ML080940352

Request for Additional Information, Relief Request (RR-89-61) for Use of Weld Overlays as an Alternative Repair and Mitigation Technique

ML080940352
Person / Time
Site:	Millstone
Issue date:	04/10/2008
From:	John Hughey NRC/NRR/ADRO/DORL/LPLI-2
To:	Christian D Virginia Electric & Power Co (VEPCO)
Thorpe-Kavanaugh Meghan, LP1-2, 415-5735
References
RR-89-61, TAC MD6965
Download: ML080940352 (9)

Text

April 10, 2008 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:

MILLSTONE POWER STATION, UNIT NO. 2 - REQUEST FOR ADDITIONAL INFORMATION REGARDING RELIEF REQUEST (RR-89-61) FOR USE OF WELD OVERLAYS AS AN ALTERNATIVE REPAIR AND MITIGATION TECHNIQUE (TAC NO. MD6965)

Dear Mr. Christian:

By letter to the Nuclear Regulatory Commission (NRC) dated October 4, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML072780147),

Dominion Nuclear Connecticut, Inc. (DNC) submitted the proposed relief request (RR) to allow use of weld overlays as an alternative repair and mitigation technique. The NRC staff has reviewed the RR submitted by DNC and has identified a need for additional information required to complete the review as set forth in the Enclosure.

The draft questions were sent to Mr. Bill Bartron, of your staff, to ensure that the questions were understandable, the regulatory basis for the questions was clear, and to determine if the information was previously docketed. During a teleconference on April 2, 2008, Mr. Barton indicated that the licensee will submit a response by April 11, 2008. No changes were made to these questions as a result of this call.

Please note that if you do not respond to this letter within the agreed-upon response time or provide an acceptable alternate date in writing, we may reject your RR under the provisions of Title 10 of the Code of Federal Regulations, Section 2.108. If you have any questions, please contact Meghan Thorpe-Kavanaugh at (301) 415-5735.

Sincerely,

/ra/

John D. Hughey, Project Manager Plant Licensing Branch I-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No.: 50-336

Enclosure:

Request for Additional Information cc w/encl: See next page

April 10, 2008 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:

MILLSTONE POWER STATION, UNIT NO. 2 - REQUEST FOR ADDITIONAL INFORMATION REGARDING RELIEF REQUEST (RR-89-61) FOR USE OF WELD OVERLAYS AS AN ALTERNATIVE REPAIR AND MITIGATION TECHNIQUE (TAC NO. MD6965)

Dear Mr. Christian:

By letter to the Nuclear Regulatory Commission (NRC) dated October 4, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML072780147),

Dominion Nuclear Connecticut, Inc. (DNC) submitted the proposed relief request (RR) to allow use of weld overlays as an alternative repair and mitigation technique. The NRC staff has reviewed the RR submitted by DNC and has identified a need for additional information required to complete the review as set forth in the Enclosure.

The draft questions were sent to Mr. Bill Bartron, of your staff, to ensure that the questions were understandable, the regulatory basis for the questions was clear, and to determine if the information was previously docketed. During a teleconference on April 2, 2008, Mr. Barton indicated that the licensee will submit a response by April 11, 2008. No changes were made to these questions as a result of this call.

Please note that if you do not respond to this letter within the agreed-upon response time or provide an acceptable alternate date in writing, we may reject your RR under the provisions of Title 10 of the Code of Federal Regulations, Section 2.108. If you have any questions, please contact Meghan Thorpe-Kavanaugh at (301) 415-5735.

