ML20086G020

Special Rept SR-91-002-02:on 910318,emergency Diesel Generator a Experienced Crankcase Overpressurization.Caused by Stuck Piston Rings.Piston & Piston Liner Replaced & Improper Temp Differential Will Be Corrected

ML20086G020
Person / Time
Site:	Waterford
Issue date:	11/27/1991
From:	Packer D ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
SR-91-002-02, SR-91-2-2, W3B5-91-0296, W3B5-91-296, NUDOCS 9112040134
Download: ML20086G020 (6)

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W Entergy Operations W3DS-91-0296 A4.05

, QA November 27, 1991 U.S. Nuclear Regulatory Commission ATTENTION: Document Control Desk Washington, D.C. 20555

SUBJECT:

Waterford 3 SE3 Docket No. 50-382 Licenee No. NPF-38 Reporting of Special Report Gentlemen Attached is Special Report Number SR-91-002-02 for Waterford Steam Electric Station Unit 3. This Special Report is submitted per 10CFR50.36(c)(2) and Technical Specificaticss 4.8.1.1.3 and 6.9.2.

Very truly yourn,

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gfhbj/-(& L D.F. Packer General Manager Plant Operations DFP/DDW/rk Attachment cci Messrs. R.D. Martin G.L. Florreich J.T. Wheelock - INPO Records Center E.L. Blake N.S. Reynolds NRC Resident Inspectors Office i

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Special Report 91-002-02 l Valid failure of Emergency Diesel Generator 'A' due to overpressurization of the crankcase.

INTRODUCTION on March 18, 1991, Waterford Steam Electric Station Unit 3 was in cold -

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 Emergency Diesel Engine Inspection procedure, MM-003-015, when the overpressurization occurred. The operator observing the EDG run depressed the emergency stop button and pulled the overspeed trip.

This event has been classified as a valid EDG failure and is being reported in accordance with Technical Specification 4.8.1.2.3.

The immediate cause of the'crankease overpressurization was stuck piston rings. Although_the root c1use of the stuck piston rings is it. determinate, ef f orts are still underway to decermine the composition of deposits f ound behind the piston rings. A possible root cause, based on vendor bulletin '

information, was an improper temperature differential between jacket cooling I

water and lube oil temperatures. -The lube oil to jacket water temperature differential has been eliminated as a-root cause. The piston and piston liner have been replaced and the improper temperature differential willibe corrected.

NARRATIVE At 0457 hours0.00529 days <br />0.127 hours <br />7.556217e-4 weeks <br />1.738885e-4 months <br /> on March 18, 1991, Waterford Steam Electric Station Unit 3 was in cold shutdown when Emergency Diesel Generator (EDG) (EIIS Identifier EK-ENG) ' A' expet.wv;ed a crankease (EIIS Identifier BLK) overpressurization.

personnel operating the EDO depressed the emergency stop push button and pulled the overspeed trip after the overpressure condition occurred. This event has been. classified as a valid EDG failure and is reported in accordance with Technical Specification 4.8.1.1.3. r u_; _ . ~ , . . _ _ . . - _ . _ _ . _ . , _ . _ . - . _ _ . - . . - _ _ . . _ , . _ _.-.,_.a. _ __

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EDG 'A' was started at 0221 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 of the 18 Month Emergency Diesel Engine Inspection procedure, MM-003-015. The purpose of the run was a pre-maintenance heatup and engine analysis prior to placing the unit out of service for the EDG 'A' refueling outage inspection. EDG 'A' had been loaded to 4400 kilohatts for 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> when l the crankcase overpressurization occurred. All 10 cyli! der relief assemblies lifted, filling the room with oil vapor. The room was exited and there were no personnel injuries. After the vapor cleared, the room was entered and a crankcase oil sample was drawn. This oil sample was found to be. within specifications. An on site fuel dilution test also yielded uatisfactory results. i An inspection of the EDG cylinders, pistons, reis (EIIS Identifier ROD),

and bearings was commenced as required by MM-00?~015. The inspection revealed that the 5 left (5L) cylinder liner (EIIS Iduntifier LNR) exhibited intermittent- 1 1/2 by 3 inch lateral rough spots or scuf f marks. Vertical l scratch marks were noted throughout the length of the cylinder. Additionally, the metal on the underside of the piston had been discolored by heat. A borescope inspection of the other cylinders indicated that they were in satisfactory condition. Disassenbly and inspection of four other pistons, SR, IL, 1R and 8L, revealed normal wear. This failure is the second failure during a valid test of EDG 'A' at Waterford 3 since the operating license-was issued. l Ccoper-Bessemer Service News Bulletin number 688, dated June 26, 1985,

- addressed'the possibility of " cylinder scuffing, piston seizure and... crankcase oxplosion" if jacket cooling water temperature was not maintained 5 degrees Fahrenholt higher than piston lube oil temperature.

