ML20205J475
| ML20205J475 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 03/25/1987 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RTR-NUREG-0053, RTR-NUREG-53 87-094, 87-94, NUDOCS 8704010321 | |
| Download: ML20205J475 (4) | |
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VINGINIA ELECTHIC AND POWEN COMPANY Hicnxoxn,VIHOINIA 20261 March 25, 1987 g
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Vera Pasutomar NortmAm oramarnown U. S. Nuclear Regulatory Commission Serial No.87-094 Attn: Document Control Desk NAPS /JHL:jmj Washington, D. C. 20555 Docket No. 50-339 License No. NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT NO. 2 INSPECTION OF THE INSIDE RECIRCULATION SPRAY PUMPS North Anna 2 License Condition 2.C(15)(c) requires that the recirculation spray pumps inside containment be removed and inspected and the bearings replaced as necessary.
This requirement originates from NUREG-0053, Supplement No. 10. " Safety Evaluation Report (SER) Related to the Operation of North Anna Power Station Units 1 and 2."
NUREG-0053 also states that the bearings of the inside recirculation spray pumps should be optically aligned as committed to by Virginia Electric and Power Company in our letter dated September 4, 1979.
It is our intention to modify this commitment such that the bearings will be optically aligned only if it is necessary to remove or replace the bearings.
Also we intend to modify the test procedure for determination of OPERABILITY following the inspection and reassembly of the Inside Recirculation Spray Pumps. The bases for these changes are discussed below.
Optical Alignment During the first refueling outage for North Anna Unit No. 2 in the Spring of 1982, the inside recirculation spray pumps were removed and inspected. No significant degradation was noted on the bearings. Following the inspection, the pumps were optically aligned.
In order to perform this alignment, the bearings had to be removed from their housings.
This process is difficult because the bearings, being made of carbon, are brittle and the removal destroyed them.
This alignment process resulted in the replacement of bearings that were previously determined to be satisfactory.
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NUREG-0053, Supplement No.
9 required the demonstration of the long-term reliability of the inside recirculation spray pumps.
The NRC and their consultants concluded that the long-term reliability could be demonstrated through the use of a modal analysis demonstrating that the natural frequencies of the pumps and column systems would not be expected to lead to unsatisfactory vibratory behavior.
NUREG-0053, Supplement No. 10 discusses the results of the modal analysis.
The analysis demonstrated that the vibrational characteristics of the inside recirculation spray pumps are similar to the vibrational characteristics of the successfully tested outside recirculation spray pumps.
(The previous testing of the outside recirculation spray pumps was discussed in previous supplements of NUREG-0053.) The analysis and the fact that the shaft of the inside recirculation spray pumps is much shorter than the shaft of the outside recirculation spray pumps should make alignments of the inside recirculation spray pumps less critical. This also demonstrates reliability of the pumps.
In a letter from Heyward, Incorporated (engineering consultant for Bingham-Williamette Company, manufacturer of the inside recirculation spray pumps), dated November 5, 1986, it was recommended that the carbon bearings not be removed from their housings unless they are to be replaced as they are brittle and would likely be damaged during removal.
It was recommended that the pumps should be disassembled to the extent that the bearings could be accessed for measurement.
Based on the recommendation not to remove the bearings from their housings, the pumps shaft being shorter than the outside recirculation spray pumps shaft making alignments less critical, and our previous experience with optically aligning the pumps af ter inspection, the pumps should not be optically aligned following their inspection unless the bearings are replaced because of above-normal degradation.
Determination of Operability Following the removal and inspection of the inside recirculation spray pumps, pump operability must be determined.
Previously, a dike was constructed around the pumps to demonstrate operability under flow conditions. This operability test takes approximately 2 days for construction and removal of the dike and approximately 3 days to perform the actual pump testing. Testing is complicated because the water becomes heated since the pumps are in a recirculation mode. This prevents obtaining stable pump bearing temperatures.
We have determined that there is no advantage to performing this type of operability test. These pumps and their bearings are designed to be run with dry conditions for short periods of time in order to determine pump operability.
Currently, periodic test procedures require that the inside recirculation spray pumps be run to determine pump operability on a quarterly basis.
This testing is performed in dry conditions and the test verifies that the pumps achieve a speed greater than 100 rpm as indicated by a rotation sensor.
No problems related to the bearings have been identified as a result of these periodic tests.
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To aid in demonstrating the reliability of the inside recirculation spray pumps, Section 6.2.2.5.2 of the Updated Final Safety Analysis Report describes the instrumentation available in the Control Room to monitor system parameters during operation and testing of the pumps. This instrumentation includes:
pump discharge pressure, containment sump and recirculation spray cooler discharge water temperature, vibration alarms and indication of-shaft rotation. Also, Technical Specification 3.6.2.2 requires that "four separate and independent containment recirculation spray subsystems, each composed of a spray pump, associated heat exchanger and flow path" shall be operable during modes 1, 2, 3, and 4.
In summary, we do not intend to perform an optical alignment of the inside recirculation spray pumps following their inspection unless replacement is necessitated and we intend to determine OPERABILITY of the pumps by testing ther. dry as we currently do on a quarterly basis.
These changes have been approved by the Station Nuclear Safety and Operating Committee.
It has been determined that the changes do not involve an unreviewed safety question as defined in 10 CFR 50.59.
If you have any questions, please contact us.
Very truly yours, pg W. L. Stewart i
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U. S. Nuclear Regulatory Commission 101 Marietta Street, N. W.
Suite 2900 Atlanta, Georgia 30323 Mr. J. L. Caldwell NRC Senior Resident Inspector North Anna Power Station I
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