ML20043G585
| ML20043G585 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 06/08/1990 |
| From: | Hunsader S COMMONWEALTH EDISON CO. |
| To: | Davis A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| NUDOCS 9006200458 | |
| Download: ML20043G585 (6) | |
Text
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./ Downers Grove,Illinols 60515
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e I'RIORITY' ROUTING June 8, 1990 J.i n t - - Esg
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pir4 Mr. A. Bert Davis N
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l Regional Administrator HL Q m
U.S. Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, 11 60137 i
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Subject:
Braidwood Station Units 1 and 2-4 Diesel Generator IDG01KB, 2DG0lKA and 2DG01KB Failures NRC Docket Noi. 50-456 and 50-457 l
Reference; a) NUREG-1276, Technical Spectfication l
b) February 28, 1990, S.C. Hunsader' letter j
to A.Bert Davis j
Dear Mr. Davis:
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Section 418.1.1.3 of reference (a) requires that all diesel generator failures, valid or non-valid, be reported to the NRC pursuant to Specification 6.9i2. -The enclosure provides the reports that address one valid and one invalid test failure experienced on diesel generator 10G01KB; one valid test failure expertenced on diesel generator 2DG01KA; and two invalid test failures experienced in diesel generator 2AG01KB.
The criteria used to determine valid tests and-fallurec is taken from section-C.2.C of Regulatory Guide 1.108.
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Reference (b) 1s the most recent report addressing diesel generator failures, submitted per~Section 4.8.1.1.3.
l Please direct any questions concerning this submittal to this office.
Very truly yours, l
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S.C. Hunsader Muclear Licensing Administrator
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S. Sands-NRR
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H. Shafer-RIII Resident Inspector-BH NRC Docket Control Desk 50 9006200458 900608 i
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1B DG FAILURE REPORT On April 16,1990, at 1124, the 1 B Diesel Generator (DG) was started in performance of an unscheduled operability surveillance,1BwOS 8.1.1.2.a-2. This run was being performed to verify proper governor control following a f ailure of a govemor component in the 2A Diesel Generator. During the performance of the surveillance the 1B DG failed to come up to rated speed and voltage in less than 10 seconds (12.8 seconds) as required by Technical Specifications. The 1B DG was l
declared inoperable and LCOAR 8.1.1-1 A was entered.
While the 1B DG was inoperable, the govemor power-dropping resistors were replaced. These resistors were identified as the cause of the aforementioned 2A DG failure. At 1828 the 1B DG was started in performance of a maintenance / troubleshooting run to check for proper governor operation following the resistor replacement, and to troubleshoot the cause of the slow start. The DG started in 7.7 seconds, it was noted that the fuel control cylinder (bimba cylinder) closed with a jerking motion rather than with a sharp motion. A malfunctioning fuel control cylinder could result in a slow DG start. At 1835 the DG was shutdown.
The fuel control cylinder and the 3-way air control valve (PC-8) located upstream of the cylinder were replaced. -In addition, a small air leak in the vicinity of the cylinder was repaired.
Following the maintenance work and a functional test of the replacement components, the 1B DG was started for a maintenance /troubieshooting E
run at 0352, on 4-17-90. The DG started in 6.52 seconds, and was-L shutdown at 0400. At 0418 the DG was restarted for another maintenance / troubleshooting run to check the start time, and if acceptable, to verify proper fuel rack alignment during a fast load sequence. The DG started in 11.49 seconds, and at 0424, it was shutdown without loading. The DG was taken O.O.S. for an extensive air start system' inspection. The inspection revealed the following:
1.
The air tubing from the left bank air distributor to the 6U9L and the:
SU8L cylinder air valves were found to be crossed.
1; 2.
The right bank starting air valve had signs of oil and scoring.
3.
The air filter upstream of the right bank distributor was somewhat 1
oily although not significantly restrictive.
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The air supply tubing to the right bank distributor was found
" finger-tight".
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3 Following correction of th'e above items, the DG was started for a maintenance / troubleshooting run at 0340 on 4-18 90. The DG started in 6.60 seconds using only the left bank air receiver. At 0348 the DG was shutdown.
An inspection of the right bank turning gear interlock revealed that the Interlock was not fully depressed when the turning gear was racked out after the maintenance work. The interlock bracket was adjusted and the DG was started for another maintenance / troubleshooting run at 0409.
The DG started in 6.27 seconds using both air receivers. At 0415 the I
DG was loaded to ;t 5500 kw in less than 00 seconds. ' At 0430 the DG was unloaded, and at 0443 ihe DG was shutdown.
At 0903 the 1B DG was started in performance of its monthly / semi annual operability surveillance,18wOS 8.1.1.2.a 2. At 1022 the surveillance was corapleted satisfactorily and the DG shutdown. At 1236 the 18 DG was declared operable and the LCOAR exited.
- The cause of the slow start has been attributed to the crossed air distributor tubing for the 6U9L and the SUBL cylinders. The additional maintenance items discovered during the troubleshooting work are i
believed to have contributed, but not to a significant degree, it has been determined that the crossing of the air tubl occurred during the 1B DG maintenance inspection during the 1989 fal efueling outage.
