Text

Request for Relief from ASME Boiler & Pressure Vessel Code,Section XI Requirements for Essential Cooling Water System (Relief Request RR-ENG-2-29)
	ML030690380
Person / Time
Site:	South Texas
Issue date:	03/04/2003
From:	Kanavos M; South Texas
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	G25, GL-90-005, NOC-AE-03001468, RR-ENG-2-29
	Download: ML030690380 (6)
	v • d • e

Nuclear Operating Company South Taw ProjedElectric Generatln$Statlon PO. Box 289 dsworth, Texas 77483 .

March 4, 2003 NOC-AE-03001468 File No.: G25 10CFR50.55a U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 South Texas Project Unit 1 Docket No. STN 50-498 Request for Relief from ASME Boiler and Pressure Vessel Code,Section XI Requirements for the Essential Cooling Water System (Relief Request RR-ENG-2-29)

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 1 refueling outage.

The flaw is a 1/2-inch diameter discoloration on the exterior of a 10" x 10" x 6" tee located on the Unit 1 Essential Cooling Water return line from the Diesel Generator #13 intercooler. 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 tee, 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, Plant Modification and Design Basis Engineering KRC/PLW

Attachment:

Request for Relief from ASME Boiler and Pressure Vessel Code,Section XI Requirements for the Essential Cooling Water System (Relief Request RR-ENG-2-29)

Project Manager on Behalf of the Participants in the South Texas Project A 47

NOC-AE-03001468 Page 2 of 2 cc:

(paper copy) (electronic copy)

Ellis W. Merschoff 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/W. C. Gunst Arlington, Texas 76011-8064 City Public Service U. S. Nuclear Regulatory Commission Mohan C. Thadani Attention: Document Control Desk U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike R. L. Balcom Rockville, MD 20852 Texas Genco, LP Richard A. Ratliff A. Ramirez Bureau of Radiation Control City of Austin Texas Department of Health 1100 West 49th Street C. A. Johnson Austin, TX 78756-3189 AEP Texas Central Company Cornelius F. O'Keefe Jon C. Wood U. S. Nuclear Regulatory Commission Matthews & Branscomb P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 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 Texas Project

Attachment NOC-AE-03001468 Page 1 of 4 SOUTH TEXAS PROJECT UNIT 1 REQUEST FOR RELIEF FROM ASME BOILER AND PRESSURE VESSEL CODE, SECTION XI REQUIREMENTS FOR THE ESSENTIAL COOLING WATER SYSTEM (RELIEF REQUEST RR-ENG-2-29)

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 Xl 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: Essential Cooling Water System, Unit 1, Emergency Diesel Generator #13 intercooler return line 10" x 10" x 6" tee (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. The subject tee combines return flow from Unit 1 train C Emergency Diesel Generator lube oil cooler and intercooler.

(c) Class: ASME Code Class 3 (d) Description of the flaw: The flaw is a 1/2-inch diameter area of recurring discoloration on a 10" x 10" x 6" aluminum-bronze tee. 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.

A2. Code Requirements from Which Relief is Requested Relief from the requirements of ASME Section XI 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 1 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

Attachment NOC-AE-03001468 Page 2 of 4 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.

B. Scope, Limitations, and Specific Considerations Bl. Scope The scope of this relief request covers minor dealloying on a 10" x 10" x 6" tee. The tee combines return flow from Emergency Diesel Generator #13, train C, lube oil cooler and intercooler.

B2. Limitations Repair of the defect will be deferred until adequate time is available for the repair, but no later than the next Unit 1 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 1 refueling outage is currently scheduled to begin in March 2003.

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 XI 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 durinq Plant Operation and Impracticality Determination The flaw was identified on November 6, 2002, during normal Unit 1 plant operations while performing the periodic examination of Essential Cooling Water large bore piping.

Attachment NOC-AE-03001468 Page 3 of 4 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 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 underside of the subject tee. 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 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.

Since dealloying is not a discontinuity, it cannot be measured by non-destructive methods. However, it can be measured after a component is cut out and sectioned.

Past examinations of a 10" x 10" x 6" tee with similar exterior surface indications of through-wall dealloying compared with the limiting curves showed that substantial margins above ASME Code Section XI requirements existed at the time the component was removed from service. This gives a high level of confidence that this tee with a single small indication of through-wall dealloying is well within code limits and is likely to remain so until the next refueling outage.

Fracture limit load and fracture mechanics analyses were performed for the subject tee using the methodology of ASME Code,Section XI (Reference 2). These analyses are similar to methods approved by the NRC in Code Case N-513. For this evaluation, the dealloyed area is modeled conservatively as a through-wall circumferential or axial crack and then analyzed for margins against either fracture or limit load failure. Safety factors were calculated for both axial and circumferential cracking. In all cases, the calculated

Attachment NOC-AE-03001468 Page 4 of 4 safety factors for Normal/Upset and Emergency/Faulted conditions exceed the ASME Section XI criteria for Class 1 piping.

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 of this relief request remains valid.