ML20202A714

Provides Request for Relief for Delaying Repair on Section of ASME Code Class 3 Piping within Essential Raw Cooling Water Sys

ML20202A714
Person / Time
Site:	Sequoyah
Issue date:	01/20/1999
From:	Salas P TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9901280262
Download: ML20202A714 (6)

Text

RA Tennessee Valley Authonty Post Othce Box P000. Soddy-Daisy. Tennessee 37379 January 20, 1999 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of Docket Nos. 50-327 50-328 Tennessee Valley Authority SEQUOYAH NUCLEAR PLANT (SQN) - REQUEST FOR RELIEF FROM AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) CODE FOR REPLACEMENT OF ASME CODE CLASS 3 PIPING This letter provides a request for relief for delaying repair on a section of ASME Code Class 3 piping withia SON's essential raw cooling water (ERCW) system. At the present time, a pin-hole leak exists on a 24-inch diameter carbon steel pipe. This pipe is a discharge pipe located downstream of Component Cooling Water Heat Exchanger OBl. The cooling medium for the heat exchanger is ERCW. The pipe from the heat exchanger provides a flow path to the plant's main discharge header for the ERCW system.

TVA has evaluated the operability of the ERCW system with regards to: (1) the structural integrity of the pipe (2) effects of spray on adjacent equipment, and (3) ERCW flow rate requirements. TVA's evaluation for operability l

indicates that the ERCW system will perform its design basis function and surrounding equipment is not adversely affected.

Leakage from the pipe is currently less than one drop per 0 \\'\

minute. The small amount of leakage has been evaluated and does not impact system function or plant operation. (\

Accordingly, TVA has elected to monitor the leakage and a mechanical pipe clamp to limit leakage will not be installed at this time.

9901290262990h2 DR p ADOCK 05000327 PDRi

U.S. Nuclear Regulatory Commission Pa'ge 2 January 20, 1999 In accordance with the guidance of NRC Generic Letter (GL) 90-05, TVA will replace the affected section of pipe prior to startup from the Unit 2 Cycle 9 refueling outage (scheduled to begin April 18, 1999). Until pipe replacement is completed, performance of a visual and an ultrasonic examination will be performed every three months to assess the pipe degradation rate.

This relief request is being submitted under 10 CFR 50.55 (a) (g) (5) (iii) and is provided in accordance with the guidance of NRC GL 90-05. Enclosure 1 provides TVA's request for relief. Enclosure 2 provides TVA commitments.

Please direct questions concerning this issue to me at (423) 843-7170 or J. D. Smith at (423) 843-6672.

Sincerely, Pe ro " as Licensing and Industry Affairs Manager Enclosures cc (Enclosures):  ;

Mr. R. W. Hernan, Project Manager Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 Regional Administrator U.S. Nuclear Regulatory Commission Region II

! Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303-3415

ENCLOSURE 1 I

SEQUOYAH NUCLEAR PLANT (SON) REQUEST FOR RELIEF i ESSENTIAL RAW COOLING WATER (ERCW)

DISCHARGE PIPING.FROM COMPONENT COOLING HEAT EXCHANGER OB1 UNIT: SON Units 1 and 2 COMPONENTS: 24-inch diameter, standard wall (0.375 inch),

carbon steel piping.

SYSTEM: ERCW ASME CODE CLASS: 3 l

FUNCTION: The ERCW discharge piping from the component _

cooling heat exchanger provides a flow path to Train B ERCW main discharge header (reference EROW system drawing from SON's Final Safety Analysis Report, Figure 9.2.2-2).

I IMPRACTICAL CODE l REQUIREMENTS: When an American Society of Mechanical l Engineers (ASME),Section XI, code repair or replacement is performed, it is required to be performed in accordance with ASME,Section XI, ,

IWA-4000 or IWA-7000, respectively, in order to j restore the systems structural integrity back to its original design requirements. j I

BACKGROUND: A through-wall leak was discovered in the ERCW system. The leak is located in a section of piping that provides a flowpath for ERCW discharge from Component Cooling Heat j

, Exchanger OB1 (leak located between ERCW valves  !

0-FCV-67-151 and 0-67-552). The flow control i i valve (0-FCV-67-151) is a normally closed i valve. Consequently, the ERCW in this section l l of piping is normally stagnant. j The leakage from the piping is currently less

! than one drop per minute. This section of l

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piping was previously ident.ified for monitoring )

under SQN's Erosion / Corrosion Program. SQN j plans to replace the affected section of piping '

l during the Unit 2 Cycle 9 refueling outage.

In addition to the leakage location, three

, other locations (approximately 4 inches in the l l axial direction from the leak) have pipe wall thickness lower than the minimum thickness required by design. An evaluation was performed in accordance with NRC Generic Letter l (GL) 90-05 for single versus multiple flaws.

t This evaluation determined that the spacing l between the flaws (S) was greater than the

! depth of the deepest flaw (d2). Accordingly, the evaluation considers the pipe locations as multiple flaws. ,

L An evaluation was performed in accordance with l NRC GL 90-05 using the through-wall method to l address the structural integrity of the piping l and to determine if'a temporary noncode repair could be performed. The results of this j evaluation show that the largest calculated i stress intensity factor ("K") for the four 5~

locations is 29.1 ksi(in) ,which is less than 5

the 35 ksi(in) criteria for ferritic steel.

Based upon the above, TVA detcumined that operability of the ERCW system is not impaired.

L TVA's preliminary root cause for the piping  ;

degradation determined the mechanism to be 4 microbiological induced corrosion (MIC). TVA' s j l evaluation for impacts due to flooding or spray -

l onto electrical equipment determined that l adjacent equipment would not be affected.

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PROPOSED  !

l TEMPORARY l i

f NONCODE REPAIR: Based on the above evaluations, TVA does not plan to install a mechanical clamp onto the l pipe since the leakage is minimal and does not

! affect operability of the ERCW system or adjacent equipment or systems. The piping is scheduled to be replaced during SON's upcoming Unit 2 Cycle 9 refueling outage (April 1999).

L The GL 90-05 evaluation shows that the piping has sufficient structural integrity for

[ continued safe operation of the plant during this time period.

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ALTERNATIVE REQUIREMENTS: A visual inspection and an ultrasonic (UT)

, examination will be performed every three I months to assess the piping degradation rate. I Based upon the inupection and UT examinations,  ;

an engineering evaluation will be performed to l determine if further remedial measures or corrective actions are needed. An ASME l Section XI repair or replacement will be  ;

performed before the completion of the Unit 2 i Cycle 9 refueling outage, which is currently  :

' scheduled to start on April 18, 1999.  !

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ENCLOSURE 2 COMMITMENTS

1. TVA will replace the affected piping in accordance with the American Society of Mechanical Engineers code prior to startup from the Unit 2 Cycle 9 refueling outage (currently scheduled to begin April 18, 1999).

2. TVA will perform visual examinations and an engineering

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evaluation based on a nondestructive examination every three months to determine if further remedial or corrective actions are needed until replacement is complete.

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