ML20210C983
| ML20210C983 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 01/10/1987 |
| From: | Rice P GEORGIA POWER CO. |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21-87, REF-PT21-87-044-000, RTR-NUREG-0302, RTR-NUREG-302 GN-1314, IEIN-86-073, IEIN-86-73, PT21-87-044-000, PT21-87-44, NUDOCS 8702090491 | |
| Download: ML20210C983 (3) | |
Text
'
Gevg a Power Corpo Post O*f,ce Bo= ' 82 i
hjoesboro. Geo<g a 308r scenene 404 m wu.=== 3413 404 724 BM4 Ei cas
-, n!i 16 A 9 ; 19 Georgia Power
- e. o. na.
i.[Q
.,4
,s January 10, 1987 United States Nuclear Regulatory Commission Region II, Suite 2900 File:
X78G03-M137 101 Marietta Street, Northwest Log:
GN-1314 Atlanta, Georgia 30323
Reference:
Vogtle Electric Generating Plant-Units 1 & 2; 50-424, 50-425; Diesel Generator Exciter Circuitry Attention:
Mr. J. Nelson Grace On January 7,1987, Mr. C. W. Hayes, Vogtle Project Quality Assurance Manager, notified Mr.
M.
V.
Sinkule of the USNRC Region II of a potentially reportable condition associated with the diesel generator exciter circuit design.
This condition was identified during a review of IE Information Notice 86-73 (Recent Emergency Diesel Generator Problems) and documented in Operations Deficiency Report ODR T-1-86-3879.
Georgia Power Company has completed its evaluation and determined that a reportable condition as defined by the reporting criteria of Part 10CFR50.55(e) and Part 10CFR21 does exist.
Based upon NRC guidance in NUREG-0302, Revision 1,
and other NRC correspondence, Georgia Power Company is reporting this condition pursuant to the reporting requirements of Part 10CFR50.55(e).
A summary of our evaluation is attached.
This response contains no proprietary information and may be placed in the USNRC Public Document Room.
Yours truly, y.G J.
P. D. Rice DJC/PDR/wkl Attachment xc:
U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C.
20555 4
H. G. Baker D. R. Altman L. T. Gucwa J. P. O'Reilly J. A. Bailey C. W. Hayes G. F. Head G. Bockhold G. A. McCarley R. E. Conway J. F. D' Amico R. W. McManus R. H. Pinson W. D. Drinkard Sr. Resident (NRC)
B. M. Guthrie C. C. Garrett (0PC)
J. E. Joiner (TSLA)
R. A. Thomas D. Feig (GANE)
NORMS Dkdo38$f(
t PDR g
EVALUATION OF A POTENTIALLY REPORTABLE CONDITION DIESEL GENERATOR EXCITER CIRCUITRY Initial Report: On January 7, 1987, Mr.
C.
W. Hayes, Vogtle Project Quality Assurance
- Manager, notified Mr.
M.
V.
Sinkule of the USNRC Region II of a potentially reportable condition associated with the diesel generator exciter circuit design.
This condition was identified during a review of IE Information Notice 86-73 (Recent Emergency Diesel Generator Problems) and documented in Operations Deficiency Report ODR T-1-86-3879.
Background Information: The emergency diesel generators (EDG) provide an onsite source of emergency electrical power to safety-related equipment to ensure their continued operation in the event of a loss of offsite power.
The diesel generators are required to automatically start anti accept load after receipt of a start signal.
IE Information Notice 86-73 reported a condition which caused a diesel generator field flash circuit to be inoperable during an emergency SI signal start following a normal engine stop.
Review of the logic for the VEGP field flash circuit reveals that the problem as described in the IE Notice does not exist at VEGP.
However, a similar problem with the exciter does exist.
The EDG exciter provides electrical current to the generator field circuit which creates the magnetic field used to create generator output voltage.
During normal operation, the exciter varies the current to the field such that generator output voltage is regulated.
The exciter normally obtains power from the output of the generator.
During startup of the EDG, a field flashing circuit applies 125 Vdc on the field circuit to rapidly cause the output voltage to rise to rated voltage such that the EDG can quickly accept load.
In response to a shutdown signal, the VEGP EDG exciter de-energizes the generator field circuit which shuts down the generator.
The exciter circuitry is designed to reset at an engine speed below 200 RPM to re-enable the exciter after the diesel generator has been stopped manually or tripped due to a normal trip (i.e., a trip that would be bypassed during an SI condition).
If an SI signal is received while the diesel is coasting down from its normal operating speed of 450 RPM to the exciter reset speed of 200 RPM (estimated to take 45 seconds), the diesel engine pneumatic control logic will override the normal stop signal and the diesel will re-accelerate to 450 RPM.
However, the exciter would have remained shut down and the generator would not have output voltage and would not have accepted load.
[
Engineering Evaluation: Had the condition associated with the exciter circuit design gone uncorrected, a loss of offsite power coincident with a postulated single failure of one EDG while the other EDG is in coast-down to 200 RPM, a complete loss of the onsite AC power could occur.
While this is a highly unlikely scenario, its occurrence concurrent with an accident results in an unanalyzed condition.
i I
t -
Quality Assurance Program Breakdown Evaluation: The root cause was a lack of design consideration in evaluating all possible circumstances under which the diesel generator's exciter must function.
The described condition is limited to the unlikely coincidence logic associated with the exciter reset speed and the EDG coast-down period.
Due to the uniqueness of this design detail, and its limited application, it is concluded that the identified condition is an isolated case and does not represent a significant breakdown in the Transamerica Delaval Inc.,
quality assurance program.
==
Conclusion:==
Based on the results of the evaluation outlined above, Georgia Power. Company has concluded that this condition is reportable pursuant to the requirements of 10CFR50.55(e) and 10CFR21.
Based on USNRC guidance in NUREG-0302, Revision 1,
and other USNRC correspondence concerning duplicate reporting, Georgia Power Company is reporting this condition pursuant to the requirements of 10CFR50.55(e).
Corrective Action: The Unit I diesel generator exciter circuitry has been modified to reset (enable) the exciter circuit upon receipt of an emergency start signal independent of the engine speed at the time.
Upon reset (enable) of the exciter circuit the field flashing circuit is enabled and if the generator voltage is insufficient the field circuit is flashed again.
Design drawing changes will be issued for the Unit 2 required design changes.
This action will be tracked by means of Program for Completion of Work (PCW) action item 28-1614.
I
__.-