ML19327B548

LER 89-019-00:on 890924,indication of High Temp for Reactor Coolant Pump RC-3A Upper Motor Thrust Bearing Received in Control Room.Caused by Damaged Cable for Bearing Resistive Temp Device.Damaged Cable replaced.W/891024 Ltr

ML19327B548
Person / Time
Site:	Fort Calhoun
Issue date:	10/24/1989
From:	Molzer D, Morris K OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-019, LER-89-19, LIC-89-865, NUDOCS 8911010208
Download: ML19327B548 (4)

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Omaha Public Power District 1623 Harney Omaha. Nebraska 68102 2247 402/536 4000 October 24, 1989 LIC-89-865 U. S. Nuclear Regulatory Commission .

Attn: Document Control Desk Mail Station P1-137 Washington, DC 20555

Reference:

Docket No. 50-285 Gentlemen: *

SUBJECT:

Licensee Event Report 89-019 for the Fort Calhoun Station Please find attached Licensee Event Report 89-019 dated October This i report is being submitted per requirements of 10 CFR 50.73(a)(2)(iv .24,)1989.

Sincerely, ,

l K J. Morris D vision Manager i Nuclear Operations i

KJM/ tem Attachment .)

c: R. D. Martin, NRC Regional Administrator A. Bournia, NRC Project Manager P. H. Harrell, NRC Senior Resident Inspector INP0 Records Center American Nuclear Insurers 1

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On September 24, 1989, Fort Calhoun Station Unit I was operr. ting at approximately 70% power in Mode 1. AT 1259 hours0.0146 days <br />0.35 hours <br />0.00208 weeks <br />4.790495e-4 months <br /> indication of high temperature for Reactor Coolant Pump RC-3A upper motor thrust bearing was received in the control room. After maximization of both the cooling water flow to the oil coolers and the oil flow to the bearing failed to reduce the indicated temperature, the Shift Supervisor initiated a controlled plant ,

i shutdown at 1320 hours0.0153 days <br />0.367 hours <br />0.00218 weeks <br />5.0226e-4 months <br />. At 1518 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.77599e-4 months <br />, with reactor power between 5 and 6 i percent, RC-3A thrust bearing temperature indication spiked to 267 degrees.

The reactor was immediately manually tripped and RC-3A was shut down. This trip is reportable pursuant to 10 CFR 50.73(a)(2)(iv). Investigation revealed the cause of the indicated high temperature to be damaged cable for the bearing resistive temperature device (RTD), although cause of the damage could not be determined. There was no evidence of actual excessive bearing temperature.

The damaged cable and the RTD were replaced. Other similar RTD wiring will be inspected and investigation into the cause of the cable damage will be completed during the 1990 refueling outage.

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On September 24 1989, at 1259 hours0.0146 days <br />0.35 hours <br />0.00208 weeks <br />4.790495e-4 months <br />, Fort Calhoun Station Unit No. I was in  :

Mode 1 and opera, ting at approximately 70% power. A high temperature alarm for Reactor Coolant Pump RC-3A upper motor thrust bearing was received on the alarm printer in the control room. ~A control room o)erator immediately called the j i point up on the plant computer and confirmed t1at the alarm was valid (the alarm setpoint is 194 degrees F). The operator then checked to ensure that RC-3A bearing oil cooler was being supplied by adequate cooling flow. Cooling water flow and temperature a)peared to be normal. The operator proceeded to maximize -

cooling flow to the lu)e oil coolers in an effort to lower the thrust bearing l temperature. Increased cooling flow did not appear to have any observable '

effect on bearing temperature.  :

The control room operatcrs referenced Operating Instruction 01-RC-9 " Reactor Coolant Pump - Normal Operation" for additional guidance. A precaution in-the procedure states that if thrust bearing shoes exceed 195 degrees F, the pump should be shutdown at once and the bearing inspected. At the time, bearing temperature was between 194 and 195 degrees F.

In an effort to decrease the bearing temperature, oil flow to the bearing was I maximized. The oil lift pump for RC-3A was started and the control switch manually held in the start position (the RCP oil lift pumps are not capable of being locked on after the RCP pump reaches 90% of rated speed). This appeared to be partially effective as the thrust bearing temperature decreased a) proximately 2 degrees F. However, the temperature drop was only momentary as t1e bearing temperature continued to slowly trend upward. When the bearing temperature exceeded 195 degrees F, the Shift Supervisor directed that the plant be shutdown at a controlled rate. At 1320, a controlled plant shutdown was initiated using appropriate operating procedures. '

The Shift Supervisor felt that a rapid shutdown at a controlled rate would be the best course of action, considering that the bearing temperature had been trending upward at a very slow rate and seemed to have stabilized at around 196 degrees F. He did not feel _that damage to the bearing would result from operating in this temperature range. He also felt that shutting the reactor coolant pump down at power and the resulting transient from the reactor trip l would be of a greater concern. '

Power was decreased at a rate of approximately 30% per hour. Indicated bearing  ;

temperature during this time varied between 195 and 200 degrees F. At approximately 10% power the turbine was taken off line. At 1518, with reactor-power between 5 and 6%, the indicated thrust bearing temperature spiked to 267 degrees F. The reactor was immediately tripped and RC-3A was shut down. The reactor trip procedure was followed with all safety functions being satisfied.

Allequipmentop(eratedasdesigned. This manual trip is reportable pursuant to 10CFR50.73(a)2)(iv).

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An investigation was initiated into the cause of the indicated high thrust

bearing temperature. A chemical analysis was performed on the bearing lube oil to determine if a catastrophic bearing failure 7 excessive wear had occurred.

Chemical analysis of the lubo oil did not subnwiate bearing failure as the cause of the high bearing temperature. In a h % a General Electric motor-service engineer inspected the motor, externai e m of the thrust bearing and the lube oil and also concluded that indicatio.5 of a high thrust bearing '

temperature were not caused by a bearing failure.

Concurrent investigation found that the wiring between the thrust bearing RTD i

(resistive temperature device) and junction box had been damaged in several L locations. The damaged wire was believed to have grounded or shorted out

! causing the erroneous temperature indication. Immediate corrective action was.

l to replace the wiring and install a new RTD. System Engineering will continue

to investigate the cause of the danaged wiring. The wiring to all of the RCP bearing RTDs will be ins)ected, and replaced if necessary, to ensure it is in.

L acceptable condition. T1ese actions are scheduled to be completed during the l 1990 refueling outage.

A review of Operating Instruction 01-RC-9 will be conducted to ensure adequate direction is given for shutting down a reactor coolant pump during similar conditions. Increased margin between the bearing temperature alarm setpoint and-the temperature at which operator action is required will be evaluated. If necessary, 01-RC-9 will be revised. These actions will be completed-by December l 31, 1989.

The safety significance of this event can be considered minimal since the RTD wiring is not safety related or Electrical Environmental Qualification equi ) ment. Temperature indication for the reactor coolant pump. bearing failed  ;

in t1e conservative direction, prompting the operator actions of shutting the -

unit and the pump down, thus avorting potential bearing damage. The manual reactor trip occurred at a low power level with the main turbine already ,

l off-line, minimizing transient effects.on the unit. Other than this manual '

i' actuation of the RPS and the associated diesel generator start, r safety system actuations occurred and all systems operated properly.

A review revealed no other cases of degraded instrumentation wiring resulting in Licensee Event Reports.

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