05000424/LER-1990-011
| ML20055C596 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 05/21/1990 |
| From: | Hairston W, Odom R GEORGIA POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| ELV-01664, ELV-1664, LER-90-011, LER-90-11, NUDOCS 9005290001 | |
| Download: ML20055C596 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| 4242090011R00 - NRC Website | |
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Georoa Fun Company
,333 hedmont Amnae
, . Altrca. Gevrg:a 30308 Tsjephone 404 026 3195 Maihng Address 40 inser est Centor Pa4 way Post Omce Box 1?95 Birrrungham, Alabama 30201 bicptuw POS 868 $501 May 21, 1990 ves:vvem wn sen W. G. Hairston, til Senior Vice Pres: dent Nacicar Orcations ELV-01664 0389 Docket No. 50-424 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555 Gentlemen:
l V0GTLE ELECTRIC GENERATING PLANT LICENSEE EVENT REPORT MANUAL REACTOR TRIP DUE TO INADVERTENT CLOSURE OF MAIN FEED REGULATING VALVE In accordance with 10 CFR 50.73, Georgia Power Company hereby submits the enclosed report related to an event which occurred on April 25, 1990.
Sincerely, L%l.yh.l $
l W. G. Hairston, Ill WGH,Ill/NJS/gm l
Enclosure:
LER 50-424/1990-011 xc: k orcia Power comoany Mr. C. K. McCoy Mr. G. Bockhold, Jr.
Mr. R. M. Odom Mr. P. D. Rushton NORMS l
U. S. Nuclear Reaulatgry Commission Mr. S. D. Ebneter, Regional Administrator Mr. T. A. Reed, Licensing Project Manager, NRR l Mr. R. F. Aiello, Senior Resident Inspector, Vogtle I
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. .. A c t . . ,~, ,, 1. e . , e . e . e ,. , ,.,, . .y. ,, ,, ,. .,,,, a ,.e. , n . i On 4-25-90, at 1257 CDT, the Unit I reactor was manually tripped due to decreasing level in steam generator (SG) No. 2. Prior to the trip, a ' Steam Generator 2 Flow Mismatch Alarm" annunciator was received and feedwater flow to SG No. 2 was observed to be decreasing raaidly. The Balance of Plant Operator attempted to increase the feedwt.ter flow ?y increasing the demand signals to Main Feedwater Regulating Valve (MFRV) No. 2 and Bypass Feedwater Regulating Valve No. 2. However, SG No. 2 level continued to fall which forced initiation of the reactor trip. The Auxiliary Feedwater System actuated as designed following the reactor trip to me.intain SG levels. By 1310 CDT, the Unit was
! stabilized in Mode 3.
l Subsequent investigation indicated that MFRV No. 2 had closed and caused the event. The MFRV apparently closed when workers installing insulation on the MFRV inadvertently bumped into and mispositioned the local control levers
- located on the side of the valve positioner. Hispositioning of the local
- control levers interrupted the control air supply to the valve positioner.
L Since the local control levers are not used for normal operations, corrective i action to prevent recurrence has been taken to remove these levers from both the l Unit I and Unit 2 MFRVs.
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Q0 42 or 0 l4 text o-. < =c e , mm on A. REQUIRE 4ENT FOR REPORT Thi' report is required per 10 CFR 50.73 (a)(2)(iv) because an unplanned mar.ua' actuation of the Reactor Protection System occurred.
B. UNIT STATUS OF TIME OF EVENT Unit I was in Mode 1 (power operation) at 82% of rated thermal power. There a was no equipment which was inoperable or in an off normal status such that it contributed to the occurrence or consequences of this event.
C. DESCRIPTION OF EVENT On 4-25-90, at approximately 1256 CDT, a " Steam Generator 2 Flow Hismatch Alarm" annunciator was received in the Unit 1 Control Room. The initial ,
indication on channels IFI-520A and IFI-521A was that feedwater flow to Steam Generator (SG) No. 2 was decreasing rapidly. Based on this indication, the Balance of Plant Operator took manual control of Main Feedwater Regulating Valve (MFRV) No. 2 and Bypass Feedwater Regulating '
Valve (BFRV) No. 2 and increased the demand signals to 100%. However, SG No. 2 level continued to fall and at approximately 20% narrow range level, a manual reactor trip was initiated by tie Reactor Operator at 1257 COT. ;
On the reactor trip, all control rods fully inserted. The Main Feedwater System isolated,. and the Auxiliary Feedwater (AFW) System actuated as designed. Control Room operators entered emergency operating procedure 19000-C, "E-0 Reactor Trip or Safety Injection", closed the "B" train Main .
l Steam Isolation Valves and began throttling AFW flow to the steam generators. This action was taken to limit Reactor Coolant System cooldown and to maintain steam generator water levels. By 1310 CDT, the unit had been stabilized in Mode 3 and unit operating procedure 12006-C, " Unit Cooldown to Cold Shutdown" was entered.
D. CAUSE OF EVENT 1
l-The direct cause of the event was determined to be that MFRV No. 2 had '
i closed. Closure of Main feedwater Isolation Valve (MFIV) No. 2 would also have caused this event; however, the alarms which would have accompanied closure of that valve were not received prior to the reactor trip.
Therefore, personnel were sent to investigate MFRV No. 2. Two non-utility craft personnel were found in the area of the valve. These personnel had been involved in installing insulation " cans" on the MFRV. An examination of the MFRV revealed that two local control levers, located one above the other on the side of the valve positioner, were in an intermediate position.
Operation of the upper control lever interrupts the control air ,
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supply to the valve positioner and operation of the bottom control lever vents air off the positioner diaphragm. The control levers are provided as ,
an option to allow local control of the valve for maintenance testing i purposes and are not used for normal operation. The craft personnel were ,
questioned, but it could not be confirmed that they had bumped or otherwise i come in contact with these control levers. However, based on the work that 1' was being performed, it was concluded that they had bumped the levers and caused the MFRV to close.
In order to verify that closure of the MFRV was the cause of the event, an ;
attempt was made to open the valve from the Control Room with the local ;
control levers still in the "as found" position. The MFRV would not open. ,
The local control levers were then placed. in their correct position and the !
MFRV opened properly on an attempt from the control room. As a final verification, the local control levers were again mispositioned and the MFRV went closed within 21 seconds. This testing confirmed that closure of the MFRV was the cause of the event and the mispositioning of the control levers was the cause for the valve closure.
I The root cause for the mispositioning of the local control levers was determined to be the location of the levers in relation to the work that was being performed. The craft personnel, while positioning the insulation ;
cans, ap)arently reached through the side rails of an access platform and ;
bumped tie control levers.
E. ANALYSIS OF EVENT >
The fail safe position for an MFRV is the closed position. Accident
- analyses indicate that the AFW System is capable of removing the stored heat of the primary water system during emergency enditions without relying on -
normal feedwater. The AFW System functioned , aperly to supply water to the '
steam generators following the reactor trip. .ised on these considerations, there was no adverse effect on plant safety on an the health and safety of .
the public.
F. CORRECTIVE ACTIONS The local control levers have been removed from the MFRVs for both Unit I e and Unit 2.
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i G. ADDITIONAL INFORMATION ,
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- 1. Failed Component Identification None i
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- 2. Previous Similar Events
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None ,
- 3. Energy Industry Identification System Codes !
" Main Feedwater System - SJ '
Auxiliary feedwater System - BA 1
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