ML18024A058

Letter Attaching a Final Report of a Deficiency in Carriage Bolt Fasteners Used on 480 Volt Motor Control Center Bus Splices

ML18024A058
Person / Time
Site:	Susquehanna
Issue date:	09/18/1978
From:	Curtis N Pennsylvania Power & Light Co
To:	Grier B NRC Region 1
References
Download: ML18024A058 (12)

Text

0 REGULATQRY INFORMATION DISTRIBUTION SYSTEM (RIDS)

DISTRIBUTION FOR INCOMING MATERIAL -3 388 REC: GRIER B H ORG: CURTIS N W DOCDATE: '09/i8/78

,NRC PA PWR 5 LIGHT DATE RCVD: 09/22/78 DOCTYPE: LETTER NOTARIZED: NO COPlES RECEIVED

SUBJECT:

LTR i ENCL FORWARDING FINAL CONSTRUCTION DEF1CIENCY REPT CONCERNING DEFICIENCY IN CARRIAGE BOLT FASTNERS USED ON 480 VOLT MOTOR CONTROL CENTER BUS SPLICES.

PLANT NAME:SUSQUEHANNA' UNIT i REVIEWER INITIAL: X JM SUSQUEHANNA - UNIT 2 DISTR IBUTER INITIAL~@~

DI TRIBUTIQN QF THIS MATERIAL IS AS FOLLOWS +4~++++++++<<+++++

NOTES:

SEND ISE 3CYS FSAR 5 ALL AMDTS CONSTRUCTION DEFICIENCY REPORT (iOCFR50. 55E)

(DlSTRIBUTION CODE BOi9)

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1 A

TWO NORTH NINTH STREET, ALLENTOWN, PA. 18101 PHONE: (215) 821-5151 NORMAN W. CURTIS Vice President. Engineering 8 Construction 821-5381 September 18, 1978 c > Pl rn~

3 'Carrl Q7 Rm Mr. Boyce H. Grier cn~

Director, Region I ~rl'k~

ra CA U. S. Nuclear Regulatory Catmission 631 Park Avenue Pl KLng of Prussia, Pennsylvania CD 17406 C/I SUSQU12iANNA, STE2% EL'ECTRIC STATION FINAL REPORT OF A DEFICIEb~ IN CARRIAGE BOLT FASTEZKRS USH3 ON 480 VOLT MOTOR CONTROL CEDER BUS SPLICES DOCK"T NOS: 50-387/50-388 LICENSE NOS:

ERs 100450/100508

'PTA-'290 '

CPPR-101/CPPR-102

'ILE 840-4 Mr. Grier:

'ear Attached'is a Definitive Report of the subject deficiency as reqLDxed by 10CFR50.55 (e) .

On August 8, 1978, J. D. Green, PP&L Resident Nuclear Quality Assurance Engineer, advised Mr. R. Gallo, Reactor Inspector, NRC Region I, that PP&L was 2n the process of evaluating the rgxz~bility of the subject deficiency.

Coincident with PP&L's verbal advisory to the Cottmission, Bechtel Quality Assurance issued YEAR-1-27 (Managanent Corrective Action Report) requesting that Bechtel Project. Engineering make a determination regarding the reporta-bility of the deficiency. The determination, affixtrting the reportability of the deficiency, was made on August 23, 1978 ard is the basis for the attached final report.

The. defective mater2al is being controlled and will be corrected. and closed out under'he provisions of the'echtel Quality Program.

Please advise should you require other information.

Very truly yours, N. W..Curtis Vice President-Engineering & Construt~n ARS.mcb Attachment 7gOP+Oi44'ENNSYLVANIA POWER IL LIGHT COMPANY

Mr. Boyce H. Grier Septenber 18, 1978 ccrc Mr. J. G. Davis (15) sting Director-Office of Inspection 6 Enforcement U. S. Nuclear Regulatory Qmnission Washington, D.C. 20555 Mr. G. McDonaM, Director (1)

Office of Managanent Information 6 Program Control U. S. Nuclear Regulatory Cpu.ssion Washix~n, D.C. 20555 Mr. Robert M. Gallo U. S. Nuclear Regulatory Caanission P;O. Box 52 Shickshiany, Pennsylvaxua 18655

FINAL REPORT A DEFICIENCY IN CARRIAGE BOLT FASTENERS USH3 ON 480 VOLT MOXOR C(MHDL CENTER THE SUSQUEHANNA. STEM 1KZCTRIC STATION D. P. Parsons SSES Electrical Group Supvr.

CP, A. M.

~c~~

e I 0 7$

Supervising Engineer-Design-Suscpxehanna A. R.

Manager-Nuclear Quality Assurance PENNSYLVANIA, PONER & LIGHT CCMPANY ALLENKNNg PENNSYLVANIA SEPT1M3ER 18, 1978

CARRIAGE BOLT DEFICIENCY GH 480V MYIQR CONXBDL CENZER BUS SPLICES P.O. 8856-E-118 AC SUSQUl5iANNA. STEAM Ef.ECTRIC STATION UNITS 1 & 2

TABLE OF CONTENTS Introduction Pg. 1 Description of the Deficiency Pgs. 1,.2 Analysis of Safety Implications Pgs ~ 2g 3 Corrective Action Pgse 3g 4 Conclusions Pg. 4

This report is presented in accordance with the requirenents of Title 10, Code of Federal Regulationsg Part 50'ection 50.55(e) .

