ML11187A323
| ML11187A323 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 06/29/2011 |
| From: | Price J Virginia Electric & Power Co (VEPCO), Dominion |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 11-336 | |
| Download: ML11187A323 (10) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 June 29, 2011 U.S. Nuclear Regulatory Commission Serial No.11-336 Attention: Document Control Desk NLOS/ETS One White Flint North Docket No.
50-338 11555 Rockville Pike License No.
NPF-4 Rockville, MD 20852-2738 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
NORTH ANNA POWER STATION UNIT 1 - Nl-14-CMP-001 USE OF WELD OVERLAYS AS AN ALTERNATIVE REPAIR TECHNIQUE FOR STEAM GENERATOR HOT LEG NOZZLES RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION In a March 30, 2011 letter, Dominion requested NRC approval for proposed alternatives to certain (ASME Code) Section Xl - 2004 Edition requirements associated with the Steam Generator hot leg nozzles repairs. The proposed alternative will permit the application of full structural weld overlay (FSWOL) that are planned to mitigate the potential for primary water stress corrosion cracking (PWSCC) susceptibility at North Anna Unit 1. In a letter dated June 9, 2011, the NRC staff requested additional information to complete the review of the proposed alternative examination requirements.
The attachments to this letter provide the requested information.
Dominion continues to request review and approval of this request to support implementation of the alternative repair technique during the North Anna Unit 1 spring 2012 refueling outage, currently scheduled to begin in March 2012.
If you have any questions regarding this submittal, please contact Mr. Thomas Shaub at (804) 273-2763.
Very truly yours, J.A rice Vic Pr sident - Nuclear Engineering Attachment
- 1. Response to Request for Additional Information - Relief Request NI-14-CMP-001
- 2. Justification for Extension of the Temper Bead Limit to 1000 Square Inches for WOL of P1 and P3 Materials.
Commitments made in this letter: None AOO I
Serial No.11-336 Docket No. 50-338 Response to Request for Additional Information Alternative Weld Overlay Page 2 of 2 cc:
U.S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257 Mr. J. E. Reasor, Jr.
Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.
Suite 300 Glen Allen, Virginia 23060 Mr. J. T. Reece NRC Senior Resident Inspector North Anna Power Station Mr. R. E. Martin NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 G-9A Rockville, Maryland 20852 Ms. K. R. Cotton NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 G-9A Rockville, Maryland 20852 Mr. M. M. Grace Authorized Nuclear Insurance Inspector North Anna Power Station
Serial No.11-336 Docket No. 50-338 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RELIEF REQUEST Nl-14-CMP-001 North Anna Power Station Unit 1 Virginia Electric and Power Company (Dominion)
Serial No.11-336 Docket No. 50-338 Response to Request for Additional Information NI-14-CMP-001 Page 1 of 5 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RELIEF REQUEST Nl-14-CMP-001 BACKGROUND By letter dated March 30, 2011, Virginia Electric and Power Company (Dominion) submitted relief request (RR) Nl-14-CMP-001 for the U.S.
Nuclear Regulatory Commission (NRC) review and approval. The licensee proposed alternatives to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section Xl, requirements associated with dissimilar metal (DM) weld repairs.
RR Nl-14-CMP-001 pertains to the use of full structural weld overlays (FSWOL) as an alternative repair technique for steam generator (SG) hot leg nozzle dissimilar metal (DM) welds at North Anna Power Station, Unit 1.
RR Nl-14-CMP-001 was submitted as a contingency in case unacceptable flaw indications are found during the examinations of North Anna, Unit 1 SG hot leg nozzle DM welds during the fourth 10-year inservice inspection (ISI) interval.
The fourth 10-year ISI interval commenced on May 1,2009 and will end on April 30, 2019.
The NRC staff has reviewed the information provided by the licensee in RR N1-14-CMP-001 and finds additional information is needed to complete its review.
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION NRC Question 1 On page 1 of Enclosure 1, Section 1 stated that the ASME Code components affected is Examination Category B-F and Item No. B9.1 1. The staff recognizes that the item no.
should be B5.70. Please clarify and/or revise the examination category and/or item no.
Dominion Response The correct examination category is B5.70.
