ML18219C264

LER 1977-004-00 Re Failure of Cooling Coil on CPN-4

ML18219C264
Person / Time
Site:	Cook
Issue date:	02/11/1977
From:	Jurgensen R Indiana Michigan Power Co
To:	James Keppler NRC/RGN-III
References
LER 1977-004-00
Download: ML18219C264 (13)

Text

UA. NUCLEAR REGULATORY COMMISSION DOCKET NUMBER hlRC FORM 195

~

12 76) 50-315 FI LE NUMBER

.NFC DISTRIBUTION FoR PART 50 DOCKET MATERIAL INCIDENT REPORT TPo FROM: DATE OF DOCUMENT

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Indiana & Michigan Power, Company 2/11/77 Rr J~-G. Kepis.er 'Bridgman, Michigan DATE RECEIVE 0

2/16/77 R, W. Jurgensen HLETTER. - - ONOTORI2EO PROP INPUT FORM NUMBER OF COPIES RECEIVED

@OR

-ACOPY I G IN AL~-,gUN C LASS I F I E D One signed copy DESCRIPTION ENCLOSURE Ltr. trans the following: ,- 15/77-04)~n 1/28/77 concerning..' ure of cool~.coil on CPN 4i ~ ~ ~ ~

o ACKNQWL'ZDGZD (4-P)

PLANT NAME:

j)0 NOT REMOVE Cook Unit No, 1 NOTE: IP PERSONNEL EXPOSURE IS INVOLVEd SEND DIRECTLY TO KREGER/J, COLLINS FOR ACTION/INFORMATION 2 16 77 RJL BRANCH CHIEF! Ziemann W 3.CYS POR ACTION LICE ASSTo: Diggs W. - CYS

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INTERNAL D IST Rl BUTION EG PILE NRC PDR

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MIPC SCHROEDER/IPPOLITO HOUSTON NOVAK/CHECK GRIMES CASE BUTLER HANAUER TEDESCO/MACCARY EISENHUT BAER SHAO VOLuIER/BUNCH KREGER/J COLLINS EXTERNAL DISTRIBUTION CONTROL NUMBER LPDR! St Jose h Mic ~

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jd 74 NRC FORM 196 (2 76)

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DONALD C. COOK NUCLEAR PLANT P.O. Box 458, Bridgman, Michigan 49106 February ll, 1'977 Mr. J. G. Keppler, Regional Director fi Of ce of Inspection and Enforcement United States Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, IL 60137 Operating Li cense DPR-58 Docket No. 50-315

Dear Mr. Keppler:

Pursuant to the requirements of Appendix A Technical Specifications and the United States Nuclear Regulatory Commission Regulatory Guide 1.16, Revision 4, Section 2.a, the following report is submitted:

RO 50-315/77-04 Si nce rely,

~ R. M. Jurgensen Plant Manager EQ/mj cc: R. S. Hunter POCRHED J. E. Dolan 'P 5HilQ G. E. Lien R. J. Vollen 8PI R. C. Callen MPSC 5 K. R. Baker RO: III UCg~R NQVLATORY COMMISSlOH Moll Sod Ion R. Malsh, Esq.

P. M. Steketee, Esq.

G. Charnoff, Esq.

G. Olson J. M. Hennigan PNSRC R. S. Keith Dir., IE (40 copies)

Di r., MIPC (4 copies)

form No. 4494 A

y, LICENSEE EVENT REPORT CONTROL BLOCK:

1 uCENSEE LICENSE EVENT NAME LICENSE NUMBER TYPE TYPF.

fop'] I" I 0 C C I O O O O O O O 0 0 4 1 1 1 1 ~01 7 89 14 15 25 28 30 31 32 REPORT REPORT CATEGORY TYPE SOUACE DOCKET NUMBEA IVENI OATF Rl PORT DATE toOgcowv~ ~T L 0 5 0 0 3 1 5 0 1 2 8 7 7 0 2 1 1 7 7 7 8 57 58 59 Bo 81 68 89 74 75 00 I

EVENT, DESCRIPTION QOg See Attachment 89 7 8 9 80 QO~]

7 8 9 80

~os 7 8 9 80 QOQ -3 5 -04 7 8 9 FAME 80 SYS'1fu CAUSE COMPONENT COMPONENT CODE CODE " COMPONENT CODE SUPPUER MANUFACTURER

