05000461/LER-1999-001, :on 990129,determined Degradation of Bearings in Two Divisions of Shutdown Sws.Caused by Improper Assembly of Motor.Revised Vendor Manuals & Procedures to Address Shaft Current Concerns for Susceptible Motors
| ML20207D543 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 03/01/1999 |
| From: | Maher B ILLINOIS POWER CO. |
| To: | |
| Shared Package | |
| ML20207D539 | List: |
| References | |
| LER-99-001, LER-99-1, NUDOCS 9903100003 | |
| Download: ML20207D543 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 4611999001R00 - NRC Website | |
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improper Assembly of Motor Causes Degradation of 8Beenngs in Two Civisions of Shutdown Service Water System EVWdT DATE (si LER NUMBER (el IW'Oftf DATE (7)
OTHER FACILITIES INVOLVED (8) 1 MONTH DAY YEAR YEAR SEQUENTIAL IEVIG40N MONTH DAY YEAR FACIUTY NAME DOCKET NUMSER i
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01 29 1999 1999 - 001 00
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UCENSEE CONTACT POR THIS L5t (12) i NAME TREPHONE NUMeER Unohda Area Ceds)
Bob Maher, Engineering Supervisor, Nuclear Station Engineering (217) 935-8881, Extension 3080 j_
Department COMPIRE ONE LINE POR EACH COMPONDIT FAILUllE DESCNSED IN THIS IWPORT (13)
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ABSTRACT (Umit to 14o0 speces,i.e., approximately 15 eingle-spaced typewritten lines) (18) on January 29, 1999, it was determined that the Division 1 and 2 shutdown service water (SX) pump motors could both have suffered similar upper guide bearing failures prior to fulfilling their design basis heat removal functions.
The cause of this event could not be positively identified. The most likely cause of this event was determined to be. improper assembly of the bearing thermocouple and bearing insulating gasket. This improper assembly allowed shaft currents to flow to the bearings resulting in bearing damage. The damaged bearings for both SX motors were repaired and reassembled. corrective actions for this event includes revising vendor manuals and procedures to address shaft current concerns for susceptible motors, evaluating operating and maintenance history for suscaptible motors to determine other potentially affected motors, developing a training seminar describing why and how components are insulated to protect against shaft currents and the importance of maintaining the insulating properties, and conducting a briefing to maintenance planners on this issue.
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9903100003 990301 PDR ADOCK 0500046F S
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NRC PORM 3084 U.S. NUCUEAR IWeULATORY COMemSSION 16190sl UCENSEE EVENT REPORT (LER) i TEXT CONTINUATION i
FACEJTY NAME (1)
DOCKET (2)
LWt NUMsER (8)
PAGE (3)
YEAR SEQUEN M nEV560N 2 OF 4
MR N Wm Clinton Power Station 06000461 1999 001 oo TEKT letmore mece le required. une eMthmalcopies of ARC Form 366N (11) i
DESCRIPTION OF EVENT
1 On January 8, 1999, at 1652 hours0.0191 days <br />0.459 hours <br />0.00273 weeks <br />6.28586e-4 months <br />, operations personnel started the Division 1 shutdown i
otrvice water (BI} (SX) pump [P] as part of surveillance procedure CPS No. 9069.01,
" Shutdown Service water Operability Test."
This surveillance procedure satisfies several Tcchnical Specification and Inservice Testing requirements including measurement of motor [NO)' vibration. At 1827 hours0.0211 days <br />0.508 hours <br />0.00302 weeks <br />6.951735e-4 months <br />, the Division 1 SX pump was shutdown. At 1942 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.38931e-4 months <br />, CPS Ns. 9069.01 was completed. Review of the results of the motor vibration reading taken during the performance of CPS No. 9069.01 disclosed that two of the three points required by.the test were above the required action range for the motor as defined by the inservice tast program. Action Request F04489 was written to investigate and repair the high vibration. The Division 1 SX pump was already inoperable at the time of the discovery of the high vibration readings as the result of a planned outage.
4 On January 9, 1999, at 0400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br />, CPS No. 9069.01 was reperformed because it was believed that the vibration probes used to take the vibration measurements may net have been j
properly attached during the performance of the test on January 8, 1999. At 0555 hours0.00642 days <br />0.154 hours <br />9.176587e-4 weeks <br />2.111775e-4 months <br /> Division 1 SX pump was shutdown as required by CPS No. 9069.01. At 0657 hours0.0076 days <br />0.183 hours <br />0.00109 weeks <br />2.499885e-4 months <br /> CPS No.
9069.01 was complete. The results of the test revealed that the vibration readings for two of the three points required by the test were above the required action range for the motor.
On January 13, 1999, the Division 1 SX motor disassembly was started to determined the c use of the high vibration measurements. This disassembly was conducted with the acsistance of a representative from the motor supplier. The disassembly revealed that the upper guide bearing of the motor had degraded. Small pits were observed on the thrust bearing shoes-and on the balls and races of the lower motor guide bearings. During the disassembly, two electrical ground paths were discovered between the thrust bearing and the motor housing. The first ground path consisted of metal shavings that were lodged in the insulating gasket beneath the thrust bearing creating a ground path to the thrust bearing.
The second ground path observed was on the upper bearing temperature thermocouple probe.
The probe was bent and touched the sides of the motor housing and oil cooler creating a ground path to the thrust bearing. This is believed to have caused shaft currents which croded away the guide bearing until it could no longer support ~an oil wedge. A thorough motor inspection was-performed including the lower bearing, no additional damage was found, cnd all degraded components were replaced. This ensured the degraded condition was restricted to the upper bearing. The Division 1 SX pump was repaired and returned to c0rvice on January 23, 1999.
