NOC-AE-03001644, Request for Relief from ASME Boiler and Pressure Vessel Code, Section XI Requirements for the Essential Cooling Water System (Relief Request RR-ENG-2-38)
| ML033580012 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 12/15/2003 |
| From: | Kanavos M South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| G25, GL-90-005, IWA-5250, NOC-AE-03001644, RR-ENG-2-38, STI: 31678075 | |
| Download: ML033580012 (6) | |
Text
Nuclear Operating Company Un&Sttn PC AU 282 f9dsrnort South JTeis P/ed Ekdfic (enm& rass7743 December.15, 2D03 NOC-AE-03001644 File No.: G25 10CFR50.55a STI: 31678075 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 South Texas Project Unit 2 Docket No. STN 50-499 Request for Relief from ASME Boiler and Pressure Vessel Code, Section Xl Requirements for the Essential Cooling Water System (Relief Request RR-ENG-2-38)
In accordance with the provisions of 10CFR50.55a(g)(5)(iii), the South Texas Project requests relief from IWA-5250 of Section Xl of the ASME Boiler and Pressure Vessel Code. Approval will allow deferral of code repair of a flaw recently identified in the service water Class 3 piping.
Repair of the flaw with a code repair at this time is impractical. In accordance with the guidance provided in Generic Letter 90-05 and subject to Nuclear Regulatory Commission approval, code repairs will be implemented no later than the next scheduled Unit 2 refueling outage.
The flaw is a through-wall dealloying defect identified as a 1/4-inch wide by 1-inch long oval discoloration located on a Unit 2 Essential Cooling Water Self-Cleaning Strainer 2B Emergency Backwash Valve 6-inch flange. The discoloration is due to through-wall dealloying. There is currently no visible leakage. Operability and functionality of the system have been maintained, and deferring repair of the flaw will not affect the health and safety of the public.
The attached relief request addresses the present condition of the flange, compensatory actions, and opportunities for effecting code repairs in accordance with the guidelines provided in Generic Letter 90-05.
If there are any questions, please contact either Mr. P. L. Walker at (361) 972-8392 or me at (361) 972-7181.
Mark E. Kanavos Manager, Design Engineering KRC/PLW
Attachment:
Request for Relief from ASME Boiler and Pressure Vessel Code, Section Xl Requirements for the Essential Cooling Water System (Relief Request RR-ENG-2-38)
Project Manager on Behalf of the Participants in the South Texas Project
NOC-AE-03001644 Page 2 of 2 cc:
(paper copy) (electronic copy)
Bruce S. Mallett A. H. Gutterman, Esquire Regional Administrator, Region IV Morgan, Lewis & Bockius LLP U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 L. D. Blaylock Arlington, Texas 76011-8064 City Public Service U. S. Nuclear Regulatory Commission R. L. Balcom Attention: Document Control Desk Texas Genco, LP One White Flint North 11555 Rockville Pike A. Ramirez Rockville, MD 20852 City of Austin David H. Jaffe C. A. Johnson U. S. Nuclear Regulatory Commission AEP Texas Central Company One White Flint North 11555 Rockville Pike Jon C. Wood Rockville, MD 20852 Matthews & Branscomb Mail Stop OWFNI7-D1 Steven R. Hom C. L. Marco U. S. Nuclear Regulatory Commission U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mail Stop OWFN/15-D21 Jeffrey Cruz U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 Richard A. Ratliff Bureau of Radiation Control Texas Department of Health 1100 West 49th Street Austin, TX 78756-3189 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 Project Manager on Behalf of the Participants in the South Tcxas Project
Attachment NOC-AE-03001644 Page 1 of 4 SOUTH TEXAS PROJECT UNIT 2 REQUEST FOR RELIEF FROM ASME BOILER AND PRESSURE VESSEL CODE, SECTION Xl REQUIREMENTS FOR THE ESSENTIAL COOLING WATER SYSTEM (RELIEF REQUEST RR-ENG-2-38)
References:
- 1. Status of Corrective Actions in the ECW System, M. A. McBurnett to Document Control Desk, dated November 1, 1988 (ST-HL-AE-2748)
- 2. Request for Relief from ASME Boiler and Pressure Vessel Code Section XI Requirements (Dealloying) (Relief Request RR-ENG-35) (Supplement 2), with attached "Calculation of Critical Bending Stress for Dealloyed Aluminum-Bronze Castings in the ECW System,"
AES-C-1 964-1, T. J. Jordan to NRC Document Control Desk, dated August 10, 2000 (NOC-AE-00000816)
Reference Code: ASME Boiler and Pressure Vessel Code,Section XI, 1989 Edition A. Introduction Al. Component for Which Relief is Requested (a) Identification: Unit 2 Essential Cooling Water Self-Cleaning Strainer 2B Emergency Backwash Valve 6-inch flange (b) Function: The Essential Cooling Water System is designed to supply cooling water to various safety-related systems for normal plant operation, normal shutdown, and during and after postulated design-basis accidents.
