NOC-AE-05001894, Request for Relief from ASME Boiler and Pressure Vessel Code, Section XI Requirements for Essential Cooling Water System (Ecw Train 1B) (Relief Request RR-ENG-2-39)
| ML052130211 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 07/19/2005 |
| From: | House K South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| G25, NOC-AE-05001894, TAC MC5191 | |
| Download: ML052130211 (10) | |
Text
Nuclear Operating Company N EN__
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'duly 19, 2005 NOC-AE-05001894 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 Xl Requirements for the Essential Cooling Water System (ECW Train 1B)
(Relief Request RR-ENG-2-39) (TAC No. MC-5191)
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 flaws recently identified in the Essential Cooling Water (ECW) Class 3 piping. Repair of the flaws 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 refueling outage for the affected unit.
Through-wall indications have been identified on the 30-inch pipe of the Unit 1 "B" train ECW system pipe below ECW valve EW-0064. Several small holes/indications were found in the aluminum-bronze pipe; however, there is no external leakage. The indications are on the ECW pipe inside wall in an area covered by a slip-on flange.
Operability and functionality of the system have been maintained, and deferring code repair of the flaw with application of a temporary non-code repair will not affect the health and safety of the public.
The attached relief request addresses the present condition of the pipe section, and implementation of compensatory and corrective actions in accordance with the guidelines provided in Generic Letter 90-05. A list of commitments in the request is provided.
If there are any questions, please contact either Mr. P. L. Walker at (361) 972-8392 or me at (361) 972-8922.
Kenneth D. House Acting Manager, Design Engineering PLW
Attachment:
Request for Relief from ASME Boiler and Pressure Vessel Code, Section Xl Requirements for the Essential Cooling Water System (ECW Train 1B)
(Relief Request RR-ENG-2-39) 1fNOAU STI: 31889099 Project Manager on Behalf of the Participants in the South Texas Project
NOC-AE-05001894 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 David H. Jaffe Arlington, Texas 76011-8064 U. S. Nuclear Regulatory Commission Richard A. Ratliff Jack A. Fusco Bureau of Radiation Control Michael A. Reed Texas Department of Health Texas Genco, LP 1100 West 49th Street Austin, TX 78756-3189 C. Kirksey City of Austin Jeffrey Cruz Jon C. Wood U. S. Nuclear Regulatory Commission Cox Smith Matthews P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 C. M. Canady J. J. Nesrsta City of Austin R. K. Temple Electric Utility Department E. Alarcon 721 Barton Springs Road City of San Antonio Austin, TX 78704
Attachment NOC-AE-05001894 Page 1 of 8 SOUTH TEXAS PROJECT REQUEST FOR RELIEF FROM ASME BOILER AND PRESSURE VESSEL CODE, SECTION Xl REQUIREMENTS FOR THE ESSENTIAL COOLING WATER SYSTEM (ECW TRAIN 1B) (RELIEF REQUEST RR-ENG-2-39)
- 1. Component for Which Relief is Requested (a)
Description:
Unit 1 Train B Essential Cooling Water 30-inch piping (Line Number 30" EW 1205-WT3) immediately downstream of valve EW-0064 from component cooling water heat exchanger 1B.
(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) Flaw Characterization and Root Cause Determination:
Through-wall indications have been identified on the 30-inch pipe of the UB" train ECW system downstream of ECW valve EW-0064. Damage consists of pitting located immediately downstream of throttle valve EW-0064 on the inside wall of the pipe in an area covered outside the pipe by a slip-on flange. Some pitting has a maximum depth of 0.75 inch with corrosion extending into the flange.
While there is some damage to the slip-on flange, the slip-on flange and the attendant welds prevent leakage from the ECW system.
Pitting is along the rim of the pipe in two discrete regions separated by approximately 11 inches. The regions are approximately 6 inches long and 6-1/2 inches long, respectively.
The root cause of the damage was apparent cavitation resulting from required throttling of the upstream valve.
