to an inability to inspect the nozzle for an additional 0.2%. See Sections 3(b) and 3(c) of Enclosure 1 to Attachment 2 of the letter to the NRC, dated March 13, 2007.

3.4.4 Required Activities The preliminary stress analysis required by the alternative request will be performed prior to the refueling outage (RFO) for which the PWOL are scheduled for installation and will be available for NRC review on site. The final stress analysis and the engineering evaluation of insurge/outsurge transients will be submitted to the NRC prior to entry into Mode 4. Also, the final plastic/elastic analysis, which includes the engineering evaluation of insurge/outsurge transients for the surge line on North Anna 2, will be completed and submitted to the NRC by December 31, 2007.

If flaw growth in the weld overlay occurs and the acceptance standards of Table IWB-3514-2 cannot be met, a determination will be made to prove if the flaw is not PWSCC. If the cause is determined to be PWSCC or the cause of the flaw cannot be determined, North Anna 1 and 2 will repair the flaw and will not use IWB-3600, IWC-3600, or IWD-3600 of ASME Code,Section XI, to accept these types of flaws.

North Anna 1 and 2 have provided: (1) the examination results of the weld overlays, (2) a discussion of any repairs to the overlay material and/or base material, and the reason for the repair within 14 days after the completion of the UT examination of full structural PWOL installations.

3.4.5 Use of a Barrier Layer to Mitigate Potential Hot Cracking The licensee states that the most recent industry experience involves the hot cracking of nickel Alloy 52M weld overlay deposits on SS base materials with higher levels of sulfur in the

austenitic SS base metal. The licensee plans to apply a weld build-up (barrier layer) approximately 0.065-inch thick of ER309L SS weld metal for the majority of the length of the PWOL build-up. The final tie-in to the existing nickel Alloy 82/182 DMWs will be performed with nickel Alloy 82 weld metal. The barrier layer will provide an improved base layer for application of the full structural PWOL that has been demonstrated by mock-up testing to significantly reduce the susceptibility to hot cracking of the first layer of the PWOL. This application of weld build-up is not counted as part of the full structural PWOL. The weld build-up will be performed in accordance with the requirements of the North Anna 1 and 2, ASME Code,Section XI Repair/Replacement program and ASME Code,Section III.

Weld filler material ER309L helps to promote primary solidification of the weld metal as ferrite in lieu of austenite. Also, this approach has been fully qualified in an ASME Code,Section IX structural welding procedure qualification (PQ). The licensees vendor performed a PQ with ER309L (0.01 weight percent Sulfur) deposited on a high sulfur (greater than 0.01 weight percent Sulfur) austenitic SS base material with a single layer of ER309L deposited in the bottom half of the groove and a single layer of E309L deposited in the top half of the groove.

The groove was subsequently filled with ERNiCrFe-7A (Alloy 52M). The intent of the PQ was to fully qualify the layer of ER309L between high sulfur SS and Alloy 52M to ASME Code,Section IX structural requirements. The 0.01 weight percent sulfur ER309L layer supported tensile tests that resulted in ultimate tensile strengths of 83 and 82.8 ksi with failures being of a ductile nature in the base material. Four transverse side bends were also performed with no indications. In addition to the PQ described above, the licensees vendor performed mock-up testing using the same heat of filler metal as used for the PQ and plans to use the same for North Anna 1 and 2 PWOL. The mock-up tests were also satisfactory.

The nozzle is LAS which involves a different alloy composition as opposed to SS. In carbon steel, the addition of manganese ties up sulfur in manganese sulfide (MnS). MnS virtually eliminates the formation of low melting point iron sulfides that contribute to the solidification cracking. To date the licensee has not seen this problem on low alloy steel welded with ERNiCrFe-7A (Inconel Alloy 52M).

The phrase structural weld layers as it relates to chromium content is used as part of Code Case N-740-1 and the licensees Enclosure 1 to require weld overlay deposited material with sufficient Cr to prevent SCC. For pressurized water reactors (PWR), to mitigate/repair Alloy 82/182 weld deposit at least 24% Cr is required in the PWOL deposit. When applying the first layer of nickel Alloy 52M PWOL over the base metal with less than 24% Cr (austenitic SS, Alloy 82/182) or almost no Cr (low alloy steel nozzle), the weld dilution from these materials may lower the first layer chemistry slightly below 24%. When this happens, the first layer cannot be credited as a structural layer (i.e., PWSCC resistant) and it is termed a sacrificial layer.

