ML19343D215

Part 21 Rept Re Stress Corrosion Cracking in Reactor Coolant Pump Motor Heat Exchanger Tubes,Initially Reported on 801202.Eddy Current Test Was Performed.Cracked Tubes Were Plugged

ML19343D215
Person / Time
Site:	Sequoyah
Issue date:	03/27/1981
From:	Mills L TENNESSEE VALLEY AUTHORITY
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
REF-PT21-81-395-000 10CFR-050.55E, 10CFR-50.55E, PT21-81-395, PT21-81-395-000, NUDOCS 8104100222
Download: ML19343D215 (3)

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PRELIMItMRY EVALUATION OF THE' ATTACHED REPORT ITOICATES LEAD R FOLL0hU? AS SFOWN BELOW:

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Mr. JamesJ. O'Reilly, Director Office of Inspection and Enforcement U.S. NuclearMegulatory Comission Region II - Sdite 3100 101 Marietta St et Atlanta, Georgia 0303

Dear Mr. O'Reilly:

SEQUOYAH !!UCLEAR PUiNT UNIT 2 - STPISS CORROSION CRACKING IN TUBING ON THE PIAC"0B COOLANT PUMP OIL COOLERS - SQRD-50-326/81 FINAL P2 PORT The subject deficiency was initially reported to !!RC-0IE Inspector R. W. Wright on December 2, 1980, in accordance with 10 CFR 50.55(e) as NCR SQH NEB 8028. Interim nports were sub:r.itted on January 2 and

-February 3, 1981. Enclosed is our final report. We consider 10 CFR 21 applicable to this deficiency.

If you have any questions concerning this matter, please get in touch with D. L. Lambert at FTS 857-2581.

Very truly yours, TENNESSEE VALLEY AUTHORITY L. M. Mills, Manager Nuclear Regulation and Safety Enclosure Mr.VictorStello,Jr., Director (Enclosure)i[

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t Office of Inspection and Enforcement U.S. Nuclear Regulatory Co::: mission Washington, DC 20555 I

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,I ENCLOSURE

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SEQUOYAH NUCLEAR PLANT UNIT 2 STRESS CORROSION CRACKING IN T3ING ON THE REACTOR COOLANT. PUMP MOTC'R C:L CCOLERS -

SQED-501328/81-11 10 CFR 50.55(e)

' FINAL -REPORT Description o

_y The 'Sequoyah'unitI1 reactor coolant'pu=p motor. lubricating oil coolers developed excessive tube leakage during the hot functional test due to stress corrosion cracking (SCC) in the tube =aterial. Examination of the tube aterial removed from one such heat exchanger. revealed that the tubes were of admirality brass which has been found to be s.sceptible to stress corrosion cracking in this application. The cracking is due :to the presence of a==enia, which in conjunction with ~

residual and' operating stresses, causes the stress

• corrosion cracking.

The a :enia present is apparently a product of the deco: position of -

hydrazine frot the co:ponent cooling syster water treatment.

I:plications to S'equoyah unit 2 were investigated, and it was determined that these heat exchanger tubes were also cade :f ad irality brass.

Safetv Inclications-Tube leakage'which could have resulted from SCC would al' low water to

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mix with the lubricating oil for the reactor coclant pump motor bearings. Water. coring in contact with the bearings?cculd possibly cause thec _to seize. This -could reduce.the pu=ps' coastdown time during a reactor-trip, 'which could adve'rsely affect the safety of.~ the plant.; Continued' forced ' circulation of ' reactor coolant is required in the short ter after reactor trip.to remove the initial decay heat l ead. # Although all four reactor coolant pu=ps 'are not required for-uniform reactor' coolant syste: cooldown,.this condition is ccn'servatively assured to be a degradation--in safety.

Corrective' Action A ; hough ~ 1t has been deter:ined that ~ the " wilt 2 reacter.ccolant pu=p motor

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heat exchangers have not leaked, TVA has' perferred an eddy current test en the tubing. A s=all number of tubes (apprcxina ely 3 out of 354 perL heat --

exchanger) had indications.cf cracks extending 20 percent er greater through the wall thickness.

In accordance with Westinghouse

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recc :endaticns, TVA 'has plugged these tubes..

The co. ponent cooling system has been flushed and the a :cnia recoved.

, The hydrazine,.which apparently decomposed and produced the a==onia, was intended to be used only on an ' interim-basis and will not be reintroduced into the~syste=.

Therefo.e,; tubing =ade of.ad=irality brass will not. be susceptible to further stress corresf on cracking.

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