ML20095E417
| ML20095E417 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/17/1992 |
| From: | Joshua Wilson TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9204270427 | |
| Download: ML20095E417 (7) | |
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t April 17, 1992 U.S.NuclearRegulatoryCommissionf ATTN Document Control Desk j
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Washington, D.C. 20555 Gentlemen:
In the Matter of
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Docket No. 50-328 Tennessee Valley Authority
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SEQUOYAH NUCLEAR PLANT (SQN) - REQUEST FOR RELIEF FROM THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME), SECTION XI, HYDR 0STATlc PRESSURE TEST REQUIREMENTS
References:
1.
TVA letter to NRC dated March 25, 1992 2.
TVA letter to NRC dated March 17, 1992 3.
NRC letter to TVA dated May 31, 1990. " Relief from Code Hydrostatic Pressure Test Requiren '.ts for Reactor Coolant System (TAC 75030) - Sequoyah Nuclear Plant, Unit =1" Enclosed is a relief request from'the ASME Code,Section XI, hydrostatic test requirements involving the reactor coolant system (RCS) and a small section of connected emergency core cooling system piping for. Unit 2.
This relief from the code requirements has become necessary as the result of the replacement of Check Valve 2-VLV-63-559.
This check valve was found to have a damaged seat-during maintenance conducted during the current Unit 2 Cycle 5 refueling outage. This valve cannot be repaired
-in-place and must be removed from the piping for replacement.
Valve 2-VLV-63-559 is a 6-inch. primary check valve in the safety injection lineyto RCS Loop 2 hot leg.
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U.S. Nuclear Regulatory Commission Page 2 April 17, 1992 Because the valve being replaced is not isolable from the RCS, a hydrostatic pressure test of the entire RCS would be required to comply with the ASME Section XI, code (1980 Edition, Winter 1981 Addenda, IWA-4400 [al).
Pursumat 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 would present an undue hardship.
This request is similar to TVA's previous hydrostatic exemptions f(r the replacement of a check valve (VLV-63-551) on Unit 1 and the replacement of Check Valves VLV-63-587, -588, and -589 on Unit 2 (References 1 and 2).
NRC apptoval of TVA's previous request for relief on Unit I was provided in the Reference 3 letter.
Replacement of the Unit 2 check valve is required to ensure that the RCS leakage requirements specified in Technical Specification Limiting Condition for Operation 3.4.6.1 and the SQN Section XI testing program are met. contains a description of the maintenance activity and the basis for TVA's exemption request. contains the request for relief.
Replacement of Check Valve 2-VLV-63-559 is tentatively scheduled during mid-loop operation following core reload on April 20, 1992.
TVA requests expeditious NRC review of the relief request such 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,
$/R J/L. Wilson ec: See page 3 l
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u U.S. Nuclear Regulatory Commission Page 3 Apr11.17, 1992 Enclosures cc (Enclosures):
Mr. D. E. LaBarge, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Sodiy Daisy, Tennessee 37379 Mr. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
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ENCLOSURE 1 I.
DESCRIPTION Or THE MAINTENANCE ACTIVITY Primar,) Check Valve 2-VLV-63-559 in the 6-inch safety injection line to the reactor coolant system (RCS) Loop 2 hot leg, has been removed and is being replaced with a new valve.
The valve location is shown on Final Safety Analysis Report, Figure 6.3.2-1.
Because of the piping configuration at the check valve, this replacement requires
'three new 6-inch butt velds and two new 2-inch socket welds.
II.
BASIS FOR RELIEF IWA-4400(a) of the American Society of Mechanical Engineers (ASME),
Section XI Code (1980 Edition, Winter 1981 Addenda' states that "After repairs by welding or the pressure reteining boundary, a system hydrostatic test sha ' se performed in accordance with IWA-5500." Code-required hydrostatic test pressures are based cn the RCS temperature. Test pressures range trom 2,280 pounds per square inch gauge (psig) at a temperature of 500 degrees Fahrenheit (F) or higher to a maximum of 2,460 psig at 100 degrees F or less. The' valve replacements, as previously described, involve sections of piping and welds that cannot be isolated from the rest of the RCS; therefore, a hydrostatic test of the entire RCS would be j:
required following the repairs and prior to the unit returning to power operation. This requirement presents an undue hardship for the following reasons:
1.
The performance of a low-temperature /high-pressure hydrostatic test (cold hydrostatic pressure test) would require removal of the RCS pressurizer safety valves and installation of blird i
In addition, pressurization of the secondary side of l.
the steam generators (SG) would be required in order to prevent overpressurization of the SG 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.
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2.
