ML20247F675
| ML20247F675 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 09/07/1989 |
| From: | Tucker H DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 8909180239 | |
| Download: ML20247F675 (4) | |
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DukeIbuer Company
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L PO Box 33198 Vice President.
1 Charlotte, NC 28242 Nudear Production
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(704)373-4531
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DUKEPOWER.
/ September ;7, ' 1989 --
i-Document Control Desk-2 U. Sm Nuclear-Regulatory Commission Washington,.D.~C. 20555
Subject:
- Catawba Nuclear. Station, Unit 1 -
Docket No. 50-413 Special Report Gentlemen:
. Pursuant to Catawba Nuclear Station Technical Specifications 4.8.1.1.3 and 6.9.2, please find at:tached a Catawba Unit 1 Special. Report regarding Diesel Generator IA. Diesel Generator 1A experienced two invalid failures on' August 9, and August 10, 1989.
Veryl truly. yours',
W kV Hal B. Tucker
' Attachments
-JGT/4/SRPIR260-xc: Mr. S. D. Ebneter Regional Administrator, Region II U. S. Nuclear Regulatory Commission 101 Fiarietta Street, NW, Suite 2900 Atlanta, Georgia 30323-Mr. W. T. Orders NRC Resident-Inspector Catawba Nuclear Station 8909180239 spopo7
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SPECIAL REPORT CATAWBA NUCLEAR STATION, UNIT 1 DIESEL GENERATOR 1A INVALID FAILURES DUE TO BEARING SENSOR FAILURES AND DIODE FAILURE Two invalid failures of Diesel Generator (D/G) 1A occurred on August 8 and 9, 1989, while Unit I was at 100% power. D/G 1A was on a monthly test schedule at the time these invalid failures occurred. There have been 0 valid failures in the last 20 valid tests and 3 valid failures in the last 100 valid tests on D/G 1A.
l D/G 1A was declared inoperable on' August 7, 1989, at 0230 hours0.00266 days <br />0.0639 hours <br />3.80291e-4 weeks <br />8.7515e-5 months <br />, for routine maintenance. Following the required maintenance, on August 8, 1989, at 0550 hours0.00637 days <br />0.153 hours <br />9.093915e-4 weeks <br />2.09275e-4 months <br />, Operations (OPS) personnel initiated start No. 789 per their Operations Procedure (OP) to perform a functional verification on the maintenance performed.
' Approximately 60 seconds into the run, the engine tripped and the following annunciators were received: High Crankcase vacuum, High Vibration, and Hi Temperature Bearings. Work Enquest (W/R) 512150PS was written for Instrumentation and Electrical (IAE) to investigate and repair the cause of the trip. IAE pressurized the tubing lines to these instruments individually to determine which sensor (s) were venting. This process revealed that the bearing temperature sensors were the cause of the engine tripping. Further investigation revealed that the sensors for bearings No. 3 and No. 6 had vented causing the loss of pressure in this tubing line. These 2 sensors were removed from the engine and examined on the bench. It was seen that both had only slightly vented, perhaps explaining the time delay before the engine tripped. Mechanical Maintenance inspected the two suspect bearings and found no abnormal indications that could have led to a high temperature. Two new bearing temperature detectors were installed and the engine was run for approximately 30 minutes and no problems occurred.
D/G 1A was started later that day to perform a functional on a Diesel Generator Engine Lube Oil (LD) system modification that had been implemented during the j
Diesel Day. During the run, an annunciator for High Stator temperature was received. The operators used the temperature selector to observe individual points and no indications were given. The D/G was shut down and W/R 512430PS was I
written to have IAE investigate and repair the problem.
On August 9, 1989, at approximately 0243 hours0.00281 days <br />0.0675 hours <br />4.017857e-4 weeks <br />9.24615e-5 months <br />, D/G 1A was started by OPS (start I
attempt No. 792) to allow 1AE to troubleshoot the stator temperature problem.
All parameters on the Engine Control Panel initially appeared normal. The operators checked to ensure the Nuclear Service Water (RN) valve to the Diesel Generator Engine Cooling Water System (KD) Heat Exchanger opened, and that the pre-lube and jacket water pumps stopped.
It was then noticed that the voltage, frequency, and speed indications were abnormal. Voltage was low, frequency fluctuated between 56 and 61 HZ, and speed fluctuated between 460 and 470 rpm.
I The operator pressed the STOP button and noticed that it took longer than normal for the engine to shutdown. About that time, the Lo Control Air Pressure annunciator was received and an air leak could be heard. The operators searched for the leak and found it downstream of the starting air valves. Air
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was blowing from a plug on the bottom of an air header at a high pressure. At that time, the D/G emergency fans suddenly started and ran for approximately 15 seconds before stopping..The Unit Fail To Start Annunciator was received then.
