Information Notice 2001-06, Centrifugal Charging Pump Thrust Bearing Damage Not Detected Due to Inadequate Assessment of Oil Analysis Results and Selection of Pump Surveillance Points
| ML011070643 | |
| Person / Time | |
|---|---|
| Issue date: | 05/11/2001 |
| From: | Marsh L Operational Experience and Non-Power Reactors Branch |
| To: | |
| References | |
| IN-01-006 | |
| Download: ML011070643 (7) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D. C. 20555-0001 May 11, 2001 NRC INFORMATION NOTICE 2001-06: CENTRIFUGAL CHARGING PUMP THRUST
BEARING DAMAGE NOT DETECTED DUE TO
INADEQUATE ASSESSMENT OF OIL ANALYSIS
RESULTS AND SELECTION OF PUMP
SURVEILLANCE POINTS
Addressees
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.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert
addressees that inadequate assessment of pump oil analysis results, combined with
surveillance testing which does not monitor all relevant pump operating conditions, may allow
severe pump degradation to go undetected. It is expected that recipients will review the
information for applicability to their facilities and consider actions, as appropriate, to avoid
problems. However, the suggestions contained in this information notice are not NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances
On June 19, 2000, while disassembling the C charging/safety injection pump (CSIP) to replace
a mechanical seal, Shearon Harris Nuclear Plant (SHNP) personnel discovered significant
damage to the outboard thrust bearing. Further examination revealed that the babbitt material
on the bearing shoes of this multi-pad thrust bearing had melted and re-solidified within the
thrust bearing cage area. On both the shoes and the sleeve of the thrust bearing, radial wear in
the direction of normal pump rotation was indicative of metal-to-metal contact between the two
surfaces. The inboard radial bearing and shaft also had minor wear. SHNP stated in a
licensee event report (Reference 1) that the most probable cause of the damage was a
momentary loss of lubrication flow to the outboard thrust bearing. An inadequate fill-and-vent of
the pump, which may have caused a momentary increase in the axial thrust on the outboard
thrust bearing, was also given as a potential root cause.
Elemental analysis of a routine pump bearing oil sample taken on September 19, 1999, using a
direct current plasma (DCP) spectrometer, revealed a 40-fold increase in the particle count in
the range of 5 to 10 microns over the previous sample taken on May 11, 1999. (The particle
count increased from 15,800 to 660,000 counts per 100 milliliter sample.) All other tested
parameters were normal. SHNP reviewed the Electric Power Research Institute (EPRI)
Lubrication Guide (Reference 2) and concluded that the size range of these wear particles was
consistent with benign wear. The bearing oil in the CSIP was replaced on December 21, 1999, and SHNP continued sampling at 6-month intervals. The next oil sample, taken on
February 23, 2000, also showed a high particle count in the 5 to 10 micron range. Trace
amounts of iron and tin were also detected for the first time. The analysis of another oil sample
taken on June 18, 2000, found that the levels of all parameters were similar to the levels in the
February 23, 2000, sample.
Each CSIP at SHNP is a Pacific Model 21/2 RLIJ, 11-stage, centrifugal pump manufactured by
Flowserve Corporation, formerly Ingersoll-Dresser Pump Company. The C CSIP is the standby
pump. During the period in which high particle counts in the three oil samples were detected, the C pump was intermittently in service to support plant operations. Surveillance testing, as
required by the SHNP inservice testing program and the SHNP Technical Specifications, was
performed on the C pump during this period. Inservice tests, including vibration measurement, were conducted during plant operation on November 13, 1999, and January 3, 2000, with the
pump operating at the normal charging flow rate of approximately 90 gallons per minute (gpm).
Performance data from both tests indicated the C CSIP met the established pump hydraulic
and mechanical acceptance criteria in the American Society of Mechanical Engineers (ASME)
Code for Operation and Maintenance of Nuclear Power Plants (OM Code), and no adverse
trends were noted. On April 23, 2000, a refueling outage test to satisfy the SHNP technical
specifications was performed successfully, with the pump achieving a flow rate of 609 gpm.
Subsequent to the discovery of the severely degraded outboard pump thrust bearing, discussions with the pump manufacturer revealed that at flow rates between approximately 250
and 600 gpm, the net axial thrust of each SHNP CSIP pump is in the direction of the outboard
thrust bearing. Therefore, SHNP concluded that during normal plant operation and surveillance
testing, the outboard thrust bearing had been either not loaded or only lightly loaded. In
addition, SHNP could not assess the capability of the C CSIP to perform its function during a
small-break, loss-of-coolant accident, in which the pump axial thrust would have fully loaded the
outboard thrust bearing.