Sincerely,

/ra/

John D. Hughey, Project Manager Plant Licensing Branch I-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No.: 50-336

Enclosure:

Request for Additional Information cc w/encl: See next page DISTRIBUTION:

PUBLIC LPL1-2 R/F RidsNrrDorlLpl1-2 RidsNrrPMJHughey RidsNrrLAABaxter RidsRgn1MailCenter RidsAcrsAcnw&mMailCenter RidsOgcRp RidsNrrPMMThorpe-Kavanaugh ADAMS Accession No.ML080940352

• Via email

• • By memo dated 4/2/08 OFFICE LPL1-2/PM LPL1-2/PM LPL1-2/LA DCI/CPNB LPL1-2/BC NAME MThorpe-Kavanaugh JHughey ABaxter*

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HChernoff DATE 4/10/08 4/10/08 04/03/08 04/02/08 4/10/08 Official Record Copy

Enclosure MILLSTONE POWER STATION, UNIT NO. 2 RELIEF REQUEST NUMBER 89-61 USE OF WELD OVERLAYS AS AN ALTERNATIVE REPAIR AND MITIGATION TECHNIQUE DOCKET NO. 50-336 TAC NO. MD6965 REQUEST FOR ADDITIONAL INFORMATION By letter dated October 4, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML072780147), Dominion Nuclear Connecticut, Inc. proposed an alternative relief request (RR)-89-61 to the requirements of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code), for mitigating primary water stress corrosion cracking (PWSCC) on dissimilar metal welds using full structural weld overlays at Millstone Power Station, Unit 2 (MPS2). To complete its review, the Nuclear Regulatory Commission (NRC) staff is requesting the following additional information:

1. It is the NRC staffs understanding that the planned weld overlays are classified as Repair Weld Overlays in accordance with Enclosure 1 of Alternative RR-89-61 and that pre-weld overlay ultrasonic test (UT) examinations will not be performed on these welds.

Please clarify if pre-weld overlay ASME Section XI, Appendix VIII, Supplement 10, UT examinations will be performed on the welds as described in RR-89-61. If repair weld overlays are intended, please describe why the requirements for mitigative weld overlays are specified in the proposed alternative.

2. Discuss whether the subject nozzles have been ultrasonically examined under the Risk-Informed Inservice Inspection (RI-ISI) program or Materials Reliability Program (MRP)-139 in previous refueling outages. If the subject nozzles have had UT examinations, discuss whether flaws have been detected in the subject nozzles.

3. Paragraph 4.2 on page 12 of the proposed alternative appears to conflict with Section 3(c) of Enclosure 1 of Alternative RR-89-61, with regard to inservice inspection (ISI) of cast stainless steel (CSS) components. Describe the ISI program plans for the structural weld overlay (SWOL) population specifically, discussing the frequency, population, and examination techniques.

4. Paragraph 2(b)(2) on page 21 of the proposed alternative requires that the slope of the overlay is not to exceed 30 degrees. This has been changed from 45 degrees as described in Code Case N-740. Confirm and describe why the 30-degree angle is more conservative than the 45-degree angle.

5. In Section 3 of Enclosure 1 on page 22 of Alternative RR-89-61, the RR states, For cast stainless steel components for which no supplement is available in Appendix VIII, the weld volume shall be examined by Appendix VIII procedures to the maximum extent practicable and the remaining volume may be examined using Appendix III.

Clarify the procedural requirements for the examination for the portions of CSS components not examined by Appendix VIII.

6. Page 19, paragraph 1(d)(3), of the submittal states that a layer of austenitic stainless steel filler metal may be applied across the austenitic stainless steel base metal to reduce the risk of cracks. Paragraph 1(e) on page 19 requires existence of certain delta ferrite content in the welded metal when austenitic stainless steel weld metal is used, therefore:

a. Identify the austenitic stainless steel weld filler metal that will be used for the butter layer.

b. Confirm that the Certified Material Test Report for the austenitic stainless steel filler wire specifies a minimum delta ferrite content.

c. Provide the maximum and minimum delta ferrite number (FN).

