ML20099E772
| ML20099E772 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/06/1992 |
| From: | Joshua Wilson TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-90-05, GL-90-5, NUDOCS 9208110083 | |
| Download: ML20099E772 (7) | |
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August 6, 1992 L
U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington,-D.C. 20555 Gentlemen:
In the Matter of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAH NUCLEAR PLAFT (SQN) - TEMPORARY REQUEST FOR RELIEF rROM AMERICAN SOCIETY OF MECliANICAL ENGINEERS (ASME) CODE FOR CIASS 3 PIPihG LEAK ON 1
THE ESSENTIAL RAW COOLING WATER (ERCW) SYSTEM
Reference:
TVA letter to NRC dated December 2, 1991, "Sequoyah Nuclear
-Plant (SQN) - Temporary Relief From American Society of Mechanical Engineers (ASME) Code for Weld Leakage on Component Cooling System (CCS) Heat Exchangers (HX'S) OB2 and 2Al" This letter'provides a temporary request for relief from the ASME code reg +.rding repair or replacement of a short section of 2-inch-diameter piping in the ERCW system. At the present time, a through-wall flaw exists in the ASME, Code Class 3 piping. This relief request is being submitted under 10 CFR 50.55(a)(g)(5)(111) and is in accordance with guidance provided by NRC staff as outlined in the above reference.
The leak is located in a section of piping on the discharge side of Thermal Relief Valve 67-539A (refer to SQN Updated Final Scfety Analysis Report, Figure 9.2.2-2).
The relief valve'provides overpressure protection (f rom thermal expansion) f or the ERCW side (shell side) of the 1A containment spray (CS) heat exchanger (IIX) when the IIX is isolated.
TVA evaluated the operability of the.ERCW and CS systems with regard to ERCW flow-rate requirements, flooding, overpressure protection of the CS HX, and the effects of spray-on adjacent equipment.
TVA's evaluation indicates that the ERCW and CS systems will perform their design basis functions.
In addition, TVA evaluated the structural integrity of the piping in accordance with NRC guidance provided in Generic Letter
-(GL) 90-05, " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping." TVA's structural-integrity evaluation indicated that the flaw satisfied the criteria of the through wall flaw approach in GL 90-05.
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g 74 9208110083 920006
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'PDR ADOCK 05000327 P.
JU.S. Nucicar Regulatory Commission Page 2
- August 6, ' 1992 Until-repair or replacement is performed, an inspection of the piping will be conducted on a weekly basis to assess structural integrity and to ensure that-there isino further degradation.
In addition, ultrasonic testing will be performed at least once every three months to assess the rate,of degradation.
It should be noted that the affected -section d piping is_ located in_a common ERCW discharge header that cannot be isolated without affecting operability of safety equipment on both
. units.
Both units would be required toLbe shut down to allow isolatir..
of the header without affecting equipment operability.
TVA's outage i
schedule for-SQN does not currently contain a dual unit outage; consequently, the, repair or replacement of this piping must be accomplished while at least one unit is operational and the piping remains' pressurized. At this time,LIVA is evaluating several repair or replacement techniques.- TVA will complete the repair or replacement before' start-up from the Unit 1 Cycle 6 refueling outage. provides TVA's request for relief from the ASME,Section XI,_
code.- Enclosure 2 contains TVA commitments associated with this l
submittal.
As 'an additional note, it is our understanding that based upon recent conversations with NRC staff, temporary relief requests are no longer needed for-coolers.whose degraded coils form an.ASME, Code Class 3
-boundary. Accordingly, TVA will cease submission of temporary relief
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requests for degraded cooler coils.
Please direct any questions concerning this issue to D. V. Goodin at (615).843-7734.
Sincerely, 1.
- $W L. Wilson Enclosures
.cc: See Page 3 4
U.S. Nuclear Ret ury Commission Page 3 August 6, 1992 MAct.1DS DVG PMB Enclosures cc (Enclosures):
Mr. D. E. LaBarge, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North f
11555 Rockville Pike Rockville, Maryland 20852 NRC.'lucident Inspector
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Sequoya5 Nuclear Plent 2600 Igou Ferry koad Soddy Daisy, Tennessee 37379 Mr. B. A. Wilson, Project Chier U.S. Nuclear Regu14 tory F..ame. : Mn Region 11 101 Marietta Street, NW, Suite 2900 k
Atla.tta, Georgia 30323
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ENCLOSURE 1 SEQUOYAH NUCLEAR PLANT (SQN)
REQUEST FOR RELIEF --ESSENTIAL RAW COOLING WATER (EROW)
RELIEF VA7NE 67-539A DISCHARGE PIPING UNIT:
'SQN tlnita 1 and 2 COMPONENTS:
Two-inch-diameter, Schedule 40, carbon-steel piping on e
the discharge side of Relief Valve 67-539A
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SYSTEM:
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.ASMZ CODE CLASS:
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FUNCTION:
' Relief Valve 67-539A provides thermal protection to the ERCW sit?e of containment spray (CS) heat exchanger (HX) 1A when the CS HX is isolaied.