In response to an NRC notice of violation (Reference 3), SHNP described corrective steps
either completed or in progress to address this issue. These included (1) counseling operators
on consequences of improper pump fill-and-vent of the CSIP, (2) establishing oil analysis
criteria for increased lubricant particle counts, (3) reinforcing expectations for disposition of
abnormal indications, (4) sampling CSIP lubricating oil quarterly instead of semi-annually,
(5) revising the maintenance procedure to ensure that the CSIP lubricating oil system will
function as expected, and (6) implementing a design modification to install temperature and
vibration proximity probes on each CSIP. NRC Requirements and Industry Guidance and Practices on Pump Condition Monitoring
The current requirements for inservice testing of safety-related pumps are specified in Section
50.55a of Title 10 of the Code of Federal Regulations (10 CFR 50.55a), Codes and
Standards. For plants which are required to update their inservice testing (IST) programs after
September 22, 2000, which is one year after the recent change to 10 CFR 50.55a (Reference
4), Subsection (b)(3) requires that safety-related pumps be tested to the 1995 Edition and the
1996 Addenda of the ASME OM Code. The Code requires that safety-related pumps be tested
biennially at +/-20% of their design flow rate, and every three months at specific reference points.
Overall vibration measurements of each pump bearing are taken as specified by the Code. The
SHNP IST program is in accordance with an earlier version of the Code, which requires pump
testing to be conducted every three months at reference points of operation readily duplicated
during subsequent tests. Pump hydraulic performance is assessed by comparing current
performance with reference values established when the pump is known to be operating
acceptably. Pump mechanical performance is assessed like hydraulic performance, unless the
specified multiple of the measured overall vibration reference value exceeds the absolute
vibration acceptance criterion.
Neither the Code nor the regulations require any specific pump condition monitoring activities to
be performed on safety-related pumps. However, the NRC has observed during inspection
activities that many US commercial nuclear power plants have some type of condition
monitoring program for their rotating machinery. These programs usually include both safety- related and non-safety-related equipment. Because no regulations cover these programs, the
testing performed, the examinations completed, and the acceptance criteria used for each
condition monitoring activity vary widely.
The EPRI Lubrication Guide includes information on the testing and analysis of lubricants. The
guide identifies particle size and wear-metal content as key properties to analyze. The guide
also provides classic warning limits for certain measured properties. The guide does not
recommend a specific warning limit for particle count. However, the guide emphasizes trending
critical properties of a specific application and establishing appropriate warning limits. When
these limits are exceeded and the results are verified, the guide recommends oil replacement
and further study if necessary.
The NRC has authorized alternatives to the Code vibration requirements based on the
performance of pump condition monitoring activities. For example, as part of an alternative to
the Code vibration acceptance criterion, one facility committed to implement a plant-specific
pump condition monitoring program for certain safety-related pumps. The NRC has determined
that this proposed alternative demonstrates an acceptable level of quality and safety. Discussion
A key factor in the failure to discover the damaged bearing before disassembly was not actively
pursuing the root cause of the abnormally high particle count in the September 19, 1999, oil
sample. The EPRI guide implies that particles less than 10 microns in size are generated from
"benign wear." The guide does not discuss the significance of changes in wear particle
concentration. However, the guide does discuss trending of parameters. SHNP performed
spectroscopic analysis of each sample and trended the results of these tests. The low weight
percent of the wear particles was apparently the reason why the elemental analysis did not
detect the presence of bearing material. Ferrography and electron microscopic scan
examination were conducted after the discovery of the bearing degradation and therefore were
not a factor in diagnosing the elevated particle count. SHNP elected to continue with a routine
oil sampling schedule despite the high particle count and the lack of a plausible root cause for
this condition. A more aggressive oil sampling schedule (e.g., weekly) would likely have
revealed the severely degraded outboard thrust bearing several months before the pump was
disassembled.
Inservice and technical specification surveillance testing did not indicate that the outboard thrust
bearing was severely damaged. The purpose of pump inservice testing is to identify
degradation before the pumps performance of its safety-related function is impaired. For the
charging pumps at the SHNP, the purpose of technical specification testing is to verify that the
pump will deliver a specific flow at the required total developed head. The failure of both tests
to indicate bearing degradation appears to have biased the decision to not investigate the
elevated particle count.
