ML18153C681
| ML18153C681 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 07/31/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18153C680 | List: |
| References | |
| NUDOCS 9108050343 | |
| Download: ML18153C681 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PERTAINING TO RELIEF REQUEST NO. P-4 OF THE INSERVICE TESTING PROGRAM VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION, UNIT NOS. 1 AND 2 DOCKET NOS. 50-280 AND 50-281 RELIEF REQUEST The licensee has requested relief from the following ASME Code,Section XI, IWP requirements:
- 1.
An inservice test shall be run on pumps 1-RS-P-2A, 1-RS-P-28, 2-RS-P-2A, and 2-RS-P-28 nominally every 3 months during normal plant operation.
- 2.
Each pump shall be run at least 5 minutes under conditions as stable as the system permits prior to measuring the test quantities.
- 3.
Measure inlet pressure and differential pressure.
LICENSEE'S BASIS FOR REQUESTING RELIEF
- 1.
The outside recirculation spray pumps take suction from the containment sump and discharge to the containment spray arrays.
To test these deep draft pumps, the pump pit and the recirculation test loop must be filled with primary grade water and vented. After the test is completed, the pump pit and recirculation piping must be slowly drained to avoid flooding the basement.
Testing is the only routine source of degradation of the pumps.
They are also maintained dry and therefore are not subject to normal corrosion or fouling expected under a wetted environment.
Considering the complexity of testing these pumps as described above, the exposure to degradation caused by frequent testing, and the dry state in which the pumps are maintained, there is no compensating increase in safety achieved by testing these pumps every 3 months.
This position is supported by ASME/ANSI OM-1987 (Part 6),
11 Inservice Testing of Pumps and Valves in Light Water Reactor Power Plants, 11 Para-graph 5.5, which states, 11 Pumps lacking required fluid inventory, (e.g.,
pumps in dry sumps) need not be tested in accordance with this Part every three months.
These pumps shall be tested at least once every two years except as provided in para. 5.4. The required fluid inventory shall be
,,- 9108050343 6~865~80 PDR ADOCK PDR p
ee provided during this test." Paragraph 5.4 describes the testing frequency of pumps in systems which are declared inoperable or not required for service.
- 2.
The test loop for these pumps contains a small volume of water. A 4-inch test recirculation line branches off the 10-inch pump discharge line a short distance from the pump.
The recirculation line discharges into the pump pit, which is a cylinder approximately 50 feet deep and 2 feet in diameter. Because of the small volume in the test loop, the hydraulic parameters stabilize quickly. Therefore, a 5-minute stabilization period is not necessary to achieve repeatable test results.
In addition, if the pump is run for too long a period, the water will heat up due to the limited water volume.
This heatup can lead to excessive pressures in the test loop.
- 3.
Inlet pressure instrumentation is not installed. However, the outside recirculation spray pumps obtain flow through a suction bell immersed in the pumps' casing. During testing, a casing level is established by filling the casing with primary grade (PG) water to provide net positive suction head (NPSH) to the pump.
Flow is recirculated through the pump, recirculation line, and back to the casing.
By establishing a casing level and maintaining it constant for the tests, any variation in pump differential pressure would be directly indicated by monitoring pump discharge pressure.
The static inlet pressure will be calculated and subtracted from the discharge pressure to yield a differential pressure.
LICENSEE'S PROPOSED ALTERNATE TESTING The licensee has proposed that the outside recirculation spray pumps be flow tested on their recirculation paths at least once every 2 years. Maintaining a constant pump casing water level from test to test by filling the casing with PG water will yield the same suction pressure for each test. The static inlet pressure will be calculated and subtracted from the discharge pressure to yield a differential pressure. After a 2-minute stabilization period, static inlet pressure, differential pressure as determined from the calculated static inlet pressure and measured discharge pressure, flow rate and vibration measurements will be taken.
EVALUATION The licensee has requested relief from the Code-required testing of the outside recirculation spray pumps. Specifically, the licensee has requested to (1) test the pumps every 2 years rather than quarterly, (2) measure parameters after a 2-minute stabilization period rather than 5 minutes, and (3) calculate, rather than measure, inlet pressure and differential pressure based on a constant pump casing water level and measured discharge pressure.
In addition, the licensee proposed to measure flow rate and vibration.
Given the complexity of the testing, and the exposure of the normally dry pumps to degradation during the procedure, testing of these pumps every 3 months is impractical and does not provide increased safety assurance. Testing the
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Iii,. '
ee pumps every 2 years will provide sufficient safety assurance given that the pumps are *normally maintained dry.
Due to the small test loop volume, the Code-required stabiliz_ation period could result in excessive system heating. Reduction of the stabilization period from 5 to 2 minutes can reasonably be expected to provide stable conditions and accurate determination of system parameters.
The lack of installed instrumentation for inlet pressure and differential pressure renders the me~surement of these parameters impractical. The proposed determination of inlet pressure based on constant level in the pump casing, and calculation of differential pressure from measured discharge pressure and calculated static inlet pressure, combined with the proposed measurement of flow rate, are
- deemed* sufficient to identify developing degradation of flow in the pump.
In addition, the proposed vibration measurements should be useful in predicting, and preventing, pump component failures.
- coNCLUSION Due to the design of the outside recirculation spray system, compliance with the.Code requirements is impractical. Conformance with the Code would only be possible if the system were redesigned, which would be a significant burden for the licensee. Accordingly, pursuant to 10 CFR 50.55a(g)(6){i), relief may be grantecl from the Code-required quarterly flow testing and from the Code require-men_ts to* al low 5 minutes for system stabilization, and to measure inlet pressure and differential pressure provided that flow testing is conducted every 2 years, at least 2 minutes is provided for system stabilization before measurements are taken, and inlet pressure and differential pressure are determined as discussed above.
The relief granted is authorized by law and will not endanger life or property or the corrunon defense and security and is otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Principal Contributor:
D. Dorman O~te:
July 31, 1991