ML20203K937

Special Rept:On 860212 & 17,Cooper Bessemer Diesel Generator 2A Failures Occurred Due to Rocker Arm Failure.Caused by Liner Misalignment W/Subsequent Head Alignment.Heads Realigned or Replaced

ML20203K937
Person / Time
Site:	Byron
Issue date:	03/11/1986
From:	Querio R COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
BYRON-86-0221, BYRON-86-221, NUDOCS 8605010088
Download: ML20203K937 (3)

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. \ Byron Nucinr StItion i ) 4450 North GIrman Church Ro;d Byron. Illinois 61010 March 11,1986 LTR: BYRON 86-0221 FILE: 2.4.700 Mr. James G. Keppler Regional Administrator Region til U. S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Filyn, Illinois 60137

Dear Sir:

This special report is submitted in accordance with Byron Station Unit 1 Operating License NPF-37 Appendix A, Technical Specification 4.8.1.1.3, reporting of Diesel Generator Failures.

This report addresses two valid tests and failures experienced on the 2A Diesel Generator. The criteria to determine valid tests and failures is in accordance with section C.2.e of Regulatory Guide 1.108.

The 2A Diesel Generator has experienced two valid tests and failures due to rocker arm failure. The first failure, which occurred on February 12,1986 caused the engine to trip on connecting rod high temperature. The second failure, which 1 occurred on February 17,1986 caused a crack in the rocker arm assembly cover.

f. - The observed crack instigated an investigation that led to the failure discovery.

The Diesel Generator was then given a normal stop signal to allow the engine to cool down.

The two failures were identical in nature, and thus will be discussed as one. The intermediate root cause was excessive friction between the crosshead member and its guide. When the camshaft rotates, each cam drives a crosshead in and out of a crosshead guide. The crosshead member is connected to a rocker arm by means of a pushrod. The rocker arm in turn opens and closes its associated intake or exhaust valves.

Cooper Bessemer (the engine manufacturer) has concluded that "the root cause of the failed rocker arms is liner misalignment which in turn causes head misalignment.

Sufficient head misalignment will cause abnormal side loading and deformation of the cam follower bushing [crosshead guide] . When the bushings are subjected to these conditions, the running clearances between the cam follower and the m*M e

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BYRON 86-0221 Page 2 bushing are inadequate, and the cam follower will stick. With the follower stuck in an intermediate position, the cylinders valve train is subjected to greater than normalloads due to combustion pressures and impact loads from the cam.

Increased loads on the valve train will utimately lead to failure of the rocker arms".

The following corrective actions have been completed to restore diesel generator integrity, and to prevent the reoccurrence of this failure.

1) The five left (SL) cylinder head on the 2A Diesel Generator was removed by Byron Mechanical Maintenance. The crosshead guides were honed out to remove any score marks caused by the friction between the crosshead member and its guide. The head was then realigned onto the engine block. Cooper Bessemer checked the realignment and agreed that it was satisfactory for normal system operation.

2) The seven left (7L) cylinder head on the 2A Diesel Generator was removed and replaced with a new cylinder head. Cooper Bessemer assisted Byron Mechanical Maintenance in realigning the new cylinder head.

3) All crosshead guides on the 2A Diesel Generator were checked for similar abnormal conditions. The ten right (10ft) cylinder head showed some sticking betweeen the crosshead and its guide. This head was removed and the crosshead guides were honed to remove any score ' marks caused by friction between the crosshead member

, and its guide. Cooper Bessemer then assisted Byron Mechanical Maintenance in realigning the head.

4) After completion of the maintenance activities the 2A Diesel Generator was run and analyzed with the En-Tronics Controls En-Spec 3000 Engine Analyzer. No abnormal conditions were detected. This indicates proper corrective action was taken.

5) The 1 A, til, and 2fl Diesel Generators were also run with the analyzer, to check for similar failures experienced by the 2A Diesel Generator.

No abnormal conditions were detected on the 1 A and IB units. The analyzer did detect abnormal noise patterns on the 2B Diesel Generator two left (2L) cylinder. Further investigation by flyron Mechanical Maintenance and the Cooper Bessemer representatives revealed a bad roller on the crosshead on the three left (3L) cylinder. The crosshead was removed and replaced with a new crosshead.

BYRON 86-0221 Page 3 Additional corrective action to be taken includes the following.

1) Byron hicchanical Maintenance willincorporate into their 18 month diesel teardown procedures a step to verify the proper alignment of the cylinder heads by checking the tolerances between the crosshead members and their respective guides. Action item Record (AIR) 6-86-069 will track the completion of the procedure change.

2) Byron Maintenance Department has ordered a new alignment tool to allow for aligning cyline liners. Upon receipt of this new tool and at a tirre when the 2A diesel is available for maintenance, the SL,7L, and 10R cylinder liners will be verified for proper align-ment. The completion of this verification is being tracked by AIR 6-86-079.

3) The SL,7L, and 10R cylinders on the 2A Diesel Generator will be monitored with an En-Spec 1000 engine analyzer monthly until these cylinder liners are realigned. AIR 6-86-80 is tracking this action.

Cooper Bessemer has issued a letter that concurs with all corrective action planned and taken.

The 2A Diesel Generator was unavailable for four days following the first failure, and for six days following the second failure. Unit I entered mode 5 three days after the second failure, due to an unrelated plant trip and surveillance outage, and remained in mode 5 through the duration of the corrective action.

These failures will have no impact on the testing frequency of the 2A Diesel Generator. Currently Technical Specification 3/4.8.1.3 applies to the 2A Diesel Generator. This specification has no requirement for altering testing frequencies due to valid tests and failures, therefore Section C.2.d of Regulatory Guide 1.108 is not applicable. These failures will be recorded for future use in determining the testing frequency upon acquisition of the Unit 2 operating license.

, X7C l{ & &i<' h R. E. Querio Station Manager Byron Nuclear Power Station REQ /JC/bf cc: J. Ilinds, NRC Resident inspector U. S. NRC Document Control Desk, Washington, D.C.

INPO Record Center CECO Distribution List M. Roberts J. Cook

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