ML20059E529
| ML20059E529 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/19/1993 |
| From: | Rueger G PACIFIC GAS & ELECTRIC CO. |
| To: | |
| References | |
| OLA-2-I-MFP-076, OLA-2-I-MFP-76, NUDOCS 9401110261 | |
| Download: ML20059E529 (5) | |
Text
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Pacific Gas and Electric Company 77 Beale Street Gregory M. Rueger San Francisco,CA 94106 Senior Vice President and f
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415/973-4684 General Manager ~
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Nuclear Power Generation
/g January 27, 1993
'93 03 28 P6 :10 PG&E Letter No. DCL-93-024 U.S. Nuclear Regulatory Commission E
ATTN:
Document Control Desk Washington, D.C.
20555 Re:
Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 Special Report 92-06, Diesel Generator 2-2 Failure to Achieve Rated Output Voltage Due to Mispositioned Slip Ring Brushes Gentlemen:
In accordance with the requirements of Diablo Canyon Technical Specifications (TS) 6.9.2 and 4.8.1.1.4 and Revision 1 to NRC Regulatory Guide (RG) 1.108, this Special Report is submitted concerning failure of Diesel Generator (DG) 2-2 to achieve rated output voltage during surveillance testing following a maintenance activity.
Using the guidance of RG 1.108, Sections B and C.2.e, this event is considered to be a valid failure. During this event, all other electrical power sources were available if called upon in the unlikely event of an actual emergency; therefore, the Limiting Conditions for Operation required by TS 3.8.1.1 were satisfied.
In accordance with RG 1.108, Section C.3.b, the following information is provided:
1.
Number of valid failures in last 100 DG 2-2 valid tests:
1 3.
Cause of failure:
The root cause for the mispositioned generator slip ring brushes was determined to be inadequate information available to personnel regarding the extent that subassemblies could be affected during required inspections.
4.
Corrective measures taken:
l a)
Immediate Corrective Action: The slip ring brushes were correctly positioned and DG 2-2 was successfully tested in accordance with Surveillance Test Procedure M-9A, " Diesel l
Engine Generator Routine Surveillance Test."
b)
To Prevent Recurrence: The maintenance manual for the DGs will be revised to include an advisory that the slip ring brushes are positioned by the same bolts that retain the shaft bearing cover.
9401110261 930819 PDR ADOCK 05000275 PDR_.
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' January Document Control Desk
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PG&E Letter No. DCL-93-024 27, 1993
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Time DG was unavailable: ~ DG 2-2 was tagged-out. for disassembly; and maintenance inspection on December.29, 1992,.at 0540 PST. The control.
switch for DG 2-2 was returned to automatic afteresuccessful performance of post-maintenance testing on December 30, 1992, at 2225 PST. Thus,.
DG 2-2 was unavailable for a total of 40. hours and 45 minutes.
~
6.
Current surveillance test interval:
31 days 7.
Confirmation of proper test interval: The total. number of valid ~
fa. ares:in the last 100 valid tests for DG 2-2'is 1, and the total.
number of valid failures in the last 20 valid tests for DG 2-2 is.1; therefore, the 31-day test interval is in compliance with. the schedule of TS Table 4.8-1 and-an accelerated testing schedule is not requirede q
Thir event has in no way affected the health and safety of the public.
Sincerely, a
/Wr
- ev Gregoiy M. Rueger cc:
Ann P. Hodgdon John B. Martin Mary H. Miller Sheri R. Peterson CPUC Diablo Distribution l
Enclosure l
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%O2403 l4 PG&E Letter N2. DCL-93-024 ENCLOSURE SPECIAL REPORT 92-06, DIESEL GENERATOR 2-2 FAILURE TO 1
ACHIEVE RATED OUTPUT VOLTAGE DUE TO MISPOSITIONED SLIP RING BRUSHES 1.
Plant Conditions Unit 2 was in Mode 1 (Power Operation) at 100 percent power.
II.
Descriotion of Event A.
Event:
On December 29, 1992, at 1449 PST, Diesel Generator (DG) 2-2 was being tested in accordance with Surveillance Test Procedure (STP)
M-9A, " Diesel Engine Generator Routine Surveillance Test." DG 2-2 started ad accelerated, but did not load since the generator output voltage only reached 105V instead of the required 110V to 128V. DG 2-2 was shut down, and an investigation identified that all four generator slip ring brushes were out of position.
On December 30, 1992, the slip ring brushes were restored to the correct positions and DG 2-2 was successfully tested in accordance with STP M-9A.
B.
Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C.
Dates and Approximate Times for Major Occurrences:
1.
December 29, 1992~at 1449 PST:
E'v'ent/ Discovery date.
DG 2-2 was started per j
STP M-9A but did not load.
2.
December 30, 1992 at 2225 PST:
DG 2-2 was declared operable after successful performance of STP M-9A.
4 D.
Other Systems or Secondary Functions Affected:
None.
E.
Method of Di:covery:
Plant personnel identified the problem during performance of STP M-9A.
5991S/85K '
o 202409 F.
Operator Actions:
None.
G.
Safety System Responses:
None.
I III. Cause of the Event A.
Immediate Cause:
The generator slip ring brushes were moved slightly out of position during a maintenance visual inspection of the end of the generator shaft for thrust load axial movement performed on December 29, 1992. The mounting bolts for the slip ring brush rigging are common with the shaft bearing cover that must be l
removed for shaft visual inspection.
During this particular l
ir.spection, the generator shaft was intentionally rotated for inspection purposes. This shaft motion, which is not normally performed, disturbed the slip ring brush positioning. The slip ring brushes are not readily visible through the removed bearing cover and were not observed to be out of position when the bearing cover was reinstalled following the shaft inspection.
No advisory or caution statements were in the written instructions regarding the inspection of slip ring brush positions in conjunction with or following ger erator shaft bearing inspections.
B.
Root Cause:
The root cause for the mispositioned generator slip ring brushes was identified to be inadequate information available to personnel regarding the extent that subassemblies could be affected during re_ quired inspections.
IV.
Analysis of the Event Safety-related (Class IE) electrical loads are-supplied from three 4160V vital buses (F, G, and H) for each unit.
Each vital bus can be supplied from the 500kV switchyard, the 230kV switchyard, the main generators, or the DGs. The DGs can provide power for engineered safeguards (Class IE) motors and loads used for emergency core cooling, reactor shutdown, and other vital safety functions when the main generators and offsite power sources are not available in the event of a loss-of-offsite power or other design-basis event.
During a design-basis event, with DG 2-2 in a degraded condition, one bus of vital 4160V power would not have been available for Unit 2 support. However, DGs 2-1 and 1-3 were available to provide power to the other two Unit 2 vital 4160V buses during the time that DG 2-2 was inoperable.
5991S/85K
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w 202409; Since only two vital buses are necessary to support DCPP accident analysis, the health and safety of the public were not adversely affected by this event.
1 V.
Corrective Actions A.
Immediate Corrective Actions:
The slip ring brushes were correctly positioned and DG 2-2 was l'
successfully tested in accordance with STP M-9A.
B.
Corrective Actions to Prevent Recurrence:
l The maintenance manual for the DGs will-be revised to-include an advisory that the slip ring-brushes are positioned by the same bolts that retain the shaft bearing cover.
VI.
Additional Information A.
Failed Components:
i None.
B.
Previous Similar Events:
None.
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4 5991S/85K.
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