Part 21 Report - 1996-601

 
 
ACCESSION #: 9606260101

                                                  PMP 7030.001.001
                                                  Attachment No. 1

NRC FORM 261A                      U.S. NUCLEAR REGULATORY COMMISSION
                                        OPERATIONS CENTER

                      EVENT NOTIFICATION WORKSHEET

NOTIFICATION    FACILITY        UNIT   CALLER'S NAME  CALL BACK: ENG
TIME            ORGANIZATION

EVENT TIME & ZONE        EVENT DATE

POWER/MODE BEFORE        POWER/MODE AFTER

                         EVENT DESCRIPTION

10CFR21 NOTIFICATION DETERMINATION MADE JUNE 19, 1996

The Cook Nuclear Plant Emergency Diesel Generators (EDGs) were made by
Worthington Compressor of Buffalo, NY and are the only machines of this
manufacture in nuclear service.  The machines are V-12 design, 4900 HP,
operating at 514 rpm.  The camshaft for each side of the engine carries
individual cams for the exhaust intake valve and the fuel injection pump
for each cylinder.  The fuel injection pump cam follower is made of
aluminum to reduce the reciprocating load and & the resultant spring
requirement (size).  The follower reciprocates in a 5-inch diameter bore
of the cast iron engine frame.  The spring causes the follower to follow
the position of the cam lobe as the camshaft rotates.  The spring and
follower are retained in the bore by a plate or cap which is secured in
contact with the top of the bore by four setscrews protruding down from
the fuel injection pump mounting plate.  The fuel injection pump is
actuated by a tappet screw which is carried by the follower and which
protrudes through a hole in the spring cover plate (called a drain cap by
the OEM).

On Saturday, April 13, 1996, while troubleshooting for a speed control
problem on the 2CD engine, the initiating signal was a loud knocking
sound which was heard in the vicinity of the number 4 rear bank (4RB)
cylinder.  Disassembly revealed that the spring was broken into three
pieces.  The cam follower and the cover plate (drain cap) were damaged by
multiple impacts of the spring pieces.  The decision was made to remove
all remaining cam follower assemblies for inspection.  Another broken
spring was found on the 6FB cylinder.  This one was in two pieces, and
the follower and cover plate were damaged similarly but less severely
than the 4RB follower and plate.  The 6FB cylinder had been performing
normally until the engine was shut down due to the 4RB noise and no noise
was noticed.

(illegible)

NOTIFICATIONS  YES  NO WILL BE
NRC RESIDENT             ANYTHING UNUSUAL OR        YES          NO
                         NOT UNDERSTOOD             (Explain above)
STATE(s)
LOCAL                    DID ALL SYSTEMS FUNCTION   YES           NO
OTHER GOV AGENCIES       AS REQUIRED?
MEDIA/PRESS RELEASE
                         MODE OF OPERATION  ESTIMATE FOR  ADDITIONAL INFO
                         UNTIL CORRECTED:   RESTART DATE: ON BACK?

(illegible)                                            Page 1 of
                                                            Rev. 0

                                                  PMP 7030.001.001
                                                  Attachment No. 1

The failed spring of the 4RB cylinder cam follower caused the follower to
be damaged such that it intermittently hung in the follower bore and was
repeatedly struck by the cam lobe.  These impacts would have an adverse
but indeterminate effect on the ability of the EDG to carry full load for
the period assumed in the safety analyzes.

Cause Description:

The failed springs from the 2CD engine were examined visually.  The
fracture surfaces were mostly damaged due to being thrown around between
the follower, plate and bore.  The spring from 4RB was observed to have a
surface discontinuity (scam) running, for at least one coil parallel to
the axis of the wire, down to a corner of the fracture surface.  As a
result of this observation, the non-failed springs removed from the 2CD
engine were examined by magnetic particle examination before being
re-installed.  No surface discontinuities were detected.  The surfaces
appeared to have been shot peened at manufacture.  The failed spring from
6FB was later examined and appeared to have a similar surface
discontinuity running parallel to the axis of the spring and ending at
the fracture surface.  However, that seam 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 springs, except with the
linear surface defect.

                                                  (Continued on page 3)

                                                       Page 2 of 3
                                                            Rev. 0

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 hours 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 a refueling outage and the EDO was undergoing a routine
surveillance test run.  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 remaining 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 first, 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.
The signal 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 1AB engine.  Since the set screws for the
spring cover plate had been found loose an the 2CV 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 set screws 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 an 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.

                                                       Page 3 of 3

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] W-4-LP    EVENT DATE:        06/20/96
                                   EVENT TIME:        00:00 [EDT)

NRC NOTIFIED BY: STEVE BREWER      LAST UPDATE 1[A]   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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