7. Page 19, paragraph 1(d)(3), of the submittal specifies that the thickness of the austenitic stainless steel filler metal over the austenitic base metal shall not be used in meeting the weld reinforcement design thickness requirements. Paragraph 1(e) provides requirements for the austenitic stainless steel weld metal. Paragraph 1(e) also requires that the austenitic stainless steel weld metal with delta ferrite content of at least 7.5 FN be considered as the first layer of the weld reinforcement. It seems that a potential conflict may exist between the requirements of paragraph 1(d)(3) and 1(e) regarding whether the first layer of the austenitic stainless steel weld metal can be credited for the weld overlay design thickness. Clarify the intent of paragraphs 1(d)(3) and 1(e).

8. Paragraphs 1(c)(1), 1(c)(1)(a), and 1(c)(1)(b) on page 18 of Enclosure 1 provide the alternative to the post-weld heat treatment (PWHT) of the Construction Code and Owners Requirements. The alternative eliminates PWHT for weld overlays when the overlay is applied to P-No.1 base material. As of March 2008, the NRC staff still has concerns with this issue and has not decided the acceptability of the elimination of PWHT in paragraphs 1(c)(1)(a) and 1(c)(1)(b).

9. As part of the installation of SWOLs at MPS2, the NRC staff requests the following information be provided to the NRC within 14 days following the completion of the UT examination of the SWOL installations:

a. Provide a report of the weld overlay examination results including a listing of indications detected. The recording criteria of the UT examination procedure to be used for the examination of the overlays requires that all indications, regardless of amplitude, be investigated to the extent necessary to provide

accurate characterization, identity, and location. Additionally, the procedure requires that all indications, regardless of amplitude, that cannot be clearly attributed to the geometry of the overlay configuration be considered flaw indications.

b. Provide a report documenting the disposition of indications using the standards of ASME Section XI, IWB-3514-2 and/or IWB-3514-3 criteria and, if possible, the type and nature of the indications. The UT examination procedure requires that all suspected flaw indications are to be plotted on a cross-sectional drawing of the weld and that the plots should accurately identify the specific origin of the reflector.

c. Provide a report discussing any repairs to the weld overlay material and/or base metal and the reason for the repairs.

10. Paragraphs g(2) and g(3) of Code Case N-504-2 require evaluations of residual stresses and flaw growth of the repaired weldments. The NRC staff believes 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.

a. Confirm that the analyses will be performed to show that the requirements of Subarticles NB-3200 and NB-3600 of the ASME Code, Section Ill are satisfied.

b. Confirm that the analyses include the crack growth calculations to demonstrate that crack growth in the weld overlay or base metal is acceptable and residual stress distribution in the weld overlay and original weld demonstrate favorable stress distribution.

c. The NRC staff requests that the licensee submit the preliminary results of the evaluations prior to entry into Mode 4 from the refueling outage and the final evaluations within 60 days of the plant restart date.

11. Paragraph I-2.1(h)(2) of Mandatory Appendix I on page 29 of Enclosure 1 provides a means of determining an adjustment temperature for the welding procedure qualification.

This adjustment temperature was not a part of Code Case N-638-1 and has, therefore, not been approved by the staff. Provide the technical basis of this requirement.

12. The staff has determined that a number of questions submitted during the review of Alternative Request IR-2-47, Revision 1, dated March 28, 2007 (ADAMS Accession No. ML070880565), for Millstone Power Station, Unit 3 (MPS3) are applicable to the review of Alternative RR-89-61. Confirm that the answers to questions 14 through 21 in your March 28, 2007, response (ADAMS Accession No. ML070880565) for MPS3 weld overlay Alternative Request IR-2-47, Revision 1, remain valid with regard to Alternative RR-89-61 for MPS2.

13. Paragraph 3(a)(3)(a) on page 23 of Enclosure 1 states, In applying the acceptance standards to planar indications the thickness t1, t2,or t3 defined in Fig. 1(b) shall be used as the nominal wall thickness in Table IWB-3514-2, provided in the base metal beneath the flaw (i.e., safe end, nozzle, or piping material) is not susceptible to stress corrosion cracking (SCC).

