Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9607240244
LICENSEE EVENT REPORT (LER)
FACILITY NAME: Donald C. Cook Nuclear Plant - Unit 2 PAGE: 1 OF 6
DOCKET NUMBER: 05000316
TITLE: Two Cam Follower Springs Found Broken on Unit 2CD
Emergency Diesel Generator Due to Manufacturing Flaw,
Part 21 Follow-up Report
EVENT DATE: 04/13/96 LER #: 96-008-00 REPORT DATE: 07/19/96
OTHER FACILITIES INVOLVED: None DOCKET NO: 05000
OPERATING MODE: 6 POWER LEVEL: 0
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR
SECTION:
50.73(a)(2)(v) & Other
LICENSEE CONTACT FOR THIS LER:
NAME: Mr. Ken Baker, Production TELEPHONE: (616) 465-5901,
Engineering Manager x2402
COMPONENT FAILURE DESCRIPTION:
CAUSE: SYSTEM: COMPONENT: MANUFACTURER:
REPORTABLE NPRDS:
SUPPLEMENTAL REPORT EXPECTED: NO
ABSTRACT:
In accordance with 10CFR21.21(c)(3)(ii) and 10CFR50.73(a)(2)(v), the
following information is submitted to fulfill both Part 21 reporting
requirements and Licensee Event Report requirements. On June 19, 1996, a
10CFR Part 21 report was made to the NRC Operations Center regarding
broken cam follower springs discovered on the Unit 2 CD Emergency Diesel
Generator (EDG) during the Unit 2 spring refueling outage. These spring
failures were analyzed and determined to possibly constitute a
significant safety hazard, as they could prevent the EDG from performing
its design function. In accordance with the guidance presented in NUREG
0302 on Part 21 reporting, this event was determined to be reportable
under 10CFR50.73(a)(2)(v), as an event or condition which alone could
prevent the fulfillment of the safety function of a system.
The defect found on both failed springs is thought to be the result of a
manufacturing flaw, which appeared as a surface discontinuity or seam,
running for at least 1 coil parallel to the axis of the wire down to the
corner of the fracture surface. The broken cam follower springs found on
the Number 4 Rear Bank and the Number 6 Front Bank cylinders were
replaced and the 2CD EDG returned to service. The Unit 2AB EDG and the
Unit 1AB and 1CD Emergency Diesel Generators were also monitored for
signs of failed springs. No evidence was found to indicate a similar
problem on the other EDGs.
Based on the results of the investigation, it was determined that the
event was of minimal safety significance. The event did not affect safe
operation of the plant, and posed no threat to the health or safety of
the public.
END OF ABSTRACT
TEXT PAGE 2 OF 6
Condition Prior to Event
Unit Two was in Mode 6, Refuel, with all fuel removed from the core.
Description of Event
On April 13,1996, the Unit 2 CD Emergency Diesel Generator (EDG)
(EIIS/EK) was started following replacement of the Number 4 Rear Bank
(4RB) fuel pump and injector. A knocking sound was heard coming from the
engine, loud enough to be heard by personnel on the other side of the
engine. The noise appeared to be coming from the vicinity of the 4RB
cylinder, and the cylinder exhaust temperatures indicated that the
cylinder was not functioning. The engine was immediately shutdown.
Upon disassembly the aluminum cam follower was found seized in its bore
in the cast iron engine frame, and the cam follower spring broken into
three pieces. The physical evidence indicated that one of the spring
pieces wedged the aluminum cam follower in its bore, causing it to seize.
The cam lobe continued to rotate and strike the cam follower, causing the
noise, and damaging the follower and loosening the set screws protruding
from the fuel pump.
Based on the results of that inspection it was decided to disassemble and
inspect all cylinders on the 2CD engine. A second broken spring was
found on the Number 6 Front Bank (6FB) cylinder. This spring was broken
into two pieces, with the follower and cover plate exhibiting evidence of
damage similar to that of the 4RB cylinder. The follower, however, had
not seized, nor were the set screws of the fuel pump loosened. The 6FB
follower was able to continue to function properly based on the following
action afforded by its own mass and the assistance of the fuel pump
spring.