(c) Class: ASME Code Class 3 (d) Description of the flaw: The flange has a through-wall dealloying defect identified as a 1/4-inch by 1-inch oval discoloration. There is no active leakage at this location. Liquid penetrant examination performed on October 20, 2003 found no indication of a linear defect (no apparent crack).
A2. Code Requirements from Which Relief is Requested Relief from the requirements of ASME Section Xl IWA-5250(a)(3) is requested so that code repair of the through-wall flaw in Essential Cooling Water piping may be deferred until the next Unit 2 outage of sufficient duration.
A3. Basis for Relief Request As stated in Generic Letter 90-05, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2 and 3 Piping," a repair is considered to be impractical if the flaw detected during plant operation is in a section of Class 3 piping that cannot be isolated for completing a code repair within the time period permitted by the limiting condition for operation of the affected system as specified in the plant Technical Specifications, and performance of code repair necessitates a plant shutdown.
Performance of code repairs within the allowed outage time for the Essential Cooling Water System at the South Texas Project, as permitted by the limiting condition for operation, may not be practical due to the potential for fit-up problems during repair.
Therefore, the South Texas Project requests this relief on the basis of impracticality.
Attachment NOC-AE-03001 644 Page 2 of 4 B. Scope, Limitations, and Specific Considerations B1. Scope The scope of this relief request covers minor dealloying on a 6-inch flange. The component is the downstream flange of the Essential Cooling Water Self-Cleaning Strainer 2B Emergency Backwash Valve.
B2. Limitations Repair of the defect will be deferred until adequate time is available for the repair, but no later than the next Unit 2 refueling outage, provided the condition continues to meet the acceptance criteria of Generic Letter 90-05 and is enveloped by the analysis described in C3 of this relief request. Compensatory action has been implemented to detect any changes in the condition of the flaw. The next Unit 2 refueling outage is currently scheduled to begin in March 2004.
B3. Specific Considerations Consequences of potential system interactions, including flooding, spray on equipment, and loss of flow to the system, have been evaluated and are bounded by Appendix 9A of the South Texas Project Updated Final Safety Analysis Report.
The Essential Cooling Water System is a low-pressure system with normal operating pressures of approximately 50 psig and a design pressure of 120 psig. Therefore, the consequences associated with failure of high-energy lines are not applicable to the Essential Cooling Water System. Flaw evaluation is addressed in paragraph C3.
The structural integrity of piping with dealloying has been evaluated for all design loading conditions including dead weight, pressure, thermal expansion, and seismic loads. The structural integrity is monitored by the following methods:
- Monthly monitoring for qualitative assessment of leakage (quantitative if measurable leaks are observed). Currently there is no measurable leakage.
- Continuation of Essential Cooling Water System large bore piping periodic walkdowns. These walkdowns are regularly scheduled VT-2 examinations. The inspection technique has proven to be an effective means of identifying dealloyed/cracked components prior to deterioration of structural integrity margins below ASME Section Xl requirements.
Structural integrity and the monitoring frequency will be re-evaluated if significant changes in the condition of the dealloyed area are found during this monitoring.
Additional discussion is provided in the South Texas Project Updated Final Safety Analysis Report, Appendix 9A, "Assessment of the Potential Effects of Through-Wall Cracks in ECWS Piping".
C. Evaluation C1. Flaw Detection during Plant Operation and Impracticality Determination The flaw was identified on October 15, 2003, during normal Unit 2 plant operations while performing the periodic examination of Essential Cooling Water large bore piping.
Performance of code repairs within the time allowed by the limiting condition for operation might not be practical due to the potential for fit-up problems during repair.
The South Texas Project prefers to perform the code repair under controlled conditions
Attachment NOC-AE-03001 644 Page 3 of 4 during a scheduled outage that is long enough for the necessary repairs to be made as long as the specific considerations listed above are met.
C2. Root Cause Determination and Flaw Characterization The root cause of dealloying is a combination of corrosion and stress. The dealloying process normally initiates from a crevice such as the area behind a backing ring, a fabrication-induced flaw, or a casting flaw. Dealloying in this case is believed to be similar to dealloying seen in other susceptible cast aluminum-bronze components. The South Texas Project has performed laboratory analyses, calculations, and proof testing on aluminum-bronze material to address dealloying and cracking in dealloyed aluminum-bronze.
