ML20056F312
| ML20056F312 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 08/20/1993 |
| From: | Tremblay L VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BVY-93-88, GL-90-05, GL-90-5, NUDOCS 9308260358 | |
| Download: ML20056F312 (3) | |
Text
e YEITMONT YANKEE NUCLEAR POWER CORPORATION
~.
Ferry Road, Brattleboro, VT 05301-7002
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x ENGINEERING OFFICE s
580 MA!N STREET
~-
ROLTON MA 01740 1508)7794711 August 20,1993 United States Nuclear Regulatory Commission BVY 93-88 ATTN: Document ControlDesk Washington, DC 20555
References:
a.
License No. DPR-28 (Docket No. 50-271) b.
USNRC Generic Letter 90-05, " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,2 and 3 Piping", dated 6/15/90
Subject:
Temporary Non-Code Repair of Service Water Piping in the Intake Structure
Dear Sir,
In accordance with Generic Letter 90-05 and 10CFR50.55a(g)(6)(i) this letter is being submitted to document actions taken by Vermont Yankee to evaluate, without immediate code repair, a small leak in the service water piping at the Vermont Yankee Nuclear Power Station, and to request relief from the requirement to perform an immediate code repair. These ac; ions were discussed with members of the USNRC staff on August 6 and 9,1993.
The Operations Department reported leakage from a three inch service water (SW) branch line off the main service water header in the intake structure. The leak is located at a weld in an unisolable portion of the branch line to the chlorination system and circulating water pump bearing lubrication supply. The leak originated from two pitting perforations of the weld connecting piping upstream of valve V70-130B. See Figure 1 attached and FSAR Figure 10.6-la for the flow diagram and arrangement of these components.
Ultrasonic examination of the weld was performed. The UT results showed several localized areas indicative of either inclusions or pitting. The indications were scattered around the circumference, with the minimum wall thickness in excess of 0.100 inches, except for one localized reading of 0.075 inches.
Engineering analyses were performed using design basis values for deadweight, pressure, thermal and seismic loading. Structural margin was determined to be adequate to ensure the integrity of the piping system. The analyses have been documented via a fonnal calculation (VYC
-1208) in accordance with our approved QA progmm.
Repair of the 3" SW-28A line upstream ofisolation valve SW-130B would require the isolation of the "A" service water strainer and the 24 inch main supply header of the "A" Service Water Subsystem. Service water loads could be supplied through the "B" service water strainer through use of system cross connect valves. However, repair of the leak is not deemed to be prudent while at power. Although the strainers are each rated for 100% flow, a malfunction such as plugging of the "B" strainer could increase the risk of a loss of service water flow. The consequences of such an event would be significantly reduced with repairs being made during shutdown conditions.
b 9308260358930820 T
PDR ADOCK 05000271 At 0g P
PDR fj (g
^ i VERMONT YANKEE NUCLEAR POWER CORPORATION United States Nuclear Regulatory Commission August 20,1993 j
Page7 A plant walkdown was conducted to assess the potential for adverse flooding or water spray impacts should the leaking pipe rupture. Line 3"-SW-28A is located in the Service Water / Fire l
Protection Pump Room of the Intake Structure. The SW/FP Pump Room contains the four service l
water pumps, the diesel and electric fire pumps and the piping, valves and strainers associated with these systems.
i Should line 3"-SW-28A ruptme, a number of components in the SW/FP Pump Room could be contacted by water spray. However, electrical equipment that could be contacted by water spray consists of pump motors and associated valves that require electrical service. There are no Motor Control Centers (MCCs) or electrical distribution panels located in the SW/FP Pump Room. To accommodate flooding, the SW/FP Pump Room contains a number of drain paths, including three 4-inch floor drains, two large (10 inen and 12 inch pipe size equivalent) pipe penetrations, and a non-water tight doorway, all of which could direct significant amounts of water back to the river in i
the event of a pipe rupture. Further, as described in Vermont Yankee Flooding Study, the complete loss of the Service Water System has been previously analyzed by considering the loss of' the Vemon Dam (resulting in loss of river water supply to the Intake Structure). As described in i
Section 10.8 of the Vermont Yankee FSAR, the Altemate Cooling Water System is designed for such an event. Additionally, the complete loss of the Intake Structure is assumed during a maximum probable flood. This would bound the loss of any selected system or subsystem within j
the structure.
j In summary, the leak is in a moderate energy Safety Class 3 piping system (design temperature
)
of 150 F and design pressure of 125 psig). Present leakage is being removed from the area by i
means of the floor drain system. Implementation of a code repair would require either a plant i
shutdown or a plant system line-up that would challenge reliable Service Wcter System operation.
i Engineering evaluations have demonstrated that the structural integrity of the piping system remains unaffected.
j i
Vermont Yankee concludes that relief fmm immediate code repair will present no undue risk to the health and safety of the public. We request that the USNRC grant relief to allow deferral of a
[
code repair until the 1993 refueling outage, which is scheduled to begin on August 28,1993. A code repair will be implemented prior to startup from the refueling outage.
l I
i Very truly yours, l
VERMONT YANKEE NUCLEAR POWER CORIORATION.
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7 Leonard A.Tremblay,Jr.
Senior Licensing Engineer cc:
USNRC Region I Administrator i
USNRC Resident Inspector-VYNP5 1
USNRC Project Manager-VYNPS l
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