The condition does not meet ASME code requirements for a Class 3 piping system.
- 2. Applicable Code Edition and Addenda ASME Boiler and Pressure Vessel Code, Section Xl, 1989 Edition
- 3. Applicable Code Requirement ASME Section Xl IWA-431 0 states:
Defects shall be removed or reduced in size in accordance with this Article. The component shall be acceptable for continued service if the resultant section thickness created by the cavity is equal to or greater than the minimum design thickness. If the resulting section thickness is reduced below the minimum design thickness, the component shall be repaired in accordance with this Article. Alternatively, the component may be evaluated and accepted in
Attachment NOC-AE-05001 894 Page 2 of 8 accordance with the design rules or either the Construction Code, or Section 1II, when the Construction Code was not Section IlIl.
Relief is requested so that code repair of the through-wall flaw at this location may be deferred until the next outage of sufficient duration but not later that the next refueling outage provided the conditions of Generic Letter 90-05, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2 and 3 Piping," are met.
- 4. Flaw Detection During Plant Operation While performing maintenance on May 17, 2005, aluminum-bronze piping downstream of throttle valve EW-0064 in Unit 1 ECW Train B was found to be damaged.
Implementing Code repairs within the allowed outage time for the affected train is not possible, and as a result a plant shutdown would be required to complete the repairs.
- 5. Impracticality Determination As stated in Generic Letter 90-05, the staff has determined that an ASME Code repair is required for code Class 1, 2, and 3 piping unless specific written relief has been granted by the NRC. However, the staff has determined that temporary non-code repair of Class 3 piping that cannot be isolated without a plant shutdown is justified in some instances.
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 to complete 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, is not practical due to the amount of time required to implement the repair, the potential for fit-up problems during repair, and other uncertainties associated with completing the task. Therefore, the South Texas Project requests approval of this relief request on the basis of impracticality.
- 6. ProDosed Alternative and Basis for Use 6.1 Temporarv Non-code Repair Method Contrary to ASME Section Xl IWA-431 0, defects were not removed prior to returning the affected train to service.
Voids and imperfections on wetted surfaces of the 30" ECW return line from CCW Heat Exchanger 1B (Line Number 30" EW 1205WT3) downstream of Valve 1-EW0064 were filled with Belzona 1111 to minimize further degradation. The Belzona application is not intended to repair the pressure boundary parts to satisfy the piping minimum wall thickness requirements. Belzona will serve solely as a barrier against erosion and corrosion until code repairs can be implemented.
Attachment NOC-AE-05001 894 Page 3 of 8 6.2 Basis for Use 6.2.1 Scope This relief request applies to damaged areas on the inside diameter of a 30-inch ECW pipe downstream of throttle valve EW-0064 for Component Cooling Water heat exchanger 1B. The damaged areas are covered external to the pipe by a slip-on flange where the pipe joins the throttle valve. The erosion has resulted in pitting of the aluminum-bronze pipe, to the point where the carbon steel material of the slip-on flange has experienced corrosion.
6.2.2 Specific Considerations 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 this relief request.
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 aluminum-bronze pipe has a nominal diameter of 30 inches and a nominal thickness of 0.25 inch. The pipe material is SB 169 CA-614 rolled and welded plate (6-8
-percent aluminum) fabricated to SA-155 tolerances. The slip-on flange material is SA-
'105 carbon steel. The slip-on flange is welded to the 30-inch aluminum bronze pipe with fillet welds at both ends. The configuration is depicted in the attached figures.
The ECW pumps and the cooling reservoir have adequate design margin and make-up capability to account for postulated small leakage and are therefore fully capable of fulfilling the design basis functions and mission times during a design basis accident (DBA).
Similar pitting of the aluminum-bronze piping at this location is expected to have occurred in the remaining ECW trains. However, based on similarity in design between the ECW trains, affected ECW trains are expected to be able to continue to perform their intended design-basis function until code-based repairs can be implemented.