A deficiency in ecpignent supplied by Cutler-Hanrner, Inc. was discovered, during construction activities being performed at the Suscpehanna Steam Electric Station (SSES) .

PP&L's A/instructor (Bechte1) g in the course of installing carriage bolts which are used to splice bus sections at the shipping splits of 480 volt nntor control center units, noted the occurrence of several cases of thread fai1ures (stripped threads) while torcpiag the bolts.

The failures and their cause were assessed far their impact on the safety of

~'peration of the plant. Based upon an evaluation of the safety implications, Bechtel Engineering has concluded that the condition is reportable under 10CFR50.55(e) because, were it to have remained uncorrected, the condition could have adverse affects on the safe operation of the plant.

DEK5GPTION GF THE DEFICIENCY The design of Suscpehanna Units 1 a 2 provides for 28 safety related. 480V abator control centers. During the installation of these 480V mntor control center sections, it was noted that the 3/8" carriage bolts supplied for

I

~ e fastening the 480V bus splice plates were experiencing random thread failures when torqued to appxmxnately 18ft./lbs.

1 Investigation of these bolt failures revealed the following facts:

l. The 3/8" diameter carriage bolts supplied hy Cutler-Hztaer for use in the 480V bus splices were supplied as a mixed packet with 1/4" thick and

. 3/8" thick nuts.

2. The instruction manual furnished by Cutler-Hamaer for the installation of the 480V MX's did not specify the proper canbination of fasteners to be used for the bus splices; thereby permitting 3/8" carriage bolts to be mated with 1/4" or 3/8" thick nuts. In add.tiOn,, the instruction manual did not provide values for toxquing the 3/8" carriage bolts.

3. All of the holt thread failures which were detected occurred when a 1/4" thick nut was uti1ized in canbination with a 3/8" diameter carriage bolt.

Cutler-Hanaier was apprised of the above information, and they advised that the correct splice fastener was a 3/8" carriage bolt with a full 3/8" thick nut torched to 18ft./lbs. The carriage bolt threaR failure has been detatznined to have been caused by the undersized (1/4" thick) "jam" nuts.

MALYSIS OF SM. f"TY IMPLICATIONS The 480V motor control systan design was reviewed and the follawLing was concluded for the worst condition, including a postulated seismic event:

The deficiency, which involves the. actual stripping of threads on some of the carriage bolts, is concealed by washers and the nuts used to fasten the bolts. If undetected, or uncorrected, this condition could permit ting surfaces, of the bus and the bus splice plates to be loosely joined at a point which was designed to c;cry 600 amperes of load current.

Under load, such loose connections could develop arcing and overheating which could result in a fire or bus fai1ure and the loss of the actor control center.

In those cases where actual thread strippirxy had not ocnowed, the undersized nuts may have, nonetheless, caused sufficient overstress on the carriage bolts that an incipient failure of the threads could exist. Mded forces fran a seismic event could cause overstressed

.bolts to fail, loosening the bus joint. Such events could result in the situation described in the preceeding paragraph.

Since thread stripping or incipient thread stripping of these carriage bolts is a rare event and could occur in any or a11 of the safeguaxds

~tor contxol centers, the possibility of a caravan mode fai1ure exists.

The. simultaneous loss of redundant motor control center feeds, which serve vital safety related loads, could result in a safety hazard to the operation of the plant.

CORRECTIVE ACTION TAKER TO CGFIRQL THE DEFICIENT ITEM Bechtel Quality Contxol issued Nonconformance Report N'o. 2855 on 8/2/78 to identify and contxol the 480V YdX."s (twenty) present1y on site for the carriage bolt deficiency being reported.

Bechtel QK generated Managanent Corrective Action Request No. 1-27 dated August.7, 1978 in order to obtain documented evidence of Bechte1 Project

Engineering's evaluation of the cause of the condition, the corrective action required, and the condition's r@artability under 10CPR50.55(e) .

CORRECTIVE ACTION KO RESOLVE THE DEFICIENCY Cuttler-Hamoer will replace all carriage bolts and nuts used for splicing links at shipping splits on MCCs with 3/8" bolts and 3/8" thickness nuts for all MCCs already installed, wil1 replace 1/4" nuts with full-nuts (3/8") for KCs that are not yet installed, and will utilized 3/8" thick nuts for MZs current1y being manufactured. (This was documented in a ~ fran Cutler-Hanaer to Bechtel dated 8/28/78.) Cutler-Hamner has updated the 480V IKC instruction book to ixmlude the recpired torque values (18ft./lbs.) and has transmitted a revised instruction manual to the Bechtel field forces.

~ CONCLUSIONS With the replacement of all 3/8" carriage bolts and nuts on all the bus splices of all motor control centers already delivered to the SSES site with correct 3/8" bolts and 3/8" thick nuts, with the correct torquing of these fasteners to 18 ft. lbs., and with all future motor contxol centers being supplied with correct hardware, the requirements of Specification 8856-E-118 Revision 6, Paragraph 9.2.1 will have been met; the deficiency will have been corrected; and the potential safety hazard wi11 have been e1iminated.

The Bechtel generated Nonconformance Report (NCR No. 2855) will not be closed until there is Quality Control verification that the 480V MCCs bus splices have been completed in accordance with the design and vendor requirements and the atterx3ant inspections have been acccmplished.