ML091000654
| ML091000654 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 04/07/2009 |
| From: | Morris J Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML091000654 (9) | |
Text
PDuke JAMES R. MORRIS, VICE PRESIDENT WEnergy Duke Energy Carolinas, LLC Carolinas Catawba Nuclear Station 4800 Concord Road / CN01 VP York, SC 29745 803-701-4251 803-701-3221 fax April 7, 2009 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555
Subject:
Duke Energy Carolinas, LLC (Duke)
Catawba Nuclear Station, Unit 2 Docket Number 50-414 Request for Relief Number 09-CN-002 Request to Utilize Alternative to the Requirements of ASME Code Case N-638-1 Response to NRC Request for Additional Information (RAI)
Reference:
Letter from Duke to NRC, dated April 2, 2009 The reference letter submitted Request for Relief 09-CN-002, which requested NRC approval to utilize an alternative to certain requirements of the subject Code Case to apply weld buildup on three of the four reactor vessel hot leg nozzles.
On April 3, 2009, the NRC electronically transmitted RAIs associated with this Request for Relief. This letter provides our docketed response to these RAIs.
The attachment to this letter contains the RAI responses. The format of the response is to restate each RAI question, followed by our response. As stated in the reference letter, Duke requests approval of this request for alternative by April 13, 2009.
There are no NRC commitments in conjunction with this RAI response.
If you have any questions concerning this material, please call L.J. Rudy at (803) 701-3084.
A-047(
www. duke-energy,corn
Document Control Desk Page 2 April 7, 2009 Very truly yours, James R. Morris LJR/s Attachment
Document Control Desk Page 3 April 7, 2009 xc (with attachment):
L.A. Reyes, Regional Administrator U.S. Nuclear Regulatory Commission, Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, GA 30303 A.T. Sabisch, Senior Resident Inspector U.S. Nuclear Regulatory Commission Catawba Nuclear Station J.H. Thompson, Project Manager (addressee only)
U.S. Nuclear Regulatory Commission Mail Stop 8-G9A Washington, D.C. 20555-0001
Document Control Desk Page 4 April 7, 2009 bxc (with attachment):
R.D. Hart L.J. Rudy D.L. Ward D.H. Llewellyn J.M. Shuping N.I. Mohr T.L. Bradley K. Douthit K.L. Ashe RGC File Document Control File 801.01 ELL-EC050 NCMPA-I NCEMC PMPA
Attachment Response to NRC Request for Additional Information
REQUEST FOR ADDITIONAL INFORMATION RELIEF REQUEST 09-CN-002 REACTOR VESSEL HOT LEG NOZZLES CATAWBA NUCLEAR STATION UNIT 2 DUKE ENERGY CAROLINAS DOCKET NO. 50-414 By letter dated April 2, 2009, Duke Energy Carolinas submitted for NRC review and approval Relief Request 09-CN-002, which provides modifications to certain requirements of Code Case N-638-1 to apply weld overlays on three of the four reactor vessel hot leg nozzles. To complete its review, the staff asks for the following additional information. The staff requests that the licensee provides response preferably no later than April 8, 2009 in order for the staff to meet the licensee's requested approval date of April 13, 2009.
- 1. (a) Describe the configuration of the remnant weld overlays on the three hot leg nozzles (axial length and thickness) and how many layers of the weld beads. (b) Discuss the angle of the slope at the toe of the remnant welds. In Code Case N-740-2, the slope at the toe cannot be more than 30 .degree with respect to the flat surface of the pipe. (c) If the slope at the toe of the weld is greater than 30 degrees, discuss whether the high slope will cause unfavorable stress concentration. (d)
Discuss how the toe is blended in with the nozzle outside surface to minimize the discontinuity between the nozzle and remnant overlay. (e) Discuss the maximum overlaid area on any of the three RPV nozzles that uses ambient temperature temper bead welding. (f) Discuss whether the remnant overlays will cause local stress concentration at the toe to affect the structural integrity of the three subject nozzles.
Response
1 a) Three layers of Alloy 52M filler material were applied using an ambient temper bead weld technique on reactor pressure vessel (RPV) hot leg nozzles 2B, 2C, and 2D.
The initial plan was for these layers to extend approximately 3.5 inches axially on the nozzle upstream from the dissimilar metal weld (DMW). This surface was subsequently prepared for a liquid penetrant and ultrasonic examination and is therefore less than the nominal 3 layer thickness. Refer to 4 c) for typical remnant dimensions.
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1 b) The taper, if greater than 30 degrees, will be analyzed in accordance with ASME Section III.
1 c) The analysis discussed in ib) above will ensure that the toe of the weld is within ASME Code allowable conditions.
