ML20043D624
| ML20043D624 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 05/31/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20043D622 | List: |
| References | |
| NUDOCS 9006080319 | |
| Download: ML20043D624 (5) | |
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UNITED STATES 8
NUCLEAR RE@ULATORY COMMISSION c
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ENCLOSURE SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR REllEF FROM CODE HYDROSTATIC PRESSURE TEST REQUIREMENTS FOR THE REACTOR COOLANT SYSTEM TENNESSEE VALLEY AUTHORITY SE0VOYAH NUCLEAR PLANT, UNIT 1 DOCKET NO. 50-327
1.0 INTRODUCTION
The Technical Specifications (TSs) for the Sequoyah Nuclear Plant, Units 1 and 2 state that the surveillance requirements for the inservice inspection of ASME Code Class 1, 2, and 3 components and inservice testing of ASME Code Class 1, 2, and 3 pumps and valves shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable Addenda as required by 10 CFR 50. Section 50.55a(g), except where specific written the Commission pursuant to 10 CFR 50. Soctions relief has been granted by(6)(i).
The ASME Code and Addenda applicable to 50.55a(a) (3) or 50.55a(g) the Sequoyah Nuclear Plant, Units 1 and 2, is the 1980 Edition, Winter 1981 Addenda.
In the letter dated May 29, 1990, the Tennessee Valley Authority (the licensee) requested relief for the reactor coolant system (RCS) and an associated safety injection line of the emergency core cooling system (ECCS) from the hydrostatic pressure testing requirements of Section XI of the ASME Code for Sequoyah, Unit 1.
The relief was requested for areas modified during the replacement of Check Valve 1-VLV-63-551 of a safety injection line to the RCS because this area cannot be isolated from the rest of the RCS for ASME Code pressure testing.
The licensee determined that conformance to the ASME Code requirement was impractical and would present an undue hard!5ip.
The purpose of this Safety-Evaluation Report (SER) is to evaluate the information submitted by the licensee in support of the its determination that conformance to the Code was impractical and an undue hardship.
The licensee stated that the need to replace the check valve was only recently identified during testing performed during the restart of Unit 1 from its Cycle 4 refueling outage.
Because replacement and Code weld examination of this check valve is presently scheduled in the early morning of May 30, 1990, the licensee requested that the staff act on its request for relief from the ASME Code on an expedited basis, i
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2 2.0 EVALUATION pescriptionofModification e
The secondary check valve (1-VLY-63-551) in the 2-inch safety injection line to the reactor coolant system Loop 1 cold leg will be removed and replaced.
This replacement will be like-for-like changeout of a 2-inch socket welded check volve.
Replacement of the check valve will include four socket welds associated with the valve, pipe, and coupling installation. A small section of piping will be removed for installation of the new check valve with a coupling due to support interference.
System:
The system is the reactor coolant system.
The modifications involve a section of piping connected to this system which provides secondary pressure isolation for the RCS/ECCS interface.
Code Requirement:
Subparagraph IWA-4400(a), 1980 Edition Winter 1981 Addenda of the ASME Code states that "Af ter repairs by welding on the pressure retaining boundary, a system hydrostatic test shall be performed in accordance with IWA-5000."
t Licensee's Basis for Relief The replacement Check Valve 1-VLV-63-551 'nvolves a section of piping and welds that etnnot be isolated from the rest of the RCS; therefore, a hydrostt. tic test of the entire RCS would be required to comply with the Code requirement.
The Code-required hydrostat!c test pressures are based on the RCS temperature.
Testpressuresrangefrom2,280poundspersquareinchgauge(psig)ata temperature of 500 degrees F or higher to a maximum of 2,460 psi at 100 deorees F nr less.
The licensee provided the following basis for the requested relief:
A.
The performance of a low-temperature /high pressure test (cold hydro-static pressure test) would require removal of the RCS safety relief valves and installation of blind flanges.
In addition, pressurization of l
the secondary side of the steam generators would be required in order to prevent overpressurization of the steam generator tubes.
These measures would result in an unusual plant configuration and require additional downtime to perform.
The additional downtime represents a substantial cost in replacement power to TVA's system.
B.
The performance of a high-temperature / low-pressure hydrostatic pressure test during startup (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 SQN, this is equal to 1.02 tines 2,235 psig, or 2,280 psig.
The setpoint for the RCS pressurizer safety valves is 2,485 psig + or - percent.
The leaktight
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e pressure for these valves has been certified by the vendor at-approximately 10 percent below the the setpoint 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 reseating of the 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 is precluded by TS 3/4.4.4.3 because this TS requires these valves to be operable in Modes 1, 2, and 3.