Information provided by the vendor revealed a reversal in the direction of the pump axial force
as a function of the pump flow rate. This pump design characteristic was unknown to SHNP
personnel before they discovered the severely degraded bearing and then talked with the
vendor. The Code does not require SHNP to account for this design condition through testing.
The technical specification full flow test after the first detection of the high particle count neither
detected this condition nor caused a catastrophic failure of the pump. This issue illustrates that
the assessment of safety-related pump performance is dependent not only on verifying
successful surveillance testing, but also on understanding (1) pump and system design and
performance characteristics, (2) performance testing results, and (3) the results of condition
monitoring activities and their correlation with known pump design characteristics and
performance test results. Generic Implications
If trends of condition monitoring data are not actively investigated when they deviate from an
established baseline, a licensee may overlook significant pump degradation that is not detected
by performance testing.
This information notice requires no specific action or written response. If you have any
questions about this notice, please contact one of the technical contacts listed below or the
appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/RA/
Ledyard B. Marsh, Chief
Events Assessment, Generic Communications
and Non-Power Reactors Branch
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical contacts: J. Colaccino, NRR Bob Hagar, Region II
301-415-2753 919-362-0601 E-mail: jxc1@nrc.gov E-mail: rch2@nrc.gov:
Attachments:
1. List of References
2. List of Recently Issued Information Notices
ML011070643 Template #=NRR-052
ÿ Publicly Available Non-Publicly Available Sensitive ÿ Non-Sensitive
OFFICE Tech Editor) REXB:DRIP EMEB:DE EMEB:DE
NAME PKleene* RHagar* JColaccino* DTerao*
DATE 04/09/2001 04/09/2001 04/10 /2001 04/18/2001 OFFICE EMEB:DE REXB:DRIP D:DE REXB:DRIP
NAME GImbro* JTappert /txk for* JStrosnider* L
DATE 04/18/2001 04/24/2001 05/03/2001
Attachment 1 References
1. Shearon Harris Nuclear Power Plant Unit 1, Docket Number 50-400, Licensee Event
Report 2000-007-01, Technical Specifications Violation Due to Inoperable Charging
Safety Injection Pump, dated March 12, 2001.
2. NP-4916-R2, Electric Power Research Institute/Nuclear Maintenance Applications
Center Lubrication Guide, Revision 2, published February 1995.
3. Shearon Harris Nuclear Power Plant Unit 1, Docket Number 05000-400, Reply to Notice
of Violation (NRC Inspection Report Numbers 50-400/00-03, 50-400/00-10) dated
March 2, 2001.
4. Federal Register, Volume 64, Number 183, Industry Codes and Standards; Amended
Requirements, (10 CFR Part 50), issued September 22, 1999.
Attachment 2 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
______________________________________________________________________________________
2001-05 Through-Wall Circumferential 04/30/01 All holders of operating licenses
Cracking of Reactor Pressure for pressurized water nuclear
Vessel Head Control Rod Drive power reactors except those who
Mechanism Penetration have ceased operations and have
Nozzles at Oconee Nuclear certified that fuel has been
Station, Unit 3 permanently removed from the
reactor vessel
2001-04 Neglected Fire Extinguisher 04/11/01 All holders of licenses for nuclear
Maintenance Causes Fatality power, research, and test reactors
and fuel cycle facilities
2001-03 Incident Reporting 04/06/01 All industrial radiography
Requirements for Radiography licensees
Licensees
2001-02 Summary of Fitness-for-Duty 03/28/01 All holders of operating licenses
Program Performance Reports for nuclear power reactors, and
for Calendar Years 1998 and licensees authorized to possess
1999 or use formula quantities of
strategic special nuclear material
(SSNM) or to transport formula
quantities of SSNM
2001-01 The Importance of Accurate 03/26/01 All material licensees
Inventory Controls to Prevent
the Unauthorized Possession
of Radioactive Material
2000-17, Crack in Weld Area of Reactor 02/28/01 All holders of operating licenses
Supp. 2 Coolant System Hot Leg Piping for nuclear power reactors except
at V.C. Summer those who has ceased operations
and have certified that fuel has
permanently removed from
reactor vessel
2000-22 Medical Misadministrations 12/18/00 All medical use licensees
Caused by Human Errors authorized to conduct gamma
Involving Gamma Stereotactic stereotactic radiosurgery
Radiosurgery (GAMMA KNIFE) treatments
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit