ML20114E619

Forwards Event Notification Worksheet Re 960413 Event Concerning Defective Cam Follower Springs for Edgs. Replacement Springs Obtained from Mfg W/O Defect

ML20114E619
Person / Time
Site:	Cook
Issue date:	06/20/1996
From:	Brewer S AMERICAN ELECTRIC POWER CO., INC.
To:	NRC
References
NUDOCS 9606260101
Download: ML20114E619 (5)

Text

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American Electric Power M 1 Riverside Plaza M l Columbus, Ohio 43215 AABERKAN (614) 223-1000 MUEK Fax (614) 223-2004 ,

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EVENT Ct.AS$1F8cATIoNist caucu tsmenocucy cerusc The Cook Nuclear Plant Emergency Diesel Generators -

san ama purinasincy ,ys TeAnse (EDGs) were made by Worthington Compressor of Buffalo, auny gy g I aufnec NY and are the only machines of this manufacture in useuzug. :M / k uwuinste nuclear service. The machines are V-12 design. 4900 so.n sbu.fusam / e4. n= HP, operating at 514 rpm. The camshaft for each side i rwvsic4Lasdaarrven>y ooco of the engine carries individual cams for the exhaust T;wranowevar N =Ta4 and intake valve and the fuel injection pump for each apfuafsniavneosuna A an' C"" #N M W "'"

cylinder. The fuel injection pump cam follower is so.monn wwomamenom made of aluminum to reduce the reciprocating load and M ""'"""* '"'

the resultant spring requirement (size). The follower O " *"'"" /

reciprocates in a 5-inch diameter bore of the cast 4

"" *" 1ron engine frame. The spring causes the follower to ausia foll w the position of the cam. lobe as the camshaft u \AWo y evT rotates. The spring and follower are retained in the -

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g.c 4 m go,,,,,, ,o,e bore by a plate or cap which is secured in contact a y%.y with the top of the bore by four setscrews protruding .;

.,4 my , an,L down from the fuel injection pump mounting plate. 'Ihe

,A f=44 iIt aa**> fuel injection pump is actuated by a tappet screw JI.\\ f w.4 # aasc which is carried by the follower and which protrudes 3 J U L**=4 59 ^"u through a hole in the spring cover place (called a

i 5 ' '8 6 8= \\ I i ^"'S drain cap by the OEM).

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I " ' "' D "' On Saturday, April 13, 1996, while troubleshooting for

"* a speed control problem on the 2CD engine, the

((c, initiating signal was a loud knocking sound which was ]

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.g ,% g ,,,, heard in the vicinity of the number 4 rear bank (4RB) j,, r.,,, c , g .o,s cylinder. Disassembly revealed that the spring was g96 f ., .. \\ anao broken into three pieces. The cam follower and the

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\ aww cover plate (drain cap) were damaged by multiple scLmenn w Now.EucRotxcr impacts of the spring pieces. The decision was made aN o , ma.mse // anAs to remove all remaining cam follower assemblies for a A mes4=vw i -s # Aars inspection. Another broken spring was found on the a Va / Am 6FB cylinder. This one was in two pieces, and the m.4 5.'Mo c.a.=ka# **^

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follower and cover plate were damaged similarly but "O ""*'V" E ' ""* less severely than the 4RB follower and plate. The "4 I *N I I ^"* GFB cylinder had been performing normally until the w4 l aw a*,/- > n a.M ' aam engine was shut down due to the 4RB noise and no noise e..S Un pdeses > 2X Aa.8 AUG .

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The failedsuch damaged spring thatonit the 4RB cylinder cam follower caused the follower to be repeatedly struck by the intermittently cam lobe. hung in the follower bore and was indeterminate effect on the ability of the nn to carry f ll lThese u oad impacts for the would have an adverse period assumed in the safety analyses.

Cause

Description:

The failed springs from the 2CD engine were examined visually. The fracture surfaces plate, andwere bore. mostly damaged due to being thrown around between the follower '

discontinuity (seam) The spring from 4RB was observed to have a surface .

the wire, down to a corner of the fracture surface. running, for at least one coil parallel to the observation, As a result of this by magnetic particle examination before being re-installedthe non-failed spring . No surface discontinuities were detected. The surfaces appeared to have been shot peened at manufacture.

have a similar surface discontinuity running parallel to the axis of theThe faile spring and ending at the fracture surface. However, that eeam was not as -

clearly discernible as that on the 4RB spring. The two failed springs had the same shot peened surface appearance as the other ten oprings, except with the i linear surface defect.

