Information Notice 2002-22, Degraded Bearing Surfaces in Gm/Emd Emergency Diesel Generators
| ML021790640 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah, Arkansas Nuclear, Surry  |
| Issue date: | 06/28/2002 |
| From: | Beckner W NRC/NRR/DRIP/RORP |
| To: | |
| Petrone C , NRC/NRR/RORP, 415-1027 | |
| References | |
| TAC M3057 IN-02-022 | |
| Download: ML021790640 (7) | |
UNITED STATES NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555
June 28, 2002
NRC INFORMATION NOTICE 2002-22:
DEGRADED BEARING SURFACES IN GM/EMD
EMERGENCY DIESEL GENERATORS
Addressees
All holders of operating licenses for pressurized- or boiling-water nuclear power reactors, including those that have ceased operations but have fuel on site.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform
addressees of the discovery of degraded bearing surfaces on the piston bearings in General
Motors/Electromotive Division (GM/EMD) emergency diesel generator (EDG) engines. It is
expected that recipients will review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. However, suggestions contained in this
information notice are not NRC requirements; therefore, no specific action or written response
is required.
Description of Circumstances
Surry Power Station, Units 1 and 2
On April 23, 2001, with both units at full power, emergency diesel generator 3 (EDG 3) was
taken out of service to investigate an increase in the silver concentration in samples of EDG
lubricating oil. The piston wristpin bearing inserts in GM/EMD diesel engines have a silver
substrate beneath a lead-tin overlay. An increasing concentration of silver in the lube oil is an
indicator of excessive wear of the bearing surfaces.
The engine manufacturer has provided detailed instructions on interpreting the results of lube
oil sample analysis. Silver concentrations in the range 0 to 1 parts per million (ppm) are
considered normal. The range 1 to 2 ppm is considered borderline, and concentrations above 2 ppm indicate a high correct condition. The manufacturer specifies several inspections, including feeling the side of piston pins in situ for signs of distress and measuring the piston-to- head clearance for the high-correct condition.
The silver content of the lube oil samples from Surry EDG 3 gradually rose from 0.63 ppm in
April 2000 to more than 2 ppm in October, but the licensee did not notice this trend because the
action level in the licensees sampling procedure was too high. In April 2001, there were
indications of abnormal wear on the wrist pin sides. Examination revealed severe damage on
the surfaces of seven of the wristpin bearings and piston carrier bearings. The silver had been
displaced from the wristpin bearing surfaces to the carrier bearing surfaces, blocking some or
all of the lubricating oil channels. The partially blocked oil channels prevented normal oil flow at
the bearing-to-wristpin interface, resulting in higher oil and bearing temperatures and wear and
extrusion of the bearing surfaces. There was base-metal-to-base-metal contact, which can
lead to catastrophic bearing failure and engine damage. Surveillance testing required by
technical specifications failed to detect the damage in the engine.
Based on the as-found condition of EDG 3, the licensee concluded that this engine was
inoperable. All 20 power-pack assemblies (cylinder, cylinder head, piston and connecting rod)
were replaced and the EDG was returned to service.
The silver concentration in the oil samples from Surry EDG 1 was also higher than historical
values but was in the 1-to-1.2 ppm range when the engine was removed from service in July
2001. Inspecting the removed power-pack assemblies, the licensee found that cylinder #8 had
a severely damaged piston wristpin bearing and a piston carrier bearing all of whose oil
channels were blocked. Seven other cylinders had partially blocked bearing oil channels. All
20 power-pack assemblies were replaced and the EDG was returned to service.
Sequoyah Nuclear Plant
In June 2001, the licensee tested an oil sample from Sequoyah EDG 2B-B and found an
increase in silver content to 1.1 ppm, indicating a borderline condition. Two months later, the
wristpin and piston carrier bearings of cylinder #11 were found to be severely degraded. The
bearing material had been worn away, oil channels were blocked, the wristpin was burned and
heavily scored, and parts of the wristpin and carrier were blued from heat. From a record
review, the cylinder #11 measured piston-to-head clearance in March 2001 had exceeded the
acceptance criteria of 0.068 inches by 0.001 inches and was significantly changed, 0.027 inches, from the previous measurement in 1999. The vendor recommends that the associated
power pack be condemned when a change of 0.030 inches is observed.
In September 2001 the licensee investigated a slightly elevated silver content in EDG 1A-A.
Performance of in-situ feel checks, visual inspections and piston-to-head clearance
measurements were unable to locate the cause of the elevated silver. Visual examination of
the disassembled power packs found damage in cylinder #1 similar to that in EDG 2B-B
cylinder #11. Technical specification required testing did not disclose the damage in either
In January 1986, damage similar to that at Sequoyah and Surry was observed in EDG 1A at
ANO. The wristpins and connecting rod bearing inserts of four cylinders were heavily scored
and burned. At that time, lube oil analysis was not done on a regular schedule. The lube oil
analysis after the discovery of the damage showed a silver content of 9.2 ppm; the action level
was 2.0 ppm. Piston-to-cylinder-head clearances in all four cylinders were found to be greater
than the 0.03 inches permitted by the manufacturer. The licensee attributed the wristpin
bearing failures to insufficient lube oil film but could not identify the mechanism. The licensee
determined that frequent visual inspections of the wristpin bearings and frequent
measurements of piston-to-cylinder-head clearance should be made. The licensee also began
monitoring and trending lube oil samples. Discussion
As a result of finding damaged bearings in their GM/EMD diesel generator engines, the three
licensees performed technical assessments and root cause analyses. The Surry licensee
contracted several technical organizations to perform independent assessments for this
purpose (see the reference at the end of this notice).