The NRC staff has reservations regarding the definition and concept of t3 in Figure 1(b) because of the measurement accuracy and inherent UT examination uncertainty.

Provide technical justification for the use of the t3 parameter or eliminate the t3 definition from paragraph 3(a)(3)(a) and Figure 1(b).

14. Paragraph 2(a)(4), on page 20 of Enclosure 1, states that For austenitic cast stainless steel components, initial inside-surface-connected planar flaws equal to 75% of the original wall thickness shall be assumed provided 90% of the examination volume, as defined in Fig. 2, is obtained. If 90% coverage is not obtained, a 100% through wall flaw shall be assumed. The NRC staff has concerns regarding use of the criterion of 90%

examination coverage in deciding the initial flaw size in crack growth calculations in Paragraph 2(a)(4). The NRC staff has provided 2 options in term of flaw size as shown in the Safety Evaluation for Arkansas Nuclear One, Unit 2 (ANO-2) weld overlay relief request dated March 17, 2008 (ADAMS Accession No. ML080660082). In the ANO-2 Safety Evaluation, the NRC staff specified the following options:

Option (1): The initial flaw depth should be postulated at 100 percent through-wall for the crack-growth calculations.

Option (2): If the 100 percent through-wall flaw is impractical or creates a hardship in the overlay design or installation, an initial flaw with 75 percent through-wall depth may be assumed in the crack-growth calculation. However, the required inspection volume for Option 2 needs to be examined at a higher frequency. The subject weld shall be UT inspected during the first or second refueling outage following the weld overlay installation. If UT is performed prior to weld overlay installation and after installation without detecting any planar flaws in the original weld and the weld overlay, the first or second refueling outage UT may be eliminated. After the first ISI examination, the required inspection volume shall be UT inspected every 10 years from the date of the installation until such time when UT is qualified to examine the cast austenitic stainless steel (CASS) portion of the required inspection volume in accordance with new performance demonstration requirements of ASME Code,Section XI, Appendix VIII. After the subject weld is examined by qualified UT for the CASS material and no planar flaws are detected, the weld may be placed in the 25 percent sample inspection population. The inspection of the overlaid weld shall not be credited to satisfy the requirement of the 25 percent sample inspection every 10 years of overlaid welds with non-CASS materials.

Accordingly, justify the requirements of Paragraph 2(a)(4), on page 20 of Enclosure 1, or use one of the above options.

15. On page 18 of the proposed alternative, the licensee states that All ASME Code references are to the 2004 Edition with the 2006 Addenda. The NRC staff has not endorsed the 2004 Edition with the 2006 Addenda code in Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a. Revise the above statement to be consistent with current code requirements.

16. On page 3 of the proposed alternative, NRC Regulatory Guide (RG) 1.147, Revision 14 and Code Case N-504-2 were cited. The NRC staff notes that RG 1.147, Revision 15 has been published and is incorporated in 10 CFR 50.55a. The staff further notes that Code Case N-504-3 has been approved as shown in RG 1.147, Revision 15. Provide additional justification regarding why Code Case N-504-2 is acceptable or determine whether the approved Code Case N-504-3 is to be used in place of Code Case N-504-2, revising the proposed alternative citing RG 1.147, Revision 15.

17. In Section 4.3, page 13 of the proposed alternative, the licensee states, The UT examination, after a completed PWOL, will be performed in accordance with ASME Code Section XI, 1995 Edition with the 1996 Addenda, Appendix VIII, Supplement 11 (Reference 7.8) with the alternatives that are used to comply with the Performance Demonstration Initiative (POI) program, contained in Enclosure 2 and will not include any UT examination of the CSS [cast stainless steel] base material because there are no current requirements for UT qualification or performance demonstration requirements that can be consistently met for this material.

