ML20042G980
| ML20042G980 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 05/11/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20042G979 | List: |
| References | |
| NUDOCS 9005160365 | |
| Download: ML20042G980 (4) | |
Text
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....9 ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF FROM CODE HYOR0 STATIC PRESSURE TEST REQUIREMENTS FOR THE REACTOR COOLANT SYSTEM TENNESSEE VALLEY AUTHORIT)
SEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-327 and 50-328
1.0 INTRODUCTION
The Techn1.1 Specifications (TSs) for the Sequoyah Nuclear Plant, Units 1 and 2, state taat the surveillance requirements for the inservice inspection of ASME Code Class 1, 2, ano 3 components and inservice testing of ASME Code Class 1, 2, and 3 pumps and valves shall be perf ormed in accordance with Section XI of the ASME Boller and Pressure Vessel Code and applicable Addenda as required by 10 CFR 50, Section 50.05a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50, Sectit ns 50.55a(a)(3) or 50.55a(9)(6)(i). The ASME Code ana Addenda applicable to the Sequoyah Nuclear Plant, Units 1 and 2, is the 1980 Edition, Winter 1981 Addenda.
In the letter dated September 29, 1989, the Tennessee. alley Authority (the licensee) requested relief for the reactor coolant system (P';) from the hydrostatic pressure testing requirements of Section XI of the ASME Code for Sequoyah, Units 1 and 2.
The relief was requested for creas modified during removal of the upper head injection system and resistance temperature device l
manifolds because these areas in the RCS are not isolateble from the rest of
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the RCS.
The licensee determined that conformance to the ASME Code requirement was impractical and would present an undue hardship.
The purpose of this Safety Evaluation Report (S R) is to evaluate the inf ormction submitted by the licensee in support of the its determination that conforriance to the Code was impractical.
2.0 EVALUATION Description of Modifir.ation A.
@per tiead injection (UHD Sy stem Removal
- Four 5-inch UHI lines that penetrate the reoctor vessel head wil~l be cut and topped.
One of the four lines will be fitted to receive piping for the reactor coolant vent sy s tem.
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Resistance Temperature Device (RTD) Manifold Removal - The RTD manifold y
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piping con"ected to the RC5 will be removeo. -The existing hot and cold leg pene w ions will be machined to accept _RTD-temperature wells. There will be e '.atal of.three wells in each loop of'the hot leg and one'well in each loop of the cold leg.
System:
The system. is the reactor coolant system. The modifications involve sections of piping connected to this system.
Code Requirement:
Subparagraph IWA-4400(a), 1980 Edition, Winter 1981 Addenda of the ASME Code t
aates that "Af ter repairs by welding on the pressure retaining boundary, a
.ystem hydrostatic test shall be performed in accordance with IWA-5000".
cicensee's Basis for Relief
'The Code-required-hydrostatic test pressures are based on the RCS temoerature.
Test pressures range from 2,280 pounds per square inch gauge (psig) at a temperature of 500 degrees F or higher to a maximum of 2,460 psi at 100 degrees F or less. The licensee provided the following basis for the requested relief:.
A.
. The performance of a low-temperature /high-pressure test (cold hydrostrdic pressure test) would require removal of the RCS safety relief valves ind installation of blind flanges.
In addition, pressurization of the second-ary side of the steam generators would be required in order to preveat overpressurization of the steam generator tubes.
These measures would l
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.
L B.
The performance of a high-temperature / low-pressure hydrostatic pressure L
test during startup (i.e., Mode 3) preseirss & problem with lif ting of the RCS pressurizer safety volvc s.
The lowest pressure allowed by the Code is 1.02 times the RCS operating pressure.
For SQN, this is equal to 1.02 times.2,235 psig, or 2,280 psig. The setpoint for the RCS pressuri-1 percent. The leaktight pressure for zer safety valves is 2,485 psig +'ythe vendor at approximately 10 percent these valves has been certified l below 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 munufacturer, this discharge could become exces-sive, ario 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 3/4.4.3 because this TS requires these valves to be operable in Modes 1, 2, and 3.
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For personnel safety reasons, it is impractical to perform the visual examination of the RCS piping following a four-hour hold period at the high-temperature / low-pressure (i.e., 500 degrees 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 L
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 RCS leakage test in Mode 3 at operating pressure and temperature. The RCS pressure for this test will be at 2,235 psig instead of at 2,280 psig for the system hydrostatic pressure test.
In addition, the required NDE will be performed to meet construction code requirements and ASME Section XI preservice requirements. The licensee stated that this provides an acceptable alternative to the Code test requirements for ensuring the structural integrity of the RCS pressure boundary.
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 interval.. At that time, the subject welds for the removal of the VH1 system l
and RTD manifolds will be subjectea to the hy& astatic test pressure and 1emperature.
Staff Evaluation:
The staff concludes that conducting a RCS hydrostatic test after the completion of the modifications would result in a hardship, and that the proposed Section XI NDE testing and the Re,S leakage at operating pressure and temperature in Mode 3 will provide adequate assurance of structural integrity of the RCS pressure boundary prior to power operation. The modifications to the RCS pressure boundary are small in scope and the leakage test will be conducted at a pressure only 2". lower than the pressure for the Code high-temperature /
t low-pressuro hydrostatic pressure test. The ASME Code requires a hydrostatic H
pressure test of the RCS near the end of the first 10-year inspection interval.
L The subject welds will, at that time, be subjected to the Code hydrostatic h
pressure and temperature.
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The high temperature / low pressure Code hyarostatic test discussed by the licensee would only be performed at a 2 percent pressure increase over the system leakage test to be conducted at operating pressure. This Code test would not provide any significant increase in determining the structural integrity or the leaktightness of the repairs over the system leakage test and, i '
therefore, the disadvantages of the Code test outweighs the benefits.
The
~ staff reconnends that the 10-year Code hydrostatic test of the RCS be performed cold (i.e., near at the lowest temperature consistent with fracture prevention-criteria).
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3.0 CONCLUSION
e The staff has reviewed and evaluated the information submitted by'the licensee in support of the relief request f rom the Section XI ASME Code hydrostatic test requirement associated with-the removal of the upper head injection (UHI) system and the resistance temperaturt-device (RTD) manifolds at the Sequoyah Nuclear Plant, Units 1 and 2.
The staff concludes that the Section XI ASME
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Code 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 pressure boundary and of safety. Therefore, pursuant to 10 CFR 50.55a(u)(3)(i), the relief should be granted as requested.-
The stuff recommends _ that the 10-year Code hydrostatic test of the RCS be performed at the lowest temperature consistent with fracture preventation criteria.
Principal Contributor: F. Litton Dated: May 11, 1990
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