NRC Question 2 On page 1 of Enclosure 1, Section 3 does not contain the ASME Code, Section Xl, Appendix VIII, Supplements 2 and 10, as the applicable ASME Code requirement, even though on page 15 of Enclosure 1, Attachment 1, Section A1.3(a)(3) specifies both supplements.
Serial No.11-336 Docket No. 50-338 Response to Request for Additional Information NI-14-CMP-001 Page 2 of 5
- a. Clarify why these supplements are not required and/or not included in the submittal as the applicable ASME Code requirement.
- b. Specify which edition and addenda of the ASME Code, Section Xl, will be used for Appendix VIII, Supplements 2 and 10.
Dominion Response Response for 2a:
The ASME Code, Section Xl, Appendix VIII, Supplement 10 is applicable for the pre-overlay weld examination and should be included as an applicable Code reference in Section 3 of Enclosure 1. The reference to Supplement 2 on page 15 of Enclosure 1, Section A1.3(a)(3) and A1.3(a)(4), should not have been included in the submittal since supplement 2 is not applicable to these welds. Please delete the reference from our submittal.
Please include the following as an applicable Code requirement in Section 3 of of our March 30, 2011 submittal:
ASME Code, Section Xl, Appendix VIII, Supplement 10 Response to 2b:
The applicable edition of the ASME Code for the implementation of Section Xl, Appendix VIII is the 2001 Edition.
Please include the following additional reference for the implementation of ASME Section Xl in Section 2 of Enclosure 1, of our March 30, 2011 submittal:
American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Section Xl -2001 Edition for the implementation of Appendix VIII.
NRC Question 3 On page 2 of Enclosure 1, Section 3 does not contain the appropriate edition and addenda of the ASME Code, Section Xl, for Appendix VIII, Supplement 11. Specify the appropriate edition and addenda of the ASME Code, Section Xl, for Appendix VIII, Supplement 11.
Dominion Response The applicable edition of the ASME Code for the implementation of Section Xl, Appendix VIII is the 2001 Edition.
Serial No.11-336 Docket No. 50-338 Response to Request for Additional Information NI-14-CMP-001 Page 3 of 5 Please include the following additional reference to, Section 3 of Enclosure 1:
American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Section Xl -2001 Edition for the implementation of Appendix VIII.
NRC Question 4 On page 9, Enclosure 1, Section 5, Subsection titled "Area Limitation," the licensee proposes to extend the temper bead surface area to up to greater than 700 in2 but less than 1000 in2 over the low alloy steel. The licensee stated that EPRI has issued Report 1021073 on June 21, 2010, entitled "Justification for Extension of the Temper Bead Limit to 1000 Square Inches for WOL of P1 and P3 Materials." The licensee stated that this report showed that WOL area could be expanded to an area of 1000 square inches without creating deleterious residual stress levels and still maintain the structural integrity of the component. The staff previously approved up to 700 in2 surface area over the low alloy steel only but not greater than 700 in2 (i.e., safety evaluation letter dated January 21, 2010, "Davis Besse Nuclear Power Station, Unit 1, relief request RR A33 for the Application of Full Structural Weld Overlays on Dissimilar Metal Welds of Reactor Coolant Piping (TAC No. ME0478)," ADAMS Accession No. ML100080573).
Provide the results of the stress analysis performed on the FSWOL for surface area up to 1000 in2 over the low alloy steel at North Anna, Unit 1.
Dominion Response The stress analyses for the FSWOL for the North Anna steam generator nozzles have not been completed to date. The basis for the acceptability of increasing the area of the WOL is the EPRI Report 1021073, "Justification for Extension of the Temper Bead Limit to 1000 Square Inches for WOL of P1 and P3 Materials," which includes justification for use of temper bead for applications up to 1000 in2. A copy of the non-proprietary report is included as Attachment 2. As indicated in our March 30, 2011 submittal, Dominion plans to submit the stress analysis for the completed FSWOL to the NRC prior to entering Mode 4 after the refueling outage.
NRC Question 5 On page 14 of Enclosure 1, Attachment 1, Section A1.2.2, Subsection (d)(3) specifies the delta ferrite content of 5-15 Ferrite Number (FN) for the stainless steel filler metal that will be used. ASME Code Case N-504-4, Section (e), states that, "The weld reinforcement shall consist of a minimum of two weld layers having as-deposited delta ferrite content of at least 7.5 FN. The first layer of weld metal with delta ferrite content of least 7.5 FN shall constitute the first layer of the weld reinforcement design thickness.
