ML19347D875
| ML19347D875 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/06/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NCR-SQN-EEB-803, NUDOCS 8104140368 | |
| Download: ML19347D875 (3) | |
Text
1:00 Chestnut Street Tower II s'
4 April 6, 1981 9
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~\\ ;f Mr. James O'Reilly, Director (A
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Office of I. eection and Enforcenent U.S. Nuclear gulatory Commission O'
Region II - Su e 3100 101 Marietta Str t Atlanta, Georgia 0303
Dear Mr. O'Reilly:
SEQUOYAH NUCLEAR PLANT UNIT 2 - 0FFSITE POWER VOLTAGE FLUCTUATION -
NCR SQN EEB 8034 - THIRD INTERIM REPORT The subject deficiency was initially reported to NRC-OIE Inspector R. W. Wright on October 20, 1980, in accordance with 10 CFR 50.55(e).
Interim reports were submitted on '!ovember 19, 1990, and February 27, 1981. Enclosed is our third interim report. We expect to submit our next report by April 15, 1981.
If you have any questions, please get in touch with D. L. Lambert at FTS 857-2581.
Very truly yours, TENNESSEE VALLEY AUTHORITY L. M. Mills, Manager Nuclear Regulation and Safety Enclosure cc:
Mr. Victor Stello, Director (Enclosure)
Office of Inspection and Enforcec:ent U.S. Nuclear Regulatory Commission Washington, DC 20555 3o/'t
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i ENCLOSURE SEQUOYAH NUCLEAR PLANT UNIT 2 0FFSITE POWER VOLTAGE FLUCTUATION NCR SQN EEB 8034 10CFR50.55(e)
THIRD INTERIM REPORT Description of Deficiency During a degraded voltage study, it was discovered that the 161-kV voltage minimum limit imposed on the operation of the 161-kV grid is not correct. This is because the 161-kV limit does not ensure l
adequate starting voltage for all safety-related 460V motors. This discrepancy is based on the present configuration of unit 1 in full power operation and unit 2 in preoperational testing.
Interim Progress TVA has calculated setpoints for future degraded voltage relaying in order to assure adequate starting voltage for all safety-related 460V motors, assuming 85 percent of rated voltage at the motor terminals.
The current leading configuration dictates that for a two-unit full-load rejection, the 161-kV grid voltage at the primary of the common station service transformers (CSST) must be no lower than 164 kV with the CSST voltage taps set on the 0 95 position. These requirements are for unit 1 in full-load operation with unit 2 in preoperational status.
The TVA assumption of 85 percent minimum starting voltage is not yet corroborated by the vendors for all the 460V motors fed from the 480V Class IE ac auxiliary power system. This assumption was selected as the design starting voltage because motors for nuclear service are conservatively applied and load torque requirements are usually well below starting torque requirements. The 85 percent starting voltage corresponds to 72 percent torque. Most loads have load torque requirements which increase with speed, i.e., fans, pumps, etc. or start unloaded such as compressors. It is, therefore, anticipated that the majority of motor drivers will have no problem starting with 85 percent of rated voltage at their terminals. The actual verification of this is proceeding on a case-by-case basis.
NEMA MG-1-20.45, 1969, requires induction motors to operate within
+ 10 percent of their rated voltage. TVA has determined that approximately 140-460V motors fed from the 480V Class 1E ao auxiliary power system could have less than 90 percent rated voltage at their i
terminals during starting. We have received documentation of minimum i
starting voltage for 17 of these motors from their vendors. Of these 17, five motors have been confirmed to start at 80 percent voltage,10
- at 85 percent voltage, and 2 at 90 percent voltage. Another eighteen motors will be replaced by June 1981 to satisfy NUREG-0588. The j
replacement motors will be rated to start with 80-percent voltage.
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. TVA is continuing to request vendor documentation on the remaining 105 motors. The two motors already identified as requiring 90-percent starting voltage are not safety related and will have administrative controls implemented which will require the unit operator verify that adequate board voltage exists prior to starting the motors.
TVA is also proceeding to incorporate design improvements which will allow a wider range of operation of the 161-kV grid and improve equipment voltages in the 480V Class 1E ac auxiliary power system.
Based upon the implementation schedule for design improvements, the minimum 161-kV grid voltage will be established to ensure that all safety-related motors are supplied with the minimum required voltage for operation when unit 1 and unit 2 are both in power operation.
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