ML20141M123
| ML20141M123 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/25/1992 |
| From: | Joshua Wilson TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9204010230 | |
| Download: ML20141M123 (7) | |
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March 25,1992 9.S. Nucleat Regulatory Cennission ATTH: Document Centrol Det.k Wahington, D.C, 20555 Gestement
!.n the Matter of
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Docket No. 50-328 Tennessee Valley Authority
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SEQUOYAll NUCLEAR Pt. ANT (SQN)
REQUST FOR RELIEF TROM Tile AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME), SECTION X1,11YDR0 STATIC PRESSURE IEST REQUIREMENTS
References:
1.
TVA letter to NitC dated March 17, 1992. "Snquoyah Nuclear Plant (SQN) - Request For Relief From The Airerican Society Of Heche11 cal Engineers (ASME),
Section XI, liydrostatic Pressure Tect Requirements" 2.
NRC letter to TVA dated May 31, 1990. " Relief from Code
(
!!ydrostatic Presouro Tcat Requirements for Reactor i
Coolant System (TAC 75030)
Sequoyab Nuclear Plant, I
Unit 1" Enclosed is a relief request f rom the ASME Ccle,Section XI, hydrc, static test requirements involving the reactor coolant system (RCS) and small sections (f connected emergency core cooling syrteta (ECCS) piping for Unit 2.
This relief from the code requirements has become necessary ar the result of the anticipated replacement of Check Valve 2-VLV-63-589.
This check valve was f ound to be leaking during testirig conducted as the unit was brought down for the Cycle 5 refueling outage.
Current I
assessments indicate that this va).ve cannot be repaired in-place and must be removed fron the' piping for replacement.
Valve 2-VLV 63-589 is a 1-1/2-inch, primary check valve in the Safety-injection line to RCS Loop 's cold leg.
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U.S. Nuclear Legulatory Commission f.e.
2 March 25. 1942 14ecause the valve being replaced is not isolable from the RCS, a h drostatic pressure test of the entire RCS would be required to
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conply with the ASME, Sect ion XI, 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 deterrulued that conformance to the code would be impractical and would present an undue hardship without corapensating increase in quality or safety. This request is similar to TVa's previous hydrostatic exemption requests f or the replacement of a check valve (VLV-63-551) on Unit 1 and the replacement cf Check Valves VLV-63-587 and -588 on Unit 2.
NRC apptcval of TVA's previous request for relief on Unit I war, provided in the Referenced 2 letter.
Replacement of 2-VLV 63-580 16. required to ensure that the RCS leakage requirernents specified in Technical Specification Limiting Condition f or Operation 3.4.6.1 and the SQN Section XI testing program continue to be met. contains a description of the maintestance activity and the basis f or WA's exernption request, contains the request.
for relief, keplacement of Check Valve 2-VLV-63-589 is tentatively scheduled during the core empt) period between March 27 and April 7, 1992, of the Unit 2 Cycle 5 refueling outage.
WA requesto NRC review of the rellef request before the replacement of the check valve such that alternatives may be considered should the relief request be denied.
Please direct questions concerning this tucue to Don V. Goodin at (615) 843-7734.
Sincerely, f
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J L. Wilson ec See page 3 i
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U.S. Nucicar Regulatory Consnission Page 3 March 25. 1992 Enclosures cc (Enclosures):
Mr. D. E. laiBarge. Project Manager U.S. Nuclear Regula*;ory Coinnission One Uhite Flint. North 11555 Rockville Pike Rockville. Marylm d 20852 NRC Resident Inspector daquoyab Nuclear Plant 2f>00 Igou Ferry Road Soddy I;aisy. Ter.nessee 3?379 Mr. B. A. Wilson. Project Chief U.S. Nuclear Regulatory Conanission Region II 101 Marietta Street. NW. Suite 2900 Atlanta Georgia 30323 I
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ENCLOSURE 1 I.
DESCRIPTION OF THE MAINTENANCE ACTIVITY
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Primary Check Valve 2-VLV-63-589 in the 1-1/2-inch, safety-Injection line i
to the reactor coolant system (kCS) 1.oop 4 cold Icg is planned to be i
removed and replaced.
