ML20059C204
| ML20059C204 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 08/23/1990 |
| From: | Noonan T DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| ND3MNO:3021, NUDOCS 9008310115 | |
| Download: ML20059C204 (5) | |
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mesnavon n nonum August 23, 1990 ND3HN0:3021 Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-64 Soecial Reoort a.
United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 Gentlemen:
The following Special Report is submitted detailing the j
recent Electro-Hydraulic Control system failure at Beaver Valley Unit 1.
Qgscriotion of Event l
On May 31, 1990, Unit 1 was operating at 100% power.
At 0817 l
hours, an automatic overpower turbine runback alarm occurred.
Operators immediately verified that unit had experienced a step I
load increase in power and taas the turbine runback at 200%/ min was functioning as desigokJ to reduce power.
The step load increase was identified as being caused by the normally closed #4 turbine governor valve failing open.
The runback signal cleared e#ter 25.4 seconds.
Operators then took manual control of i
I turbine load to further reduce power in a controlled manner.
The plant was stabilized at 98% power by 0915 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.481575e-4 months <br />.
During both the ruitback and the load reduction, the #4 governor valve remained in L
its full open position.
After the plant was stabilized, operators notified Maintenance and initiated an investigation into the cause of the failure.
At 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br />, after reviewing the governor valve control system and the lack of valve response during the load reduction, operators attempted to close the valve using its test circuit.
The valve would not close.
At 1025 hours0.0119 days <br />0.285 hours <br />0.00169 weeks <br />3.900125e-4 months <br />, with Maintenance personnel observing, operators again attempted to close the valve using the test circuit.
The valve again failed to move.
Further investigation by Maintenance identified that the #4 governor servo card was de-energized.
The servo card vendor was contacted at this time for assistance in the troubleshooting efforts.
03303 9008310115 900823 i
PDR ADOCK 05000334
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.ND3MNO 3021 I
Page two At 1055 hours0.0122 days <br />0.293 hours <br />0.00174 weeks <br />4.014275e-4 months <br />, before the problem with the servo card was resolved, the #4 governor valve failed closed.
This caused power 4
to reduce to approximately 73% and the Reactor Coolant System (RCS) temperature to increase.
Maximum RCS temperature during this transient was 579 degrees Fahrenheit.
This is approximately 10 degrees above the RCS programmed control temperature for 73%
power.
The condenser steam dumps actuated to restore the RCS temperature to its programmed value.
Operators manually increased turbine load to close the steam dumps.
Operators locally isolated hydraulic fluid to the #4 governor valve to ensure that it would remain closed.
i Cause of Event This event resulted from a failure of an electrolytic capacitor in the #4 governor valve servo card.
This card had been installed as part of a design change to the turbine control system during the previous refueling outage.
This design change allowed the operators to transfer the governor valves from their normal " partial Arc" control scheme to " Full Arc" control.
Under partial arc control, the governor valves operate in an l
overlapping sequence.
At 100% load in partial arc control, the
- 2 and #3 governor valves are fully open, the #1 valve is throttled to approximately 40% open and the #4 valve is fully closed.
This configuration minimizes steam throttling lossee and is'the preferred mode of control for long term steady-state operation.
The full arc control installed by the design change i
defeats the governor valve sequencing scheme and causes all governor valves to respond together.
This type of control provides for uniform heating during turbine startup and minimizes thermal transients caused by governor valve testing during power L
operation.
Investigation of the #4 governor valve servo card determined that l
when the card was manufactured, the involved capacitor was l
installed in an incorrect polarity.
The capacitor's positive lead was connected to the negative terminal on the servo card and its negative lead connected to the card's positive terminal.
This resulted in degradation and eventual failure of the l
capacitor, causing the capacitor to short.
With this capacitor I
shorted, the servo card caused the governor valve to open.
The high current through the shorted capacitor rapidly caused the capacitor to overheat and eventually fail to an open circuit.
