IR 05000373/1993022
| ML20057G080 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 10/05/1993 |
| From: | Hague R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML20057G071 | List: |
| References | |
| 50-373-93-22, 50-374-93-22, NUDOCS 9310200149 | |
| Download: ML20057G080 (6) | |
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U.S. NUCLEAR REGULATORY COMMISSION REGION Ill l
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Report Nos.
50-373/93022(DRP); 50-374/93022(DRP)
l Docket Nos.
50-373; 50-374 License Nos.
NPF-ll; NPF-18 l
Licensee:
Commonwealth Edison Company j
Executive Towers West III i
1400 Opus Place Suite 300 i
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Downers Grove, IL 60515 i
Facility Name:
LaSalle County Station, Units 1 and 2
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Inspection At:
LaSalle Site, Marseilles, Illinois Inspection Conducted: July 29 through September 16, 1993 Inspector:
C. Phillips
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Approved By:
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%. L. Ha e, Chief Date Rea to rojects Section 1C Inspection Summary i
Inspection from July 29 throuah September 16. 1993 (Recorts No. 50-373/93022(DRP): 50-374/93022(DRP)).
l Areas Inspected: A special inspection was conducted by the resident inspector into the circumstances surrounding inadequate oil supply to the 0, lA, and 2A l
diesel generator cooling water pump bearings on July 29, 1993.
Result s: One violation was identified which involved an inadequate
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maintenance procedure in regard to setting bearing oil levels (paragraph
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4.a.).
One open item was identified which involved developing corrective actions that address the root causes of the event and developing a method to l
l ensure consistent lubrication is provided to the pump bearings.
Plant Operations Performance in this area was good.
The operability decisions were appropriate.
Enaineerina and Technical Support j
t Performance in this area was acceptable.
The root cause analysis of the event
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l was satisfactory.
The corrective actions developed at the time of the l
inspection did not address all the root causes.
9310200149 931007 PDR ADOCK 05000373 e l G
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DETAILS 1.
Persons Contacted
- J. Schmeltz, Operations Manager
- J. Lockwood, Regulatory Assurance Supervisor
- H. Vinyard, Assistant System Engineering Supervisor
- T. Nauman, Master Mechanic
- J. Bell, Maintenance Staff Supervisor M. Santic, Maintenance Superintendent
- Denotes those attending the inspection exit meeting.
The inspector also talked with and interviewed several other licensee employees during the course of the inspection.
2.
Backaround The NRC became concerned with the adequacy of lubrication to safety related pump bearings after a maintenance error at the Quad Cities station rendered a diesel generator cooling water pump inoperable.
Guidance was provided to the stations from Commonwealth Edison (CECO)
corporate to perform plant walkdowns and further clarify instructions used oy operations and maintenance concerning sightglasses and oilers.
This inspection specifically investigated the circumstance surrounding the events involving the diesel generator cooling water pumps. These pumps not only provide cooling to the diesel generators, but also the emergency core cooling system (ECCS) pump room coolers.
3.
Event Description On July 29, 1993, system engineering walked down safety related pumps to determine if the oiler levels were properly set.
The 0 and 2A diesel generator cooling water pumps (DCCWP's) wore found to have both the inboard and outboard pump bearing oil levels below the level required to provide adequate lubrication.
The inboard pump bearing oil ievel on the 1A DGCWP was also found to be below the required level and the outboard bearing was found to be above the specified level.
The oil level is crucial in that the bearings are actually lubricated by a slinger ring dipping into the oil and spraying the bearings with oil.
The design is such that too high a level can be just as bad as too low because the slinger ring will float on top of the oil and not spray the bearings.
The tolerance level as approximately one-sixteenth of an inch in either direction.
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There was a discrepancy between the fact that the oil levels were too low for the slinger rings to be providing adequate lubrication and the fact that pump flow and vibrations were not indicating any deterioration in the integrity of the bearings.
Because of this discrepancy, it was determined that the 2A DGCWP inboard bearing would be physically inspected because it had the greatest margin of error.
The inspection showed that the oil level was insufficient for the slinger ring to reach it.
The original design of the pump had greased bearings.
The pumps were changed to oiled bearings upon installation.
Grease still existed in the bearing races supplying lubrication.
The pump was considered operable by the licensee.
In order to restore the
oil level to its required height, a modification to the piping was required.
In addition to a piping modification, a different type of oiler was installed. After this was done, the oil was returned to the proper level.
It was unknown if other pumps also had greased bearings.
It was determined that the 1A DGCWP would be inspected upon the return of the 2A DGCWP.
The 1A DGCWP had been run on May 24, 1993, for its inservice testing surveillance.
Flow and vibration on this pump were normal with no degrading trends.
It was not anticipated that bearing problems existed on this pump.
Inspection of the inboard pump bearing showed that the bearing cage had failed.
The balls were sitting in the bottom of the race; however, they appeared to be undamaged.
Vibration testing
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failed to show this problem.
Later analysis showed that the bearing cage failed due to a lack of lubrication. Apparently the bearing had failed before the trending of the bearing vibrations started.
The
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licensee declared the 1A DGCWP inoperable and commenced repairs.
It was postulated that since the pump showed no signs of degradation, i.e. reduced pump flow or high vibration, that the bearing was carrying little to no load. There was a short distance between the pump outboard bearing and the motor inboard bearing so this explanation was plausible.
The 1A DGCWP bearing was replaced, oil levels were restored to the required level, and the pump was returned to service. The 0 DGCWP was then removed from service and inspected.
Both bearings on the 0 DGCWP contained grease.
The oil levels were restored to the expected level and the pump was returned to service.
4.
Event Evaluation The licensee conducted a root cause analysis and produced a list of corrective actions in response to this event which were still in the process of on-site review at the time this evaluation was performed.