The performance of a high-temperature / low-pressure hydrostatic 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 il percent. Even though the hydrostatic test pressure is well below the lift setpoint, the potential for small steam leaks occurring through the valve increases as RCS' pressure approaches _the setpoint. The leak-tight pressure for these valves has been certified 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 lift. According to the valve manufacturer, this discharge could become excessive, and the i
proper reseating of the relief valves would not be possible.
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2 such a_ case, it-would be necessary to cool the unit back down and depressurize the RCS to repair the valves. Gagging or I
removal of the valves for installatien of a blind flange cannot be performed within the LCO action timeframe required by Technical-Specification (TS) 3/4.4.3.
This TS requires these valves to be operable in Modes 1, 2 and 3.
3.
For personnel safety retnons, it is impractical to perform the
~ visual examination of the RCS piping following a 4-hour hold period at the high-temperature / low-pressure (500 degrees F) c condition. Paragraph IWA-5245 of the ASME,Section XI, 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-hour hold time) to r
200 degrees F for performance of the visual examination (VT-2).
The provision for lowering the RCS temperatare will require several start-up tests to be performed again during the second1heatup. This places the plant in transition from heatup
-to cooldown 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 additional days of outage time for reperforming start-up tests.
III. ALTERNATIVE TESTING In lieu of the required-hydrostatic pressure 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-63-559 will b~s tested at full RCS-pressure (2,235 psig).
The new welds upstream of 2-VLV-63-559 will be tested at approximately 2,000 psig using a temporary hydrostatic pump.
Each new weld will be visually I
inspected for leakage 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-63-559 for SQN Unit 2.
Conformance to the code requirements for_hydrostatically pressure testing the entire RCS' following theLsubject maintenance has been. determined by TVA to L
result in undue hardship. -TVA. finds that the reduced pressure test while in Mode 3, in-conjunction.with the NDE of the welds and the l
weld' design, provides an acceptable alternativa for ensuring the l
structuralLintegrity of the RCS pressure boundary. This relief L
request isLsubmitted in accordance with 10 CFR 50.55a(a)(3) and
- 10. CFR 50.55a(g)(5)(iii).
i
of ENCLOSURE 2 i
Unit:
2' Systems Emergency Core Cooling System (ECCS)
TVA Drawing:
47W811-1 Component:
2-VLV-63-559 Class:
American Society of Mechanical Engineers (ASME), Code C1ssa 1 (TVA Class A) i Function:
Provides primary pressure isolation boundary for the reactor coolant system (RCS) ECCS interface.
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Code l
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 IWA-5000."
Basis for Relief:
The replacement of Check Valve 2-VLV-63-559 involves a.
section of piping and welds that cannot be isolated from the rest of the RCS; 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 pressurizer safety valves and installation of. blind flanges. -In addition, pressurization of the secondary side of-the steam generators (SG) would be required in order to prevent overpressurization of the SG 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 performancc-of a high-temperature / low-pressure hydrostatic test'during start-up (i.e., Mode 3) presents a problem with lifting of'the RCS pressurizer safety valves. The lowest pressure allowed by the code is 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 (psig), or 2,280 psig.
The setpoint for the RCS pressurizer safety valves is 2,485 psig 11 percent.
The leak-tight pressure for these valves has been certified by the vendor at i
approximately 10 percent below the setpoint w-
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pressure, or 2,236 psig. Above this pressure, the valves begin to discharge small amounts of steam prior to full lift. According to the valve manufacturer, this discharge could become excessive, and the proper rescating of +.he relief valves would not be possible.
In such a case, it would be necessary to 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 performed within the limited condition of operation action timeframe required by Technical Specification
-(TS) 3/4.4.3.
This TS requires these valves to be operable in Modes 1, 2, and 3.
3.
For personnel safety reasons, it is impractical to perform the visual examination of the RCS piping following a 4-hour hold period at the high-temperature / low-pressure (500 degrees Fahrenheit
[F]) condition.
Paragraph IWA-5245 of the ASME,Section XI Code recognizes the high temperature levels that would be encountered by examination personnel and thereby allows the RCS temperature to be lowered (followinF the 4-hour hold time) to 200 degrees F for performance of the visual examination (VT-2). The-provision for lowering the RCS tempet.;ure will require several start-up tests to be performed again during the second power ascension. This places the plant in transition from heatup to cooldown and requires approximately two to three additional days of outage time for reperforming start-up tests.
1 Proposed Alternative:
In lieu of a hydrostatic pressure test, TVA proposes to perform the following:
-1. -The downstream welds-will be tested in conjunction with the RCS leak test that is performed during restart in Mode 3 at normal operating pressure.
2; The upstream welds 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.
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