ML062620261

Relief Request 06-GO-001 Request for Additional Information

ML062620261
Person / Time
Site:	Catawba, McGuire, Mcguire
Issue date:	09/11/2006
From:	Morris J Duke Energy Carolinas, Duke Energy Corp, Duke Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML062620261 (10)

Text

JAMES R. MORRIS P Duke . Vice President, Nuclear Support 1 Energy Nuclear Generation Duke Energy Corporation 526 South Church St.

September 11, 2006 Charlotte, NC 28202 Mailing Address:

U. S. Nuclear Regulatory Commission EC07H / PO Box 1006 ATTN: Document Control Desk Charlotte, NC 28201-1006 Washington, DC 20555-0001 704 382 6401 704 382 6056 fax james. morris@duke-energy.corn

SUBJECT:

Duke Power Company LLC d/b/a Duke Energy Carolinas, LLC (Duke)

McGuire Nuclear Station, Units 1 & 2 Docket Numbers 50-369 and 50-370 Catawba Nuclear Station, Units 1 & 2 Docket Numbers 50-413 and 50-414 Relief Request 06-GO-001 Request for Additional Information On July 27, 2006 Duke submitted Relief Request 06-GO-001 pursuant to 10 CFR 50.55a(a)(3)(i),e requesting NRC approval to use alternatives to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), Section Xl inservice inspection (ISI) requirements for the McGuire and Catawba Nuclear Stations, Units I & 2. This proposed alternative approach is to support application of full structural weld overlays on various pressurizer nozzle-to-safe end welds and will provide an acceptable level of quality and safety.

On August 30, 2006, the NRC Staff electronically requested additional information regarding several issues contained within the relief request. The Duke response is attached.

Ifyou have any questions or require additional information, please contact Mary Shipley at (704) 382-5880.

Sincerely, James R. Morris Enclosure A-o+-7 www duke -energi. -:irn

Nuclear Regulatory Commission September 11, 2006 Page 2 W. D. Travers, Region IIAdministrator U.S. Nuclear Regulatory Commission Sam Nunn Atlanta Federal Center, 23 T85 61 Forsyth St., SW Atlanta, GA 30303-8931 J. F. Stang, Jr., Senior Project Manager (CNS & MNS)

U. S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-8 H 4A Rockville, MD 20852-2738 J. B. Brady NRC Senior Resident Inspector McGuire Nuclear Station NRC Senior Resident Inspector Catawba Nuclear Station

Nuclear Regulatory Commission September 11, 2006 Page 3 bxc:

R. L. Gill (EC050)

C. J. Thomas (MG01RC)

K. L. Crane (MG01 RC)

R. D. Hart (CN01RC)

L. J. Rudy (CN01RC)

D. S. Rome (CN01VP)

K. E. Nicholson (CNOIRC)

M. R. Hatley (MG05SE)

H. V. Dinh (MG05SE)

M. D. Hunt (MG05SE)

M. A. Pyne (EC07C)

Ricky Branch (MG01 MM)

G. J. Underwood (EC05A)

D. H. Llewellyn (EC07C)

C. R. Frye (EC07C)

J. M. Shuping (EC07C)

W. 0. Callaway (CN03SE)

J. F. Bumgarner (CN03SE)

A. J. Hogge, Jr. (EC05A)

J. J. McArdle (EC05A)

R. K. Rhyne (EC05A)

R. N. McGill (CN03PS)

J. F. Swan (MG01 MM)

North Carolina Municipal Power Agency Number 1 Saluda River Electric Cooperative, Inc.

Piedmont Municipal Power Agency North Carolina Electric Membership Corporation MNS MasterFile MC-801.01 (MG01DM)

CNS MasterFile CN-801.01 (CN04DM)

ONS MasterFile ON-801.01 (ON03DM)

ELL

Relief Request 06-GO-001 Response to Request for Additional Information Page I of 7

1. Provide the interval over which relief is requested to perform the proposed structural weld overlays.

Response

The full structural weld overlays will ba installed during the third interval for each of the units included in the relief request.