The second and all subsequent layers of the Alloy 52M full structural PWOL deposit will exceed 24% Cr and will be counted as structural weld layers.

The term barrier layer is not referenced in either ASME Code,Section III or Enclosure 1 (Code Case N-740-1). It is a licensee phrase used to describe a layer of weld metal build-up applied to the austenitic SS pipe and safe end to reduce the amount of sulfur available for pick-up when applying the subsequent Alloy 52M full structural PWOL. Final NDE of the barrier layer will utilize the methods and acceptance criteria of ASME Code,Section III. The barrier layer uses filler materials expected to result in a first layer deposit analysis containing less than 24% Cr, and from a functional standpoint, it is considered similar to the sacrificial layer

described above. The barrier layer will increase the pipe and safe end thickness and will not be utilized as part of the full structural PWOL. Following application of the full structural PWOL, the barrier layer will be examined by PDI UT in accordance with Enclosure 1 of the alternate request as part of the outer 25% of the pipe through-wall thickness.

3.4.6 Duration of the Proposed Request The licensee states that the alternative requirements of CMP-022R1/023R1 will be applied for the duration of up to and including the last outage of the current, third 10-year ISI interval. This includes inservice examination requirements for the six applied PWOL locations for each unit identified in Section 3.2 above and will be applied in accordance with Enclosure 1 of Alternative Requests CMP-022R1 and CMP-023R1.

4.0 NRC STAFFS EVALUATION Alternative Requests CMP-022R1/023R1, consist of 3 parts: (1) Attachment 1, Use of a Barrier Layer to Mitigate potential Hot Cracking, (2) Attachment 2, Use of Weld Overlays as an Alternative Repair Technique, which includes Table 1, PDI Program Modifications to Appendix VIII, Supplement 11, and (3) Enclosure 1, Alternative Requirements for Dissimilar Metal Weld Overlays, including Mandatory Appendix I, Ambient Temperature Bead Welding, as modified by the licensees October 1, 2007, letter. Currently, the NRC staff has endorsed the use of Code Cases N-504-2, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping Section XI, Division 1, and N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [gas tungsten arc welding] Temper Bead Technique Section XI, Division 1, in Regulatory Guide 1.147, Revision 14. The NRC staff has not endorsed the use of Code Cases N-740, N-740-1, or N-638-2. Therefore, the NRC staff used the requirements of Code Cases N-504-2 and N-638-1 to aid in the evaluation of Alternative Requests CMP-022R1/023R1 as NRC-approved criteria associated with similar full structural PWOL applications. of the alternate request is based on Code Case N-740-1, Dissimilar Metal Weld Overlay for Repair of Class 1, 2, and 3 Items,Section XI, Division 1, with modifications.

Code Case N-740-1 was developed as the result of industrys need to repair (reduce or mitigate) flaws (suspected or confirmed) generated from Primary Water Stress Corrosion Cracking (PWSCC) via application of weld overlay. Also, the code case offers relief from post weld heat treatment (PWHT) by allowing the use of a temper-bead weld process. Code Case N-740-1 is essentially a combination of Code Cases N-504-2 and N-638-2.

The licensees alternative request is intended as a proactive approach to mitigate potential effects of PWSCC by means of a full structural PWOL, to fulfill the surface and geometric requirements of ASME Code,Section XI, Appendix VIII and permit the use of a PDI qualified UT examination. The proposed alternative will be employed at North Anna 1 and 2 during each units current third 10-year ISI interval. The full structural PWOL will be applied to the DMW Alloy 82/182 between LAS nozzles and SS safe ends. Nickel base Alloy 82/182 filler metal has been discovered to be susceptible to environmentally assisted cracking when exposed to reactor plant primary water (PW), a phenomenon referred to as PWSCC. In general, some damaging factors that may possess a strong influence on the SCC behavior of nickel-based alloys have been identified as PW hydrogen partial pressure, alloy chromium content, carbide precipitation, grain-boundary properties and temperature. Structural weld overlays have been