1 d) The ASME stress analysis bounds the worst as left taper at the toe of the weld remnant.
1 e) As mentioned in 1 a) the width of the weld deposit on the nozzle was originally predicted to be approximately 3.5 inches. The adjacent weld deposit to the DMW was removed for approximately 1.5 inches to facilitate the MRP-139 R1 examination. Therefore approximately 2 inches of weld deposit remains. Due to the circumference of the nozzle the area is on the order of 200 square inches.
1 f) The following analyses will be performed and documented in an ASME Section III Code Compliant calculation to ensure the subject nozzles are left in an acceptable condition.
The referenced calculation will provide a bounding condition for the remnant weld overlay remaining on the three hot leg nozzles. This allows some flexibility in the field to minimize dose-intensive hand grinding so that the in-field conditions are acceptable within the bounding condition. This bounding condition will include angle of slope of the toe of the remnant weld.
The calculation will include analysis to support the use of slopes at the toe of the weld greater than 30 degrees.
The calculation will include bounding information on the amount of overlay material to remain on any hot leg nozzle. This discussion will address implications of structural integrity associated with the remnant weld material.
- 2. In the second row of the table in Attachment 1 of the relief request, the licensee stated that it will not inspect the area around the remnant weld of at least 1.5 times the component thickness or 5 inch, whichever is less (in the axial distance).
The staff does not agree with this alternative in light of indications found in the toe of the weld overlay. The 2
indications were found in the toe of the Alloy 52M and the stainless steel buffer layer on the pipe. The remnant overlays on the nozzles do not have the stainless steel buffer layer and, therefore, do not have the same weld configuration as the overlay in which indications were found. However, in light of the indications detected and removal of some portion of the overlays from the nozzles, the staff believes that the area around the remnant weld overlays needs to be examined by PT.
Also, Code Case N-740-2 requires PT of the adjacent base material (adjacent to the overlay) for at least i inch from each side of the overlay. Clarify.
Response
A liquid penetrant test (PT) was performed on the remnant weld and adjacent base metal over an area at least 1/2 inch inboard and outboard of the weld deposit. No rejectable indications were identified.
- 3. (a) Discuss the results of ultrasonic testing (UT) and penetrant testing. (PT) of the three hot leg nozzles, dissimilar metal welds (DMWs), similar metal welds (SMWs), safe ends, and pipe after the weld overlays have been removed. (b) Discuss the UT and PT results of the remnant overlays on the three subject nozzles in the relief request. .(c) If indications are found in any of the above components, discuss whether the indications will affect the structural integrity of the components if the indications are remained in service.
Response
3 a) PT and UT were performed on the remnant weld deposit as described in the Request for Relief. The acceptance criteria for the UT were in accordance with NB-5330.
The acceptance criteria for the PT were in accordance with NB-5350.
The DMW, SMW, safe ends, and pipe are not a part of this Request for Relief and have been dispositioned in accordance with ASME Code and industry commitments.
No rejectable indications at these locations were identified.
3 b) PT and UT were performed on the remnant weld deposit.
No recordable or rejectable indications at these locations were identified.
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3 c) There were no recordable or rejectable indications identified in the weld or base materials of the nozzles, safe-ends, or piping.
- 4. (a) Discuss the results of the stress analysis to show that the "as-left" condition of the hot leg nozzles with associated DMWs, SMWs, safe ends and pipe satisfies the allowable stresses of Subarticles NB-3200 and NB-3600 of the ASME Code,Section III. (b) Discuss the schedule when the stress analysis report will be submitted to the NRC. Also, discuss the schedule when the residual stress analysis will be submitted to the NRC. (c)
Discuss the approximate weight of the remnant overlays on each of the three nozzles.
Response
4 a) The stress analysis will be documented in an ASME Section III Code Compliant calculation. The analysis of the revised configuration is based on a 3-D finite element model to determine thermal and mechanical stresses using the ANSYS computer program, consistent with previously approved overlay applications on the Catawba Unit 2 pressurizer.
4 b) The calculation including the stress analysis is in progress and will be completed prior to Mode 4. The residual stress analysis will be completed within 45 days of the unit returning to service. These calculations will be available onsite for review.
4 c) The remaining weld deposit is expected to be on the order of 2 inches long by 0.275 inches thick and extends for the full circumference of the pipe. For a density of pWOL = 0.293 pounds/cubic inch, an approximate 200 square inch surface area, and an assumed 0.275 inch thickness equates to less than 20 pounds. This additional mass is insignificant when compared to the weight of the nozzle.
- 5. Confirm that the weld material used in the remnant overlay is Alloy 52M only.
Response
The remnant weld deposit on the hot leg nozzles consists entirely of Alloy 52M weld filler material.
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