05000416/LER-1982-080, Update LER 82-080/01X-4:on 821004,capscrew on Div 2 Standby Diesel Generator Securing Rear Crankcase Cover to Engine Block Cracked.Caused by Fatigue Due to Engine Operation. Capscrews Replaced

Update LER 82-080/01X-4:on 821004,capscrew on Div 2 Standby Diesel Generator Securing Rear Crankcase Cover to Engine Block Cracked.Caused by Fatigue Due to Engine Operation. Capscrews Replaced

ML20087M622
Person / Time
Site:	Grand Gulf
Issue date:	03/21/1984
From:	Byrd R, Dale L MISSISSIPPI POWER & LIGHT CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
AECM-84-0168, AECM-84-168, LER-82-080-01X, LER-82-80-1X, NUDOCS 8403300113
Download: ML20087M622 (5)

LER-2082-080, Update LER 82-080/01X-4:on 821004,capscrew on Div 2 Standby Diesel Generator Securing Rear Crankcase Cover to Engine Block Cracked.Caused by Fatigue Due to Engine Operation. Capscrews Replaced

Event date:
Report date:
4162082080R00 - NRC Website

text

M Update Report - Previous Report Date 8/31/83 NN asemamov enessuneen Attachment to AECM-84/0168

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REPORT 0 ATE 80 EVENT DESCRIPTIO88 A8eO PnOSASLE COfeSE00EteCES h W lWith the unit in Cold Shutdown. a special insoection on the Division 2 l o IStandby Diesel denerator was conducted. During this inspection, one ofj

. o le l lthe capscrews which secures the rear crankcase cover to the engine blockl g lwas discovered to be defective. This report is submitted pursuant to 1 o s IT.S.6.9.1.12.e and 1. The event had no effect on the health and safety l 1

lF[i] lof the public and did not constitute a threat to plant safety. The l lo is i D I iv. 1 and 3 D/Gs were operable at the time the defect was discovered. l 7 .. =

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CAdSE DESCRiPTIO86 AND COMMECTIVE AC7 hoses h g g (The capscrew broke while being checked for the correct torque. 1 gj lIt is believed that the capscrew had partially cracked due to fatigue  :

, , iduring engine operation prior to the torque check. The capscrew and g g l20 others were replaced. A design change has been completed which j g,,,,g {eplaced the original capscrews with higher strength capscrews. j

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Attachment to AECM-84/0168

• Page 2 of 3 Supplementary Information to LER 82-080/01 X-4 Mississippi Power & Light Company Grand Gulf Nuclear Station - Unit 1 Docket No. 50-416 Technical Specification involved: N/A Reported Under Technical Specification: 6.9.1.12.e and i Event Narrative This is an update to a previous report submitted on August 31. 1983. The following patagraphs describe the event reported.

The special inspection of the 21 capscrews which secure the rear crankcase cover to the engine olock of the Division 2 Standby Diesel Generator revealed that c: e capscrew had failed. The capscrews were SAE Grade 5, 5/8 NC X 1-3/4".

The maintenance work order which led to the discovery of the failed capscrew had been initiated as follow-up to a previous, similarly failed capscrew on the same Division 2 Standby Diesel Generator rear crankcase cover. This situation was previously reported to the NRC in Potentially Reportable Deficiency (PRD) 82/14 under 10CFR50.55e. The first failure occurred on March 15, 1982, during the 24-hour load test performed during the Pre-Operational Test Program. The failure of March 15, 1982, resulted in a generator fault caused by the head of the broken capscrew becoming lodged between the generator stator and rotor while the generator was at 100% load. This resulted in the generator tripping on Generator Differential Current. The generator was subsequently replaced. The capscrews securing the rear crankcase cover were inspected for correct tightness and found to be below the required 60 ft-lbs. The capscrews were replaced on both Division 1 and 2 Diesel Generators and torqued to the required 60 ft-lbs.