used for several years on piping of both boiling water reactors (BWR) and PWRs to inhibit the growth of flaws while establishing a new structural pressure boundary. The structural weld overlay will control growth in PWSCC flaws and maintain weld integrity by producing compressive stress in the DM weld. The full structural weld overlay will be sized to meet all structural requirements independent of the existing weld. Furthermore, the overlay will produce a UT examinable surface. Due to their close proximity, adjacent stainless steel RCS piping-to-stainless steel safe end SMW will be incorporated into the area of the weld overlay.

The basis for the licensees proposed alternatives are provided in Alternative Requests CMP-022R1/023R1, dated March 13, 2007 and modified by the licensees letter dated October 1, 2007. The licensee proposed to use Enclosure 1 of the alternate request, with modifications, to install the full structural PWOL. The PWOL is proposed as an alternative to the ASME Code,Section XI, IWA 4000 requirements. For inspection of the full structural PWOL, the licensee proposed using the PDI program as an alternative to the ASME Code requirements of Section XI, Appendix VIII, Supplement 11. The NRC staff has evaluated the licensees basis for the proposed alternatives and notes that Enclosure 1, based on Code Case N-740-1, is not approved for use by the NRC in RG 1.147, Revision 14. However, the NRC staff recognizes that Code Case N-740-1 (currently not endorsed by the NRC) does provide alternatives to the ASME Code equivalent to those approved in Code Cases N-504-2 and N-638-1. The NRC staffs evaluation of the proposed alternatives to ASME Code,Section XI, IWA-4000 and Appendix VIII, Supplement 11 are provided as follows.

As stated in Section 4.3.1, Required Activities, of Alternative Requests CMP-022R1/023R1, of the letter to the NRC, dated March 13, 2007, the licensee provided the following: 1) results within 14 days, of the completion of UT examinations on installed PWOL, and 2) a discussion including the reason for any repairs to the weld overlay and/or base metals.

4.1 General Requirements Code Case N-504-2 and/or Appendix Q of ASME Code,Section XI, require certain specifications and surface conditions of the applicable base metal (carbon steel, SS, and Alloy 82/182), the weld overlay filler metal (Alloy 52M) and the chromium content of the weld overlay deposits to be met to allow use of the PWOL technique. Section 1.0 of Enclosure 1 of revised RR CMP-022R1 and CMP-023R1, provides corresponding requirements to those in N-504-2 and Appendix Q. The licensee will deposit a barrier layer of ER309L SS filler metal on the base metal as a contingency for preventing possible hot cracking, which may result from high sulfur content in austenitic SS base material. The tendency of certain metals to exhibit hot cracking is caused by the segregation at grain boundaries of low-melting constituents (e.g., sulfur) in the weld metal. This may result in grain-boundary tearing under thermal contraction stresses. Hot cracking may be minimized by employing low impurity welding metals.

The licensee will install the barrier layer, ER309L, on the austenitic SS pipe and safe end only and stop short of the Alloy 82/182 weld material. The final tie-in to the existing nickel Alloy 82/182 weld will be performed with nickel Alloy 82 weld metal. Acid etching may be employed to identify the original Alloy 82/182 weld joint-to-safe-end interface as a precaution against weld over of the DMW with ER309L. Welding over the nickel base ENiCrFe-3 (Inconel 182) joint with an iron based ER309L electrode may cause cracking in the ER309L. The Alloy 82 will be welded from the tie-in to the mid point (approximately) of the Alloy 82/182 weld joint and

completed with weld overlay Alloy 52M. An informational liquid penetrant (LP) examination will be performed on the relevant portion (the SS safe end) of the PWOL first layer. If indications of hot cracking are identified, as determined by the welding engineer, the suspect nickel alloy weld metal will be completely removed along with any indications in the underlying base metal of the SS safe end. Complete removal of the nickel alloy weld metal shall be verified by acid etch and the resulting cavity will be LP inspected. Next, a weld build-up will be applied to the cavity using SS weld material for the bulk of the build-up with the final tie-in to the existing nickel alloy weld being performed using nickel alloy weld metal. This weld build-up will serve two purposes: (1) to restore the SS base metal to its original contour, and (2) to provide an improved base layer for application of the PWOL by reducing the amount of sulfur available for pick-up when applying the subsequent Alloy 52M full structural PWOL thereby reducing susceptibility to hot cracking.