The NRC staff agrees with the licensee that UT is not qualified to examine cast austenitic stainless steel (CASS). However, this does not preclude the use of best effort examinations performed per Appendix III of the ASME Code,Section XI. Provide the basis for why the proposed alternative will not include UT examination of the CASS base metal.

18. Paragraph 3(b)(1), on page 25 of Enclosure 1, states, For weld overlays with cast austenitic stainless steel base materials only planar flaws that might have propagated into the weld overlay are required to be located and sized.

Clarify why only planar flaws are required to be located and sized.

19. In Section 4.2, on page 12 of the Attachment, the licensee states, DMWs [dissimilar metal welds] made with CSS base material will be designed for a minimum design life of 10 years and will require corresponding increased frequencies for inservice UT examination not to exceed every 10 years.

Please clarify whether DMWs made with CSS base material are designed for 10 years or if the weld overlays installed on DMWs made with CSS material are designed for a minimum of 10 years. In either case, provide additional justification why a weld or a weld overlay is designed for only 10 years.

20. The following typographical errors were identified in the proposed alternative and should be revised:

a. Figure 2, on page 25 Enclosure 1, is titled FIG. 2 PRESERVICE AND INSERVICE EXAMINATION VOLUME E-F-G-H, however, the figure is annotated as A-B-C-D. Clarify the correct examination volume.

b. Section I-2, on page 27 of Mandatory Appendix I, states, the welding procedures and the welding operators shall be qualified in accordance with Section IX and the requirements of I-1 and I-2, however paragraphs I-2.1, Procedure Qualification and I-2.2 Performance Qualification appears to be the appropriate reference. Clarify the references in the above referenced statement from Section I-2.

c. Section I-2.1(e), on page 28 of Mandatory Appendix I, cites paragraph I-1(f) when describing the location and orientation of the test specimens, however the cited reference discusses welding material controls whereas paragraph I-2.1(f) discusses location and orientation. Clarify the correct reference.

d. Section I-2.1(f), on page 28 of Mandatory Appendix I, cites paragraph I-1(e) when referring to the base metal test, however the cited reference discusses the minimum temperature of the welding area prior to welding whereas paragraph I-2.1(e) discusses the base metal test. Clarify the correct reference.

Millstone Power Station, Unit No. 2 cc:

Lillian M. Cuoco, Esquire Senior Counsel Dominion Resources Services, Inc.

Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385 Edward L. Wilds, Jr., Ph.D.

Director, Division of Radiation Department of Environmental Protection 79 Elm Street Hartford, CT 06106-5127 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 First Selectmen Town of Waterford 15 Rope Ferry Road Waterford, CT 06385 Charles Brinkman, Director Washington Operations Nuclear Services Westinghouse Electric Company 12300 Twinbrook Pkwy, Suite 330 Rockville, MD 20852 Senior Resident Inspector Millstone Power Station c/o U.S. Nuclear Regulatory Commission P.O. Box 513 Niantic, CT 06357 Mr. J. Alan Price Site Vice President Dominion Nuclear Connecticut, Inc.

Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385 Mr. J. W. "Bill" Sheehan Co-Chair NEAC 19 Laurel Crest Drive Waterford, CT 06385 Mr. Evan W. Woollacott Co-Chair Nuclear Energy Advisory Council 128 Terry's Plain Road Simsbury, CT 06070 Ms. Nancy Burton 147 Cross Highway Redding Ridge, CT 00870 Mr. Chris L. Funderburk Director, Nuclear Licensing and Operations Support Dominion Resources Services, Inc.

Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711 Mr. William D. Bartron Licensing Supervisor Dominion Nuclear Connecticut, Inc.

Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385 Mr. Joseph Roy, Director of Operations Massachusetts Municipal Wholesale Electric Company Moody Street P.O. Box 426 Ludlow, MA 01056 Mr. David A. Sommers Dominion Resources Services, Inc.

5000 Dominion Boulevard Glen Allen, VA 23060-6711