Alternatively, the first layers of at least 5 FN may be acceptable based on evaluation."
Serial No.11-336 Docket No. 50-338 Response to Request for Additional Information NI-14-CMP-001 Page 4 of 5 Discuss whether the requirements of ASME Code Case N-504-4, Section (e), will be satisfied.
Dominion Response.
The requirements of ASME Code Case N-504-4 Section (e) will not be satisfied and do not apply to the weld overlay.
In accordance with Attachment 1, Section A1.2.2, Subsection (d)(3) of our March 30, 2011 submittal, the stainless steel filler material is applied as a buffer layer only and is not considered weld reinforcement nor will it be counted towards the design thickness requirements specified for the weld overlay.
NRC Question 6 On page 16 of Enclosure 1, Attachment 1, Section A1.3, Subsection (b)(1) of the March 30, 2011 submittal specifies the axial length of the weld overlay to be 0.75 /Rt. Clarify if this distance is required to be applied to both sides of the weld overlay (i.e., the nozzle side and the safe end side).
Dominion Response As required by Enclosure 1, Attachment 1, Section A1.3, Subsection (b)(1) of the March 30, 2011 submittal, 'The axial length and end slope of the weld overlay shall cover the weld and heat affected zones on each side of the weld, as well as any stress corrosion cracking susceptible base material adjacent to the weld, and provide for load redistribution from the item into the weld overlay and back into the item without violating applicable stress limits of NB-3200." This sentence requires that the axial length in question applies to both sides of the susceptible weld.
NRC Question 7 On page 18 of Enclosure 1, Attachment 1, Footnote 1 of Figure Al -1 states that "Dimension b is equivalent to the nominal thickness of the nozzle or pipe being overlaid, as appropriate." Dimension b is the UT distance away from the toe of the original weld.
The above requirement is inadequate and inconsistent with Footnote 2 of Figure Al -2 which requires that the examination extent shall be at least 1/2 inch beyond the as-found flaw. The staff suggests the following wording:
"...Dimension b is equivalent to the nominal thickness of the nozzle or pipe being overlaid, as appropriate; however, it shall not be less than Y2 inch from the toe of the original weld..."
Serial No.11-336 Docket No. 50-338 Response to Request for Additional Information NI-14-CMP-001 Page 5 of 5 Revise Footnote 1 of Figure Al-1 or justify why the proposed footnote 1 of Figure Al-1 is adequate.
Dominion Response Figure A1-1 of Enclosure 1, Attachment 1 of the March 30, 2011 submittal, provides visual definitions of the acceptance examination volume and thicknesses for the-weld overlay itself. Figure A1-2 defines the Preservice and Inservice Examination Volume.
As such, the figures are not related. In addition, dimension b of Figure Al-1 does not define the examination extent. Dimension b is equivalent to the nominal thickness of the nozzle or pipe being overlaid which varies accordingly with the component and defines whether t, or t2 is utilized when applying the flaw acceptance standards of IWB-3514.
Dimension b is used to divide region A-B-C-D of Figure Al-l(b) into three regions (A-E-H-D, E-F-G-H, and F-B-C-G) for the purpose of defining t, and t2 for application of the acceptance standards of ASME Code IWB-3514 as described in Section A1.4(a)(3).
NRC Question 8 On Page 9 of Enclosure 1, "Analyses and Verifications," Item No. 1 states that inside diameter (ID) weld repairs shall be assumed in the stress analyses to effectively bound any actual weld repairs that may have occurred in the nozzles. Discuss the repaired flaw size that was assumed in the stress analyses.
Dominion Response The stress analysis conservatively assumes an original construction repair weld was made that extended from the inside diameter 50% through wall for 360 degrees.
Serial No.11-349 Docket No. 50-338 Response to Request for Additional Information NI-14-CMP-001 JUSTIFICATION FOR EXTENSION OF THE TEMPER BEAD LIMIT TO 1000 SQUARE INCHES FOR WOL OF P1 AND P3 MATERIALS North Anna Power Station Unit 1 Virginia Electric and Power Company (Dominion)
2 EECTRIC POWER RESEARCH INSTITUTE Justification for Extension of Temper Bead Limit to 1000 Square Inches for WOL of P1 and P3 Materials