An area of recurring discoloration on aluminum-bronze piping was found on the flange close to the flange-to-pipe weld. Discoloration of aluminum-bronze indicates a through-wall dealloying defect. However, the small size of the discolored area indicates the dealloying is relatively minor. There is currently no leakage or surface accumulation of moisture at this location.
C3. Stress and Fracture Evaluation The South Texas Project has performed laboratory analyses, calculations, and proof-testing on welded aluminum-bronze material to address dealloying and cracking in dealloyed material. The process of dealloying of aluminum-bronze has been described in previous communications with the NRC (Reference 1).
The South Texas Project has analyzed through-wall flaws in Essential Cooling Water piping and found that degradation progresses slowly. Rapid or catastrophic failure due to dealloying defects is not a concern. Dealloying produces detectable leakage before flaws reach a limiting size that would affect the operability of the Essential Cooling Water System. The flaws are monitored and inspected to ensure detection of leakage.
These compensatory actions taken following discovery of this condition provide assurance that changes in the condition will be monitored and analyzed for further action as needed.
Previous stress evaluations of flanges by Bechtel assumed 100% of the joint material had been dealloyed. The evaluations used lower material strengths obtained by actual tensile tests of dealloyed samples. ASME Code stress allowable is verified using the lower dealloyed material strength. Since dealloying is only visible at one small location on the 6-inch flange next to the flange-to-pipe weld, the analysis assuming 100%
dealloying conservatively envelopes this condition and demonstrates an acceptable margin with respect to ASME Section III requirements.
For fracture analysis, limit load and fracture mechanics analyses were performed using the methodology of ASME Code, Section Xl. These are also similar to methods approved by NRC in Code Case N-513. The dealloyed area is modeled conservatively as a through-wall circumferential crack to determine the margin to failure. Fracture mechanics analyses correlating critical bending stress versus crack size have been performed for all flange sizes (Reference 2).
Flanges have been the majority of dealloyed components exhibiting leaks. The Code requirements for margin of safety have been maintained in the case of flanges previously cut out and analyzed.
Attachment NOC-AE-03001 644 Page 4 of 4 C4. Augmented Inspection Augmented monthly inspections have been implemented to detect any changes in the size of the discolored area or leakage. A significant change in the flaw will require additional engineering attention to confirm that the technical justification for this relief request remains valid.
Text
Nuclear Operating Company Un&Sttn PC AU 282 f9dsrnort South JTeis P/ed Ekdfic (enm& rass7743 December.15, 2D03 NOC-AE-03001644 File No.: G25 10CFR50.55a STI: 31678075 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 South Texas Project Unit 2 Docket No. STN 50-499 Request for Relief from ASME Boiler and Pressure Vessel Code, Section Xl Requirements for the Essential Cooling Water System (Relief Request RR-ENG-2-38)
In accordance with the provisions of 10CFR50.55a(g)(5)(iii), the South Texas Project requests relief from IWA-5250 of Section Xl of the ASME Boiler and Pressure Vessel Code. Approval will allow deferral of code repair of a flaw recently identified in the service water Class 3 piping.
Repair of the flaw with a code repair at this time is impractical. In accordance with the guidance provided in Generic Letter 90-05 and subject to Nuclear Regulatory Commission approval, code repairs will be implemented no later than the next scheduled Unit 2 refueling outage.
The flaw is a through-wall dealloying defect identified as a 1/4-inch wide by 1-inch long oval discoloration located on a Unit 2 Essential Cooling Water Self-Cleaning Strainer 2B Emergency Backwash Valve 6-inch flange. The discoloration is due to through-wall dealloying. There is currently no visible leakage. Operability and functionality of the system have been maintained, and deferring repair of the flaw will not affect the health and safety of the public.
The attached relief request addresses the present condition of the flange, compensatory actions, and opportunities for effecting code repairs in accordance with the guidelines provided in Generic Letter 90-05.
If there are any questions, please contact either Mr. P. L. Walker at (361) 972-8392 or me at (361) 972-7181.
