ML20128N063
| ML20128N063 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 02/16/1993 |
| From: | Tuckman M DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9302220475 | |
| Download: ML20128N063 (3) | |
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. Ikke Ibu&r Company hlS.Tecuts G. wrba Nudeur Generation Department
- i' ice hesident ~
, 4800 Concord Road (803)Dl4203 Oflite
- York, SC?9145 -
-- (803)MI 306 fax DUKE POWER February 16,1993 U. S. Nuclear Regulatory Commission -
ATTN: Document Control Desk Washington, DC :20555
Subject:
- Catawba Nuclear Station, Unit 1 Docket No. 50-413 Special Report Invalid Failum of Diesel Generator 1B Pursuant to Tecimical Specification 4.8.1.l.3 and 6.9.2, find attached a Special Report-concerning the Unit 1 Diesel Generator B (DG IB), invalid failure that occurred 'on November 24,1992.
This Special Report is: beingisubmittedulate" because of-an administrative oversite.
4 Very tmly yours, N. h.
- M M. S. Tuckman CRUDGlB293. DOC J
Attachment
.xc: S. D. Ebneter -
Regional Administrator, Region II::
W. T. Orders i
Senior Resident Inspector R.- E. Martin, ONRR' 4
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SPECIAL REPORT l
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CATAWBA NUCLEAR STATION 1
DIESEL GENERATOR IB INVALID PAILURE DUE TO LOW LUBE OIL PRESSURE j
An invalid failure of Diesel Generator (DG) IB occurred on November 24,1992 at 0834 i
hours due to a low lube oil pressure trip. The false low lube oil pressure signal was
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caused by having too small of a design pressuru rans for low lube oil pressure i
transmitter. Unit I was at 100% powei at the time this failure occunr4 Operations j
(OPS) vas in the process of nmning DG IB for its monthly Periodie Test (irr) win the failure occurred. There have been 0 valid failures in the last 20 valid tests and b valid i
failures in the last 100 valid tests. DG IB remains on a monthly operability test schedule j
in accordance with Technical Specification 4.8.1.1.2 Table 4.81; There is no
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unavailability time associatal with this failure.
l DG IB was manually staded on November 24,1992 for the OPS PT (stan #1013). The i
engine mn for approximate'~ l minute when it tripped on low lube oil pressure. Oil pressure as read on ILDPO:il7C was well above the 35 psi hw lube oil pressure trip j
setpoint. OPS restarted the engine and no other problems were noted. The PT was then j
completed.
OPS initiated a work request for-Instmmenta; ion and Electrical (IAE) i personnel to investigate ud repair the cause of the trip : However,-it was decided to
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conduct the work at a later date because there was not an operability concern. This was a j
non emergency trip that would not effect the engine's ability to nm when called upon by an emergency start (LOCA or Blackout) signal from the sequencer. The work request was schedule for December 15,1992 during the diesel day for DG 1B.
The De mber 15,1992 diesel day was canceled due to problems with the Control Room l
Area '
lation system and rescheduled for January 12, 1993. On December 23,1992, j
DG ll is given an emergency stan signal by IAE personnel in order for OPS to l
perfonn meir monthly PT, Once again, approximately one minute into the nm, the low lube oil pressure trip annuciator was receiveds The engine did not trip _because the engine j
was given an emergency stan signal _. Several seconds later the annuciator' cleared. - As l
before, all pressures appeated to be nonnal. The engine nm' was ' complete without -
funher problems.
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Systems and Component Engineering personnel'have noticed in the past that lube oil pressure sometimes increases to approximately 90 psi on engine starts,. The range of the
- transmitter that monitors lube oil pressure is only 0-60 psi. This tnmsmitter sends a i
corresponding 4-20 'mA' signal to an Analog Optical Isolator (AOI), which in turn feeds the 'Alann Monitor that perfonns the tripping funct. ion. The component engineer l recalled a similar probl m on another system that involved the same model of-AOI (E-Max # -
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.175D127 8), When the input to the AOI is over-ranged to a cenain point, the output fails L
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fails low. This over ninged point is unigee to each AOI, but is typically around 26 mA.
If the AO! was over-ninged and its output had failed low at the time the group 11 lockout was removed, the engine would trip. When DG IB was taken out of service on January 12, 1993, the input pressure at which AOI failed low was checked. The output was found to fall low at 81 psi input pressure to the transmitter (equivalent to an input of 25.78 mA). This supported the previous argument and was detennined to be the cause of the problem. IAE personnel were instructed to replace this A01 with one fonn stock that had a higher dmpout point. One was installe ; that did not fall until 27,75 mA. The engine was mn on January 13,1993 for a functional verification and no further problems were noticed.
This invalid failure was classified as a design problem due to the improper ranging of the lube oil inmsmitter. The 0-60 psi input range is not su ficient enough to accommodate r
the pressure increases seen on engine starts. The 3 low low tube oil tninsmitters on all 4 engines were added per Nuclear Station Modifications CN 11101 (Unit 1) and CN 20486 (Unit 2) to replace the pneumatic emergency trip sensor. During the last outage on Unit 1 (IEOC6), the pneumatic non emergency trips were replaced per CN 11149. As part of this modification, one of the low low lube oil pressure transmitters.vas used via an AOI to obtain a signal to the new alann monitor for the low lube oil p: essure trip. This modification will be performed on Unit 2 this outage per NSM CN-20528.
A work request has been initiated for DG 1 A to verify that the dropout point for its AOI will not cause any problems. As part of NSM CN-20528 to be perfonned during the current outage on unit 2 DGs, the range for the lube o!! tninsmitters will be increased from 0 60 psi to 0100 psi. This w'il ensure no overranging can occur. Unit I pressure transmitters will be re-range <l per exempt change CE-4000.
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