ML20046D372
| ML20046D372 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 08/10/1993 |
| From: | Packer D ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RTR-REGGD-01.108, RTR-REGGD-1.108 SR-91-002-03, SR-91-2-3, W3F1-93-0159, W3F1-93-159, NUDOCS 9308180288 | |
| Download: ML20046D372 (11) | |
Text
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Entergy raterer oPer ti a iac.
POBcx0 Operations 7<u=
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D. F. Packer
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e W3F1-93-0159 A4.05 PR August 10, 1993 U.S. Nuclear Regulatory Commission Attn:
Document Control Desk Washington, D.C.
20555
Subject:
Waterford 3 SES Docket No. 50-382 License No. NPF-38 Reporting of Special Report Gentlemen:
Attached is Special Report Number SR-91-002-03 for Waterford 3 Steam Electric Station Unit 3.
Revision 0 was issued per Technical Specification 4.8.1.1.3 and 6.9.2 and Regulatory Guide 1.108 to document the emergency diesel generator overpressurization event.
Revisions 01 and 02 were issued to provide the root cause of the event (which was still under investigation in revision 0) and the results of the emergency diesel generator inspection during Refuel Outage 4, respectively.
This revision, revision 03, culminates four reports issued to you concerning the March 18, 1991, emergency diesel generator crackcase overpressurization.
Throughout our investigation, Waterford 3 personnel have had several discussions with the Staff to provide the most current information available regarding the root cause investigation and corrective measures for this event.
This report, therefore, provides additional information concerning the most likely root cause based on stable isotope analysis of piston carbon deposits, outside technical expert assistance and extensive diesel engine inspections.
160071 9308180288 930810 I
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C[7 PDR ADOCK 05000382 f
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1 Reporting of Special Report j
W3F1-93-0159 Page 2 i
August 10, 1993 l
l Because this report represents an extensive rewrite of Revision 2 of SR-91-002, revision bars will not be used to identify changes to this report.
t Very truly yours, i
A~f II Jm D.F. Packer General Manager - Plant Operations j
l DFP/CJT/ssf l
Attachment l
cc:
J.L. Milhoan, NRC Region IV j
G.L. Florreich J.T. Wheelock (INPO Records Center)
[
R.B. McGehee N.S. Reynolds l
NRC Resident Inspectors Office I
Administrator - LRPD i
F SPECIAL REPORT SR-91-002-03 i
i REPORTABLE OCCURRENCE On March 18, 1991, Waterford Steam Electric Station Unit 3 was in cold f
shutdown when Emergency Diesel Generator (EDG) ' A' experienced a crankcase overpressurization. The EDG was being run in accordance with the prerequisites of the 18 month EDG Inspection Procedure, MM-003-015, when the overpressurization occurred. This event is classified as a valid failure in accordance with Regulatory Guide 1.108 and was reported in accordance with Technical Specification (TS) 4.8.1.1.3.
This failure was the second failure during a valid test of EDG
'A' since the operating licensee was issued. The current surveillance test interval for EDG ' A' is at least once per 31 days.
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t This surveillance test interval is in accordance with the schedule of Regulatory Position C.2.d of Regulatory Guide 1.108.
INITIAL CONDITIONS l
Plant Power:
0%
4 Mode:
5 Procedures Being Performed Specific to this Event:
MM-003-015, "18 Month Energency Diesel Engine Inspection" Technical Specification LCOs in Effect Specific to this Event:
None l
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Major Equipment Out of Service Specific to this Event:
None
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EVENT DESCRIPTION On March 18, 1991, at 0221 hours0.00256 days <br />0.0614 hours <br />3.654101e-4 weeks <br />8.40905e-5 months <br />, EDG (EIIS Identifier EK-ENG)
'A' was manually started to permit an analysis of the diesel engine prior to i
performing the 18 month surveillance inspection required by MM-003-015. MM-003-015 requires that the engine analysis be performed after the EDG has been J
loaded for a minimum of one hour and the operational temperature has t
stabilized at continuous loaded operation. During the engine analysis and after the diesel had operated for approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 37 minutes, a crankcase overpressurization occurred. All ten cylinder relief assemblies lifted, filling the room with oil vapor.
The operator observing the EDG run
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depressed the emergency stop button and pulled the overspeed trip.
The room was exited and there were no personnel injuries.
EVENT CHRONOLOGY i
(dates and approximate times of occurrences) l March 18, 1991 t
0221 EDG ' A' was manually started to commence the prerequisite 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> continuous run and analysis of the diesel engine prior to performing the 18 month surveillance inspection required by MM-003-015 and Work Authorization (WA) 01071020. This inspection is required to be P
performed by Technical Specification 4.8.1.1.2.e at intervals not to exceed 24 months.