The licensee reported that the PQ reports for qualifying the temper-bead section of the weld reinforcement and for overlay of the buttered P3 nozzle material were performed using austenitic nickel alloy ERNiCrFe-7 (Alloy 52 UNS N06052) or ERNiCrFe-7A (Alloy 52M, UNSN06054) filler metals. These filler materials were selected for their enhanced resistance to PWSCC. The Cr content of Alloy 52 and 52M is identical at 28-31.5%, providing superior corrosion resistance. Alloy 52M will be used for the full structural PWOL. Alloy 52M contains a higher Niobium content (0.5-1%), which acts as a stabilizer providing resistance to intergranular corrosion. Its chemistry acts to pin grain boundaries inhibiting separation between grains and hot tearing during weld puddle solidification. Also, the difference in composition improves weldability. Moreover, Alloy 52M exhibits ductile properties and toughness similar to austenitic SS piping welds at PWR operating temperature. These filler materials are suitable for welding over the ferritic nozzle, the Alloy 82/182 weld, and the adjacent austenitic SS elbow/pipe/reducer-to-safe end welds and components.

Delta ferrite (FN) measurements are not required per Enclosure 1 of the alternate request for weld overlay repairs made of Alloy 52/52M weld metal. The staff finds this acceptable because welds of Alloy 52/52M are 100% austenitic and contain no FN due to their high nickel composition (approximately 60% nickel).

4.2 Crack Growth Consideration and Design Code Case N-504-2 and/or Appendix Q of ASME Code,Section XI, provide requirements for the weld overlay design and crack growth calculations. Section 2 of Enclosure 1 of CMP-022R1/023R1 provides the corresponding requirements. The proposed mitigative full structural weld overlays are designed to contain the assumed flaw in the underlying base material or weld and is based on the limiting case of the two as follows: (a) 100-percent through-wall for the entire circumference, or (b) 100-percent through-wall for 1.5 inches or the combined width of the weld plus buttering, whichever is greater, in the axial direction for the entire circumference.

Section 2(a) of Enclosure 1 of the revised RR states that flaw characterization and evaluation requirements shall be based on the UT examination results. Section 4.3 of the alternative request states that the licensee will not perform a UT examination on the DMW prior to weld overlay installation. The NRC staff observes that the condition of the original welds may not be known without conducting a UT examination of the DMW prior to weld overlay installation. This

observation is based on UT examination being qualified to detect only the outer 25 percent of the original weld (or base metal) following installation of the overlay. The condition of the remaining inner 75 percent of the original weld would not be known.

However, Section 2(a)(2) of Enclosure 1 requires for mitigative overlays, that initial postulated flaw size assumptions for crack growth calculations shall be consistent for various pre-installation examination situations such as, an axial flaw 100 percent though the original wall thickness set at length of 1.5-inches, or the combined width of the weld plus buttering, whichever is greater, be used for the crack growth calculations. In addition, Section 2(a)(2)(b) requires that if no UT examination is performed prior to the application of the overlay, a postulated 360-degree circumferential flaw 100 percent though the original wall thickness shall be assumed for the crack growth calculations. Any actual flaw would not exceed the depth of these assumptions and would be detectable by the qualified post weld overlay UT examinations. The NRC staff finds that Section 2(a)(2)(b) is acceptable because the assumed flaw size for the crack growth calculation is a conservative assumption, which cannot be exceeded by any actual flaw.