Cause of the Event
Examination of the failed springs revealed a surface discontinuity, or
seam, running for at least one coil parallel to the axis of the wire down
to the corner of the fracture surface. This flaw is thought to be a
manufacturing flaw.
The physical appearance of the two springs removed from the Unit 2CD EDG
support that the springs had been broken for some period of time. The
fracture surfaces of both springs were oxidized, had rounded edges, and
the 4RB spring had a burnished appearance on the underside of the coils,
indicating collision damage with itself and surrounding material after it
fractured. Both of these mechanism would require a length of time to
wear chrome-vanadium valve spring quality steel, which typically has a
hardness in the range of 40 to 55 Rockwell C scale.
TEXT PAGE 3 OF 6
Cause of the Event (cont'd)
The nature of the fatigue failure and the endurance limit of ferritic
materials supports that the springs had been fractured for some time, and
that springs with similar discontinuities would be expected to have
failed by now. At the time of discovery of this failure, each of the
springs in the Unit 2CD engine had approximately 25 million stress
cycles. While there is a lack of detailed material specifications for
this spring material and there is a high degree of variability in the
individual data points used to generate stress-cycle data presented in
"S-N curves" , by comparison with published endurance limits and typical
design practices it would be expected that springs with surface
discontinuities such as the seams noted in the 4RB and 6FB springs to
have a fatigue life less than 10 million cycles. Of the remaining ten
springs removed from the 2CD EDG for visual inspection and magnetic
particle inspection, none were damaged or showed signs of surface
discontinuities, supporting the conclusion that any flawed springs would
have failed by this point in their life. This conclusion would be
equally applicable to the springs in the 2AB EDG, which have experienced
approximately 23 million stress cycles, and is even stronger for the Unit
1 AB and CD EDGs, whose springs have experienced approximately 33 and 34
million stress cycles, respectively.
Analysis of Event
This event is being reported in accordance with 10CFR21.21 (c)(3)(ii) and
10CFR50.73(a)(2)(v).
The event had an adverse effect on the ability of the 2CD EDG to carry
full load for the period assumed in the safety analyses. Due to this
adverse, but unquantifiable, effect on the engine, it was determined that
a substantial safety hazard could exist, and a 10CFR Part 21 report was
appropriate.
10CFR21.21 (c)(3)(ii) requires a written report within 30 days following
receipt of the information by the responsible corporate officer on the
identification of a defect or failure to comply. The written report is
required to include the following information:
(i) Name and address of the individual informing the
Commission:
Eugene E. Fitzpatrick
Vice President, Indiana Michigan Power
1 Riverside Plaza
Columbus, OH 43215-2373
(ii) Identification of the facility which fails to comply or
contains a defect:
Donald C. Cook Nuclear Plant, Unit 2
Indiana Michigan Power
Emergency Diesel Generator (EDG) 2CD
TEXT PAGE 4 OF 6
Analysis of Event (cont'd)
(iii) Identification of the firm constructing the facility or
supplying the basic components which contains a defect:
Worthington Compressor now owned by Dresser Rand Co.
Buffalo, New York 100 Chemung Street
Painted Post, NY
14870
(iv) Nature of the defect and the safety hazard which is
created or could be created by such defect:
The Unit 2CD EDG number 4 rear bank (4RB) cylinder fuel
injection pump cam follower spring failed. This spring
has surface discontinuity, or seam, running for at least
one coil parallel to the axis of the wire down to the
corner of the fracture surface. The catastrophic failure
of this spring caused the aluminum cam follower to seize.
The resulting loss of power on the 4RB cylinder represents
an approximately 8.33 percent loss. The engine governor
would automatically feed the remaining 11 cylinders extra
fuel to compensate for the 4RB cylinder loss. Tests have
been conducted which indicate that the EDGs can sustain a
10 percent overload. Therefore, it is believed that the
remaining 11 cylinders on the EDG could have performed
their intended function for at least two hours. The
spring failure and subsequent 4RB cylinder power loss
would, however, have an adverse, but indeterminate, effect
on the EDG to carry a full load for the period assumed in
the safety analysis.