Mark E. Kanavos Manager, Design Engineering KRC/PLW
Attachment:
Request for Relief from ASME Boiler and Pressure Vessel Code, Section Xl Requirements for the Essential Cooling Water System (Relief Request RR-ENG-2-38)
Project Manager on Behalf of the Participants in the South Texas Project
NOC-AE-03001644 Page 2 of 2 cc:
(paper copy) (electronic copy)
Bruce S. Mallett A. H. Gutterman, Esquire Regional Administrator, Region IV Morgan, Lewis & Bockius LLP U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 L. D. Blaylock Arlington, Texas 76011-8064 City Public Service U. S. Nuclear Regulatory Commission R. L. Balcom Attention: Document Control Desk Texas Genco, LP One White Flint North 11555 Rockville Pike A. Ramirez Rockville, MD 20852 City of Austin David H. Jaffe C. A. Johnson U. S. Nuclear Regulatory Commission AEP Texas Central Company One White Flint North 11555 Rockville Pike Jon C. Wood Rockville, MD 20852 Matthews & Branscomb Mail Stop OWFNI7-D1 Steven R. Hom C. L. Marco U. S. Nuclear Regulatory Commission U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mail Stop OWFN/15-D21 Jeffrey Cruz U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 Richard A. Ratliff Bureau of Radiation Control Texas Department of Health 1100 West 49th Street Austin, TX 78756-3189 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 Project Manager on Behalf of the Participants in the South Tcxas Project
Attachment NOC-AE-03001644 Page 1 of 4 SOUTH TEXAS PROJECT UNIT 2 REQUEST FOR RELIEF FROM ASME BOILER AND PRESSURE VESSEL CODE, SECTION Xl REQUIREMENTS FOR THE ESSENTIAL COOLING WATER SYSTEM (RELIEF REQUEST RR-ENG-2-38)
References:
- 1. Status of Corrective Actions in the ECW System, M. A. McBurnett to Document Control Desk, dated November 1, 1988 (ST-HL-AE-2748)
- 2. Request for Relief from ASME Boiler and Pressure Vessel Code Section XI Requirements (Dealloying) (Relief Request RR-ENG-35) (Supplement 2), with attached "Calculation of Critical Bending Stress for Dealloyed Aluminum-Bronze Castings in the ECW System,"
AES-C-1 964-1, T. J. Jordan to NRC Document Control Desk, dated August 10, 2000 (NOC-AE-00000816)
Reference Code: ASME Boiler and Pressure Vessel Code,Section XI, 1989 Edition A. Introduction Al. Component for Which Relief is Requested (a) Identification: Unit 2 Essential Cooling Water Self-Cleaning Strainer 2B Emergency Backwash Valve 6-inch flange (b) Function: The Essential Cooling Water System is designed to supply cooling water to various safety-related systems for normal plant operation, normal shutdown, and during and after postulated design-basis accidents.
(c) Class: ASME Code Class 3 (d) Description of the flaw: The flange has a through-wall dealloying defect identified as a 1/4-inch by 1-inch oval discoloration. There is no active leakage at this location. Liquid penetrant examination performed on October 20, 2003 found no indication of a linear defect (no apparent crack).
A2. Code Requirements from Which Relief is Requested Relief from the requirements of ASME Section Xl IWA-5250(a)(3) is requested so that code repair of the through-wall flaw in Essential Cooling Water piping may be deferred until the next Unit 2 outage of sufficient duration.
A3. Basis for Relief Request As stated in Generic Letter 90-05, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2 and 3 Piping," a repair is considered to be impractical if the flaw detected during plant operation is in a section of Class 3 piping that cannot be isolated for completing a code repair within the time period permitted by the limiting condition for operation of the affected system as specified in the plant Technical Specifications, and performance of code repair necessitates a plant shutdown.
Performance of code repairs within the allowed outage time for the Essential Cooling Water System at the South Texas Project, as permitted by the limiting condition for operation, may not be practical due to the potential for fit-up problems during repair.
Therefore, the South Texas Project requests this relief on the basis of impracticality.
Attachment NOC-AE-03001 644 Page 2 of 4 B. Scope, Limitations, and Specific Considerations B1. Scope The scope of this relief request covers minor dealloying on a 6-inch flange. The component is the downstream flange of the Essential Cooling Water Self-Cleaning Strainer 2B Emergency Backwash Valve.
B2. Limitations Repair of the defect will be deferred until adequate time is available for the repair, but no later than the next Unit 2 refueling outage, provided the condition continues to meet the acceptance criteria of Generic Letter 90-05 and is enveloped by the analysis described in C3 of this relief request. Compensatory action has been implemented to detect any changes in the condition of the flaw. The next Unit 2 refueling outage is currently scheduled to begin in March 2004.
B3. Specific Considerations Consequences of potential system interactions, including flooding, spray on equipment, and loss of flow to the system, have been evaluated and are bounded by Appendix 9A of the South Texas Project Updated Final Safety Analysis Report.
