ML20207C318
| ML20207C318 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 07/22/1988 |
| From: | George Thomas PUBLIC SERVICE CO. OF NEW HAMPSHIRE |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NYN-88102, NUDOCS 8808050296 | |
| Download: ML20207C318 (5) | |
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George S.Thomcs V ce President Nuclear Production a s.,a. a m.
New Hampshire Yankee Division July 22, 1988 United States Nuclear Regulatory Commission Washington, DC 20555 Attention: Document Control Desk
Reference:
Facility Operating License No. NPF-56, Docket No. 50-443
Subject:
Diesel Generator Special Report Gentlemen:
On February 24, 1988, at 1039 hours0.012 days <br />0.289 hours <br />0.00172 weeks <br />3.953395e-4 months <br /> during post-maintenance testing of the B Train Emergency Diesel Generator, a low lube oil pressure trip occurred.
In accordance with Regulatory Position C.3.b of Regulatory Guide 1.108, Revision 1, August 1977, this would be considered a non-valid start failure which is reportable pursuant to Technical Specifications 4.8.1.1.3 and 6.8.2.
The cause of the low lube oil pressure trip has been attri' outed to an eight week maintenance outage resulting in slower than normal engine acceleration during the initial engine start following the outage. The lowsr than normal acceleration and consequent low lube oil pressure resulted in the engine monitoring system, which is normally delayed during engine start, to trip the engine once the time delay expired. An investigation to determine the root cause of the engine start failure was initiated, and a test 1,rogram was developed to determine the following:
- 1) if the lube oil pressure was actually low, or
- 2) if the monitoring circuit, which is bypassed during the start sequence, was energized early, or l
- 3) if prior maintenance activities caused the engine to be left in a !
condition that could have resulted in a trip.
After performing six engine starts while monitoring various engine parameters, the condition (s) which existed during the trip could not be '
recreated, and the start failure was classified as an isolated incident. Test results indicate that sufficient margin exists in the timing circuit to prevent further occurrences a~1 that none of the above items caused the engine trip.
8808050296 ADOCK880722 0500044,3 PDR PDC S
P.O. Box 300. Seabrook, NH 03874 . Telephone (603) 474 9574 h
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j . United States Nuclear Regulatory Commission July 22, 1988 j Attention: Dc'ument Control Desk Page 2 l
i l DISCUSSION The engine trip circuit is bypassed during the engine start cycle to l prevent spurious trip and alarm inputs. During the start process a time delay relay is energized by the operation of either the engine coolant. pressure ,
switch or the engine tachometer speed switch. After a delay of seven seconds, l the time delay relay activates the engine trip circuit.
The information gathered from subsequent tests clearly shows the time j duration of the engine tachometer speed and coolant pump pressure switches to j be approximately the same, averaging 5.5 seconds after the start signal. The ;
trip circuit then becomes functional between 6.8 and 7.5 secondo later.
Information from the engine trip indicates the trip circuit actuated at the i same time the time delay relay initially energized. The Station computer l indicates that engine lube oil pressure was low when the time delay relay actuated.
It appears that during the engine start the engine coolant system fluid inertia may have caused a pressure spike which resulted in premature actuation of the pressure switch. This would have resulted in the time delay relay being energized early. At this time the engine speed would have been insufficient to develop the necessary pressure to actuate the low lube oil pressure switch and resulted in the engine trip. The engine trip function was available earlier than designed and resulted in a trip on low lube oil pressure. The subsequent testing clearly shows the engine trip functioned -
satisfactorily and the exact cause of the low lube oil pressure trip actuation is not known. A design change is being developed to relocate the coolant ,
pressure switch to the pump discharge so that pressure monitoring will be more uniform and not subject to other cooling system flow conditions. i
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It may also be possible that due to instrument calibrations during the I maintenance period the time delay relay was timed out or in a condition that the monitoring trip circuit tripped the engine. This would fit the sequence of events that occurred resulting in the engine low lube oil trip presented by i the Station computer.
Further investigation with the equipment vendor regarding this problem concluded that failures of this type have not been observed by other like equipment users.
ADDITIONAL INFORMATION A review of the Emergency Diesel Generator operating log book was performed starting with initial license receipt (October 1986) to the present.
reported.
The review determined that other start failures were not adequately The following other start failures are being reported to bring this subject up to date.