Paragraphs g(2) and g(3) of Code Case N-504-2 require evaluations of residual stresses and flaw growth of the repaired weldments. Similar evaluations are required in Section 4.2 of Alternative Request CMP-022R1/023R1 which fulfill these required evaluations. For example, Section 2(b)(8) of Enclosure 1 of the revised RR states that the effects of any changes in applied loads, as a result of weld shrinkage from the entire overlay on other items in the piping system shall be evaluated. The report will include crack growth calculations to illustrate that crack growth in the weld overlay or base metal is acceptable and residual stress distribution in the weld overlay as well as the original weld demonstrate favorable stress distribution. The licensee stated that this stress evaluation conclusion is true for all nozzle structural mitigative weld overlay assessments except the portion of the ASME Code,Section III analysis dealing with the surge line overlay, which will address the insurge/outsurge transients. This portion of the analysis will utilize an engineering evaluation of these transients applying data from a DC Cook ASME Code,Section III analysis that qualified the design for seven heat-up and cool-down plus thirty insurge/outsurge cycles. The licensee will perform the preliminary analysis prior to the outage for which the overlays are scheduled for installation and will be available on site for NRC review. The seven heat-ups and cool-downs with thirty insurge/outsurge cycles represent a very conservative limit placed on interim operation and are associated with the interim analysis. Interim measures are not meant to correlate with an operating cycle-specific number. These limiting insurge/outsurges are not expected to occur in the next seven operating cycles based on one heat-up and one cool-down cycle. The North Anna 1 and 2 specific ASME Code,Section III analysis will be completed by December 31, 2007, at which time the seven heat-ups and cool-downs with thirty insurge/outsurge cycle restrictions will be resolved. The number of heat-ups and cool-downs are currently monitored and recorded by procedure. The NRC staff finds that the licensee will provide timely stress analyses of the nozzles as a result of PWOL, and, therefore, this issue is closed.

4.3 Examination and Inspection The ASME Code, Code Case N-504-2 allows the use of weld overlay repair by deposition of weld reinforcement on the outside surface of the pipe in lieu of mechanically reducing a defect to an acceptable flaw size.

Both Code Case N-504-2 and/or Appendix Q of ASME Code,Section XI require specific acceptance, pre-service and in-service examinations of the installed weld overlay. Section 3 of of CMP-022R1 and CMP-/023R1 provides corresponding requirements.

4.3.1 Acceptance Examination Section 3(a)(2) of Enclosure 1 of CMP-022R1/023R1 requires surface examinations of installed full structural PWOL and adjacent base material shall comply with the acceptance criteria of the Construction Code or NB-5300 of ASME Code,Section III. Section 3(a)(2) also requires UT examinations of the installed weld overlay to assure adequate fusion/bond with base metal and to detect welding flaws. The required acceptance examination surface volume and thickness are defined in Figure 1 of Enclosure 1. Planar flaws detected in the weld overlay acceptance examination shall meet the preservice examination standards of Table IWB-3514-2.

The proposed acceptance criteria are consistent with Code Case N-504-2 and Appendix Q of Section XI, except as follows: Section 3(a)(2) of Enclosure 1of the alternate request, requires that For planar indications outside this examination volume, the nominal wall thickness shall be t2" as shown in Fig 1(c) of Enclosure 1 for volumes A-E-H-D and F-B-C-G. Volumes A-E-H-D and F-B-C-G are defined in Figure 1(c) and refer to the portion of the weld overlay that is 1/2 inch away from the original weld. The NRC staff notes that a UT examination is not qualified to examine the inner 75 percent of the base metal after weld overlay installation. Therefore, the t2" dimension, which is the weld overlay thickness plus pipe thickness, should not be a parameter for the acceptance criteria of IWB-3514-2 because the t2" dimension includes the 75-percent depth of the base metal. Furthermore, larger flaws would be permitted to remain in service within the weld overlay if the t2" dimension were used establishing a non-conservative application.

The NRC staff notes that the pressurizer LAS nozzles and SS safe ends have not had a history of PWSCC. However, Alloy 600 DM weld material has had a history of PWSCC and the purpose of the weld overlay is to mitigate flaws suspected or confirmed from PWSCC of the DM weld. Volumes A-E-H-D and F-B-C-G as defined in Figure 1(c), pertain to the portion of the weld overlay that is not required to support the pressure boundary function of the PWOL or base metal. If larger flaws are allowed to remain in service in this portion of the weld overlay, the structural integrity of the portion of the PWOL that covers the original weld will not be adversely affected. Therefore, the NRC staff finds that the use of the t2" dimension is acceptable because the base metal of the pressurizer nozzle and safe ends at North Anna 1 and 2 are not susceptible to PWSCC, as indicated by their history.