The Essential Cooling Water System is a low-pressure system with normal operating pressures of approximately 50 psig and a design pressure of 120 psig. Therefore, the consequences associated with failure of high-energy lines are not applicable to the Essential Cooling Water System. Flaw evaluation is addressed in paragraph C3.
The structural integrity of piping with dealloying has been evaluated for all design loading conditions including dead weight, pressure, thermal expansion, and seismic loads. The structural integrity is monitored by the following methods:
- Monthly monitoring for qualitative assessment of leakage (quantitative if measurable leaks are observed). Currently there is no measurable leakage.
- Continuation of Essential Cooling Water System large bore piping periodic walkdowns. These walkdowns are regularly scheduled VT-2 examinations. The inspection technique has proven to be an effective means of identifying dealloyed/cracked components prior to deterioration of structural integrity margins below ASME Section Xl requirements.
Structural integrity and the monitoring frequency will be re-evaluated if significant changes in the condition of the dealloyed area are found during this monitoring.
Additional discussion is provided in the South Texas Project Updated Final Safety Analysis Report, Appendix 9A, "Assessment of the Potential Effects of Through-Wall Cracks in ECWS Piping".
C. Evaluation C1. Flaw Detection during Plant Operation and Impracticality Determination The flaw was identified on October 15, 2003, during normal Unit 2 plant operations while performing the periodic examination of Essential Cooling Water large bore piping.
Performance of code repairs within the time allowed by the limiting condition for operation might not be practical due to the potential for fit-up problems during repair.
The South Texas Project prefers to perform the code repair under controlled conditions
Attachment NOC-AE-03001 644 Page 3 of 4 during a scheduled outage that is long enough for the necessary repairs to be made as long as the specific considerations listed above are met.
C2. Root Cause Determination and Flaw Characterization The root cause of dealloying is a combination of corrosion and stress. The dealloying process normally initiates from a crevice such as the area behind a backing ring, a fabrication-induced flaw, or a casting flaw. Dealloying in this case is believed to be similar to dealloying seen in other susceptible cast aluminum-bronze components. The South Texas Project has performed laboratory analyses, calculations, and proof testing on aluminum-bronze material to address dealloying and cracking in dealloyed aluminum-bronze.
An area of recurring discoloration on aluminum-bronze piping was found on the flange close to the flange-to-pipe weld. Discoloration of aluminum-bronze indicates a through-wall dealloying defect. However, the small size of the discolored area indicates the dealloying is relatively minor. There is currently no leakage or surface accumulation of moisture at this location.
C3. Stress and Fracture Evaluation The South Texas Project has performed laboratory analyses, calculations, and proof-testing on welded aluminum-bronze material to address dealloying and cracking in dealloyed material. The process of dealloying of aluminum-bronze has been described in previous communications with the NRC (Reference 1).
The South Texas Project has analyzed through-wall flaws in Essential Cooling Water piping and found that degradation progresses slowly. Rapid or catastrophic failure due to dealloying defects is not a concern. Dealloying produces detectable leakage before flaws reach a limiting size that would affect the operability of the Essential Cooling Water System. The flaws are monitored and inspected to ensure detection of leakage.
These compensatory actions taken following discovery of this condition provide assurance that changes in the condition will be monitored and analyzed for further action as needed.
Previous stress evaluations of flanges by Bechtel assumed 100% of the joint material had been dealloyed. The evaluations used lower material strengths obtained by actual tensile tests of dealloyed samples. ASME Code stress allowable is verified using the lower dealloyed material strength. Since dealloying is only visible at one small location on the 6-inch flange next to the flange-to-pipe weld, the analysis assuming 100%
dealloying conservatively envelopes this condition and demonstrates an acceptable margin with respect to ASME Section III requirements.
For fracture analysis, limit load and fracture mechanics analyses were performed using the methodology of ASME Code, Section Xl. These are also similar to methods approved by NRC in Code Case N-513. The dealloyed area is modeled conservatively as a through-wall circumferential crack to determine the margin to failure. Fracture mechanics analyses correlating critical bending stress versus crack size have been performed for all flange sizes (Reference 2).
Flanges have been the majority of dealloyed components exhibiting leaks. The Code requirements for margin of safety have been maintained in the case of flanges previously cut out and analyzed.
Attachment NOC-AE-03001 644 Page 4 of 4 C4. Augmented Inspection Augmented monthly inspections have been implemented to detect any changes in the size of the discolored area or leakage. A significant change in the flaw will require additional engineering attention to confirm that the technical justification for this relief request remains valid.