NOC-AE-07002120, Inspection and Mitigation of Alloy 82/182 Pressurizer Butt Welds - Revised
| ML070600123 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 02/22/2007 |
| From: | Rencurrel D South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| G25, NOC-AE-07002120, STI: 32121087 | |
| Download: ML070600123 (10) | |
Text
Nuclear Operating Company South Texas ProjectElectric GeneratingStation P. Box 289 Wadsworth, Texas 77483 -A/-- --
February 22, 2007 NOC-AE-07002120 File No.: G25 10 CFR 50.55a U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 South Texas Project Units 1 and 2 Docket No. STN 50-498, STN 50-499 Inspection and Mitiqation of Alloy 82/182 Pressurizer Butt Welds - Revised
Reference:
Letter, David W. Rencurrel to Document Control Desk, "Inspection and Mitigation of Alloy 82/182 Pressurizer Butt Welds," dated January 30, 2007 (NOC-AE-06002099)
In October 2006, while performing inspections of pressurizer Alloy 82/182 butt welds in accordance with MRP-1 39, a PWR licensee discovered several circumferential indications in the pressurizer surge, safety, and relief nozzles. Because of the potential importance of this issue, STP Nuclear Operating Company (STPNOC) commits to the following actions taken or planned at the South Texas Project (STP) for inspecting or mitigating Alloy 82/182 butt welds on pressurizer spray, surge, safety, and relief lines.
Pursuant to a request by the NRC staff, STPNOC submits this letter superseding the referenced correspondence and associated actions. Text changes from the preceding correspondence in the following discussion are identified by change bars in the margin.
Inspection/Mitigation Schedule Unit 1 The affected Alloy 82/182 butt weld in the STP Unit 1 pressurizer surge line has been mitigated and inspected. Details concerning the mitigated location are provided in the attached Table 1.
Results of completed inspections are attached as Table 3. Remaining STP Unit 1 pressurizer nozzle butt weld mitigation activities will be completed after December 31, 2007, during the Spring 2008 refueling outage. This scheduled date is acceptable as justified below. Inspection of the remaining pressurizer butt welds at STP Unit 1 will be performed in accordance with industry guidance (MRP-1 39).
Unit 2 Inspection of pressurizer Alloy 82/182 butt welds at STP Unit 2 in accordance with industry guidance (MRP-139) has not yet been completed. STPNOC intends to complete all of the mitigation and inspection activities on these locations in refueling outage 2RE12 (Spring 2007).
Details concerning STP Unit 2 inspection and mitigation activities are provided in the attached Table 2. Results of completed inspections are attached as Table 4. The inspection of pressurizer butt welds at STP Unit 2 will be performed in accordance with industry guidance (MRP-1 39).
STI: 32121087
NOC-AE-07002120 Page 2 of 4 Reporting Within 60 days of unit restart, STPNOC will report the details of the inspection results of any unmitigated pressurizer nozzle Alloy 82/182 weld examination and any corrective or mitigative actions taken.
Results of bare metal visual (BMV) examinations of pressurizer Alloy 82/182 butt weld locations performed at power will be reported to the NRC within 60 days of the inspection.
Previous Inspection Results The results of previous inspections of pressurizer butt welds at STP Units 1 and 2 are provided in Tables 3 and 4, respectively. There have been no relevant indications.
Monitoring Program Until mitigation is complete, STPNOC will monitor Unit 1 and Unit 2 for leakage on a daily basis when the unit is in mode 1, 2, or 3.
Action Levels and Responses to Action Levels Exceeded Action levels and responses as described below will be implemented for Unit 1 and for Unit 2 beginning March 1, 2007, until mitigation for that unit is complete.
Action level for day-to-day changes:
0.1 gpm increase from one day to the next, sustained for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with at least 0.1 gpm not confirmed from sources other than the pressurizer nozzle welds.
Identification of the 0.1 gpm leak increase starts the 72-hour action clock. The clock continues until either: 1) the leak rate increase is reduced below 0.1 gpm; or 2) the increase in leakage is found to originate from other than the pressurizer nozzle welds.