Waterford 3 had not received this bulletin from the vendor, but a consultant who was familiar with bulletin 688 noted that Waterford 3 EDG logs showed that picton lube oil temperature was being maintained 4 degrees lower than piston lube oil temperature. The fact that this temperature differential condition had existed at Waterford 3 on both EDGs for several years with no deleterious effects and the fact that none of the other EDG 'A' cylinders or EDG *B'

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..v- had scuff marku caste doubt that the improper temperature f

e atial is the root caus:. Based on determinations made by the vendor S

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f4-4 en outetde consultant, the improper temperature differential has been

, j e. .v 3 &s a root Cause. I n i

_ y review of . "y experience revealed that crankcase over-

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'N ' s au r i za'.- lor .it r plants have teen attributed to metal cuttings in m.,

3 I i ~1 piston pin oil grooves, improper piston pin fit-up, piston bushing failuro,

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l oil puma bearing failure, a loose pirton pin bolt, and water leaks.

Adn. :lonally, tour c mkcase overpressurizations attributed to piston to liner 7

y seizutes have indeterminate root causes. All of these root causes have been systematical;y eliminated during the root cause investigation. Specifically, no v.;etal cuttings were found in EDG 'A'. An improper piston pin fit-up would hcVe cea 1d a piston seizure soon after the initial EDG start. The vendor determined that although tea piston bushings needed ta be reconditioned, the piston bushings could have been used in their previous condition. The EDG lube oil pump functioned satisfactorily. No loose piston pin bolts were noted and tha crankcase oil sample was within specification.

EDG 'A' was declared operable at 1930 on A;ril l'e, 1991. The following items wera replaced during the refuelin tage 5L cylinder liner and piston assembly, SR piston assembly, IL piston assembly, and 5 and 1 rod bearings.

L The IL and Sh pistons sna bashings were reconditioned.

After further ant. .s of the cylinder SL compcnenta associated with the uverpresburization Jent, the vendor concluded that the overpressurizati was caused by stuck piston rings. Deposits from an unknown source ouilt u; {

behind the rings until the rings were no longer free to move. Additional deposith forced the compression rings agait.st the liner and significantly reduced lubrication. The lack of lubrication resulted in ring chatter and increased surface temperttures on the piston and liner, As temperatures increased, the chrome pJeting on the liner cracked und began spalling off. A piece of chrome plate debris lodged between the piston and liner. The resulti:E riction caused the piston area around the debris to become incandescent. The ineandescent area ignited the crankcase oil vapor causing

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the crankcase overpressurization (REF: Cooper Energy Services Materials Laboratory deport ID#1345).

An independent engineering consultant has also concluded that the overpressurization event was caused by stuck rings on cylinder SL. The results from chrome thickness measurements they performed on the liner provided more information pointing toward stuck rings. The liner exhibited excessive wear in the area associated with ring travel, especially in the ring reversal areas. The rings were bearing heavily on the liner indicating that the rings became stuck.

The cause for the o umulation of deposits behind the rings is not known.

The deposits could be fuil oil or lube oil residue. A review of the EDG work history did not find any past problems which might have caused the buildup. A past cylinder combustion problem could not be found from the review of cylinder exhaust temperature and peak firing pressure data. Also, the SL injector nozzle satisfactorily passed a bench test after the incident. An oil sample, fuel oil sample and samples of the deposits have been sent to a lab for mass spectrometry analysis to try to determine the nature of the deposits.

Specifically:

1. Are the deposits from fuel oil, lube oil or both?

2. Did the deposits buildup over a long o- short period of time?

The answer to these questions may provide a ciae as to the root cause of the

- stuck rings.

Based on the inepection results of the other cylinders, the stuck ring condition on cylinder SL is considered to be an isolated incident. To ensure that no incipier.t fsilure mechanis.os aJe active, however, EDG 'A' will be inspected durinn the next refueling outage. During this inspection, at ? east six pistons will be pulled from a sampling of cylinders. Liner chrome thickness and piston tin thickness etl1 be measured to determine lif abnormal wear is occurring. Piston ringe will be checked for residue buildtp and debris. If residue buildup is found, a sample will be analyzed. All l cylinders from which the pistons are not removed will be inspected by borescope. Additional pistons will be pulled as necessary based on inspection

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results. The results of the EDG 'A' inspection will determine if any-pistons are to be pulled from EDG 'B'. All cylinders on EDG 'B' will at least be

-inspected by boroscope.- Waterford 3 will have outside technical exper;*

assist with the cylinder inspections of EDG 'A' to help ensure a thorough evaluation.

The current surveillance test interval for EDG 'A' and 'B' is at least once pir 31 days. This surveillance test interval is in conformance w4th the .

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schedule of Regulatory Position C.2.d. The crankcase relief assemblies functic,ned 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.

i Plant Contactt W.R. Brian,-Plant Engineering Superintendent, 504/c64-3127.

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