0242 EDG 'A' is loaded to approximately 4400 kilowatts.
2 t
0458 EDG 'A' experiences a crankcase overpressurization. All ten cylinder relief assemblies lifted, filling the room with oil vapor.
i 0503 The operator observing the EDG run depressed the emergency stop push button, pulled the overspeed trip and exited the room with other l
personnel in the area.
No personnel injuries occurred.
EDG 'A' is l
declared inoperable.
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0758 After the oil vapor cleared, the room was entered and a crankcase oil sample was drawn. This oil sample was found to be within l
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specifications. An on-site fuel dilution test also yielded satisfactory l
results.
0800 Preparations for entering the EDG 'A' crankcase to perform the inspections required by MM-003-015 and WA 01071020 have commenced.
April 2, 1991 l
1045 The inspections required by MM-003-015 and WA 01071020 are complete.
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April 12, 1991 l
1930 EDG 'A' is declared operable.
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CAUSAL FACTORS Entergy Operations, Inc. believes that the root cause of this event was the i
gross cylinder tr cylinder load imbalance that existed on EDG ' A' prior to Refuel Outage 2.
It is believed that this condition caused an excessive buildup of carbon deposits behind the upper compression rings of piston 5L.
These deposits built up behind the piston rings until the rings were stuck and no longer free to move.
Eventually, additional deposits forced the compression rings against the cylinder liner and significantly reduced lubrication.
The lack of lubrication resulted in ring chatter and increased surface temperatures on the piston and liner. As the temperatures increased, the chrome plating on the liner cracked and began spalling off.
A piece of chrome plating debris from the liner lodged between the piston and liner.
The resulting friction caused the piston area around the debris to become I
incandescent, thus igniting the crankcase oil vapor.
Stable isotope analysis was performed on the deposit samples taken from piston SL during Refuel Outages 4 and 5.
The data from this analysis indicates that the deposits are approximately 75% fuel oil combustion products and 25%. lube oil residue.
Additionally, the data indicates that the deposits were not I
formed mainly during the recent cycle of operation associated with the I
failure.
Efforts to balance the cylinder firing pressures on EDG ' A' and EDG 'B' were initiated during Refuel Outage 2.
A review of peak firing pressure data taken before this outage shows that EDG ' A' was grossly out of balance. The cylinder with the highest average peak pressure was in fact SL (the failure t
cylinder). Also, of the seven cylinders with the highest peak firing 4
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pressures, five of them corresponded to pistons found during Refuel Outages 4 and 5 with stuck rings or abnormal wear.
The peak firing pressure data for EDG 'B' taken before Refuel Outage 2 indicates that this diesel was also out of balance, but to a far less degree than EDG ' A.'
This helps explain why the EDG 'B' cylinders inspected during Refuel Outage 5 showed significantly less deposit buildup (considered normal).
The stable isotope analysis data together with the pre-Refuel Outage 2 peak i
firing pressure data support the root cause determination. Moreover, five specific findings support the belief that the upper compression rings on l
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piston 5L were stuck and no longer free to move.
First, the SL rings were I
found stuck from a heavy buildup of deposits.
Second, the 5L piston ring j
lands for the top two compression ring grooves exhibited " blow-by" patterns characteristic of stuck rings.
Third, the top two compression rings were heavily worn.
Fourth, the cylinder liner in the ring reversal area of the top two compression rings was severely worn.
Finally, during Refuel Outage 5 diesel engine inspections, other pistons were found with stuck or restricted rings.
CORRECTIVE MEASURES During Refuel Outage 4, Waterford 3 performed an inspection of the EDG 'A' cylinders, pistons, rods (EIIS Identifier ROD), and bearings as required by MM-003-015. Additionally, technical experts from Law Engineering and Cooper-Bessemer assisted.in the cylinder inspections. The inspections revealed that the cylinder liner (EIIS Identifier LNR) for piston 5L exhibited intermittent 1.5 by 3 inch lateral rough spots or scuff marks. Vertical scratch marks were note.1 throughout the length of the cylinder. Additionally, the metal on the 5
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1 underside of the piston had been discolored by heat. A borescope inspection of the other cylinders indicated that they were in satisfactory condition.
.i Disassembly and inspection of four othar pistons (SR, IL,1R and 8L) revealed normal wear.
In consequence of these inspections, the following items were replaced:
piston SL and its cylinder liner, piston SR, piston IL, and 5 and 1 rod bearings. Additionally, the Il and SR pistons and bushings were reconditioned.
During Refuel Outage 5, thirteen pistons were pulled from the cylinders of EDG
'A' and inspected in accordance with MM-003-015 and WA 01086706. Twelve of these pistons were cleaned and reinstalled in the diesel engine with new l
J rings.