The licensees generally agreed about the failure mechanism and the probable root causes.
The damage to the wristpin was consistent with a lubrication-deprived failure. Wear and
extrusion of the softer silver substrate material is the result of insufficient lubrication or use of a
lubricant with insufficient film strength to remain on the bearings between engine starts. The
problem is possibly aggravated by oil chemistry.
The failure is initiated by repeated engine starts under marginal lubrication conditions. The
silver-and-lead bearing material is displaced into the oil channels of the wristpin bearing, limiting
or preventing lubricant flow across the full surface of the bearing. When the channels are
substantially or completely blocked, the bearing material wears away until the steel wristpin
contacts the steel bearing shell and the bearing fails. Initially, the damage occurs only while the
engine is starting, i.e., until the lubricating system supplies oil to the bearing. However, after
the oil channels are substantially blocked, the bearing is lubrication-deprived and damage can
continue and potentially accelerate while the engine is operating.
From the information provided by the Surry licensee (see reference), the change to
nonchlorinated oils appears to be the root cause of their bearing failures. Chlorine compounds
previously were added specifically to impart extra extreme pressure (EP) resistance to the
base lube oil. This EP resistance property provides oil adherence to the bearings when the
engine is not run for an extended period, thereby preserving some lubrication for the next start.
However, these chlorine compound additives were determined to be carcinogenic and posed
disposal problems. Therefore, licensees had changed to a non-chlorinated formulation.
Feedback obtained by the licensee from additive formulation experts in the oil industry and from
bearing manufacturers confirms that the chlorinated additive in the earlier lube oil was a paraffin
wax and was there as an extreme-pressure lubricant.
Although the licensee changed to an oil that met the engine vendors specifications, the
nonchlorinated formulation apparently had not been specifically qualified for the standby duty
typically required of diesel engines provided for nuclear power plants. Such oils have been
used successfully in locomotive and marine applications in which engines operate continuously
for long periods, and shutdowns are infrequent and of relatively short duration.
The problems at Surry, Sequoyah and ANO indicate that the recommended limits for silver in
the lube oil need to be reexamined. The current 2 ppm limit at which specific actions are
required may not be an appropriate limit for the more stringent demands on the lube oil during
extended standby duty. The limit is based upon uniform wear from all cylinders and not for the
detection of abnormal degradation on single or a few bearings. It may also be prudent to do
more frequent oil analyses and more frequent visual inspections of the relevant engine parts at
lower or at step changes in, silver concentrations. Furthermore, with elevated silver
concentrations, successful completion of surveillance tests feel checks, and piston-to-head
clearance measurements may not be sufficient to confirm that the piston wristpin and piston
carrier bearing are free of severe damage. Although not observed at these three plants, degraded turbocharger bearings can also result in elevated silver concentrations. This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/RA/
William D. Beckner, Program Director
Operating Reactor Improvements Program
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical Contacts: Jai R. Rajan, NRR
Kerry D. Landis, RII
301-415-3066
404-562-4510
Email: jrr@nrc.gov
Email: kdl@nrc.gov
Paul E. Fredrickson, RII
Linda Smith, RIV
404-562-4530
817-860-8137 Email: pef@nrc.gov
Email: ljs@nrc.gov
Reference: Letter dated December 12, 2001, from Virginia Electric and Power Company to the
NRC, transmitting technical reports on the root cause of the wristpin damage in the Surry Power
Station emergency diesel generators (Accession Nos. ML 0136001720 [Part I] and
ML 0136002070 [Part II])
Attachment: List of Recently Issued NRC Information Notices
DOCUMENT NAME: G:\\REXB\\RAB1\\IN-EDG4.WPD
- See previous concurrence
OFFICE RSE:RORP:DRIP
Tech Editor
R-II
R-II
NAME
CDPetrone
PKleene*
Pfredrickson *e-mail
KLandis *email
DATE
06/12/2002
04/04/2002
06/12/2002
06/12/2002 OFFICE R-IV
BC:EMEB:DE
SC:OES:RORP:DRIP
PD:ROR:DRIP
NAME
Lsmith *email
GImbro
TReis
WDBeckner
DATE
06/12/2002
06/25/2002
06/27/2002
06/28/2002
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit
Attachment 1 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information
Date of
Notice No.
Subject
Issuance
Issued to
_____________________________________________________________________________________
2002-21 Axial Outside-Diameter
Cracking Affecting Thermally
Treated Alloy 600 Steam
Generator Tubing
06/25/2002
All holders of operating licenses
for pressurized-water reactors
(PWRs), except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2002-19
Medical Misadministrations
Caused By Failure to Properly
Perform Tests on Dose
Calibrators for Beta-and Low- Energy Photon-Emitting
Radionuclides
06/14/2002
All nuclear pharmacies and
medical licensees.
2002-18
Effect of Adding Gas Into
Water Storage Tanks on the
Net Positive Suction Head For
Pumps
06/06/2002
All holders of operating licenses
for nuclear power reactors, except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2002-17 Medical Use of Strontium-90
Eye Applicators: New
Requirements for Calibration
and Decay Correction
05/30/2002
All U.S. Nuclear Regulatory
Commission medical licensees
that use strontium-90 (Sr-90) eye
applicators.
2002-16
Intravascular Brachytherapy
Misadministrations
05/01/2002 All Medical Licensees.
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