When the capacitor failed open, the servo card caused the governor valve to close.
porrective Actions l
The following actions were taken in response to this event:
1)
As stated above, after the #4 governor valve had closed Operations immediately isolated it to prevent it from inducing further transients.
The valve remained isolated until its control problem was corrected.
Augu;t 23, 1990
,ND3MNot3021
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Page three i
i 2)
The Chemistry Department performed a radiciodine analysis of the Reactor Coolant immediately after this event.
A second analysis was performed 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> later.
Neither analysis found any indication of increased iodine activity.
3)
A Reactor Flux Map was initiated for core inspection at 0530 hours0.00613 days <br />0.147 hours <br />8.763227e-4 weeks <br />2.01665e-4 months <br /> on June 1, 1990.
No anomalies were noted and the neutron flux distribution was verified to be normal.
4)
The similtr capacitors on the servo cards for the other j
governor and throttic valves were inspected and verified to be correctly installed.
Safety Analysis There were no safety implications due to this event.
The initial u
transient that occurred when the #4 governor valve failed open is bounded by analysis in Beaver Valley Unit 1 UFSAR Section 14.1.10, " Excessive Load %ncrease Incident" and Section 7.7.1.4.2
" Automatic Turbine Load Runback".
The second transient that occurred when the #4 governor valve failed shut is bounded by analysis in UFSAR Section 14.1.7, " Loss of External Electrical Load and/or Turbine Trip" and Section 7.7.1.8.1 " Load Rejection Steam Dump Controller".
The first transient involved a step increase in Main Steam demand.
This initially increased reactor power above 100%.
As assumed in the UFSAR analysis, an automatic turbine runback occurred to prevent an overpower Reactor Trip.
Based on computer data collected during the event, the peak reactor power that occurred during the transient was no greater than 107.4%.
This IS consistent with the peak overpower value range assumed by the UFSAR.
Following the turbine runback, operators took timely action to stabilize the plant and reduce power to less than 100%.
The second transient involved an approximate 25% loss of turbine load.
The condenser Steam Dump system functioned as designed to compensate for this transient.
Operators stabilized the plant l
and isolated the #4 governor valve without incident.
l Very truly your, Swsh A T. P. Noonan l
General Manager Nuclear Operations DC/sl Attachment
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Augu';t 23, 1990
.ND3MNot3021
.Page four cct Mr. T. T. Martin, Regional Administrator United States Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406 C. A. Roteck, Ohio Edison 76 S. Main Street Akron, OH 44308 Mr. A. DeAgazio, BVPS Licensing Project Manager United States Nuclear Regulatory Commission Washington, DC 20555 J. Beall, Nuclear Regulatory Commission, BVP$ Senior Resident Inspector Larry Beck Cleveland Electric 6200 Oak Tree Blvd.
Independence, Ohio 44101 INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, GA 30339 G.
E. Muckle, Factory Mutual Engineering, Pittsburgh 3 Parkway Center Room 217 Pittsburgh, PA 15220 Mr. J. N. Steinmetz, Operating Plant Projects Manager Mid Atlantic Area Westinghouse Electric Corporation Energy Systems Service Division Box 355 Pittsburgh, PA 15230 American Nuclear Insurers c/o Dottie Sherman, ANI Library The Exchange Suite 245 270 Farmington Avenue Farmington, CT 06032 Mr. Richard Janati l
Department of Environmental Resources t
P.
O.
Box 2063 16th Floor, Fulton Building Harrisburg, PA 17120 Director, Safety Evaluation & Control Virginia Electric & Power Co.
P.O.
Box 26666 l
One James River Plaza l
Richmond, VA 23261
Augu:t 23, 1990'
-.ND3MNO 3021 Page five-W. Hart 3 cy Management Analysis Company 132671 High Bluff Drive San Diego, CA 92130-2025 J. M. Riddle NUS Operating Service Corporation Park West II
. Cliff Mine Road D
Pittsburgh, PA 15275 I
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