ML070370206
| ML070370206 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 01/25/2007 |
| From: | Leidich G FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 3304 | |
| Download: ML070370206 (10) | |
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76 South Main Street FirstEnergy Nuclear Operating Company Akron, Ohio 44308 Gary R. Leidich 330-384-5770 President and Chief Nuclear Officer Fax: 330-384-5669 Docket No. 50-346 License Number NPF-3 Serial Number 3304 January 25, 2007 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555-0001
Subject:
Inspection or Mitigation of Alloy 600/82/182 Pressurizer Butt Welds at the Davis-Besse Nuclear Power Station Ladies and Gentlemen:
In August 2005, the Electric Power Research Institute (EPRI) issued the Materials Reliability Program: Primary System Piping Butt Weld Inspection and Evaluation Guidelines, MRP-139. In March 2006, FirstEnergy Nuclear Operating Co. (FENOC) inspected the Alloy 600/82/182 butt welds in the Davis-Besse Nuclear Power Station (DBNPS) pressurizer spray line, surge line, and three relief nozzles. These inspections were performed in accordance with the MRP-139 guidelines, using Performance Demonstration Initiative (PDI) qualified procedures. The examinations identified no indications in any of the areas scanned in the Alloy 600/82/182 butt welds for the spray, surge, and three relief nozzles; however, examination coverage on the pressurizer spray nozzle safe end to pipe and surge nozzle to safe end dissimilar metal welds was insufficient to satisfy minimum requirements (>90%). Additional details relevant to the current status of inspection or mitigation activities are contained in Attachment 1.
FENOC will remove the DBNPS from service in December 2007 to support necessary inspection or mitigation activities for the pressurizer spray nozzle safe end to pipe and surge nozzle to safe end dissimilar metal welds, in order to satisfy the MRP-139 inspection criteria. It is FENOC's current intention to perform the refueling activities that were previously planned for spring 2008 at this time. Additionally, to support the aforementioned mitigation activities, FENOC is accelerating the development of a request for Nuclear Regulatory Commission approval of a proposed weld overlay repair alternative, in accordance with the requirements of 10 CFR 50.55a.
FENOC enhanced the DBNPS reactor coolant system (RCS) integrated leakage program during the 13th refueling outage, which ended in 2004. The program exceeds acceptance criteria required by the DBNPS technical specifications. Leakage data is captured on a A4l/0
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Page 2 of 2 daily basis for trend analysis, and measurements are periodically validated with other plant data. The FENOC and DBNPS management teams have reinforced strong ownership and maintained fleet visibility of this program by including leakage monitoring discussions daily in fleet status calls, as well as monthly in routine management meeting presentations. Through improved program requirements and ownership, reactor coolant system pressure boundary leakage is being actively monitored.
Additional details relevant to the RCS integrated leakage program are contained in.
FENOC appreciates the opportunity to submit its plans for ensuring pressurizer weld integrity at the DBNPS. As appropriate, FENOC will provide additional detail regarding the status of Alloy 600/82/182 pressurizer weld inspection and mitigation activities at all FENOC nuclear facilities, consistent with industry efforts under the coordination of the Nuclear Energy Institute.
Regulatory commitments associated with this letter are listed in Attachment 2. FENOC staff is available to meet with the NRC to discuss any information in this letter. If there are any questions or if additional information is required, please contact Mr. Gregory H. Halnon, Director - FENOC Fleet Regulatory Affairs, at (330) 315-7500.
Sincerely, Gary R. Leidich Attachments:
- 1.
Davis-Besse Nuclear Power Station Current Mitigation and Inspection Status, Inspection Results, and RCS Leakage Monitoring
- 2.
NRC Executive Director for Operations NRC Region III Regional Administrator NRC Project Manager - Davis-Besse Nuclear Power Station NRC Resident Inspector - Davis-Besse Nuclear Power Station Marvin S. Fertel, Nuclear Energy Institute James H. Riley, Nuclear Energy Institute
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Page 1 of 7 Davis-Besse Nuclear Power Station Current Mitigation and Inspection Status, Inspection Results, and RCS Leakage Monitoring
- 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 Function Material Outage Start Date Outage Designation Description Designation (MM/YYYY)
Designation Weld # RC-PZR-Nozzle to Safe End RFO 14 02/2006 RFO 15 MRP-139 examination requirements have WP-102 Weld and Safe End been met.
