ML20126D086

Forwards Request for Temporary Relief from ASME Code for Class 3 Piping Leak on Essential Raw Cooling Water Sys, Containment Spray Pump 1B-B Room Cooler.Relief Needed to Repair pin-hole Leak in Section of Discharge Piping

ML20126D086
Person / Time
Site:	Sequoyah
Issue date:	12/18/1992
From:	Fenech R TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9212240028
Download: ML20126D086 (5)

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Tennessee vooy Aur%dy Ocw OU.ce Bon Mn SadWCa sy, Tennessa 373797m Robert A Fenech V,ce Presdont. seauoyan NucWv Plant December 18, 1992 U.S. Nuclear Regulatory Commission ATTN Document Control Desk Washington, D.C. 20555 Centlemen:

In the Matter of ) Docket No. 50-327 Tennessee Valley Authority )

SEQUOYAH NUCLEAR PLANT-(SQN) - TEMPORARY REQUEST FOR RELIEF FROM AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) CODE FOR CLASS ;3 PIPING LEAK ON THE ESSENTIAL RAW COOLING WATER (ERCW) SYSTEM - CONTAINMENT SPPAY PUMP 1B-B ROOM COOLER

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, regarding 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)(iii) and is in accordance with guidance provided by NRC staff as outlined in the above reference.

The pin-hole leak is located in a section of piping on the discharge side of Containment Spray Pump 1B-B room cooler (refer to SQN Updated-Final Safety Analysis Report, Figure 9.2.2-4). The discharge piping provides a flow path for the ERCW syrtem water exiting the-room cooler. TVA evaluated the operability of the-ERCW system with regard to ERCW flow-rate requirements, flooding, and the effects'of-spray on adjacent equipment. TVA's evaluation indicates that the ERCW system will perform its design basis function. In addition. TVA evaluated the structural integrity of the piping in accordance with NRC guidance provided in  !-

Generic' Letter (CL) 90-05, " Guidance for Performing Temporary Non-Code  ;

Repair-of ASME Code Class 1, 2, and 3 Piping." TVA's . .

I g'QO((ptructural-integrityevaluationindicatedthattheflawsatisfied:the j

criteria of the through-wall flaw approach in GL 90-05.

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l U.S. Nuclear Regulatory Commission Page 2 j December 18, 1992 i

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 is no further degradation. .In addition, ultrasonic testing will be performed at least once every three months to assess the l rate of degradation. .TVA will complete the repair or replacement before-start-up (Mode 2) from the Unit 1 Cycle 6 refueling outage. This refueling outage is scheduled to begin_ April 2, 1993, and end June 9, 1993. '

Enclosure 1 provides TVA's request for relief from the ASME Section XI-code. Enclosure 2 contains TVA commitments associated with this submittal.

L' Please direct any questions concerning this issue to D. V. Goodin at

-(615) 843-7734.

Sincerely,

& h$.f.'

Robert A. Fenech Enclosures cc (Enclosures): '

Mr. D..E. LaBarge', Project Manager

'U.S. 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 Mr. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission ,

Region II.

_101-Marietta Street, NW, Suite:2900-

. Atlanta, Georgia 30323-0199

ENCLOSURE 1

. SEQUOYAH NUCLEAR PLANT (SQN)

REQUEST FOR RELIEF - ESSENTIAL RAW COOLING WATER (ERCW) i CONTAINMENT SPRAY PUMP 1B-B ROOM COOLER DISCHARGE PIPING UNIT: SQN Unit 1 COMPONENTS: Two-inch-diameter, Schedule 40, carbon-steel piping on the discharge side of the Containment Spray Pump 1B-B room cooler SYSTEM: ERCW ASME CODE CLASS: 3 FUNCTION: The discharge piping provides a flow path for the ERCW system water exiting the pump room cooler.

IMPRACTICAL CODE REQUIREMENTS: When an American Society of Mechanical 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 restore the system's structural integrity back to its original design requirements.

BACKGROUND: On November 23, 1992, a pin-hole leak was discovered'on the discharge piping of Containment Spray Pump.1B-B room cooler. Upon discovery of the leak. TVA evaluated the operability of the ERCW system and the containment spray (CS) system in accordance with Technical Specifications (TS) 3/4.7.4 and 3/4.6.2, respectively.

Since the leak is on the discharge piping of the CS pump room cooler, the supply of water to the room cooler is not affected. The loss of water is very small (approximately-one drop per second) and it is not-affecting any other safety-related equipment in the -

surrounding area. TVA also evaluated the structural' l integrity of the piping system in accordance with

( TS 3/4.4.10 and determined that the structural integrity of the piping system is not impaired. Based upon the above, TVA determined the operability of the ERCW and CS systems is not impaired.

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i An evaluation was performel in accordance with NRC Ceneric Letter 90-05 (through-wall flaw method) to address the structural integrity of the piping and to determine if a temporary noncode repair could be performed. The results of this evaluation show that the calculated-stress intensity factor "K" of 3.6 ksi(in)0.5 was less than 35 ksi(in)0.5 criteria for ferritic steel.

The preliminary root cause for the piping degradation is considered to be microbiological 1y 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. The piping was examined for approximately 14 inches on both sides of the leak. UT of the two-inch-diameter. Schedule 40 piping (nominal wall thickness of 0.154 inch) indicated two areas that were below minimum wall thickness. One area was in the vicinity of the leak and the other area was a spot approximately 12 inches from the leak (0.070 inch thick). The calculated minimum wall is 0.0768. The remainder of the pipe showed remaining wall thicknesses ranging from 0.085 inch to 0.154 inch.

PROPOSED TEMPORARY NONCODE REPAIR: A temporary noncode repair consisting of a rubber gasket and a radiator hose clamp has been employed to limit or stop the leakage. This temporary noncode repair has been evaluated for effects on the system because of deadweight and seismic forces and proved to have no effect on the system.

ALTERNATIVE REQUIREMENTS: 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 least once a week to ensure structural integrity is maintained. UT will also be performed at least once every three months to assess the piping degradation rate. Based upon the weekly walkdowns and UT examinations, an engineering evaluation will be performed to determine if further remedial measures or corrective actions are needed. An ASME Section XI code repair or replacement will be performed before the completion of the Unit 1 Cycle 6 refueling outage that is currently scheduled to begin April 2, 1993, and end June 9, 1993.

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. ENCLOSURE 2

, COMMITMENTS

1. TVA will repair or replace the affected essential raw cooling water system piping (Containment Spray Pump 1B-B room cooler) before '

start-up from the Unit 1 Cycle 6 refueling outage.

2. A walkdown of the affected- piping will be' performed at least once a week to ensure structural integrity is maintained. Weekly monitoring will continue until repair or replacement is complete.

3. Ultrasonic testing (UT) will be performed at least once every three months to assess the rate of degradation. This testing will continue until repair or replacement is complete.

4. An engineering evaluation will be performed once every three months ,

following the UT to determine if further remedial measures or corrective actions are needed.

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