ML20214H822

Interim Deficiency Rept Re Diesel Engine Generator Rocker Arm Failure.Initially Reported on 870217.Test/replacement Program Started,Contingent on Receipt of Replacement Exhaust Rocker Arms from Cooper-Bessemer

ML20214H822
Person / Time
Site:	Braidwood
Issue date:	05/15/1987
From:	Hunsader S COMMONWEALTH EDISON CO.
To:	Davis A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
3091K, NUDOCS 8705270511
Download: ML20214H822 (4)

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. .Il A E One Fwst Nabonel Plaza, CNcago, Illinois ~

QE Address Reply 10: Post Omco Box 767 CNca00. lilinois 00000 0767

'May'15, 1987' Mr. A.' Bert Davis Regional Administrator U. S. Nuclear Regulatory Commission

~199 Rooseve1t-Road Glen Ellyn, IL 60137

Subject:

Braidwood S'tation Unit 2 10 CFR 50.55(e) Interim Report Diesel Engine-Generator Rocker Arm Failure NRC Docket No. 50-457 References-(a): S. C. Hunsader letter to A. B. Davis-t dated March 17, 1987 i-(b): S. C. Hunsader letter to A. B. Davis dated April 2, 1987

Dear Mr. Davis:

On February 17, 1987, Commonwealth Edison company notified your office of a potential deficiency reportable pursuant to 10 CPR 50.55(e) regarding the subject failure at our Braidwood Station. Reference (a) provided information concerning this matter to fulfill the thirty day reporting requirement. Reference (b) provided an interim report regarding an additional rocker arm failure. For tracking purposes, this deficiency was assigned Number 457/87-01. The purpose of this letter is to provide an interim report regarding our investigation to date on these rocker arm failures. Additionally, this interim report addresses independent actions that commonwealth Edison Company'is taking to improve our confidence in the reliability of the diesel generators.

Should you or your staff have any questions on this, please contact this office.

Respectfully, C Y ._ : k S. C. Hunsader Nuclear Licensing Administrator Attachments cc: NRC Resident Inspector - Braidwood 3091K IfI 8705270511 870515 ADOCK 05000457;.

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4 BRAIDWOOD STATION UNIT 2

( 10 CFR 50.55(e) No. 457/87-01 INTERIM REPORT Cooper-Bessemer Reciprocating (Cooper-Bessemer) the diesel generator manufacturer, has provided a status report, dated April 13, 1987, detailing their investigation into the rocker arm failures at Braidwood Station. The following provides a summary of that investigation:

.On February 6, 1987, Commonwealth Edison reported to NRC Region III that during a 24-hour test run of the 2A Diesel Generator on February 4, 1987 five (5) of twenty.(20) cylinders showed rocker arm damage. At that time NRC Region III generated a preliminary Notification of. Event or Unusual Occurance report. As noted in the April 13, 1987 Cooper-Bessemer report, the February 4, 1987 failure was caused by seized crossheads.

On February 17, 1987 N - mwealth Edison notified NRC Region III of another rocker arm failure on cylinder 5R for the 2A Diesel Generator that occurred on February 13, 1987. Similarly on March 30, 1987 Commonwealth Edison informed NRC Region III of inlet and exhaust rocker arm failure in cylinder SR for the 2B Diesel Generator that occurred on March 29, 1987.

Cooper-Bessemer has advised that the cause of the February 13, 1987 and March 29, 1987 failures remain unexplained at this time. However, based on their previous " serious problem free" history with four cycle engine cylinder heads between 1945 and January, 1987, and that 7 of 8 engines at Byron and Braidwood Stations currently appear to be free from further rocker arm breakage, Cooper-Bessemer has recommended that a 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> proving run be completed on Braidwood Station 2B Diesel Generator to demonstrate rocker arm acceptance. This 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> proving run is planned for late May or early June, 1987. (Attachment 1 provides a summary of diesel generator run hours through April 30, 1987 that show successful long-term operation).

Commonwealth Edison company has conducted an investigation of  :

the February 4, 13 and March 29, 1987, Braidwood Station diesel generator l rocker erm failures. The investigation has focused on the tensile strength of rocker arm material. A methodology has been devised which relates Brinell hardness of rocker arm castings to tensile strength using  !

portable hardness test equipment. At'this time commonwealth Edison l Company is conservatively concluding that exhaust rocker arms with a tensile strength of less than 20 kai could be susceptible to failure, l

l Based on the investigation results to date, Commonwealth Edison Company has decided to do hardness test on rocker arms in diesel

, generators at the Byron and Braidwood Stations and to replace all exhaust

( rocker arms with a tensile strength of less than 20 ksi. This action is being taken as a conservative measure to improve our confidence in the-reliability of the diesel generators. The test / replacement program has been started at the Byron and Braidwood Stations, contingent on receipt of replacement exhaust rocker arms from Cooper-Bessemer. This program will continued based on the ability to orderly remove the diesel generators from service for testing and to subsequently perform the exhaust rocker arm replacement.

While we did experience corresponding intake rocker arm failures with each exhaust rocker arm failure at Braidwood Station, we believe these intake failures are secondary failures due to the exhaust failures. We believe intake rocker arm low strength is unrelated to intake rocker arm failure at this time. We further believe that the 20 kai replacement threshold at this time is an appropriate threshold. We have experienced rocker arm failures on diesel generators with a low number of run hours. As Attachment 1 also shows, significant successful run hours have been experienced on diesels even with exhaust rocker arms having a 20 ksi or less tensile strength. However, in a longer term effort to further improve our confidence in the diesel generator reliability, we plan to replace rocker arms with less than 30 ksi tensile strength.

Over this testing / replacement period, Commonwealth Edison company considers the Cooper-Bessemer diesel generators at the Byron and Braidwood Stations to be operable based on the Cooper-Bessemer status report letter. The only exception is Braidwood Station 2B diesel generator which is still undergoing preoperational testing and requires a ,

100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> proving run. f Commonwealth Edison Company awaits Cooper-Bessemer's final report addressing the February 13 and March 29, 1987 rocker arm I I

failures. When this information is received, a final report will be submitted.

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.'s ATTACIDEDIT 1

' Diesel Generator Run Hours through April 30, 1987 3

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Diesel Generator Run Hours i Byron Station lA 651.6 Byron Station IB 528.7 i

j Byron Station 2A 561.7 4

Byron Station 2B 310.3 i

Braidwood Station lA 415.3 f

Braidwood Station IB 645.7 Braidwood Station 2A 289.5

+ Braidwood Station 2B 139.6 1

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