ML19318D225

Ro:On 800329,RHR Motor Failed.Caused by Failure of Lower Guide Bearing.Instructions Issued to Operate RHR Sys at Full Flow Conditions.Fans on Motor Shaft Ends Being Replaced. Failed Motor Replaced W/New Motor

ML19318D225
Person / Time
Site:	Peach Bottom
Issue date:	06/30/1980
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:
References
NUDOCS 8007080216
Download: ML19318D225 (2)

Text

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PHILADELPHIA ELECTRIC COMPANY ..

2301 MARKET STREET P.O'. BOX 8699 PHILADELPHIA. PA.19101 taisi s41-4ooo June 30, 1980 Docket Nos. 50-277 50-278 Mr. Boyce H. Grier, Director Office of Inspection & Enforcement Regian I US Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406

Dear Mr. Grier:

This letter is to provide you with information  !

concerning a failure of a RHR motor which occurred on Unit 2 while in the shutdown cooling mode of operation. This motor failure occurred on March 29, 1980.

The failed motor was subsequently removed from the RHR room and dismantled for inspection purposes. This inspection revealed that the lower guide bearing of the motor had failed causing the rotor shaft to lose its horizontal restraint. In addition to damage to the guide bearing, damage was also identified in the motor thrust bearing, the rotor iron, the stator wedges, and the motor windings. These weld cracks, however, could have existed prior to the guide bearing failure since similar failures have occurred on other RHR pump motors.

As a result of the rotor fan weld cracks which were identified during the Unit 3 outage in the fall of 1979, and the failure of the Unit 2 motor which occurred in March of 1978, vibration information was obtained on several RHR pump motors at the lower bearing. This vibration data indicated that the vibration at the lower motor bearing increases significantly if the RHR pumps are run at less than 3000 gpm. *11b ra ti on levels measured on various pump motors increase from a nominal 1 to 3 mils at flows above 3000 gpm to a value of 8 to 12 mils when the pump was operating at minimum flow conditions (below 3000 gpm).

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Mr. Boyce H. Grier Pago 2 f It is possible that the increased vibration which is experienced at the lower flows during shutdown cooling operation may have coneributed to the failure of the lower Euide bearing of the RHR motor.

In order to prevent further damage to RHR motor components and prevent failures, instructions have been issued to shift personnel to operate the RHR system only at full flow conditions. It should be pointed out that these pumps operate at full flow during the torus cooling mode of operation as well as the low pressure coolant injection mode of operation which is their safety function. Therefore, failures are not expected to ,

occur during operation of these pumps in response to plant  ;

transients or accident conditions. During the present Unit 2 ,

refueling outage, the fans on each end of the motor shaft are being replaced with modified fans using better fabrication l techniques. The failed motor has been replaced with a new motor of similar qualifications. The Unit 3RHR motor fans will be

< replaced during the Unit 3 refueling outage in the Spring of 1981.

The immediate corrective actions taken and the guidance ,

provided to the shift on the operation of these pumps should l prevent recurrence. The Mechanical Engineering Division is investigating the piping and systems to determine whether additional modifications are required.

Very truly yours,

/

. . oney Su rintendent Generation Division

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