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United States Nucle:r Regulstory Commission July 22, 1988 Attention: Document Control Dzsk Page 3 l
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- 1) On November 14, 1986, during a semi-annual operational surveillance '
test on the B Emergency Diesel Generator, a start duration of 10.23 seconds was recorded by a stop watch. This exceeded the required ten second start time duration. All other surveillence test requirements were successfully completed. Due to the inherent inaccuracies of manual timing with a stop watch, a modification was implemented to monitor the D-G start time using the Station computer. Since.the computer monitoring modification was completed, no further start time failures have occurred. This is considered a valid start failure in that the engine did not reach the required rated voltage and frequency within the specified time. However, this start failure has been attributed to inherent inaccuracies in stop watch operation.
- 2) On January 10, 1987, during a monthly surveillance test on the B Emergency Diesel Generator, an engine low lube oil pressure alarm was received, and the engine was shutdown. A review of activities prior to conducting the surveillance test found that engine lube oil system maintenance had been performed and that this maintenanca activity
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most likely left air in the system which caused the alarm. The engine lube oil system was checked for air and the surveillance test was successfully completed the same day. This start failure is considered to be non-valid.
- 3) On February 5, 1987, during a monthly surveillance test on B Emergency Diesel Generator, an engine low lube oil pressure alarm was received and the engine was tripped. A review of activities prior to conducting the surveillance test found that engine lube oil system maintenance had been performed and that this maintenance activity most likely left air in the system which resulted in the trip. The engine lube oil system was checked for air and the surveillance test was successfully completed the same day. This start failure is considered to be non-valid.
- 4) On September 7, 1987, during post-maintenance testing on the A Emergency Diesel Generator, a fuel oil leak developed which required the engine to be shutdown. Corrective actions were performed and successful testing was completed the same day. This start failure is considered to be non-valid.
- 5) On January 15, 1988, during a post-maintenance run of the A Emergency Diesel Generator, the auxiliary coolant pump started which caused the system relief valve to open thus draining the engine cooling system. The operator shut down the engine preventing any possible engine damage. The auxiliary coolant pump started due to trouble-shooting activities involving the aftercooler valve pressure control loop. This start failure is considered to be non-valid.
Unitsd States Nuclear Regulatory Commission
- July 22, 1988 Attention: Document Control Desk Pags 4
- 6) On January 22, 1988, during a post-maintenance engine run on the A Emergency Diesel Generator, the auxiliary coolant pump started. The ,
engine was shutdown by procedure. Y.e operation of the auxiliary I coolant pump is acceptable under ec.etgency conditions; however, the operation of the engine driven co.aant pump and the auxiliary coolant !
pump during nonemergency conditions requires stopping the engine to reset the auxiliary coolant pump start circuit. The auxiliary l coolant pump started as a result of a plugged sensing line snubber to l a pressure control loop. Corrective actions were taken to prevent a ,
reoccurrence of this type in the future. This start failure is i considered to be non-valid.
The above non-valid start failures do not count toward events that are l considered as valid start failures. The one valid start failure does not !
cequire any additional diesel generator testing to be performed as defined by Seabrook Station Technical Specifications Table 4.8-1.
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CORRECTIVE ACTIONS l l
Reportability of the above diesel generator start failures, valid or non-valid, was not completed as required within the 30 day time frame. The reason these events were not properly identified, documented, and reported is ;
the fault of the reporting system with regard to the Emergency Diesel Generator.
Procedures have been revised to address the reportability of diesel generators. ;
The procedures now require notification of all emergency diesel generator failures to the Regulatory Services Department for reportability assessment. 1 The lack of timeliness has also been brought to the attention to the responsible departments and should not be repeated in the future. I l
If you request have any questions regarding this report, please contact Mr. Robert A. Gwinn at (603) 474-9574, extension 4056. ,
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Very truly yours, l
A George S. Thomas
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-l United States Nuclear Regulatory Commission July 22, 1988 I Attention: Document Control Desk Page 5 l
cc Mr. William T. Russell l Regional Administrator Region I United States Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 Mr. Victor Nerses, Project Manager Project Directorate I-3 Division of Reactor Projects United States Nuclear Regulatory Commission Washington, DC 20555 Mr. A. C. Cerne NRC Senior Resident Inspector Seabrook Station Seabrook, NH 03874 s
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