[oa~j ~ZZ ~e H T 5 X C H A T 3 3 0 7 8 9 10 11 12 17 47 48 CAUSE OESCRIPTION foOI See Attachment 7 8 9 80 toes 7 8 9 80

~10 7 89 FACAIIY METHOD OF 80 STAIUS 55 POWER OTHER STATUS DISCOVERY DISCOVERY OESCF8PTION

~oo o 44 b

45

. Coil Was Leaking 7 8 9 10 12 13 48 80 FORM OF AMOUNT OF ACTIVITY LOCATiON OF RELEASE

~ 7 8 9 10 11 44 45 80 PERSONNEL EXPOSURES 7 89 12 13 80 PERSONNEL INSURIES NUMSER DESCRIPTION

~>4 ~00 0 HII 7 89 11 12 80 OFFSITE CONSEQUENCES Q~g NA 7 89 80 LOSS OR DAMAGE TO FACILITY TYPE DESCRIPTION Q~g Z HA 7 89 10 80 PUBLICITY HA 7 8 9 80 AOOITIONAL FACTORS Jig HA 7 89. 80 7 89 80 David G. Mizner (616) 465-5901 PHONE:

GPO 881 ~ 667

0 FAILURE OF COOLING COIL ON CPN-4 Investi ation Re ort Leakage had been detected in hay, 1976, from the 83 steam generator main steam line containment penetration (CPN-4) cooling coil on the containment side of the penetration. The cooling coil water supply was valved out and the coil was then examined during the refueling outage. Examination showed that the cooling coil was cracked in the first pass in several locations between 6 o'lock and 8 o'lock. The cooling coil was removed in February, 1977 by grinding the attach-ment welds. Areas of'the carbon steel penetration head adjacent to and under-neath the austenitic stainless steel cooling coil were magnetic particle examined.

Cracks in the head were found in the same relative location as the cooling coil cracks, that is, along the attachment seam and adjacent plug welds. Subsequent grinding to remove the cracks indicated that they were less than one half inch in depth.

Examination indicated that the cracking of the cooling coil was typical of stress corrosion, and this was subsequently confirrred by metallographic examination.:

Cracking in the penetration was first thought to be due to cracks propagating from the cooling coil through the attachment welds. However, subsequent magn'etic pa'rticle examination'showed that some of the cracks were outside the plug welds and would not have propagated from the cracks in the cooling coil. A boat sample containing a magnetic indication was removed from the penetration for metallographic examination. This indicaiion was found to be composed of several intergranular cracks. It was readily apparent that these cracks were not due to fatigue, but were typical of stress corrosion.

Under normal cooling water flow, stress corrosion cracking of the cooling coil could not occur. Componen cooling water supplied to these coils is demineralized and inhibited with technical grade sodium nitrate. For the corrodant to have become sufficiently concentrated, the cooling water flow must have been reduced so that alternate wetting and drying occurred in the cooling coil. Stress cracking of the cooling coil permitted water to enter the space between the cooling coil and

.penetration head. Similar wetting and drying is believed to have occurred in this annulus and caused concentration of a corrodant which initiated cracking in the penetration head. Cracking occurred at the attachment welds which would have higher stresses than the surrounding material which is an annealed forging.

Neither corrodant which caused cooling coil failure and cracks in the penetration head has been identified Stress cracking of austenitic stainless steel. is relatively common and easily explained. Stress cracking of low strength carbon steel is unexpected and w are attempting to identify 'the corrodant. The most likely culprit is sodium nitrate formed by oxidization of sodium nitrite, which is added to the cooling water as a corrosion inhibitor. Intergranular stress corrosion cracking has been reported by nitrates in low carbon steels with carbon less than .22K.

The reduction in water flow in the cooling coil was most likely due to blockage-in the line that existed vhen the unit was started. There are two cooling coils on each penetration head. Th cooling water to the coils is supplied in parallel, with a common inlet valve and outlet check valve. Although these systems were flushed, the flushing procedure that was used would not indicate blockage of one of the two coils.

4 The cooling coil on CPN-3 is fed by the same inlet valve as the failed cooling coil, and could have been subject to the same concentration mechanism. thatThethis line was flushed before plant operation and therefore it is apparent line was originally clean. Cooling water flow through the two coils on CPN-3 have been subsequently checked and both coils have been found to be satisfactory.