Flow Control Valve (FCV) 67-539A is located in a small section of piping that leads-from the upstream sida of FCV-67-126 to the s'ownsteam side of FCV-67-126. FCV-67-126 is the ERCW discharge isolation valve for CS HX 1A.
IMPRACTICAL CODE REQUIREMENTS
- When an American Society of Mechanical Engineers (ASME),Section XI, code repair or replacement is f
performed, it is required to be conducted in accordance with ASME,Section XI, IWA-4000 or IWA-7000
+moctively, to restore structural Integrity to the original design requirements. WA's schedule for repair or replacement is during the Unit 1 Cycle 6 refueling outage.
Temporary relief from the code
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requirement is requested until that time.
11ACKGROUND:
On June 2, 1992, Icakage was observed by Maintenance personnel on a small section ci 2-inch ERCW piping downstream of Relief Valve 67-539A (see SQN Final Safety Analysis "eport, Figure 9.2.2-2).
The size of
'the'opensng in the pipe is approximately 1/2 inch by 1/4 inch.
Upon discovery of the leak, TVA evaluated 7
the operability of the ERCW system and CS in accordance with Technical Specifications 3/4.7.4 and 3/4.6.2, respectively.
Since the leak is located on a section of piping that is connected to SQN's ERCW n.ain discharge heedet (1A), the loss of ERCW from the leak does not.affwet the supply of cooling water to any safety-related equipment.
In addition, the function of the thermal relief valve (67-539A) associated with protection of the CS HX is not affected.
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~2-P The ain discharge header empties into a discharge 4
channel out in the yard that is at atmospheric prensure. Consequently, the system pressure at the leakage point is five-to-ten pounds per square inch above atmospheric pressure (static water head between the dir. charge channel and the leak).
Water is expelled intermittently from the leak (the total estimated
-leakage is less than 1/2 gallon per minute).
Since the internal pipe pressure at the leakage point is i
sufficiently small, there are no adverse etfects to l
surrounding equipment because of spray. A funnel and a t
drain hose have been installed to route leakage to a nearby floor drain._ Based on the above discussion, TVA determined that operability of the *".CW system and CS is not impaired.
An evaluation was performed in accordance with NRC
. Generic Letter 90-05 (through-wall flaw method) to address the' structural integrity of the piping with the leakage present.
The results of this evaluation indicate that the calculated-stress intensity factor "K" of 20.33 (1,000 pcunds per square inch
[k 41[in] U.5) was less than the 35 kai(in) 0..
cri,sria for ferritic steel.
I The preliminary root cause for the piping degradstion is considered to be microbiologically induced corrosion. This cannot be accurately assessed until the piping is physically removed and examined.
Ultrasonic testing (UT) was performed to assess overall degradation of the affected piping.
UT of the two-inch-diameter, Schedule 40 piping (nominal-wall thickness of 0.154 inch) indicated-the pipe wall to be
.between 0.100 to.0.150 inch thick.
Two locat' as along the pipe were found to be 0.070 inch thick an
.ine L
' location 0.080 inch thick. A single location adjacent
.to the leak was found to be 0.050 inch thick.
PROPOSED TE!PORARY.
NONC0DE REPAIR:
A temporary noncode repair consisting of a sheetmetal clamp with'a rubber gasket has been employed to limit leakage.- This temporary repair has been evaluated for effects on the syste'n because of deadweight and seismic forces and proved to have no effect on the system. The funnel:and drain hose will remain in place to capture fand control eay leakage by the gasket.
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j; ALTERNATIVE REQUIREMENT 03 TVA will continue to operate with a temporary noncode
- repair until a code repair or replacement of the pipe can be. performed. A walkdown will be performed at h ast once a week to ensure structural integrity is j
naintained. UT will also be performed at lea,St once avery three months to assess the piping degradation rate.
Based upon the weekly walkdowns and'UT examinatic,ns, an engineering evaluation will be performed to detertnine if further remedial measures or corrective actions are needed.
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TVA will. repair or replace the affected essential raw cooling water I
system piping before start-up from the Unit 1 Cycle 6 refueling
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outage.
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A walkdown of the affected piping will be performed at least once a l
week to ensure structural integrity is maintained. Weekly monitoring will continue until repair or replacement is complete.
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Ultraronic testing (UT) will be performed at least once every three months to assess the rate of degradation. This testing will continue l
until repair or replacement is complete.
4 An engineering evaluation will be performed once every three months i
following the UT to deterraine if further remedial measures or corrective actions are needed.
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