4" Spray Nozzle to Full Structural Weld Overlay (FSWO)
Safe End Weld planned. Mitigation is performed in conjunction with Weld RC-MK-A-90-FW56.
Weld # RC-MK-A-Nozzle Safe End to RFO 15 12/2007 RFO 15 A best effort ultrasonic examination was 90-FW56 Pipe Weld performed in the spring 2006, but the examination coverage of the MRP-139 4" Spray Nozzle Required Examination Volume was less than Safe End to 90%.
Stainless Steel Pipe Weld Full Structural Weld Overlay (FSWO) planned.
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Page 2 of 7 MRP-139 Volumetric Mitigation Nozzle Inspection Requirement Completed or to Met or to be Met be Completed Comments
- Function, Susceptible Outage Start Date Outage Material Designation Description Designation (MM/YYYY)
Designation Weld # RC-PZR-Nozzle to Safe End RFO 14 02/2006 RFO 15 MRP-139 examination requirements have WP-91-W/X Weld been met.
3" Safety Valve Full Structural Weld Overlay (FSWO)
Nozzle to Safe End planned.
Weld Weld # RC-PZR-Nozzle to Safe End RFO 14 02/2006 RFO 15 MRP-139 examination requirements have WP-91-Y/Z Weld been met.
3" Safety Valve Full Structural Weld Overlay (FSWO)
Nozzle to Safe End planned.
Weld Weld # RC-PZR-Nozzle to Safe End RFO 14 02/2006 RFO 15 MRP-139 examination requirements have WP-91-Z/W Weld been met.
2V2" Relief Valve Full Structural Weld Overlay (FSWO)
Nozzle to Safe End planned.
Weld Weld # RC-PZR-Nozzle to Safe End RFO 15 12/2007 RFO 15 A best effort ultrasonic examination was WP-23 Weld performed in the spring 2006, but the examination coverage of the MRP-139 10" Surge Nozzle Required Examination Volume was less than to Safe End 90%
Weld Full Structural Weld Overlay (FSWO) planned.
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Page 3 of 7
- 2.
Results of Previous Inspections Weld # RC-PZR-WP-102 - 4" Spray Nozzle to Safe End Weld RC-PZR-WP-102 joins an A508 CL1 stainless steel cladded carbon steel nozzle to a SB-166 Alloy 600 safe end utilizing Alloy 82/182 weld material.
Weld RC-PZR-WP-102 was examined in the spring 2006 during RFO 14. This examination was performed with the ultrasonic examination method utilizing procedures qualified to the Performance Demonstration Initiative (PDI) requirements for the examination of dissimilar metal welds. 100% of the examination volume required by Figure 5-2 of MRP-139 to detect circumferential flaws was interrogated. No indications were noted.
Weld # RC-MK-A-90-FW56 - 4" Spray Nozzle Safe End to Stainless Steel Pipe Weld RC-MK-A-90-FW56 joins a SB-166 Alloy 600 safe end to an A-376 TP316 Stainless Steel pipe utilizing Alloy 82/182 weld material.
Weld RC-MK-A-90-FW56 was examined in the spring 2006 during RFO14. This examination was performed with the ultrasonic examination method utilizing procedures qualified to the Performance Demonstration Initiative (PDI) requirements for the examination of dissimilar metal welds. Due to safe end tapers, less than 90% of the examination volume required by Figure 5-2 of MRP-139 to detect circumferential flaws was interrogated. The PDI examination procedures require for axial scans (examination for circumferential flaws), the examination volume be interrogated with both the 450 and 600 inspection angles. Approximately 64.5% of the examination volume to detect circumferential flaws was interrogated with both angles.
Approximately 93.5% of the examination volume was interrogated with one of the two angles while approximately 6.5% of the examination volume was not interrogated by either angle. No indications were noted. The areas interrogated are illustrated below.