Peretimt examination has been performed and no indications were found. There is reasonable assurance that this coil was not subject to the same alternate wetting and drying and is still satisfactory It is our intention, however, to remove the cooling coil on CPN-3 and examine the underlying penetration at a subsequent, major outage and when a replacement cooling coil is available, but no later than our next refueling outage.

Stress analysis of the penetration head has been reviewed with the manufacturer.

Analysis indicates that stresses in the area where cracks occurred are low, and that they decrease. substantially beneath the surface.

Analysis of chips taken from the cracked head area indi cate that the material conforms to the specified material, SA350, Grade LF1. Test reports from the material supplier were verified and in accordance with the specifi cation.

Continued operation of the plant without examining the surface of the CPN-3 penetration head does not have an adverse effect on the safety of the plant or public. CPN-3 has performed satisfactorily with the same cooling water for an additional 6 1/2 months after failure of the coil on CPN-4.

DONALD C. COOK NUCLEAR PLANT P.O. Box 458, Bridgman, Michigan 49106 February 11, 1977 Mr. J. G. Keppler, Regional Director Office of Inspection and Enforcement United States Nuclear'Regulatory III Commission'egion 799 Roosevelt Road Glen Ellyn, IL 60137 Operating Li cense DPR-58 Docket No. 50-315

Dear Mr. Keppler:

Pursuant to the requirements of Appendix,A, Technical Specifications and the United States Nuclear Regulatory.,Commission Regulatory Guide 1.16, Revision 4, Section 2,a, the following report is submitted:

RO 50-315/77-04 Si nce rely,

~ R. W. Jurgensen Plant Manager RWJ/mj cc: R. S. Hunter J. E. Dolan G. E. Lien R. J. Vollen BPI R. C. Callen MPSC K. R. Baker RO: III R. Walsh, Esq.

P. W. Steketee, Esq.

G. Charnoff, Esq.

G. Olson J. M. Hennigan PNSRC R. S. Kei th Dir., IE (40 copies)

Dir., MIPC (4 copies)

Form No. 4494 LICENSEE EVENT REPORT CONTROL BLOCK: (PLEA8E PRINT ALL REQUIRED INFORIVIATION) 6 l.CEN SEE LICENSE EVENT NAME LCENSE NUMBER TYPE T YPF.

[op'j MI 0 c c I o 0 0 0 0 0 0 0 0 4 1 1 1 1 ~0011

~

7 8.9 '14 15 25 26 30 31 32 REPORT REPORT CATEGORY TYPE SOURCE OOCKFT NUMBER EVENI OATF ro>>oRT oATr.

IoO~I cow~ T L 05 0 0 3 '1 5 0 1 2 8 7 7 0 2 1 1 7 7 7 8 57 58 59 60 61 68 69 74 75 80 EVENT OESCRIPTION Qo 2 See Attachment 7 8 9 80 7 89 80 7 8 9 80

~OS 7 89 80 toOI LE - -"3 0 7 8 9 PRME 80 SYSTEM CAUSE COMPONENT COMPONENT COBE COOE COMPONENT COOE SUPPLE:R MANUFACTURER 7

IU8 9 LTXzl 10 LNJ 11 12 H T E x c H 17 A

43 44 T 3 3 0 47 N

48 CAUSE OESCRIPTION toOs] See Attachment 7 8 9 80

[OD9) 7 8 9 80

~10 7 89 80 Q~g 7 8 FAClllrY STATUS

~s 9

'oo 10 0 POWER o

12 13 OTHERSTATUS NA 44 METHOD OF OISCOVERY b

45 46 Coil Was OISCOVERY OESCRIP TION Leaking 80 FORM OF AMOUNT OF ACTIVITY LOCATION OF RELEASE NA

-7 8 9 10 11 44 45 '80 PERSONNEL EXPOSURES NUMBER TYPE OESCRIPTION pig ~00 0 Z NA 7 89 11, 12 13 80 PERSONNEL INJURIES NUMBER OESCRIPTION