Diesel Generator Engine Starting Air System (VG) pressure for both tanks was 50 psig and the air leak had stopped. VG Pressure then began rising. Operations placed the D/G in the maintenance mode and wrote W/R 512460PS for IAE to investigate the cause for the D/G'failing to maintain voltage, frequency, and speed at normal values.
IAE investigated the problem and discovered a failed diode (CR4) and SCR (SCR-3) in the voltage regulatory circuitry. These two items were replaced and the D/G was started and ran for 32 minutes, during which time it was loaded to 1000 kw, 2500 kw, 4000 kw, and 5750 kw with no problems observed. Operations satisfactorily performed their periodic test (PT) on D/G 1A and it was declared operable on August 9, 1989, at 1755 hours0.0203 days <br />0.488 hours <br />0.0029 weeks <br />6.677775e-4 months <br />.
Following the invalid failure on start attempt No. 792, thorough research was performed to determine why the D/G behaved as it did when OPS tried to shut it down. The following is an explanation of what occurred in the control system to cause the D/G fans to start and VG pressure to be lost. Only one train of circuit for D/G 1A is described.
1.
When the D/G was started, the diode failed, preventing voltage from rising to its normal value of 4160VAC.
2.
That prevented undervoltage relays UVhl and UVR2, which are set at a voltage value between 3920 and 4025VAC, from being energized.
3.
Because UVR1 and UVR2 never reached their set value, relays R11A and R11B, the Ready To Load relays, never energized.
4.
That prevented contacts R11A-6, and R11B-6 from opening in the field flash circuitry, and caused R13 and R14 to remain sealed in during the D/G run.
5.
When the STOP button was pressed, the shutdown cylinder (to close the fuel rack) extended causing pressure switch PS-9 N.O. contacts to close, which reset Run Relay R1B.
6.
When R1B reset, contacts R1B-1 closed. This provided a path through R13-1, R11A-6, Speed Switch SS1-K1 (above 200 rpm) or Time Delay Relay TD1-4 (after 3 seconds), R9-7, R1B-1, and PS32X-3 to R4, the starting relay.
7.
Contacts R4-4 closed to energize the air start solenoid valves SOL 1L and SQL2R, and TD1. This caused VG to roll the engine, explaining the slow shutdown. The air leak heard was caused by the air start solenoid valves still being open when the diesel coasted down and stopped as VG pressure dropped.
8.
When VG pressure had dropped to a point that it could not longer hold the shutdown cylinder extended or the 2 minute delay period from the Shutdown Logic Board elapsed, the shutdown cylinder retracted causing the N.C.
contacts of PS-9 to close.
4 9.
This caused Run Relays R1, RIA, Rib, and RIC to latch. The following events then occurred:
a.
Contact R1B-1 cpened, de-energizing R4 and closing the air start solenoid valves.
b.
Contact RIC-7 closed, starting the D/G emergency ventilation fans.
c.
Contacts R1-4 and R1A-4 closed to provide power to the 15 second Fail To Start tima delay relays TD4 and TD5.
10.
After 15 seconds, TD4 and TD5 energized, closing contacts TD4-1 and TD5-1 to Relay AUX R2.
When AUX R2 energized contact AUX R2-12 closed to energize Isolation Device ID2, which gave the annunciator for Unit Fail To Start.
l-Diode CR4, found failed following start attempt No. 792, is an International Rectifier P/N IN3740R. Resistance checks revealed that the diode was shorted in both directions indicating it was not performing its intended function. Each of the 6 diodes in the voltage regulator bridge rectifier circuit have a heat sensitive label attached that darkens at 270 degree F.
The label for CR4 had darkened slightly, indicating the diode may have overheated. After every D/G run, the heat sensitive labels on the diodes are inspected to ensure no overheating is occurring. Lockwashers and nuts are to be added to each diode and SCR per Variation Noticer
-2145 (Unit 1) and CE-2146 (Unit 2) to ensure better heat transfer to the heat ank that they are mounted to.
In addition, SCR 3 which was originally thought to have failed apparently had not.
Subsequent tests showed that it functioned properly.
The bearing temperature sensors found vented on start No. 789 are a Calcon Model No. 3434 and are designed to vent at a temperature of 228 degree F.
Upon examination, the sensors were seen to be only partially extended with the solder not fully melted. Becausb these sensors were not fully venting, it is believed that they gradually failed over time. W/Rs 1332, 1333, 1334, and 1335MES have been written to replace all 10 of these sensors in each D/G during upcoming outages. The D/G pneumatic control system will also be replaced with an electronic system per Nuclear Station Modifications CN-11149 (Unit 1) and CN-20528 (Unit 2).
These modifications will replace the presently installed bearing temperature pneumatic switches with RTD that can produce an output temperature signal in addition to a trip function.
D/G 1A was logged out of service for a total of 63 hours7.291667e-4 days <br />0.0175 hours <br />1.041667e-4 weeks <br />2.39715e-5 months <br /> and 25 minutes during this incident.
JGT104/lcs
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