Action level for changes relative to a baseline:
0.25 gpm above a baseline sustained for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with 0.25 gpm not confirmed from sources other than the pressurizer nozzle welds The baseline is to be established using historical data collected within seven days after achieving 100% power after plant startup from the most recent bare metal visual inspection of the welds.
Response to action level exceeded:
Once the 72-hour evaluation period is complete and the leak rate is still elevated, place the unit in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 within the next 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, and perform a bare metal visual inspection of unmitigated pressurizer surge line, spray, safety, and relief nozzle butt welds and safe-end butt welds containing Alloy 82/182 material.
A bare metal visual examination is to be performed if evidence of leakage from a source other than the pressurizer is identified but the leak rate from that source can not be quantified. If the leakage from the other source can be quantified, and leakage is below the action levels, the unit can be returned to Mode 1 and a BMV examination is not required.
Advanced Non-Linear Finite Element Analysis Additional refined crack growth calculations of the limiting pressurizer nozzle Alloy 82/182 weld configuration are being developed using three-dimensional finite element analysis as described in correspondence from Marvin D. Fertel, Nuclear Energy Institute, to Luis A. Reyes, Executive Director of Operations, NRC, dated January 26, 2007. Modeling a changing crack shape, rather than a semi-elliptical flaw shape, is expected to result in a significant increase in the estimated
NOC-AE-07002120 Page 3 of 4 time between through-wall penetration and rupture for the limiting case nozzle. The status of this effort will be provided by May 31, 2007.
Contingency Planning STPNOC will adopt contingency plans to shut down by December 31, 2007, if technical information being developed by MRP through advanced finite element analyses does not provide reasonable assurance to the NRC that PWSCC crack conditions will remain stable and not lead to rupture without significant time from the onset of detectable leakage.
Commitments made in this letter are listed in attachment 5. Changes to any of the information contained in this letter will be provided to the NRC for review prior to making a formal revision.
STPNOC staff is available to meet with the NRC to discuss any of the information in this letter.
If there are any questions, please contact either Mr. Ph ip L. Walker at (361) 972-8392 or me at (361) 972-7867.
avid W. Rencurrel Vice President, Engineering and Alliances PLW
Attachment:
- 1. Table 1, South Texas Project Unit 1 Inspection and Mitigation Summary for Alloy 600/82/182 Pressurizer Butt Welds
- 2. Table 2, South Texas Project Unit 2 Inspection and Mitigation Summary for Alloy 600/82/182 Pressurizer Butt Welds
- 3. Table 3, South Texas Project Unit 1 Previous Inspection Results
- 4. Table 4, South Texas Project Unit 2 Previous Inspection Results
- 5. List of Commitments
NOC-AE-07002120 Page 4 of 4 cc:
(paper copy) (electronic copy)
Regional Administrator, Region IV A. H. Gutterman, Esquire U. S. Nuclear Regulatory Commission Morgan, Lewis & Bockius LLP 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Mohan C. Thadani U. S. Nuclear Regulatory Commission Richard A. Ratliff Steve Winn Bureau of Radiation Control Christine Jacobs Texas Department of State Health Services Eddy Daniels 1100 West 49th Street Marty Ryan Austin, TX 78756-3189 NRG South Texas LP Senior Resident Inspector Ed Alarcon U. S. Nuclear Regulatory Commission J. J. Nesrsta P. 0. Box 289, Mail Code: MN1 16 R. K. Temple Wadsworth, TX 77483 Kevin Polio City Public Service C. M. Canady Jon C. Wood City of'Austin Cox Smith Matthews Electric Utility Department 721 Barton Springs Road C. Kirksey Austin, TX 78704 City of Austin
Attachment 1 NOC-AE-07002120 Page 1 of 1 Table 1: South Texas Project Unit 1 Inspection and Mitigation Summary for Alloy 600/82/182 Pressurizer Butt Welds MRP-139 Volumetric Mitigation Nozzle Inspection Requirement Completed or to Met or to be Met be Completed Comments Susceptible Otg tr aeOtg Material Outage Start Date Outage Function / Designation Description Designation (MM/YYYY) Designation 1RE14 04/2008 To be completed Mitigate by Full Structural Weld Spray / RC1003BB 1 RE14 Overlay and inspect. This outage will occur after 12/31/2007.