4.3.2 Preservice Examination Section 3(b) of Enclosure 1 of CMP-022R1/023R1 requires a pre-service UT examination of the installed weld overlay and the upper (outer) 25 percent of the original pipe wall thickness. The required examination volume is defined in Figure 2 of Enclosure 1of the alternative request.

As stated in Section 3(b)(2) of Enclosure 1, if a flaw is detected in the outer 25 percent of the base metal or original weld during the pre-service examination, the as-found flaw size would be used for the crack growth evaluation. The NRC staff does not believe this is a conservative assumption for the crack growth calculation if the original weld was not examined prior to

installing the PWOL. The current UT examination is qualified only to detect flaws in the outer 25 percent of the pipe base metal after a weld overlay is applied. With the limited UT qualification, the condition of the inner 75 percent of the pipe base metal would not be known.

A conservative assumption would be to assume existence of a crack of 75-percent through-wall depth in the inner 75-percent pipe base metal. The 75-percent depth flaw should be added to the depth of the crack found in the outer 25 percent of the pipe base metal. This worst-case crack (the sum of two flaws) should be used to calculate crack growth. The licensee shall only use the actual UT determined through-wall dimension in the crack growth analysis for flaws that are detected by the qualified UT examination to be entirely within the outer 25 percent and do not breach the interface between the outer 25 percent and inner 75 percent of the original base metal or weld metal thickness. However, in Section 2(a)(2)(b) the licensee states that 100%

original through-wall thickness shall be used satisfying this conservative assumption. In addition, the NRC staff finds that Section 3(b)(3) adequately addresses a conservative flaw size to be used in the crack growth calculation by not allowing the use of ASME Code acceptance criteria that exceed the preservice examination standards of Section 3(b)(2). Therefore, the proposed pre-service examination requirements in Section 3(b) of Enclosure 1 of Alternative Requests CMP-022R1/023R1 are acceptable.

In the letter dated October 1, 2007, the licensee stated that due to a localized fabrication repair in the original DMW buttering region of A safety valve nozzle PWOL, at North Anna Unit 1, the examination resulted in less than the required volume shown in Figure 2 of Enclosure 1 to of the letter of March 13, 2007. The calculated composite coverage of the required examination volume is 99.8%. To achieve 100% coverage would require modification or machining of the nozzle area. In this configuration the composite coverage is sufficient to provide early indication of any flaws introduced through operational effects without additional modification.

The staff concludes, based on the preceding discussion, that compliance with the ASME Code required preservice and in-process examinations for the North Anna Unit 1 A safety valve nozzle PWOL provides an acceptable level of quality and safety.

4.3.3 Inservice Examination Section 3(c) of Enclosure 1 the revised RR provides requirements for UT inservice examinations with the examination volume defined in Figure 2 of Enclosure 1. Section 3(c)(4) allows flaws in PWOL to be accepted by IWX-3640 of ASME Code,Section XI. The NRC staff agrees with use of the acceptance criteria of IWB-3600 for flaws in the weld overlay if the flaw growth is caused by fatigue. However, flaw growth caused by PWSCC is considered of greater risk and the NRC staff finds such a growth mechanism in PWOL unacceptable. Section 4.3.1 of the alternate request added the following requirement:

If flaw growth in the weld overlay occurs and the acceptance standards of IWB-3514-2 cannot be met and the cause is determined to be PWSCC or cannot be determined, North Anna 1 and 2 will repair the flaw and will not use IWB-3600, IWC-3600, or IWD-3600 to accept these types of flaws.

The NRC staff finds the above requirement acceptable because the licensee will not use IWX-3600 to accept suspected PWSCC flaws in PWOL.

4.4 Mandatory Appendix 1--Ambient Temperature Temper-Bead Welding Code Case N-638-1 provides requirements for ambient temperature temper bead welding.

