ML20094M330
| ML20094M330 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/23/1992 |
| From: | Joshua Wilson TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9203310043 | |
| Download: ML20094M330 (6) | |
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.e n4 J L WMon am n.n wu w n m m March 23, 199' U.S. Nuclear Regulatory Commission ATIN:
Document Control Desk Washington, D.C. 20555 Gentlemen:
In the Matter of
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Dock:t Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAH NUCLEAR PLANT (SQN) - REQUEST FOR RELIEF FROM THE AMERICAN SOCIFTY OF MECHANICAL ENGINEERS (ASME), SECTION XI, HYDROSTATIC PRESSURE TEST REQUIREMENTS Enclosed is a request for relief from the ASME,Section XI, hydrostatic test requirements involving the main feedwater system for Units 1 and 2.
This relief is necessary because of the replacement of feodwater nozzle transition pieces on the steam generators (S/Gs). During the forced shutdown of Unit 1 on March 19, 1992, for resolution of ice condenser lower-inlet door impairments, leakage from insulation on the feedwater line to S/G No. 3 was observed and increased leakage into the reactor building pocket sump was detected.
The source of the leakage was subsequently determined to be a through-wall crack in the feedwater nozzle transition piece to S/G No. 3.
Replacement of the feedwater transition piece is necescary to reestablish the structural integrity of the feedwater system.
The associated failure analysis is still ongoing and applicability to the remaining Units 1 and 2 transition pieces is under evaluation.
In recognition of the potential for further replacements, this relief is being requested for all eight transition pieces for both units.
The nozzle transition piece is a 16-inch, catside-diameter code Class 2 component. 11be replacement of these transition pieces will require cutting and removing the transition piece and adjacent 16-inch elbow and the remaking of three 16-inch butt welds.
TVA's ASME,Section XI, program requires that the new welds be subjected to a hydrostatic pressure test before returning the system to service. The location of g
these welds in the feedwater system is immediately upstream of the S/G
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U.S. Nuclear Regulatory Commission Page 2 March.23, 1992
'Because the new welds in the feedwater piping are not isolable from the S/Gs, a hydrostatic pressure test of the S/G and the main steam piping up to the main steam isolation valves would be required to comply with t..e requirements of Eection XI of the ASME code (1980 Edition, Winter 1981 Addenda, IWA-4400(a).
Pursuant to 10 CFR 50.55a(a)(3) and 10 CFR 50.55a(g)(5)(iii) TVA has determined that conformance to the code would be impractical and result in undue hardship without a compensating increase in the level of quality and safety.
-Enclosure.1 contains a description of the maintenance activity. contains the request for relief.
TVA has considered the use af code Case N416 in this matter. However, TVA anticipates incorporating code Case N498 into SQN'sSection XI program upon its approval by NRC.
TVA recognizes that the incorporation of N498 into SQN'sSection XI program will preempt the use of N416.
TVA requests expeditious NRC review of this relief request so that alternatives may be considered should the relief request be denied.
Please direct questions concerning this issue to Don V. Goodin at (615) 843-7734.
Sincerely, S n^ -
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L. Wilson Enclosures cc (Enclosures):
Mr. D.-E. LaBarge, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North.
11555 Rockville Pike Rockville, Maryland 20852
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NRC Resident Inspector L
Sequoyah Nuclear Plant 2600 Igou Ferry-Road i
Soddy Daisy, Tennessee 37379 Mr.'B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II
' Marietta Street, NW, Suite 2900-t lanta, Georgia 30323 l
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ENCLOSURE 1 BACKGROUND: On March 19, 1992, with the unit operating in hot staadby, TVA was performing an inspection of the Unit 1 ice condenser lowcr-plenum-inlet doors when leakage f rom the insulation on the feedwater line to Steam Generator (S/G) No. 3 was observed.
Increased leakage to the reactor building pocket sump was also noted.
Following further evaluation of the situation, the unit was taken to cold shutdown and an investigation was started to determine the exact location of the leak.
Scaffolding and lighting were installed and insulation removed at the S/G No. 3 nozzle-to-feedwater joint. A through-wall crack approximately two inches in length on the outside diameter (seven inches in length on the inside diameter) was identified through radiographic examination. Note that a visual examination had indicated a cae-inch crack on the outside diameter. The attached figure indicates the affected area.