1 RE13 10/2006 Completed Mitigated by Full Structural Weld Surge/ RC1 412NSS 1 RE13 Overlay and inspected. Mitigation is complete.*
1RE14 04/2008 To be completed Mitigate by Full Structural Weld Safety! RC1004NSS 1 RE14 Overlay and inspect. This outage Nozzle-to-safe will occur after 12/31/2007.
end weld 1RE14 04/2008 To be completed Mitigate by Full Structural Weld Safety/ RC1009NSS 1 RE14 Overlay and inspect. This outage will occur after 12/31/2007.
1RE14 04/2008 To be completed Mitigate by Full Structural Weld Safety!/ RC1012NSS 1 RE14 Overlay and inspect. This outage will occur after 12/31/2007.
1RE14 04/2008 To be completed Mitigate by Full Structural Weld Relief! RC1015NSS 1 RE14 Overlay and inspect. This outage will occur after 12/31/2007.
STPNOC completed the ultrasonic examination for the STP Unit 1 pressurizer surge nozzle weld overlay on October 24, 2006. No relevant indications were found. Two non-relevant indications were detected that were found to be acceptable per the standards of ASME Section Xl, IWB-3514-2 and/or IWB-3514-3 criteria for their respective size and position. These indications are laminar-type flaws located in the first weld layer at the base metal interface. No repairs to the overlay material and/or base metal were required or performed. The results were submitted to the NRC November 1,2006 (ML063170071).
Attachment 2 NOC-AE-07002120 Page 1 of 1 Table 2: South Texas Project Unit 2 Inspection and Mitigation Summary for Alloy 600/82/182 Pressurizer Butt Welds MRP-139 Volumetric Mitigation Nozzle Inspection Requirement Completed or to Met or to be Met be Completed Comments Susceptible Outage Start Date Outage Function Designation Material Description Designation (MM/YYYY) Designation Spray / RC2003BB 2RE1 2 04/2007 To be completed Mitigate by Full Structural Weld 2RE12 Overlay and inspect Surge / RC2412NSS 2RE1 2 04/2007 To be completed Mitigate by Full Structural Weld 2RE12 Overlay and inspect Safety RC2004NSS Nozzle-to-safe end 2RE12 04/2007 To be completed Mitigate by Full Structural Weld weld 2RE12 Overlay and inspect Safety / RC2009NSS 2RE12 04/2007 To be completed Mitigate by Full Structural Weld 2RE12 Overlay and inspect Safety/ RC2012NSS 2RE12 04/2007 To be completed Mitigate by Full Structural Weld 2RE12 Overlay and inspect Relief / RC2015NSS 2RE12 04/2007 To be completed Mitigate by Full Structural Weld 2RE12 Overlay and inspect
Attachment 3 NOC-AE-07002120 Page 1 of 1 Table 3: South Texas Project Unit 1 Previous Inspection Results Nozzle Refueling Outage Inspection Type(s) Inspection Results Spring 1995 UT & PT Spray/ RC1003BB Spring 2005 VT-1 & BMV No relevant Indications Fall 2006 VT-1 & BMV Spring 1991 UT & PT Surge/ RC1412NSS Spring 2005 VT-1 & BMV No relevant Indications Fall 2006 VT-1 & BMV Fall 1989 UT &PT Safety / RC1 004NSS Spring 2005 VT-I & BMV No relevant Indications Fall 2006 VT-1, BMV & PT Fall 1992 UT &PT Safety/ RC1009NSS Spring 2005 VT-1 & BMV No relevant Indications Fall 2006 VT-1 & BMV Fall 1992 UT & PT Safety / 6RC1012NSS Spring 2005 VT-1 & BMV No relevant Indications Fall 2006 VT-1 & BMV Fall 1989 UT &PT Relief / 6RC1 01 5NSS Spring 2005 VT-1 & BMV No relevant Indications Fall 2006 VT-1 & BMV
Attachment 4 NOC-AE-07002120 Page 1 of 1 Table 4: South Texas Project Unit 2 Previous Inspection Results Nozzle Refueling Outage Inspection Type(s) Inspection Results Spring 1997 UT & PT Spray / RC2003BB Spring 2004 VT-1 & BMV No relevant Indications Fall 2005 VT-1 & BMV Spring 1997 UT & PT Surge / RC2412NSS Fall 2005 VT-1 & BMV No relevant Indications Fall 1990 UT & PT Safety / RC2004NSS Spring 2004 VT-1 & BMV No relevant Indications Fall 2005 VT-1, BMV Fall 1995 UT & PT Safety/ RC2009NSS Spring 2004 VT-1 & BMV No relevant Indications Fall 2005 VT-1 & BMV Fall 1995 UT & PT Safety/6RC2012NSS Spring 2004 VT-1 & BMV No relevant Indications Fall 2005 VT-1 & BMV Fall 2002 UT & PT Relief / 6RC2015NSS Spring 2004 VT-1 & BMV No relevant Indications Fall 2005 VT-1 & BMV
Attachment 5 NOC-AE-07002120 Page 1 of 2 LIST OF COMMITMENTS The following table identifies the actions in this document to which the STP Nuclear Operating Company has committed. Statements in this submittal with the exception of those in the table below are provided for information purposes and are not considered commitments. Please direct questions regarding these commitments to Philip Walker at (361) 972-8392.