Belzona coatings have been used in various components at the South Texas Project as protective coatings for erosion and corrosion control. Subsequent inspections of these components have demonstrated that Belzona coatings perform well in an immersed ECW environment. The use of Belzona coatings does not pose a threat to the piping, downstream components, or the safety function of the ECW system.
6.2.3 Flaw Evaluation The structural integrity of the flanged piping was assessed using the "through-wall flaw" evaluation approach in Section C-3a.of NRC Generic Letter 90-05. This approach evaluates the flaw stability by linear elastic fracture mechanics (LEFM) methodology.
Enclosure 1 to Generic Letter 90-05 details the methodology. Analysis using "Limit Load" methodology was used to determine allowed maximum critical crack size and bending loads.
Attachment NOC-AE-05001894 Page 4 of 8 To summarize the results:
s = stress at the flaw location s = 8.2 ksi K = stress intensity factor K = 38.426 Stresses Pressure + Faulted Thermal Dead Weight Stress (psi) 4632 7797 2396 Allowable Stress (psi) 18000 43200 27000 Safety Margin 3.88 5.5 11.2 The current flaw size and the bending loads are less than the respective allowed critical crack size and the bending loads determined by the limit load methodology.
Structural integrity analysis shows that at the locations of maximum stress in the piping, very large cracks would be required to cause sudden failure. Through-wall cracks are expected to be detected well before they reach a size sufficient to result in such failure.
6.2.4 Auqmented Inspection The ECW piping is readily accessible; consequently, through-wall system leakage resulting from deterioration of the ECW piping can be detected during weekly VT-2 inspections. Nondestructive examination using ultrasonic or radiographic testing is not feasible due to the configuration and dimensions in the affected area.
6.2.5 Conclusion Areas of significant damage discovered during this inspection of Train B Essential Cooling Water System (ECW) have been repaired using non-code repair methods.
Defects were not removed prior to returning the affected train to service. This is acceptable for continued train operation until code-based repairs can be completed because:
- Stress safety margin without complete replacement of the flaws is at least 3.88.
- There is continued protection against system leakage from the flaws at this location because of the welded slip-on flange.
- Visual checks can determine if leaking is in progress.
These temporary repairs of the degraded piping between the two fillet welds provide added assurance that the flange and pipe are acceptable until the next available outage of sufficient duration to perform the code repair as per guidance provided in Generic Letter 90-05.
Attachment NOC-AE-05001 894 Page 5 of 8
- 7. Duration of Proposed Alternative Code repair will be deferred until adequate time is available for the repair. Temporary non-code repair is applicable until the next scheduled outage exceeding 30 days, but no later than the next refueling outage, provided the condition continues to meet the acceptance criteria of Generic Letter 90-05 and is enveloped by the analysis. The next Unit 1 refueling outage is currently scheduled to begin in October 2006.
Attachment NOC-AE-05001 894 Page 6 of 8 Commitment Through-wall system leakage resulting from deterioration of the ECW piping can be detected during weekly VT-2 inspections.
Inspections are in progress and are being tracked as condition report action 05-7071-14.
Attachment NOC-AE-05001 894 Page 7 of 8 SLIP-ON FLANGE 30 in.
'A in.-* 4-SA-1 05 STEEL FLANGE ._ ALUMINUM-BRONZE PIPE
- ~ -
33 in.
ALUMINUM-BRONZE X0 WELD
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I - . 1 - 3/8 in. T.
3-1/2 in.
9g< 2-1/8 in.
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4"
^
"IaALUMINUM-BRONZE WELD 30 in. b 36 in.
39 in.
Attachment NOC-AE-05001 894 Page 8 of 8 CARBON STEEL SLIP-ON FLANGE DETAIL ALUMINUM-BRONZE TO
/ CARBON STEEL WELD
- ALUMINUM-BRONZE PIPE
_/ P I
ALUMINUM-BRONZE TO CARBON STEEL WELD I- 3/8 in.
PIPE CENTERLINE