This replacement will be like-for-like changcout i
of the check valve. The valve location is shown on Final Safety Analysis
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Report Figure 6.3.2-1.
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[AS,JS,, FOR RELTEF IWA-4400(a) of the American Society of Mechar.ical Englueers (ASME).
Section XI code (1980 Edition. Wintor 1981 Addenda) states that "After repairs by welding on the pressure retaining boundary, a oystem l
hydrostatic test shall be performed in accordance with IWA-5000."
Code-required hydrostatic test pressures are based on the RCS temperature.
Test prussures range from 2.280 pounds per square inch i
l gauge (psig) at a temperature of 500 degrees Fahrenheit (F) or higher to a maximum of 2,400 psig at 100 degrees F or less.
The valve reptar:ement, as previously described involves sections of piping and welds that cannot be isolated from the rent of the RCS therefore, a hydrostatic l -
test of the entire RCS would be required following the replacement and i
prior to the unit returning to power operation.
This requirement presents an. undue hardship for the following reasons:
1.
The performance et a low-temperature /high-pressure hydrostatic test f
(cold hydrostatic pressure test) would require removal of the RCS l
safety-relief valves and installation of blind flanges.
In addition.
l pressurization of the secondary side of the steam generators (S/Ca) would be required in order to prevent overpressurization of the S/G tubes. These measures result in unusual plant configuration and require additional downtime to perform. The additional downtime represents a substantial cost in replacement power to TVA's system.
'2.
The performance of a high-temperature / low-pressure hydrostatic I
l pressure test during start-up (i.e.
Mode 3) presents a problem with lifting of the RCS pressurizer safety valves. The lowest hydrostatic test pressure allowed by the code is 1.02 times the RCS operating pressure, or 2.280 psig. The setpoint for the RCS pressurizer safety valves is 2.485 psig 11 percent.
Even though the hydrostatic test pressure is well below the1 11ft setpoint. the potential for j
small-steam leaks occurring through the valve increases as RCS pressure approaches the setpoint. The leak-tight pressure for these valves.has been certifled by the vendor at approximately 10 percent below the setpoint pressure. Above this pressure, the valves begin to discharge small amounts of steam prior to full lif_t.
Accordir,1 to the valve manufacturer this discharge could become excessive. and the' proper reseating of the relief valves would not be possible.
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2 auch a case. LL would be necessary io cool the unit back down and depressurize the RCS to repair the valves. Gagging or removal of the valves for installation of a blind flange cannot be perf ormed within the limited condition of operation action timef rame required by Technict.s fpecliication (TS) 3/4.4.3.
This TS requires these valves to be operable in Modes 1, 2, and 3.
3.
For personnel safety reasona, it is impractical to perform the visual examination cf the RCS piping following a 4-hour hold period at the high-temperature / low-pressure (500 degrees F) condition.
Paragraph IWA-5245 of the ASME Section X1, code recognizes the high temperature levels that would be encountered by examination personnel and thereby allows the RCS temperature to be lowered (following the 4-hnur hold time) to 200 degrees F for performance of the virual examination (VT+2).
The provision for lowering the RCS temperature will require several start-up tests to be performed again during the second heatup. This places the plant in transition f rom heatup to couldown and imposes additional thermal cycles on the RCS that are limited by Sequoyah Nuclear Plant (SQN) TS 5.7.1.
The transition timeframe will also require two to three additionni days of outage time for reperforming start-up tests.
111. ALTERNATIVE TESTING In lieu of the required hydrostatic prosaure test, TVA proposes to perform a reduced-pressure test on the new welds and component while in Mode 3.
The new welds downstream of 2-VLV-63-589 will be tested at full RCS pressure (2,235 psig). The new weld upstream of 2-VLV-63-589 will be tested at approximately 7,000 psig using a temporary hydrostatic pump. Each new weld will be visually inspected for lenkage during these reduced pressure tests.
The required nondestructive examination (NDE) will be performed on each new weld to meet construction code requirements.
IV.
CONCLUSION TVA requests relief from the hydrostatic pressure test requirements of the ASME,Section XI, code for replacement of Check Valve 2-VLV-63-584 for SQN Unit 2.