(Continued on pg. 3)

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., J0N-20-1996 14:36 AEPSC NGD 1 614 223 2004 P.,04/04 l

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The surface defects are apparently seams resulting from the manufacturing process. The raw material may have had a defect that was elongated when the wire was drawn.

The broken springs were discovered when the engine had approximately 1660 hours0.0192 days <br />0.461 hours <br />0.00274 weeks <br />6.3163e-4 months <br /> of operation. This would correspond to 25.5 million cycles of the spring (s) . It is not known how long the springs were broken prior to being discovered, but it is believed they were functional during the preceeding surveillance since no unusual sounds were heard. This type of spring is designed for essentially infinite life and typically operates without trouble absent surface or subsurface defects or high stress.

Effects of the Failure on Plant Operation:

This fuel injection pump cam spring follower failure had no immediate detrimental effect on the Cook Nuclear Plant unit 2 operation. Unit 2 was in 6 refueling outage and the EDG was undergoing a routine surveillance test run.

l The initiating signal, a loud knocking sound, was discernable for this first time during this surveillance test run on April 13, 1996.

Corrective Action:

The remaini.ng 10 springs were examined by magnetic particle examination. No surface defects or cracks were discovered. Replacement springs, cam followers, and cover plates were obtained to replace those that were damaged.

All parts were cleaned and reinstalled, The engine was operated at slow speed 2irst, then at half load as combustion pressures were checked. Then a full load run was made and pressures checked again. Some timing adjustments were necessary due to the tappet adjustments being disturbed in the disassembly.

As a precautionary measure and out of concern for the engines on Unit 1, the Unit 1 engines were run at reduced load while acoustically monitoring the cam followers. This monitoring was performed using a mechanical stethoscope, an acoustic monitor, and a vibration monitor. No abnormal noises were identified ,

in any of the cam followers. All of them had similar acoustic signatures. l The oignal was strong and clear. The vibration readings were also very  !

consistent between cylinders, ranging between 0.5g and 1.7g on 1CD engine and between 0.4 and 1.8g on LAB engine. Since the set screws for the spring cover ,

plate had been found loose on the 2CD 4RB follower (the one that made all the '

noise originally), an inspection plug at each follower bore was removed prior to the runs so that the plate and setscrews could be observed during the run.

All these were found to be tight and maintaining the plate down '

on the top of the follower bore.

The 2AB engine was not run at that time (4/16) since it was in a refueling outage inspection as planned. Acoustic monitoring performed later revealed a noise near one of the other cam followers which was somewhat different than that on the other cylinders. That cam follower assembly was disassembled for inspection on 6/5/96; no problems were found.

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Page 3 of 3 vnym n n,

4 POWER REACTOR EVENT NUMBER: 30653 FACILITY: COOK REGION: 3 NOTIFICATION DATE: 06/20/96 UNIT: [1] [2] [] STATE: MI NOTIFICATION TIME: 09:43 [ET]

RX TYPE: [1] W-4-LP, [2] if-4-LP EVENT DATE: 06/20/96 EVENT TIME: 00:00[EDT]

NRC NOTIFIED BY: STEVE BEEWER LAST UPDATE DATE: 06/20/96 HQ OPS OFFICER: RUDY KARSCH NOTIFICATIONS EMERGENCY CLASS: NOT APPLICABLE 10 CFR SECTION:

CCCC 21.21 UNSPECIFIED PARAGRAPH VERN HODGE NRR UNIT SCRAM CODE RX CRIT INIT PWR INIT RX MODE CURR PWR CURR RX MODE -

1 N Y 100 POWER OPERATION 100 POWER OPERATION 2 N Y 100 POWER OPERATION 100 POWER OPERATION EVENT TEXT CAM FOLLOWER SPRINGS FOR THE EMERGENCY DIESEL GENERATORS (EDGs) ARE DEFECTIVE AND COULD CAUSE THE EDGs TO FAIL. THESE EDGs ARE MANUFACTURED BY WORTHINGTON. REPLACEMENT SPRINGS OBTAINED FROM THE MANUFACTURER DO NOT APPEAR TO HAVE THE DEFECT.

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