Mandatory Appendix 1 of Enclosure 1 of CMP-022R1 and CMP-023R1 is based on Code Case N-638-2. The major difference between the two documents is discussed below.

Paragraph 1(b) of Mandatory Appendix 1 states that the maximum area of the weld overlay based on the finished surface over the ferritic base material shall be 500 square inches.

Code Case N-638-1 allows only 100 square inches over the ferritic base material. Section 4.1 of the alternate request added that the ASME committee has indicated inside diameter compressive stress levels remain essentially the same between 100 square inches and 500 square inches in relation to weld overlay applications. The presentation slides entitled, "Bases for 500 Square Inch Weld Overlay Over Ferritic Material," were provided to the NRC staff in a public meeting held on January 10, 2007 (ADAMS Accession No. ML070470565).

Additional justification is provided in Electric Power Research Institute (EPRI) Report 1014351, "Repair and Replacement Applications Center: Topical Report Supporting Expedited NRC Review of Code Cases for Dissimilar Metal Weld Overlay Repairs, December 2006."

Based on a review of the information provided, the NRC staff concludes that the 500-square-inch weld area limit over the ferritic base metal is acceptable. The EPRI report provided results of finite element analyses demonstrating that the stresses of a nozzle with the 500-square inch weld area will not adversely affect the integrity of the pressurizer nozzle. In addition, Code Case N-638-1 requirements are based on a groove weld design for which the finished surface area requirement also allows the depth of the weld to be no greater than one-half of the ferritic base metal thickness. The code case is adapted for use with the SWOL design which is a surface design with slight depth of penetration and minimal induced stresses as compared to a groove weld design.

The NRC staff finds that the requirements of Enclosure 1 together with Mandatory Appendix 1 of the alternate request are consistent with the intent of provisions approved in Code Cases N-504-2 & N-638-1 including Section XI, Appendix Q, of the ASME Code. Therefore, the proposed alternative is acceptable.

4.5 Modifications to Appendix VIII, Supplement 11 The U.S. nuclear utilities created the PDI program to implement performance demonstration requirements contained in Section XI, Appendix VIII, of the ASME Code. Moreover, the PDI program is designed for qualifying equipment, procedures and personnel to examine weld overlays in accordance with the UT criteria of Appendix VIII, Supplement 11. Preceding the Supplement 11 program, EPRI maintained a performance demonstration program for weld overlay qualification under the Tri-party Agreement1. In lieu of having two programs with similar objectives, the NRC staff recognized the PDI program2 for weld overlay qualifications as an acceptable alternative to the Tri-party Agreement. Although the PDI program was developed for ISI at BWR plants, it is applicable to PWR plants like North Anna 1 and 2, because the application for PWOL use is the same concept.

The PDI program is routinely assessed by the NRC staff for consistency with the current ASME Code and proposed changes. The PDI program does not fully comport with the existing requirements of Supplement 11. PDI presented the differences at public meetings in which the NRC participated3, 4. The differences involve flaw location within test specimens and fabricated flaw tolerances. The changes in flaw location permitted using test specimens from the Tri-party Agreement and the changes in fabricated flaw tolerances provide UT acoustic responses similar to responses associated with intergranular stress corrosion cracking. The differences between the PDI program and Supplement 11 are presented in Table 1, PDI Program Modifications to Appendix VIII, Supplement 11, of Enclosure 1 of CMP-022R1/023R1.

The NRC staff evaluated the differences proposed by the licensee between the PDI program and Appendix VIII, Supplement 11 in the licensees revised RR. The NRC staff concludes that an acceptable level of quality and safety is incorporated into the licensees proposed RR.

5.0 CONCLUSION

S The NRC staff has reviewed the licensees submittal and has determined RRs CMP-022R1/023R1 will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the use of the Alternative Request CMP-022R1/023R1 in lieu of the requirements contained in the 1989 edition of the ASME Code, for North Anna 1 and the 1995 edition through 1996 addenda for North Anna 2 of ASME Code,Section XI, IWA-4000, and in the 1989 edition for North Anna 1 and 1995 edition through 1996 addenda for North Anna 2 of Section XI, Appendix VIII, Supplement 11, for the following items:

1 The Tri-party Agreement is between NRC, EPRI, and the Boiling Water Reactor Owners Group (BWROG), Coordination Plan for NRC/EPRI/BWROG Training and Qualification Activities of NDE (Nondestructive Examination) Personnel, July 3, 1984.