TVA is in the process of conducting further nondestructive examination and evaluation of the flaw, along with preparations for removt. and replacement of affected piping.
TVA is also planning to perform similar examinations on the remaining Unit 1 S/Gs and all of the Unit 2 S/Gs.
A detailed failure analysis and investigation are ongoing.
MAINTENANCE ACTIVITY:
Once nondestructive examinations are completed and the area of the flaw or potential flaws is bounded. TVA will remove the affected section of material from the system.
As apprcpriate, a metallurgical examination will be performed on the flawed material to determine the mode of failure. TVA will perform replacement of the material in accordance with American Society of Mechanical Engineers,Section XI. IWA-7000.
The replacement transition piece is composed of ASME, SA-508 alley steel and the replacement elbow is carbon steel conforming to ASME, SA-420.
Both the elbow-to-transition piece and the transition piece-to-nozzle welds will be Gas Tungsten / Shielded Metal Arc welds in accordance with ASME,Section IX.
The nozzle weld will be P-3 to P-3 utilizing SFA 5.28 Class ER80S-D2 electrodes for the root and hot pass and SFA 5.5, Class E8018-C3 for the remainder. The elbow-to-transitien piece weld will be P-1 to P-3 utilizing SFA 5.28 Class ERSOS-D2 electrode for the root and hot pass and SFA 3.5 Class E8018-C3 electrode for the remainder.
The elbow co existing pipe weld will similarly use the GT-SM welding process and employ SFA 5.18 Class E70S-3 electrodes for the root and hot pass, and SFA 5.1 Class E7018 electrodes for the remainder.
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ENCLOSURE 2 Request for Relief Unit:
" and 2 Systems Main Feedwater System TVA Drawing:
47W803-1 Component:
Steam generator (S/C) nozzle transition pieces Class:
American Society of Mechanical Engineers (ASME), Code Class 2 Function:
Provides feedwater-to the S/G Code Requirement:
IWA-4400(a), 1980 Edition, Winter 1981 Addenda of the ASME Boiler and Pressure Vessel Code,Section XI, "After repairs by welding on the pressure retaining boundary, a system hydrostatic test shall be performed in accordance with IWA-5000."
Basis for Relief: The replacement of the S/G nozzle transition pfeces involves piping and welds that cannot be isolated from the S/G and the main steam piping. Therefore, a hydrostatic pressure test of the entire S/G would be required to comply with the code requirement. This presents an undue hardchip for the following reasons:
1.
The performance of a hydrostatic test on the new 16ita11ation welds for replacement of the nozzle transition piece and elbow piping requires the n
pressurization ol 'tue feedwater lines f rom the feedwater check valves, through the entire secondary side of the S/G and the main steam line up to the main steam isolation valve. This is an unusual plant configuration that would require, extensive preparations from both physical and system oparation standpoints.
It would additionally be necessary to analyze _the loading w.i the main steam lines to determine whether temporary supports are necessary for the' additional loading of the water.
2, The main steam safety-relief valves are set at pressures ranging from 1064 to 1117 pounds per square inch (psig). For Code Class 2 components with design temperatures greater than 200 degrees Fahrenheit, the code requires a test pressure of 1.25 times the lowest-relief-valve-settings, which protects that component. The required test pressure for this repair would therefore be 1330 psig. This test pressure would require the removal or gagging of the main-steam safety valves, and the installation of a temporary relief valve set at the maximum allowed test pressure.
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The additional unit downtime to-perform these hydrostatic tests would present a significant expense to TVA in replacement power for the TVA system. The increase-in safety or quality afforded by these tests, above that of the proposed alternative, is not commensurate with this expense.
Proposed-Alternative In lieu of a hydrostatic pressure test, TVA proposes to perform the following:
1.
=The new welds will receive a radiographic examination and supplemented ultrasonic-examination of the final weld.
This sequence of nondestructive examination is designed to detect any existing fabrication induced flaws.
2.
Pursuant to IWA-5242, a visual examination (VT-2) will be performed in conjunction with a system leakage test per IWA-5211(c).
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