Weld RC-MK-A-90-FW56 - 4" Pressurizer Spray Nozzle Safe End to Pipe Weld Area examiined with one angles Are a ea ea dwithbth angles
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Page 4 of 7 Weld # RC-PZR-WP-91-W/X - 3" Safety Valve Nozzle to Safe End Weld RC-PZR-WP-91-W/X joins an A508 CL1 stainless steel cladded carbon steel nozzle to a SA-182 TP316 stainless steel safe end utilizing Alloy 82/182 weld material.
Weld RC-PZR-WP-91-W/X was examined in the spring 2006 during RFO14. This examination was performed with the ultrasonic examination method utilizing procedures qualified to the Performance Demonstration Initiative (PDI) requirements for the examination of dissimilar metal welds. 100% of the examination volume required by Figure 5-2 of MRP-139 to detect circumferential flaws was interrogated. No indications were noted. This weld was also liquid penetrant examined in RF14 with no indications noted.
Weld # RC-PZR-WP-91-Y/Z - 3" Safety Valve Nozzle to Safe End Weld RC-PZR-WP-91-Y/Z joins an A508 CLU stainless steel cladded carbon steel nozzle to a SA-182 TP316 stainless steel safe end utilizing Alloy 82/182 weld material.
Weld RC-PZR-WP-91-Y/Z was examined in the Spring 2006 during RFO 14. This examination was performed with the ultrasonic examination method utilizing procedures qualified to the Performance Demonstration Initiative (PDI) requirements for the examination of dissimilar metal welds. 100% of the examination volume required by Figure 5-2 of MlRP-139 to detect circumferential flaws was interrogated. No indications were noted.
Weld # RC-PZR-WP-91-Z/W -21/2" Relief Valve Nozzle to Safe End Weld RC-PZR-WP-91-Z/W joins an A508 CL1 stainless steel cladded carbon steel nozzle to a SA-182 TP316 stainless steel safe end utilizing Alloy 82/182 weld material.
Weld RC-PZR-WP-91-Z/W was examined in the spring 2006 during RFQ14. This examination was performed with the ultrasonic examination method utilizing procedures qualified to the Performance Demonstration Initiative (PDI) requirements for the examination of dissimilar metal welds. The PDI examination procedures require for axial scans (examination for circumferential flaws), the examination volume be interrogated with both the 450 and 600 inspection angles.
Approximately 91% of the examination volume required by Figure 5-2 of MRP-139 to detect circumferential flaws was interrogated with both angles while 100% of the examination volume was interrogated with one of the two required angles. No indications were noted.
Weld #RC-PZR-WP 10" Surge Nozzle to Safe End Weld RC-PZR-WP-23 joins an A508 CLI stainless steel cladded carbon steel nozzle to an A-336 CL F8M stainless steel safe end utilizing Alloy 82/182 weld material.
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Attachment I Page 5 of 7 Weld RC-PZR-WP-23 was examined in the spring of 2006 during RFO14. This examination was performed with the ultrasonic examination method utilizing procedures qualified to the Performance Demonstration Initiative (PDI) requirements for the examination of dissimilar metal welds. Due to nozzle tapers, less than 90% of the examination volume required by Figure 5-2 of MRP-139 to detect circumferential flaws was interrogated. The PDI examination procedures require for axial scans (examination for circumferential flaws), the examination volume be interrogated with both the 450 and 600 inspection angles. Approximately 31% of the examination volume required by Figure 5-2 of MRP-139 to detect circumferential flaws was interrogated with both angles. Approximately 98% of the examination volume was interrogated with one of the two angles while approximately 2% of the examination volume was not interrogated by either angle. FENOC commissioned EPRI to review the examination coverage to ascertain how significant of a circumferentially-oriented flaw could go potentially undetected utilizing the examination techniques employed during the spring 2006 examination. Through examinations performed on a B&W Owner's Group Surge Nozzle mockup in conjunction with the PDI samples, EPRI concluded that there was a substantial level of confidence that flaws having a 30% or greater through-wall dimension would be detected in the areas not examined by both angles. No indications were noted during the spring 2006 examination. The areas interrogated are illustrated below.