~00 0 NA 7 89 11 12 80 OFFSITE CONSEQUENCES Q~g NA 7 8 9 80 LOSS OR OAMAGE TO FACILITY TYPE DESCRIPTION

~16 Z NA 7 89 10 80 PUBLICITY

[iirJ NA 7 89 80 AOOITIONAL FACTORS

[ii~] NA 7 89 80 7 89 80 David G. Wizner" (616) 465-5901 NAME. PHONE:

or o eer. eel

e FAILURE OF COOLING COIL'ON CPN-4",

Investi ation Re ort Leakage had been detected in tray, 1976, from the'$3 steam generator main steam line containment penetration (CPN-4) cooling coil on the containment side of the penetration. The cooling coil water supply was valved out and the coil was then examined during the refueling outage. Examination showed that the cooling coil was cracked in the first pass in several locations between 6 o'lock and 8 o'lock. The cooling coil was removed in February, 1977 by grinding the attach-ment welds. Areas of the carbon steel penetration head adjacent to and under-neath the austenitic stainless steel cooling coil were magnetic particle examined.

Cracks in the head were found in the same relative location as the cooling coil cracks, that is, along the attachment seam and adjacent plug welds. Subsequent grinding to remove the cracks indicated that they were less than one half inch in depth.

Examination indicated that the cracking of the cooling coil was typical of stress corrosion, and this was subsequently confirmed by metallographi c examination;.

Cracking in the penetration was first thought to be due to cracks propagating from the cooling coil through the attachment welds. However, subsequent magnetic particle examination showed that some of the cracks were outside the plug welds and would not have propagated from the cracks in the cooling coil. A boat sample containing a magnetic indication was removed from the penetration for metallographic examination. This indication was found to be composed of several intergranular cracks. It was readily apparent that these cracks were not due to fatigue, but were typical of stress corrosion.

Under normal cooling water flow, stress corrosion cracking of the cooling coil could not occur. Component cooling water supplied to these coils is demineralized and inhibited with technical grade, sodium nitrate. For the corrodant to have become sufficiently concentrated, the cooling water flow must have been reduced so that alternate wetting and drying occurred in the cooling coil. Stress cracking of the cooling coil permitted water to enter the space between the cooling coil and penetration head. Similar wetting and drying is believed to have occurred in this annulus and caused concentration of a corrodant which initiated cracking in the penetration head. Cracking occurred at the attachment welds which would have higher stresses than the surrounding material which is an annealed forging.

Neither corrodant which caused cooling coil failure and cracks in the penetration head has been identified. Stress cracking of austenitic stainless steel is relatively common and easily explained. Stress cracking of low strength carbon steel is unexpected and we are attempting to identify the corrodant. The most likely culprit is sodium nitrate formed by oxidization of sodium nitrite, which is added to the cooling water as a corrosion inhibitor. Intergranular stress corrosion cracking has been reported by nitrates in low carbon steels with carbon less than .22K.

The reduction in water flow in the cooling coil was most likely due to blockage in the line that existed when the unit was started. There are two cooling coils on each penetration head. The cooling water to the coils is supplied in parallel, with a common inlet valve and outlet check valve. Although these systems were flushed, the flushing procedure that was used would not indicate blockage of one of the two coils.

'0 The cooling coil on CPN-3 is fed by the same inlet valve as the failed cooling coil, and could have been subject to the same concentration mechanism. The line was flushed before plant operation and therefore it is apparent that this line was originally clean. Cooling water flow through the two coils on CPN-3 have been subsequently checked and both coils have been found to be satisfactory.

Penetrant examination has been performed and no indications were found. There is reasonable assurance that this coil was not subject to the same alternate wetting and drying and is still satisfactory It is our intention, however, to remove the cooling coil on CPN-3 and examine the underlying penetration at a subsequent major outage and when a replacement cooling coil is available, but no later than our next refueling outage.

Stress analysis of the penetration head has been reviewed with the manufacturer.

Analysis indicates that stresses in the area where cracks occurred are low, and that they decrease substantially beneath the surface.

Analysis of chips taken from the cracked head area indicate that the material conforms to the specified material, SA350, Grade LF1. Test reports from the material supplier were verified and in accordance with the specification.

Continued operation of the plant without examining the surface of the CPN-3 penetration head does not have an adverse effect on the safety of the plant or public. CPN-3 has performed satisfactorily with the same cooling water for an additional 6 I/2 months after failure of the coil on CPN-4.

s, ~E