A review of the maintenance history of this pump and motor was performed. The most likely time for the ground paths to be created was during November 1996, when the oiler cooler [CLR) for the motor upper bearing was removed,-repaired, and reinstalled.
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TEXT CONTINUATION FACEJTY NARAE (1)
DoCEET (2) ist NURISER 18)
PAGE (3) 4 b
YEAR SEQUE N L REValON 3 OF 4
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Clinton Power Station 05000461 1999 001 00 TEXT (Wme,e space le requkeef, one aedrianalcooles of MC Form 366N (1Tl Scced on the information obtained during'the disassembly of the Division 1 SX pump and knowledge that the_ oil cooler for the Division 2 SX motor was removed, repaired, and rcinstalled in January 1997, it was determined that it was prudent to inspect the Division 2 SX' motor for similar damage. The Division 2 SX motor was disassembled for inspection cterting on January 23, 1999.
Inspection of its upper guide bearing disclosed that it was in the early stages of degradation. The thrust bearing thermocouple was found to have a damaged insulation sleeve causing a ground path which could create shaft currents. There wso no visible pitting on the thrust shcas or lower guide bearing rollers as had been seen on the Division 1 SX motor. A thorough motor inspection was performed, including the lower bos:-ing, and no additional damage was found, all degraded components were replaced. This en:ured the degraded condition was restricted to the uppar bearing. The Division 2 SX pump was returned to service on January 29, 1999.
On January 29, 1999, a review of the results of the SX pump motor inspections determined th:t the condition of the bearings was such that it could not be conclusively determined that the SX pump motors would be able to operate for thirty days as required in a loss of coolant accident.
Based on this information the condition was determined to be reportable in accordance with 10CFR50.72, "Immediate Notification Requirements for Operating Nuclear Power Reactors," and 10CFR50.73, " Licensee Event Report System." When this determination was made the plant was in Mode 4 (Cold shutdown) with the reactor (RCT) level being maintained between 70 and 100 inches and temperature was being maintained between 95 and 115 degrees Fahrenheit. Reactor pressure was atmospheric.
No automatic or manually initiated sifety system responses were necessary to place the plant in a safe and stable condition. No equipment or components were inoperable at the ctart of this event to the extent that their inoperable condition contributed to this cvsnt.
CAUSE'OF THE EVENT Ths cause of this event could not be positively identified. The most likely cause of this event was determined to'be improper assembly of the motor bearing thermocouple and bearing inculating gasket. This allowed shaft carrents to flow to bearings resulting in bearing damage. The cause could not be positively identified due to the inability to determine a current path through the damaged guide bearing. The current path identified on each of the motors'was through the thrust bearing which is electrically isolated from the guide besring.
CORRECTIVE ACTIONS
The damaged bearings for both SX motors were repaired and reassembled. Prior to returning tha motors to service, the upper motor bearings were checked to ensure that they were electrically isolated. The Division 3 SX pump motor was not inspected as it is a different d;31gn~and is not as susceptible to shaft current damage.
NRC FORM 306A to.19000
NRC PORM 300A U.S. NUCLEAR REGULATORY CORMASSION te-190ek LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION PACEJTY NAME (1)
DOCKET (2)
LER NUMBER lel PAGE (3)
YEAR SEoUENTIAL REVmON 4 OF 4
NR NUMsER Clinton Power Station 05000461 1999 001 00 TEKT (Wmore mece in required, une e&Gthmalcopies of MIC Form 36&N (11l A list of motors that are most susceptible to shaft currents was developed. The procedures end vendor manuals associated with these motors will be revised, as necessary, to ensure thr.t the' insulating requirements are identified (including recording as-found and as-left resistance levels), precautions necessary to avoid damaging insulation during maintenance cre included, and instructions are provided on how to verify the integrity of insulation after completion of maintenance on the component. The operating and maintenance history i
for the susceptible motors was. evaluated to determine if any other motors needed to be inspected. This evaluation concluded that no other safety-related motors required further 1
inspection. Also, a training seminar describing why and how components are insulated to protect against shaft currents and the importance of maintaining their insulating properties will be prepared and presented to maintenance personnel. Prior to completion of tha maintenance training seminar, and the procedure and vendor manual revisions, a briefing en LLS issue will be given to maintenance planners.
ANALYSIS OF EVENT
This event is reportable under the provisions of 10CFR50.73(a)(2)(vii) as an event where a ningle cause or condition caused two independent trains to become inoperable in a single system designed tot shutdown the reactor and maintain it in a safe shutdown condition, remove residual heat, or mitigate the consequences of an accident. The potential failure of both SX motors from two difforent independent trains due to bearing degradation cetisfies this definition.
Tha SX pumps are designed to provide cooling water to safety-related equipment and heat exchangers in the plant in the event of a loss of coolant accident or loss of offsite power.
1 Th3 design basis requires these pumps to operate for thirty days following an event that r: quires their operation.
If the Division 1 SX pump had been required to operate for a loss of coolant accident or loss of offsite power and the vibration of the motor increased to the point of failure then the Division 2 SX pump would normally have been available to cupport the redundant Division 2 components. However, given the as-found condition of the Division 2 SX motor, it is uncertain that this motor would have supported continuous operation for thirty days as required by the design basis.
ADDITIONAL INFORMATION
A review of previous Licensee Event Reports submitted in the last two years reveals that th re were no other reports submitted for motor bearing failures or degradation.
Tha bearing was contained 6 siemens-Allis motor model number 119.
For further information on this event contact Bob Maher, Engineering Supervisor, Nuclear Stction Engineering Department,'at (217) 935-8881, extension 3080.
NRC FoMA SOSA 16-19 del
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