2. Provide the current inservice inspection interval for Catawba and McGuire Units I and 2. Include interval start and end dates.

Response

Catawba Unit 1 third interval: Begin 6/29/2005 End 6/29/2015 Catawba Unit 2 third interval: Begin 10/15/2005* End 8/19/2016 McGuire Unit I third interval: Begin 12/11/2001 End 12/01/2011 McGuire Unit 2 third interval: Begin 3/1/2004 End 2/28/2014

• Interval started early to get both units on same code.

3. Section 6.0 "Weld Overlay Design and Verification" of the submittal states that the following will be performed after the completion of the preemptive weld overlay (PWOL):

(4) Shrinkage will be measured during the overlay application. Shrinkage stresses at other locations in the piping systems arising from the weld overlays will be demonstrated not to have an adverse effect on the systems. Clearances of affected support and restraints will be checked after the overlay repair, and will be reset within the design ranges as required.

(5) The total added weight on the piping systems due to the overlays will be evaluated for potential impact on piping systeým stresses and dynamic characteristics.

(6) The as-built dimensions of the weld overlays will be measured and evaluated to demonstrate thit they equal or exceed the minimum design dimensions of the overlays.

It is the staffs expectation that the above activities be performed prior to start-up. Verify that the task outlined in 6.0 (4), 6.0 (5) and 6.0 (6) of the July 27, 2006 submittal will be completed prior to start-up.

Response

The analyses and evaluations described in items 4 through 6 will be completed prior to entry into Mode 4.

4. Section 6.0 of the July 27, 2006 submittal indicates that the overlay design will not take credit for the underlying primary water stress corrosion cracking (PWSCC) susceptible material. 6.0 (2) states that "potential crack growth will be evaluated due to PWSCC as well as due to fatigue crack growth in the original DMW [dissimilar metal weld]." In order to perform fracture mechanics analysis, what crack size is assumed to already exist in the original weld ?. Ifthe assumed crack size is not 360 degrees and 100% through-wall, provide the assumed flaw size and a bases for the assumed flaw size given that welds will not receive a volumetric examination prior to welding.

Response

Relief Request 06-GO-001 Response to Request for Additional Information Page 2 of 7 The design basis flaw for the purpose of structural sizing of the overlay is assumed to be 360 degrees and 100% through the original wall thickness of the DMW. For the crack growth analysis the initial flaw size is assumed to be 360 degrees and 75% through the original wall thickness.

The 75% through-wall assumption is selected based upon the PDI-qualified inspection of the overlay at the conclusion of the weld overlay process, which includes the outer 25% of the original weld. Ifflaws are detected in the post-overlay inspection, they will be evaluated in accordance with the requirements of Code Case N-504-2 and Appendix Q.

5. Given that the proposed weld overlay encompasses the stainless steel safe end to stainless steel RCS piping, provide the specification and grade of filler metal used to join the safe end to the RCS piping for each safe end to be weld overlayed.

Response

All the stainless steel safe end to RCS piping welds were made with filler material conforming to AWS class E308 or ER308 for chemistry as required by ASME Section III, subsection NB-2000.

6. Table 3 of the July 27, 2006 submittal indicates that the NDE requirement under 4.0(b) of N-638-1, ultrasonic examination of the 1.5T band on either side of the overlay, will not be met. If this requirement cannot be met, please discuss the achievable amount of area that can be successfully examined for each preemptive weld overlay weld design configuration you wish to apply. Secondly, clarify whether the ultrasonic test examination will be performed to the maximum extent achievable. Although the July 27, 2006 submittal references Code Case N-638-3 in support of the relief request, the staff notes that Code Case N-638-3 has not been endorsed by the NRC.