Commitment CR Action Expected Completion The inspection of the remaining pressurizer butt welds at STP Unit 1 will 07-2473-7 04/21/2008 be performed in accordance with industry guidance (MRP-1 39).
The inspection of pressurizer butt welds at STP Unit 2 will be performed 07-2473-8 04/27/2007 in accordance with industry guidance (MRP-1 39).
Within 60 days of unit restart, STPNOC will report the details of the 07-2473-9 06/20/2008 inspection results of any unmitigated pressurizer nozzle Alloy 82/182 weld examination and any corrective or mitigative actions taken. (Unit 1)
Within 60 days of unit restart, STPNOC will report the details of the 07-2473-17 06/26/2007 inspection results of any unmitigated pressurizer nozzle Alloy 82/182 weld examination and any corrective or mitigative actions taken. (Unit 2)
Results of bare metal visual (BMV) examinations of pressurizer Alloy 07-2473-18 06/20/2008 82/182 butt weld locations performed at power will be reported to the NRC within 60 days of the inspection. (Unit 1)
Results of bare metal visual (BMV) examinations of pressurizer Alloy 07-2473-19 06/26/2007 82/182 butt weld locations performed at power will be reported to the NRC within 60 days of the inspection. (Unit 2)
The results of inspections or mitigation of pressurizer Alloy 82/182 butt 07-2473-10 06/20/2008 weld locations will be reported to the NRC within 60 days of startup from the outage in which they were performed. (Unit 1)
The results of inspections or mitigation of pressurizer Alloy 82/182 butt 07-2473-20 06/26/2007 weld locations will be reported to the NRC within 60 days of startup from the outage in which they were performed. (Unit 2)
Remaining STP Unit 1 pressurizer nozzle butt weld mitigation activities 07-2473-11 04/21/2008 will be completed after December 31, 2007, during the Spring 2008 refueling outage.
Until mitigation is complete, STPNOC will monitor Unit 1 and Unit 2 for 07-2473-12 03/01/2007 leakage on a daily basis when the unit is in mode 1, 2, or 3. Action levels and responses as described in the letter to which these commitments are attached will be implemented for Unit 1 and Unit 2 beginning March 1, 2007, until mitigation for that unit is complete.
Attachment 5 NOC-AE-07002120 Page 2 of 2 Additional refined crack growth calculations of the limiting pressurizer 07-2473-14 05/31/2007 nozzle Alloy 82/182 weld configuration are being developed using three-dimensional finite element analysis. The status of this effort will be provided by May 31, 2007.
STPNOC will adopt contingency plans to shut down by December 31, 07-2473-15 12/31/2007 2007, if technical information being developed by MRP through advanced finite element analyses does not provide reasonable assurance to the NRC that PWSCC crack conditions will remain stable and not lead to rupture without significant time from the onset of detectable leakage.
Changes to any of the information contained in this letter will be 07-2473-16 04/21/2008 provided to the NRC for review prior to making a formal revision.