ML19031C052

04/02/1976 Letter Detailed Analysis and Report on Nos. 11 and 12 Auxiliary Feedpump Bearing Failures

ML19031C052
Person / Time
Site:	Salem
Issue date:	04/02/1976
From:	Schwalje E Public Service Electric & Gas Co
To:	Knuth D NRC/IE
References
Download: ML19031C052 (2)

Text

PS~G Public Service Electric and Gas Company 80 Park Place Newark, N.J. 07101 Phone 201 /622-7000 April 2, 1976 Dr. Donald F. Knuth, Director U. S. Nuclear Regulatory Commission Office bf Inspection and Enforcement 7920 Norfolk Avenue Bethesda, Maryland 20014 D_ear Dr. Knuth:

NO. 11 AND 12 AUXILIARY FEEDPUMP BE4RI~9 FAILURES NO. 1 UNIT SALEM NUCLEAR GENERATING STATION DOCKET NO. 50-272 On March 15, 1976 a verbal report was made to Region 1, Office of Inspection and Enforcement, advising that the outboard bearing of No. 12 Auxiliary Feedpump failed. This failure was similar to the outboard bearing failure of No. 11 Auxiliary Feedpump. This report was in accordance with provision of 10CFR50.55(e).

The following is a detailed analysis and report on the subject failure:

Description During Hot Functional Testing of the No. 1 Unit, the Auxiliary Feedwater pumps, (9 stage, horizontal split casing type) were being operated for extended periods at minimum flow conditions to supply make-up water to the steam generators. During this testing, both No. 1 Unit Auxiliary Feedwater pumps experienced thrust bearings failures, requiring replacement of their entire rotating elements. Thrust bearings for these pumps are ring lubricated, two row, balltype bearings.

Analysis of Occurrence Investigation subsequent to the failures has revealed the following:

During operation of the pump, at minimum flow, an abnormal amount of axial oscillation of the pump shaft was observed, which could put considerable stress on the thrust bearings. According to the pump manufacturer; this type of movement is common to this model pump but it is greatly aggravated by operating at minimum flow.

Under these conditions, damage to the thrust bearings is possible.

The Energy People 95-2001 (400M) 5-73

Dr. D. F. Knuth 4/2/76 Corrective Action The manufacturer (Byron-Jackson) is still investigating this problem; however, several actions have been taken to minimize the forces exerted against the thrust bearings.

1. The low-flow orifice originally designed for 50 gpm flow was modified to allow approximately 200 gpm flow.

2. New rings were ~achined and installed for the bearing retainers.

3. The two thrust bearing rows were originally installed to take thrust in two directions.

On the manufacturer's recommendation one

_bearing row was reversed so that both races resist in the direction of greatest thrust.

4. The bearing clearance from the retainer was reduced from .0005/.0007 to .0002.

5. The oil level in the bearing housing was lowered.

Safety Implications There are no safety implications of these failures. Hot Functional Testing is conducted prior to initial core load. As such, the pumps were being operated in a mode different from that which they were designed for.

During normal operation of the plant, the Auxiliary Feedwater pumps will not be required to operate for extended periods on minimum flow and therefore this type of problem would not be expected to occur.

If you desire additional information on this subject, we will be pleased to discuss it with you.

Very truly yours,

/\/]~ '

/7 k*/V'~-j-z-E.(N. SchwaV-Je Mahager of Quality Assurance Engineering and Construction Department CC Mr. J. P. O'Reilly King of Prussia, Pa.