Weld RC-PZR-WP 10" Pressurizer Surge Nozzle to Safe End Weld SS Clad
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Page 6 of 7
- 3.
Reactor Coolant System (RCS) Leakage Monitoring Multiple inputs are used to evaluate RCS leakage at the DBNPS, including RCS inventory balance, containment normal sump level, containment normal sump flow monitoring, containment radiation monitors, and an under vessel leakage detection system. These inputs are utilized to establish responses for unidentified step changes in leakage as low as 0.05 gallons per minute and rates of change as low as 0.04 gallons per minute per month. Site operating procedures define the action level and appropriate response based on the observed leakage criteria. The action levels are defined in the following table followed by the appropriate responses.
Entry Conditions Sustained Step Changes Rate of Change of Leak Cumulative Leakage in Leak rate(l) rate(
Action Level UIDENTIFIED or UNIDENTIFIED UNIDENTIFIED IETFE Normal orato<
50,000 gal
< 0.05 gpm
< 0.04 gpm/month Operation I
> 50,000 - 75,000 gal
Ž0.05 - 0.075 gpm
Ž0.04 - 0.06 gpm/month
> 75,000 - 100,000
> 0.075 - 0.1 gpm
> 0.06 - 0.12 gpmlmonth gal III
> 100,000 gal
> 0.1 gpm
> 0.12 gpm/month (1) Step Change that exceeds the average of the previous three days and is sustained for three days (2) Calculated over a seven-day span and extrapolated to one month.
Normal Operation Conduct scheduled area walk downs Action Level I This action level contains steps that will provide an increased focus on parameters and indications that would help to characterize the increase in unidentified leakage. In
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Page 7 of 7 addition to elevating the visibility of this information, walkdowns of systems, structures, and components are triggered to be performed. Also, review of operational data radiation surveys and from key systems is initiated. If any leakage detection instrumentation is out of service, repairs are expedited. Consideration is given, based on the information gathered, on whether additional monitoring and leak detection instrumentation trending is warranted.
Action Level II In addition to repeating the steps of Action Level I, an extended leak rate calculation is completed, area walkdowns are expedited, containment airborne activity monitor filters are checked for traces of boron, and an item is added to the forced outage list to perform an inspection of the RCS for leakage. A plant shutdown within 90 days is highly recommended if in this Action Level.
Action Level III In addition to performing the actions of Action Levels I and II, a shutdown for a containment inspection for RCS leakage is performed within 30 days. The shutdown would be a Mode 3 shutdown or below, depending on the plant conditions. If it is determined to be pressure boundary leakage, whether located at an Alloy 600 dissimilar metal weld or not, Technical Specification requirements for Pressure Boundary Leakage will require a shutdown to Mode 5.
There is significant discussion at the Pressurized Water Reactor Owner's Group (PWROG) about leakage monitoring program changes. However, the PWROG has not yet developed a uniform approach that achieves desired results without potential unintended consequences. It is expected that the PWROG will provide a uniform leakage monitoring program to the industry in February 2007. FENOC intends to evaluate the uniform leakage monitoring program to determine any changes that should be made to the DBNPS leakage monitoring program.
Docket Number 50-346 License Number NPF-3 Serial Number 3304 Page 1 of 1 COMMITMENT LIST The following list identifies those actions committed to by the FirstEnergy Nuclear Operating Company (FENOC) in this document. Any other actions discussed in the submittal represent intended or planned actions by FENOC. They are described only for information and are not regulatory commitments. Please contact, Mr. Gregory H. Halnon, Director - FENOC Fleet Regulatory Affairs (330-315-7500) with any questions regarding this document or associated regulatory commitments.
COMMITMENTS DUE DATE FENOC will remove the DBNPS from service in 12/31/2007 December 2007 to support necessary inspection or mitigation activities for the pressurizer spray nozzle safe end to pipe and surge nozzle to safe end dissimilar metal welds, in order to satisfy the MRP-139 inspection criteria.