(v) The date on which the information of such defect was
obtained:
June 19, 1996
(vi) In the case of a basic component which contains a defect,
the number and location of all such components in use at
the facility subject to the regulations in this part:
The Donald C. Cook Nuclear plant has four 12 cylinder
EDGs, for a total of 48 springs.
(vii) The corrective action which has been, is being, or will be
taken; the name of the individual or organization
responsible for the action; and the length of time that
has been or will be taken to complete the action:
This information provided under the "Corrective Action"
section of this LER.
(viii) Any advice related to the defect that has been, is being
or will be given to purchasers or licensees:
None
TEXT PAGE 5 OF 6
Analysis of Event (cont'd)
In accordance with the guidance present in NUREG 0302, Revision 1,
"Remarks Presented at Public Regional Meetings to Discuss Regulations
(10CFR Part 21) for Reporting of Defects and Noncompliance", regarding
reportability of Part 21 events as LERs, it was determined that this
event was conservatively reportable under 10CFR50.73(a)(2)(v) as a
condition that alone could have prevented the fulfillment of the safety
function of structure or systems that are need to: (A) Shut down the
reactor and maintain it in a safety shutdown condition; (B) Remove
residual heat; (C) Control the release of radioactive material; or (D)
Mitigate the consequences of an accident.
This event occurred while the unit was shutdown and defueled. With the
unit in this configuration, in Mode 6, there is no requirement for the
EDGs to be operable. Subsequent evaluation of the failure of both the
4RB and 6FB springs led to the conclusion that the fracture of the
springs had occurred early in their life cycle. During the test run on
April 13, 1996 the 4RB cylinder seized, even though the spring is assumed
to have been broken for some period of time. Previous surveillance tests
on the Unit 2CD EDG were successful, and supports the operability of the
EDG up until the time that the cylinder noise was heard.
It has been concluded that the unit was in an inherently safe, defueled
condition in which the safe operation of the unit was not affected. The
event is concluded to be of minimal safety significance, and one which
posed no threat to the health or safety of the public.
Corrective Action
The remaining 10 springs on the Unit 2CD EDG were examined by magnetic
particle examination. No surface defects of 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 a slow speed, then at half load as combustion
pressure were checked. A full load run was made and pressure again
checked. All parameters were satisfactory.
Acoustic monitoring was performed on the 2AB EDG. The acoustic
monitoring revealed an anomalous noise in one of the cam followers. The
cam follower was disassembled and inspected, however, no problems were
found.
The Unit 1 EDGs 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, and all exhibited
similar acoustic signatures with a strong, clear signal. The
vibration readings were consistent between cylinders, ranging between
0.5g and 1.7g on the 1CD engine and 0.4g and 1.8g on the 1AB engine.
The set screws for the spring cover plate had been found to be loose on
the 2CD EDG 4RB follower, therefore an inspection plug at each follower
bore was removed prior to the engine runs so that the plate and setscrews
could be observed during the runs. All were found to be tight, and had
maintained the plate in position on top of the follower bore.
As a further preventive action, the cam follower springs from the 1AB,
1CD and 2AB EDGs will be removed to inspect them or surface
discontinuities at the next outage of sufficient duration.
TEXT PAGE 6 OF 6
Failed Component Identification
None
Previous Similar Events
None
ATTACHMENT TO 9607240244 PAGE 1 OF 1
American Electric Power
Cook Nuclear Plant
One Cook Place
Bridgman, MI 49106
616 465 5901
AEP
AMERICAN
ELECTRIC
POWER
July 19, 1996
United States Nuclear Regulatory Commission
Document Control Desk
Rockville, Maryland 20852
Operating Licenses DPR-74
Docket No. 50-316
Document Control Manager:
In accordance with the criteria established by 10 CFR 50.73 entitled
Licensee Event Report System the following report is being submitted:
96-008-00
Sincerely,
A. A. Blind
Site Vice President
/mbd
Attachment
C: H. J. Miller, Region III
E. E. Fitzpatrick
P. A. Barrett
R. F. Kroeger
S. J. Brewer
M. R. Padgett
G. Charnoff, Esq.
D. Hahn
Records Center, INPO
NRC Resident Inspector
*** END OF DOCUMENT ***