During the outage the 1B DG exhaust manifold was replaced which required the dissassembly and the reassembly of the distributor air tubing. After completion of the maintenance inspection, all DG t
surve llance. testing was successfully completed and the DG was declared operable.
-On December 4,1989 during performance of the monthly owrability test, the 1B DG ex aerlence a " slow start" of 13.8 seconds to ach eve rated i
L speed and vo tage. This was in excess of the 10 seconds specified in the Technical Specifications. The 1B DG was declared inoperabie and the appropriate Technical Specification Actiori Statements were entered and complied with.-
As 3 art of the trouble shooting procedure an inspection of the fuel racks anc fuel pumps was conductec An additionalisolation valve was closed
-on an unused air receiver. This receiver had previously been isolated by a check valve. During a test run of the DG lt had been identified that the receiver had shown an increase in pressure during the starting air cranking sequence. It was theorized that the check valve leakage had lowered the air pressure in the starting air distribution system which had resulted in the slow start. After completing these actions several test starts were performed. The DG start times were below the limit and acceptable. The monthly operability test was successfully completed.
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On December 6,1989 the 1B was declared operable.
The 1B DG successfully completed the Monthly Operability tests conducted January 2, January 29, February 26, and March 26,1990 with start times acceptable and normal.
Corrective actions to prevent recurrence include the correction of the items identified during the A 3ril 16-18th troubleshooting, the planned inspection of the 1 A,2A & 23 DG air start tubing, and various enhancements to the 18 month ma!ntenance procedure including additionalinspections and post-maintenance testing requirements.
The 4-16-90 slow start has been determined to be a valid failure. The 4-17-90 slow start, during the maintenance / troubleshooting run, has been determined to be an invalid f ailure in accordance with Regulatory Guide 1.108, position C.2.e.7. The 12-4-89 slow stait had prevlously been identified and reported as a valid failure.
The 18 DG shall be tested weekly until seven consecutive failure free demands have been performed and the number of failures in the last 20 valid demands has been reduced to one or less. Pursuant to Regulatory Guide 1.108, position C.3.b.7, as of 4-18-90, the 1 A DG had 2 valid failures and the 1B DG had 3 valid failures in the last 100 valid Unit 1 DG tests.
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2A DG FAILURE REPORT At 0315 on April 16,1990, the 2A Diesel Generator (DG) was started in performance of a four hour warm-up run prior to its scheduled 18 month voltage, the DG speed began oscillating betwacc 300 and 600 ) rpm. The maintenance inspectico. After achieving rated speed (600 rpm and 2A DG was immediately shutdown. At 09131,vas identified that the cause of the speed oscillations was a failure of one of tne two parallel govemor power voltage-dropping resistors in the DC power feed to the govemor. Both of the resistors were replaced. At 1607 the 2A DG was started for a maintenance / troubleshooting run. After verifying proper govemor speed control, the DG was shutdown at 1615. At 1653 the 2A-DG was started in periormance of its monthly operability surveillance.
Tb T surveillance was completed satisfactorily and the DG shutdown at 1819. At 2118 the 2A DG was declared operable.
Subsequent to the 2A DG failure, the dropping resistors in the 1 A and 1B DG's were replaced. The dropaing resistors In the 2B DG were replaced on April 4,1990 as the result o< an Invalid Failure on the 2B DG.
This failure has been determined to be valid in accordance with Regulatory Guide 1.108. This failure is the first valid f ailure in the last 37 valid 2A DG tests. Pursuant to Regulatory Guide 1.108, position C.3.b.7, as of 4-16-90, the 2A DG had 4 va id failures and the 2B DG had 1 valid f ailure in the last 100 Unit 2 valid DG tests.
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i 2B DG FAILURE REPORT was started in At 0805 on April 4,1990, the 2B Diesel Generator (DG)is was the first performance of a maintenance / troubleshooting run. Th
.run of the DG following the comaletion of its 18 month maintenance inspection. Following the start tie DGs speed was 608 rpm versus the expected 600 rpm, and the o wrator had no speed control. The DG was shutdown at 0834. At 1031 tie DG was restarted for a second maintenance / troubleshooting run to investigate the lack of speed control.
' The DG again had no speed control and the speed was 608 rpm.
Voltage control was functional. The DG was shutdown at 1103.
Troubleshooting performed on the DG revealed that the lack of speed -
control was the result of the two parallel govemor power-dropping 4
resistors falling open. The f ailed resistors interrupted the power supply to the governor's electronic circuits and the mechanical only portion of a
the govemor controlled the DG at 608 rpm.
The failed resistors were replaced and the DG was started for a maintenance / troubleshooting run at 1550 on 4-4-90. All governor functions operated properly and the DG was shutdown at 1920.
These f ailures have been determined to be invalid in accordance with Regulatory Guide 1.108, position 0.2.e.7.
The 2B DG continues to be tested monthly in accordance with Technical i
Specification 4.8.1.1.2. Pursuant to Regulatory Guide 1.108, position -
C.3.b.7, as of 4-4-90, the 2A DG had experienced 3 valid f ailures in the 58 valid test since the completion of pre-operational testing, and the 2B DG had experienced 1 valid failure in the 40 valid tests since the '
completion of pre-operational testing.
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