Response

(a) Code Case N-638-1 addresses the use of the temper bead welding technique including those welds made in deep cavities in ferritic material. In the case of weld overlays to be applied at MNS/CNS, this technique will be used to apply a non-ferritic overlay to the P3 ferritic nozzle base material adjacent to the dissimilar metal weld (DMW). The PDI qualified ultrasonic examination procedure is designed and qualified to examine the entire volume of the overlay weld as well as the region of the P3 material containing the weld heat affected zone (HAZ) and a volume of unaffected base material beyond the HAZ. In addition to verifying the soundness of the weld, a purpose of these examinations is to assure that delayed cracking that may be caused by hydrogen introduced during the temper bead welding process is not present. In the unlikely event that this type of cracking does occur, it would be initiated on the surface on which the welding is actually performed or in the HAZ immediately adjacent to the weld. The most appropriate technique to detect surface cracking is the surface examination technique that Duke will perform on the weld overlay and the adjacent base material in a band at least 1.5 times the thickness of the base material on either side of the overlay. The maximum achievable inspection volume is 100% of the volume susceptible to weld induced flaws.

(b) Duke does not propose to perform ultrasonic examination to the maximum achievable extent in the 1.5T band on either side of the overlay. While it would be possible to extend the examination volume to a larger extent on either side of the weld overlay, it would not be possible with current technology to ultrasonically inspect 100% of the volume within 1.5 times the thickness of the base material because of geometric considerations. Inspection of an increased volume would result in increased dose to inspection personnel without a compensating increase in safety or quality

Relief Request 06-GO-001 Response to Request for Additional Information Page 3 of 7 because there is no plausible mechanism for formation of new flaws or propagation of existing flaws in the region. The overlay volume is small relative to the volume of the underlying pipe and does not present the same concerns as those related to welds in deep cavities contemplated by the requirements of Code Case N-638-1. Therefore, the examinations tailored for overlay inspection and required by Code Case N-504-2 and Appendix Q as modified in the request for relief provide full assurance that the weld and adjoining base material are fully capable of performing their intended function. Approval by ASME Code in 2005 and 2006 of Code Cases N-638-2 and N-638-3 respectively recognizes that inspection of the larger volume is not necessary to assure quality and safety.

(c) The NRC has previously granted relief on this specific issue for temper bead welding for use at other plants for the reasons mentioned above. Specifically, San Onofre Nuclear Generating Station Unit 2 in the Spring of 2006, Millstone Power Station, Unit No. 3 in January 2006, and Three Mile Island Unit I in Fall 2003 have received approval to use inspection methods essentially identical to those proposed by Duke.

7. The submittal indicates that the weld surface areas over ferritic material for the subject weld overlays are expected to be approximately 120 square inches for the surge line nozzles. Provide a discussion on how the information in the white paper referenced in your submittal directly applies to the configuration of the surge line nozzles and supports your request to exceed the current 100 sq in limitation in Code Case N-638-1. Also discuss operational experience at other nuclear power plants with weld overlays that exceed 100 sq in. Although the submittal references requirements of Code Case N-638-3 as justification for increasing the allowable overlay surface area, the staff notes that Code Case N-638-3 has not been endorsed buy the NRC.

Response

The white paper referenced in our submittal was part of an ASME Code action that sought (and succeeded) in relaxing an arbitrary limitation that was included in N-638 to restrict the use of the 2

ambient temperature bead welding to a surface area of less than 100 in . Later revisions to this Code Case (N-638-2 and 2N-638-3), approved 2 by ASME Code in 2005 and 2006 respectively, have extended the 100 in limit to 500 in2 .

2 The white paper addressed three potential technical concerns that the 100 in limitation may have been intended to prevent: residual stresses, tempering of the weld HAZ, and the possible (but unlikely) development of delayed hydrogen cracking in the underlying ferritic base material. The applicability of the white paper to the MNSICNS surge nozzle weld overlay design is addressed individually for each of these potential concerns below:

(0) Residual Stresses - Using as an example a BWR Feedwater Nozzle, the white paper cites 2 ferritic2 EPRI sponsored analyses [1] of an overlay that just equaled 100 in coverage over the100 in base metal. Two axisymmetric finite element models were created, one with the steel weld overlay and the other with the weld overlay extended on the nozzle side until it blended into the nozzle taper surface (approximately 126 in2 ). Figure 1 shows the post overlay residual stress on the nozzle inside surface for both models. It is seen that the extended overlay configuration did not significantly alter the residual stress results, and if anything, made the axial stresses even more compressive.