The follow-up work order, performed on October 4,1982, instructed that each of the capscrews securing the rear crankcase cover to the engine block be checked for correct torque (60 ft-ibs). Three of the capscrews were found to be less than 40 fr-lbs (20, 23, and 35 ft-lbs). The work order further instructed that any capscrews not within 2 ft-lbs of the required 60 f t-lbs be torqued within the acceptable range. When the capscrew (which was found at 20 ft-lbs originally) was tightened it sheared off approximately one inch from the bottom side of the head before reaching 60 ft-lbs. Another work order was subsequently issued and the 21 capscrews on the Division 2 Diesel Generator rear cover were replaced with new replacement capscrews and torqued to 60 ft-lbs. An inspection of the Division 1 Diesel Generator revealed no problems (the Division 3 Diesel Generator is supplied by a different manufacturer so no inspection was required).

Attachm:nt to

• AECM-84/0168

.. Page 3 of 3 Nuclear Plant Engineering has attributed the cause of failure to fatigue cracking. - A Design Change (DCP 82/4183) has been completed which replaced the original crankcase capscrews with a higher (SAS40 Grade B24) strength type on both Division 1 and 2 Diesel Generators. Design Change Package (DCP) d2-0039 installed protective screens on the generator air gaps to prevent the entrance of foreign materials which could result in generator damage.

A test program was developed, the Division 2 diesel was instrumented and data was collected during a test run. This data was considered unacceptabic. MP&L plans to' perform additional testing and vibration analysis. However, based on inspections of bolts removed from the covers since that tine, we conclude that the high strength bolts and the i protective screens are adequate to prevent recurrence. This is ]

submitted as a final report. 1 l

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E MISSISSIPPI POWER & LIGHT COMPANY Helping Build Mississippi P. . 1 O. J ACKSON MISSISSIPPI 39205 March 21, 1984 NUCLEAR PRODUCTION DEPARTMENT U.S. Nuclear Regulatory Commission Region II 101 Marietta St., N.W., Suite 2900 Atlanta, Georgia 30303 Attention: Mr. J. P. O'Reilly, Regional Administrator

SUBJECT:

Grand Gulf Nuclear Station Unit 1 Docket No. 50-416 License No. NPF-13 File: 0260/L-835.0 Update Report - Division 2 Standby Diesel Generstor Rear Crankcase Cover Capscrew Defective LER 82-080/01 X-4 AECM-84/0168 This letter submits an update to a previous update report submitted on August 31, 1983. The event for which the report was submitted occurred on October 4, 1982, when during a special inspection, one of the capscrews which secure the rear crankcase cover to the engine block of the Division 2 Standby Diesel Generator was discovered defective. The report was submitted purcuant to Technical Specification 6.9.1.12.e and i.

A design change (DCP 82/4183) has been completeci which replaced the original crankcase bolts with a higher strength grade. Design Change Package 82/0039 installed protective screens on the generator air gaps to prevent the entrance of foreign materials which could result in generator damage.

As reported in the last update, a test program was developed, the Division 2 diesel was instrumented and data was collected during a test run. This data was considered unacceptable. MP&L plans to perform additienal testing and vibration analysis. However, based on inspections of bolts removed from the covers since that time, we conclude that the high strength bolts and the protective screens are adequate to prevent recurrence. This is submitted as a final report. Attached is LER 82-080/01 X-4 with Supplementary Information.

Yours truly,

. h.

L. F. Dale Manager of Nuclear Services EB2/SHH:rg Attachment cc: See next page ()ppyg]4Lihf'l Member Midc'!e South Utilities System Jd'2L gg

AECM-84/0168

' aga 2 MISSISSIPPI POWER Q Ll2HT COMPANY cc: Mr. J. B. Richard (w/a)

Mr. R. B. McGehee (w/o)

Mr. T. B. Conner (w/o)

Mr. G. B. Taylor (w/o)

Mr. Richard C. DeYoung. Director (w/a)

Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission Washington. D. C. 20555 Document Control Desk (w/a)

U. S. Nuclear Regulatory Commission Washington, D. C. 20555

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