The inspector's event evaluation included the capability to have previously identified this problem, management's operability decision, the adequacy of the root cause investigation, the adequacy of the corrective actions taken, and the reportability of the event.
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a.
Capability To Previously identify The Problem This problem could have and should have been previously identified.
The licensee received a letter from Crane Deming in March 1984 indicating the proper oil level and what the oil level tolerance was.
Following the receipt of the letter, no inspection of the pumps was made to ensure proper oil level. The correct oil level was included in maintenance procedures post dating the letter.
However, the 1/8 inch tolerance of the oil level was not included.
Maintenance was performed to repair broken oil fill lines on the 0 DGCWP in 1985, and the 1A DGCWP in 1986.
The failure to include this critical tolerance into the maintenance procedure was a violation of 10 CFR 50, Appendix B, Sectic, V (50-373/93022-01(DRP)).
b.
Manaaement's Operability Decision The licensee's operability decision on the DGCWP's was good.
After the oil levels were found out of tolerance, the initial operability decision on all the diesel generator cooling water pumps was based on the length of time the condition had existed and the satisfactory flow and vibration results from inservice test surveillances. The levels out of tolerance and the good flow and vibration results were contradictory.
The licensee did not initially understand how the bearings were receiving lubrication. When the 2A DGCWP was inspected, it was realized that the bearing was lubricated by residual grease. 'It was not known if the other pump bearings had grease in them. The decision to place the 1A DGCWP out-of-service and inspect the bearings was good.
After the 1A DGCWP inboard bearing was found damaged, the licensee did not declare the 0 DGCWP inoperable prior to a physical inspection.
That decision would have resulted in a technical specification 3.0.3 shutdown due to the inoperability of both division 1 and division 2 ECCS pumps.
Room cooling for the residual heat removal (RHR) pumps, which were necessary to bring the units to cold shutdown, would be inoperable. With the 1A DGCWP out-of-service and division 2 RHR pumps inoperable, it would have forced the units to shutdown with the division 1 RHR pumps and operate the 0 DGCWP to cool the room.
The decision to restore the 1A DGCWP to service and then take the 0 DGCWP out-of-service for inspection was made after discussions with Region 111.
c.
Root Cause Determination The root cause analysis appeared to identify all the potential causes of the problem. They were:
1.
Oilers were improperly positioned due to improper procedures.
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Oilers were improperly set because the criticality of the setting tolerances were not realized by the installer.
3.
Oiler settings were inadvertently altered during improper
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filling of the reservoirs.
4.
Oilers were improperly set due to the adjustment limitations
placed on them by the oiler piping geometry.
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Oilers were set improperly because of a fundamental misunderstanding of their operating principles.
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Oilers were improperly set due to inaccurate setting i
methodology.
What actually caused the levels to be out of tolerance could have
been any one of the above or a combination of causes.
The root
cause investigation failed to research pump work history.
The analysis stated that since proper procedures existed now, this effort would be a waste of time.
The inspector did review past
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l work perforced on the 0 and 1A DGCWP.
This review showed that there is very little difference between the current procedure
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requirements for oiler level adjustment and those used in the i
past.
d.
Corrective Action Effectiveness The inspector evaluated the corrective actions while they were still in the on-site review process. The proposed corrective actions at the time of the inspection failed to address all the potential root causes identified.
The need to determine an accurate oiler setting methodology, to ensure that levels would be adjusted properly in the future, was not listed as a corrective action. The analysis stated that proper procedures currently exist. LaSalle Maintenance Procedure (LMP)-GM-50, " Crane Deming Model 5063/5064 Pump Maintenance" rev. 2, does not include critical level tolerances and a change was not generated to include them.
One of the long term corrective actions was to evaluate the need of a surveillance to ensure that proper oiler settings of safety-related machines is maintained.
LaSalle operating surveillance (LOS)-DG-Q1 and Q2, 0 and 1A(2A) Diesel Generator Auxiliaries Inservice Test, includes a check, required by ASME Section XI, to i
ensure oil levels are normal.
ASME Section XI did not elaborate on the correct cethod to observe proper oil levels.
The levels were checked by observing that there was oil in the bubbler reservoir which, in this case, does not adequately ensure the proper level.
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The determination of corrective actions that adequately address the potential root causes of the event and the development of a way of ensuring proper oil level in order to provide consistent lubrication to the DGCWP bearings is an open item (50-373/93022-02(DRP)).
e.
Event Reportability Because only division 2 of Unit 1 (B and C RHR pumps) was inoperable for less than its allowed LCO, the event was not reportable.
5.
Event Safety Sionificance The actual safety significance of this event was minimal. All bearings that were inspected, with the exception of the 1A DGCWP inboard bearing, were lubricated by the existing grease in the bearing race.
The licensee was correct in declaring the pump inoperable. However, based on past performance characteristics and evidence that there was no load on the inboard bearing, the pump may have run as required if called upon.
The potential safety significance was indeterminate.
Not having a proper methodology to set the oiler level and not training the operators on how to properly fill the oilers without changing the level setting could have resulted in multiple pump failures had the bearings not been pre-greased.
These failures would probably have occurred during acceptance testing or during surveillance testing of the equipment.
6.
Open Items Open items are matters which have been discussed with the licensee, which will be reviewed further by the inspector, and which involve some action on the part of the NRC or licensee or both. An open item disclosed during the inspection is discussed in Paragraph 4.d.
7.
Exit Interview The inspector met with licensee representatives (denoted in Paragraph 1)
during the inspection period and at the conclusion of the inspection period on September 16, 1993.
The inspector summarized the scope and results of the inspection and discussed the likely content of this inspection report. The licensee acknowledged the information and did not indicate that any of the information disclosed during the inspection could be considered proprietary in nature.
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