C.
For personnel safety reason, it is impractical to perform the visual examination of the RCS piping following a four hour hold period at the high-tem)erature/ low-pressure (i.e., 500 degrees F) condition.
Paragrapi 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-hour hold time) to 200 degrees F for performance of the visual examination (VT-2).
The provision for lowering the RCS temperature will require several startup tests to be performed again during the second power ascension.
This places the plant in transition from heatup to cooldown, requires additional thermal cycles on the RCS that are limited by TS 5.7.1, and requires two to three additional days of outage time for reperforming startup tests.
Proposed Alternative The licensee proposed performing a leakage test of the new valve, welds, and adjoining ECCS piping in Mode 3.
The welds down stream of 1-VLV-63-551 will be visually inspected for leakage at a test pressure of approximately 2,000 pounds per square inch (psi) at Mode 3 operating temperatures.
This is below the RCS operating pressure of 2235 psi to prevent pumping water into the RCS and unseating the primary bcundary check valve.
This test will be accomplished by using a temporary hydrostatic pump to pressurize the section of pising between the primary and secondary cneck valves (i.e., valves 1-V.V-61-560 and 1-VLV-63-551, respectively). The weld on the upstream side of.-VLV 63-551, will be visually ins sected for leakage at a pressure of approximately 1,500 psi. This is the ligh pressure of the safety injection pumps upstream of Check Valve 1-VLV-63-551.
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addition, the required Code non-destructive examination (NDE) will be performed prior to entry into Mode 3 to meet construction code require-ments. The licensee stated that this should provide an acceptable alterna-tive to the Code test requirements for ensuring the structural integrity of the RCS and ECCS pressure boundary.
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The licensee also stated that a Code RCS hydrostatic pressure test will be performed at Sequoyah near the end of the 10-year inservice inspection i
l interval.
At that time, the subject welds for the check valve will be l
subjected to the hydrostatic test pressure and temperature.
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4 Staff Evaluation:
The check valve in question is the secondary boundary check valve for its safety injection line.
There is another check valve, the primary boundary check valve, between Check Valve 1-VLV-63 551 and the RCS.
The primary boundary check valve will be subjected to the RCS pressure but the intervening space between the primary and secondary check valves will not be at RCS pressure unless the primary check valve leaks.
If it leaks, which is not abnormal, the pressure in the intervening space will rise with the leakage until reac11ng the RCS pressure.
Because there are Technical Specifications requirements on the maximum allowed leakage for power operation for these check valves, this will take time and there are drain lines to reduce the pressure, if needed, on the secondary check valve.
Upstream of the secondary check valve should not be subjected to RCS pressure.
The high temperature / low pressure Code hydrostatic test would only be performed at a 10 percent pressure increase over the system leakage test to be conducted at about 2000 psi downstream of the secondary boundary check valve.
This Code test would not provide any significant increase in determining the structural integrity or the lea (tightness of the repairs over the system leakage test and, therefore, the disadvantages of the Code test outweighs the benefits.
The staff concludes that conducting a RCS hydrostatic test af ter the completion of the modifications would result in a hardship and that the r
proposed Section XI NDE testing prior to Mode 3 and the leakage test in Mode 3 will prosids acequate assurance of structural integrity cf the RCS and ECCS l
pressure boundary prior to power operation. The modifications to the pressure boundary are small in scope and the leakage test will be conducted l
at a maximum pressure which the ECCS piping should see during unit operation.
The piping upstream of Check Valve 1-VLV-63 551 has two check valves between it and RCS pressure.
The ASME Code requires a hydrostatic pressure test of the RCS near the end of the first 10-year inspection interval.
The subject welds will, at that time, be subjected to the Ccde hydrostatic pressure and temperature.
3.0 Conclusion The staff has reviewed and evaluated the information submitted by the licensee in support of the relief request from the Section XI ASME Code hydrostatic test requirement associated with the replacement of check valve 1-YLV-63-551 at the Sequoyah Nuclear Plant. Unit 1.
The staff concludes that the Section XI ASME Code pressure test requirement is a hardship to perform and the performance of NDE testing and the alternative leakage test provide adequate assurance of structural integrity of the RCS and ECCS pressure level of quality and safety, pursuant to 10 CFR 50.55a(g)provides an ade boundary and of safety.
Because the alternative testina (3)(1), the relief should be granted as requested.
Principal Contributor:
J. Donohew and R. Hermann Dated: May 31, 1990 l
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SQN Reading S. Black B. Wilson L. Watson l
F. Hebdon J. Brady LA J. Donohew OGC B. Grimes E. Jordan ACRS(10)
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