The Feedwater nozzle configuration modeled in [1] was roughly similar to the MNS and CNS

Relief Request 06-GO-001 Response to Request for Additional Information Page 4 of 7 surge nozzles; however it is not necessary to rely on this similarity, since nozzle specific residual stress analyses are being conducted as part of the Duke PWOL project. The resulting post-overlay inside surface residual stress distributions for the MNS/CNS surge nozzles are shown in Figure 2. It is seen from this figure that the MNS/CNS surge nozzle weld overlay design, with its

-120 in2 coverage over the ferritic steel base metal, creates favorable compressive residual stresses on the inside surface of the nozzle.

(b) HAZ Tempering - The white paper cites past programs which have demonstrated that temper bead welding using automatic GTAW provides adequate tempering of the HAZ in P-1 and P-3 materials and does not degrade strength or fracture toughness for temper bead weld overlays.

Reference [2] presents results of a bimetallic weld overlay mockup of a 12 inch diameter, SA-508 2 alloy Class 2 low alloy steel nozzle. The overlay applied to this nozzle covered -119 in of the low steel nozzle (approximately the same as the MNS/CNS surge nozzle overlay). Microstructure and microhardness measurements were performed on the HAZ of this overlay, as well as mechanical property tests (Charpy and Tensile) of a groove weld in the same nozzle with similar coverage area. The mechanical property results verified that the weld overlay repair did not degrade the strength or toughness of the low alloy steel HAZ. Microstructure and microhardness results demonstrated adequate tempering of the material, such that Hydrogen embrittlement would not be expected. This demonstration was conducted on a weld overlay geometry with essentially identical low alloy steel (LAS) coverage as the MNS/CNS surge nozzle overlay.

(c) Delayed Hydrogen Cracking - Inspections of the above described mockup, as well as extensive inspections of temper bead weld overlays in mockups and in the field, have been 2

performed, of overlays with LAS coverages ranging from less than 10 in up to and including 325 in . These have shown that hydrogen induced cracking has not been a problem with repairs 2

produced by the automatic GTAW temper bead process. The process is by its nature a low hydrogen process, and diffusion of hydrogen is very rapid for low alloy steels. Nonetheless, the post weld soaks specified in the Code are intended as post hydrogen bake outs permitting NDE after the repair has retumed to ambient temperature. N-638, since itdoes not impose the post weld bake, requires a 48-hour hold time prior to NDE, to verify that the unlikely event of hydrogen induced cold cracking has not occurred. The Duke weld overlay procedure will conform to the 48-hour hold time requirement prior to performing NDE. Furthermore, the metallurgical aspects discussed above are independent of the surface area of the repair but related to parameters of the qualified welding procedure.

Finally, it is important to note that the above theoretical arguments have been proven in practice by extensive field experience with temper bead weld overlays, with LAS coverage ranging from less than 10 in2 up to and including 325 in2. Table 1 below provides a partial list of such applications. It is seen from this table that the original DMW weld overlay was applied over 20 years ago, and WOLs with LAS coverage in the 100 in2 range have been in service for 5 to 15 years. Several overlays have been applied with LAS coverage significantly greater than the 100 in2 . Relief requests for these large overlays have been previously approved. These overlays have been examined with PDI qualified techniques, in some cases multiple times, and none have shown any signs of new cracking or growth of existing cracks. One such specific incidence

[Constellation Energy Relief Request (ML060240110) for Calvert Cliffs] was referenced in Duke's original submittal.