Conformance to the code requirements for hydrostatically pressure testing the entire RCS following the subject maintenance has been determined by TVA to result in undue hardship. IVA finds the reduced pressure test while in Mode 3, in conjunction with the NDE of the welds and the weld design, provides an acceptable alternative for ensuring the structural integrity of the RCS pressure boundaty.
This relief request is submitted in accordance with 10 CFR 50.55a(a)(3) and 10 CFR 50.55a(g)(5)(lii).
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ENCLOSURE 2 Unitt 2
Systems Emergency Core Cooling System (ECCS)
TVA Drawing: 47W811-1 Component 2-VLV-63-589 Classt American Society of Mechanical Engineers (ASME), Code Class 1 (TVA C1ssa A)
Function:
Provides primary pressure isolation bounce,ry for the reector coolant system (RCS) ECCS interface.
Code
-Requirement:
IWA-4400(a),1980 Edition, Winter 1981 Addenda of the ASME Boiler and Pressure Vessel Code,Section XI, states that "After repairs by welding on the pressure retaining boundary, a system hydrostatic test shall be performed in accordance with 1WA-5000."
Basis for Relieft The replacement of Check Valve 2-VLV-63-589 involves a section of piping and welds that cannot be isolated f rom the rest of the RCSt therefore, a hydrostatic test of the entire RCS would be required to_ comply with the code requirement.
This presents an undue hardship for the following reasons:
1.
The performance of a low-temperature /high-pressure test (cold-hydrostatic pressure test) would require removal of the RCS safety-relief valves and installation of blind flanges.
In addition, pressurization of the secondary side of the steam generators (S/Gs) would be required in order to orevent overpressurisation of the S/G tubes. These measures result in unusual plant configuration and require additional downtime to perform. 'the addi.tional downtime represents a substantial cost in replacement power to TVA's system.
2.
Tbc performance of a high-temperature / low-pressure hydrostatic pressure test during stort-up (i.e., Mode 3) presents a problem with lif ting of the RCS pressurizer safety valver. The 10wert pressure allowed by the code 1s-1.02 times the RCS operating pressure..For Sequoyah Nuclear Plant (SQN), this is equal to 1.02 times 2,235 pounds, per square inch (paig), or 2,280 psig. The setpoint for the RCS pressurizer. safety valves is 2,485 psig 11 percent. The leak-tight pressure for these salves has been certified by the vendor at approxiuately_10 percent below the setpoint pressure, or 2,236 psig. Above this pressure,-the valves begin to discharge small anounts of steam prior to full lift. According to the valve manufacturer, this discharge could become excessive, and the proper rescating of the relief valves would-not'be possible.
In such a case, it I
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a would be necessary to cool the unit back down and depressurire the RCS to repair the valves.
Gagging or temoval of the valver for ins.ta11ation of a blind flange cannot be performed within the limited condition of operation action timef rune required by Teci<nical Specif Ication (TS) 3/4.4.3.
This TS requires these valveu to be operable in Modes 1, 2, and 3.
3.
For personnel safety reasons, it is impractical to perform the visual examination of the i<CS piping following a 4-hour hold period at the high-tempercture/ low-pressure (500 degrees Fahrenheit (F)) condition.
Paragraph IWA-5245 of the ASME Section XI, code recognir.en the high tempe.
re levels that would be encountered by examination persern.el and thereby allows the RCS temperature to be lowered (following the 6-hour hold tirne) to 200 degrees F for performance of the visual examination (VT-2).
The provision for lowering the RCS teroperature will require several start-up tests to be performed again during the second power ascension. This places the plint in transition from heatup to cooldown and requires approxitr.ately two to three additional days of outage time for reperforming start-up tests.
Proposed Alternativet in lieu of a hydrostatic pressure test. TVA proposes to perform the follow!ng:
1.
The downr.tream welds will be tested in conjunction with the RCS leak test that is performed during restar*. in Mode 3 at normal operating pressure.
2.
The upstream weld will be tested by use of a hydrostatic pump at a test pressure of approximately 2,000 psig.
In addition, the required nondestructive examinations will be performed to meet construction code requirements.
PLO90205/513 1
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