ML17317B262

Forwards LER 79-019/01T-0

ML17317B262
Person / Time
Site:	Cook
Issue date:	06/07/1979
From:	DOLAN J E INDIANA MICHIGAN POWER CO.
To:	KEPPLER J G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML17317B263	List: ML17317B262 ML17317B264
References
AEP-NRC:00216, AEP-NRC:216, NUDOCS 7906150329
Download: ML17317B262 (3)

Text

INDIANA F MICHIGAN POV/EP.COMPANY P.O.BOX 1S BOWLING G R E EN STATION NEW YORK, H.Y.1000a Donald C.-Cook Nuclear Plant Units 1 and 2 Docket Hos.50-315 and 50-316 License Nos.DPR-58 and DPR-74 June 7, 1979 AEP:HRC:00216 i'r.Dames G.Keppler, Regional Director Office of Inspection and Enforcement U.S.tluclear Regulatory Commission Region Ill 799 Roosevelt Road Glen Ellyn, Illinois 60137

Dear I'1r.Keppler:

This letter and the accompanying report in the orm of six attachments supplement fir.D.V.Shaller's letter of flay 26, 1979 concerning the small cracks identified in the main feedwater elbows at the Donald C.Cook Plant Units 1 and 2.The report, submitted in accordance wi th Technical Specification 6.9.1.8.i, detail s the results of AEP's investigation into this matter, the corrective actions taker, the test program to be implemented on the feedwater system, and a safety evaluation of this event.On ttay 19, 1979 Unit t<o.2 was brought to cold shutdown condition to determine the source of non-radioactive water that was building up in the containment sump.Investigation on Nay 20, 1979 revealed small cracks in elbows of the main feedwater lines to steam generators 1 and 4.f1r.Shaller informed i1r.K.R.Baker, NRC Region III Inspector, of these findings that same day.In each of the four steam generator secondary lines, a vertical 14-inch carbon steel feedwater pipe is welded to a 14-inch by 16-inch reducer, which in turn is welded to a 16-inch carbon steel elbow.This 16-inch elbov is welded directly to a 16-inch low alloy nozzle on the steam generator.

The cracks were found in the 16-inch feedwater elbows adjacent to the feedwate1 elbow,'.tean gererator nozzle welds.These cracks initiated outside of the heat affected zones of the welds.6'ry Yir.'ames G.Keppler Regional Director-2-June 7, 1979 AEP:NRC:00216 IExamination of the elbows has indicated the cracks initiated at the top'of'the inner surface of the elbow at a machined discontinuity required for the weld-end preparation.

'I Radiographic examinations of the nozzle/feedwater line weld regions for Unit 2 steam generators Nos.2 and 3 showed indication of cracks in the same area of the elbows.The same areas in Unit I were subsequently radiographed and indications were found in the 16-inch elbows of the,eedwater lines to steam generators No.2,3 and 4.This discovery of crack indications was promptly reported to Region III.We were not able to detect the presence of indications in the 16-inch elbow to steam generator No.I in Unit I using radiographic techniques becauseof the unique conditions of the backing ring.Subsequent liquid penetrant examination indicated cracking in this elbow.The wall thickness of the 16-inch elbow is approximately 50 percent.greater than that of the steam generator nozzle.To compensate for this differ nce in wall thickness, the weld preparation included machining and beveling a step on the inside of the elbow to match the thickness of the steam generator nozzle at the point of the weld.Stresses concentrated in this thinner section adjacent to the weld and were magnified at the point of discontinuity.

The highest design stress point in the feedwater line inside the containment is at the 90'4-inch elbows at the bottom of the vertical riser.The 14-inch elbows are in the same vertical plane as the affected 16-inch elbows.Five of the 14-inch elbows were radiographed.

No indications were found.Samples of the cracked areas of the 16-inch elbows were sent to two laboratories for retallurgical examination.

Reports from the metal-lurgical examinations showed that the crack propaga ion.was caused by high-cycle fatigue assisted by corrosion.

Further details of'the metallurgical examination are described in Attachment 2.After remval of the 16-inch elbows, the inside of the Unit 2 steam generator nozzles were examined by the liquid penetrant method.Light, pitting and intermittent linear indications were noted on the nozzle counter-bores.Subsequent visual inspection of the Unit I nozzles showed similar pitting in the nozzle counterbore region.We are replacing the 16-inch elbows to all steam generators in Units I and 2.These new elbows do not have the sharp discontinuities on the pipe inner surface, and the strength of the elbow in the weld area has been increased.

The pits and indications on the steam generator nozzles Hr.James G.Keppler Regional Oi rector-3-June 7, 1979 AEP: NRC: 00216 are being blended out.The stress concentration at the nozzle counter-bore is being reduced with the addition of a 1/2-inch radius fillet.Me are implementing a program to determine the characteristics of the high cycle fatigue.This program includes the installation of strain, temperature, pressure and vibration instrumentation at significant points on the piping system of two feedvater lines in Unit 2.Oetails of the new 16-inch elbow, the nozzle repairs and instrumentation.

are in Attachment 5.The safety implications of this event at Cook Nuclear Plant have been carefully analyzed by our safety review committees.

It was concluded that the condition identified did notadversely affect the health and safety of the general public.It divas.concluded that the return of-the units to power with the newly designed elbows will have no adverse effect on the general public.Operation of Unit 2 with the instrumentation program will indicate whether there is any need for further corrective action.A safety evaluation is given in Attachment 6.Me expect to begin startup of Unit 2 by June 13, 1979 and Unit 1 by June 20, 1979.Very truly yours, JED kb Attachrrints ohn E.Dolan Vice President cc: R.C.Callen G.Charnoff R.S.Hunter R.M.Jurgensen N.C.t1oseley, NRC 0.V.Shaller, Bridgman R.E.Masse RO:ZZZ P.W.Steketee, Esa..R.Walsh, Esp.G.Charnoff, Esa.R.C., Callen MPSC J.M.Hennigan G.Olson PNSRC J.F.Stietzel Dir., ZE (40 copies)Diz., MZPC (4 copies)