2 US NRC Letter from William H. Bateman to Michael Bratton, Weld Overlay Performance Demonstration Administered by PDI as an Alternative for Generic Letter 88-01 Recommendations, January 15, 2002 (ML020160532).

3 US NRC Memorandum from Donald G. Naujock to Terence Chan, Summary of Public Meeting Held June 12 through June 14, 2001, with PDI Representatives, November 29, 2001 (ML013330156).

4 US NRC Memorandum from Donald G. Naujock to Terence Chan, Summary of Public Meeting Held January 31 -

February 2, 2002, with PDI Representatives, March 22, 2002 (ML010940402).

The proposed alternative is approved for the full structural PWOL of the DM and SM welds of the pressurizer surge line, safety valve, and relief valve nozzles at North Anna 1 and 2. The PWOL will include the adjacent stainless steel elbow/pipe/reducer-to-safe-end welds. The approval applies to each of the welds listed in Section 2.2 and generically depicted in Figure 1 of RRs CMP-022R1/023R1. A full structural PWOL (designed for the worst-case flaw) will be applied in accordance with the requirements of Enclosure 1 of RR CMP-022R1/023R1, followed by UT examination upon completion. No pre-repair UT will be performed.

The UT examination of the completed PWOL will be accomplished in accordance with ASME Code,Section XI, 1998 edition including addenda through 2000 for North Anna 1 and 2, Appendix VIII, Supplement 11, as modified by the licensees October 1, 2007, letter and to comply with the PDI program as listed in Attachment 2, Enclosure 1 of CMP-022R1/023R1.

The effective period of Alternative Request CMP-022R1/023R1 will be up to and including the last outage of the current third 10-year ISI interval which includes the inservice examination requirements of Enclosure 1 of the alternative request for the six applied weld overlay locations for North Anna 1 and 2, which ends on April 30, 2009, and December 13, 2010, respectively.

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

Principal Contributor: D. Tarantino Date: December 19, 2007

North Anna Power Station, Units 1 & 2 cc:

Mr. David A. Christian Senior Resident Inspector Senior Vice President North Anna Power Station and Chief Nuclear Officer U. S. Nuclear Regulatory Commission Virginia Electric and Power Company P. O. Box 490 Innsbrooks Technical Center Mineral, Virginia 23117 5000 Dominion Boulevard Glen Allen, VA 23060-6711 Mr. Daniel G. Stoddard Site Vice President Mr. C. Lee Lintecum North Anna Power Station County Administrator Virginia Electric and Power Company Louisa County Post Office Box 402 Post Office Box 160 Mineral, Virginia 23117-0402 Louisa, Virginia 23093 Dr. Robert B. Stroube, MD, MPH Ms. Lillian M. Cuoco, Esq. State Health Commissioner Senior Counsel Office of the Commissioner Dominion Resources Services, Inc. Virginia Department of Health 120 Tredegar Street, RS-2 Post Office Box 2448 Richmond, VA 23219 Richmond, Virginia 23218 Dr. W. T. Lough Mr. Mark D. Sartain, Director Virginia State Corporation Commission Nuclear Safety & Licensing Division of Energy Regulation Virginia Electric and Power Company Post Office Box 1197 North Anna Power Station Richmond, Virginia 23218 P. O. Box 402 Mineral, VA 23117 Old Dominion Electric Cooperative 4201 Dominion Blvd.

Glen Allen, Virginia 23060 Mr. Chris L. Funderburk, Director Nuclear Licensing & Operations Support Dominion Resources Services, Inc.

Innsbrook Technical Center 5000 Dominion Blvd.

Glen Allen, Virginia 23060-6711 Office of the Attorney General Commonwealth of Virginia 900 East Main Street Richmond, Virginia 23219