The 4L piston was replaced with a new one. As committed to in Special i
Report SR-91-002-02, a sample of only six pistons were initially pulled for j
inspection.
These pistons included two that had been pulled during the
)
previous outage (8L and SL) and four pistons (3R, 2R, 6L, and 2L) that had l
l never been pulled.
The remaining seven pistons (3L, 4L, 4R, 6R, 7L, 7R, and l
8R) were pulled due to the conditions of the pistons pulled from the initial sample.
The remaining three pistons which where not pulled were inspected with borescope per MM-003-042, " Ten Year Emergency Diesel Engine Inspection "
]
Thus, during Refuel Outages 4 and 5 a total of sixteen pistons were pulled and l
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inspected on EDG
'A.'
l Of the six pistons pulled in the initial sample, three of the four that had never been pulled had heavy carbon deposits between the upper compression ring i
and the ring groove and normal carbon deposits on the lower rings. The heavy carbon deposits were most pronounced cn pistons 3R and 2R.
The upper compression ring on piston 3R was found to be bound up by carbon and i
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restricted when moved by hand. The upper compression ring on piston 2R had carbon buildup that prohibited movement in one area so that it did not move freely as designed. The carbon deposits on the remaining piston (2L) were not as heavy.
The pre-Refuel Outage 2 peak firing pressure data showed cylinder 2L to be underloaded.
No problems were identified on the two p.stons (5L and 8L) that had been previously pulled.
The carbon on these pistons was very j
sof t and easily removed, coming off in large flakes.
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I Of the seven additional pistons pulled and inspected due to the conditions of i
the six cylinders pulled in the initial sample, all seven had heavy carbon i
buildup between the upper compression ring and ring groove. The upper 1
compression ring on piston 8R exhibited some restricted radial ring travel but not to the same degree as 2R.
Piston 4L showed signs of hand polishing (a-manual Efiling of piston surface imperfections performed at the factory) near i
the base of the skirt.
The hand polishing did not go down to the base metal l
1' and did not appear to be coming in contact with the liner. Also, the piston i
showed signs of tin wear below the second oil control ring.
In this area, the surface of the piston was still smooth and no discoloration due to heating nor scratches due to scuffing were observed. Because the appearance of this wear pattern was unfamiliar, piston 4L was replaced.
[
t Based on the results from EDG
'A,' four pistons (6R, 7R, 8R,.and 4L) were initially pulled from EDG
'B' and inspected for piston / cylinder damage, carbon residue and stuck rings in accordance with MM-003-015 and WA 01101224.
These four pistons did not have the heavy carbon buildup that EDG 'A' had and there were no stuck rings. All cylinders not pulled were inspected with a borescope per MM-003-042 and WA 01099355. One additional piston (IR) was pulled based l
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on the results of thi.s borescope inspection; the cylinder liner had I
indications of tin smear.
Piston IR and its liner were replaced.
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In concert with the inspections on EDG 'A' and EDG
'B,'
technical experts from r
Cooper-Bessemer and Law Engineering were available and provided assistance with the diesel enaine inspections. The expert from Law Engineering performed liner chrome thickness and piston tin thickness measurements to determine if l
abnormal wear was occurring on EDG
'A.'
The expert from Cooper-Bessemer l
assisted with the inspections on both EDG 'A' and EDG
'B.'
l The expert from Law Engineering found that the liner chrome thickness l
measurements did not reveal significant chrome thickness loss on the observed i
l liners. The piston tin thickness measurements revealed that on all but one l
I piston (4L) the tin was not completely worn through. The tin which was l
remaining was smooth and without discontinuities. The expert believed that the pattern of tin wear was the result of the natural adaptation of the individual piston to the contour of its companion cylinder liner.
i The expert from Cooper-Bessemer observed the inspections on EDG 'A' and EDG
'B' and noted that all observed oil rings showed normal wear, while the compression rings showed different levels of wear. The Cooper-Bessemer expert concluded from his observations that the EDG ' A' and EDG 'B' would have been able to run in the as found condition for hundreds of hours without experiencing any mechanical trouble. Moreover, the expert stated that the condition of the piston at 3R on EDG 'A' and the piston and cylinder at IR on EDG 'B' would have caused the need for earlier than normal maintenance, but did not cause an immediate threat to.the safe operation of the engines.
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SAFETY SIGNIFICANCE i
This event is classified as a valid failure of EDG
'A.'
This failure was the s
second failure during a valid test of EDG 'A' since the operating license was issued.
The crankcase relief assemblies functioned as designed and EDG 'B' remained operable throughout the time that EDG ' A' was out of service.
Therefore, this event did not present a hazard to the health and safety of the
- public, SIMILAR EVENTS No previous similar events were identified.
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