Relief Request 06-GO-001 Response to Request for Additional Information Page 5 of 7 Residual Axial Stress Along Inside Wall 5 Length of 100 IM2 Weld Overlay I 4

0

-5

-10 7-15

-20

-25 --e- 100 inA12

-- Extended

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 Axial Distance (Y)From Weld Centerline (in)

Residual Hoop Stress Along Inside Wall 0-

-Legt ofIMWZWeld O,,erly

-10 40 -20

-30 - .- Exten

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 Axial Distance (Y)From Weld Centerline In)

Figure 1 Residual Stress Distribution from White Paper (see Text)

Relief Request 06-GO-001 Response to Request for Additional Information Page 6 of 7 McGuire/Catawba Pressurizer Surge Nozzle ID Surface Axial Residual Stress Safe End( PWSCC SmC**mbI Nozzle (LAS)

I

/'\' Region I I 10 I I

-2. .0... ..

D1.8 1.6 IA 12 0 0.8 0.6V.4 *2 0.0 -0.2 -0. -0.6 -0.8 -1.0 -1.2 -1.4 -1.6 -1.8 - 0

• I I- - - - - --- - - -- --- -- - - - - - - - - - - - - - - - - -

U'

- Post-WOL4-70F

-60 ------------------------- ----------

• --- Post-WOL4-650F

.- s60 - - -...........................................-------

B I

• I

-70 . . . . . . .. . . . . .. . . . . . . . . . . . . . .

Distance from ID Weld Repair Centerline (in)

McGulre/Catawba Pressurizer Surge Nozzle ID Surface Hoop Residual Stress Sale End (SS) PWSCCstnolwlme Nozzle %MA) 20 1.8 1.6 1A 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1. 1.6 -1.8 -2.0 S

.5 U

I --------------------------- -. ........ ...

Post-WOL4-70F

--70 I I

• h I Distance firom ID Wel Repair Centerline (in)

Figure 2 Calculated Residual Stress Distribution for McGuire and Catawba (see Text)

Relief Request 06-GO-001 Response to Request for Additional Information Page 7 of 7 Table 1 - Dissimilar Metal Weld Overlay Experience Plant Component Nozzle Diameter Approx. LAS Coverage Date (in) (in2)

April 2006 Davis Besse Hot leg drain nozzle 4 16 February 2006 SONGS Unit 2 PZR spray nozzle 8 50 safety/relief nozzles 6 28 November Kuosheng Unit 2 Recirculation outlet 22 250 2005 nozzle April 2004 Susquehanna Unit Recirc. inlet nozzle 12 100 1 Recirc. outlet nozzle 28 325 November 2003 TMI Unit I Surge line nozzle 11.5 75 October 2003 Pilgrim Core spray nozzle 10 50 CRD return nozzle 5 20 October 2002 Peach Bottom Units Core spray nozzle 10 50 2&3 Recirc. outlet nozzle 28 325 CRD return nozzle 5 20 October 2002 Oyster Creek Recirc. outlet nozzle 26 285 December Duane Arnold Recirc. inlet nozzle 12 100 1999 June 1999 Perry Feedwater nozzle 12 100 June 1998 Nine Mile Point Unit Feedwater nozzle 12 100 2

March 1996 Brunswick Units I & Feedwater nozzle 12 100 2

February 1996 Hatch Unit I Recirc. inlet nozzle 12 100 January 1991 River Bend Feedwater nozzle 12 100 March 1986 Vermont Yankee Core spray nozzle 10 50 References (Question 7):

1. "Justification for the Removal of the 100 Square Inch Limitation for Ambient Temperature Temper Bead Welding on P-3 Material", EPRI-NP- 1011898, February 2005.

2. "Inconel Weld-Overlay Repair for Low-Alloy Steel Nozzle to Safe-End Joint", EPRI NP-7085-D, January 1991.

8. Is Code Case N-416-2 currently implemented within the current ISI programs at Catawba and McGuire Units I and 2.

Response

Code Case N-416-2 is not listed within the current ISI Program Plan. The requirements of Code Case N-416-2 were incorporated into Section XI and are implemented in ASME Boiler and Pressure Vessel Code Section XI 1998 Edition through 2000 Addenda applicable to the third inspection interval for each of the units for which relief is requested.