PNO-I-79-001, on 790922,stable Natural Circulation Flow Was Lost.Caused by Diminishing Heat Input from Core

PNO-I-79-001:on 790922,stable Natural Circulation Flow Was Lost.Caused by Diminishing Heat Input from Core

ML20125B160
Person / Time
Site:	Three Mile Island
Issue date:	09/25/1979
From:	Conte R, Keimig R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
To:
References
PNO-I-79-001, PNO-I-79-1, NUDOCS 7910240452
Download: ML20125B160 (2)

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- Date: September 25,-1979 l

w . .a i PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-I-79-01 1 l

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This creliminary notification constitutes EARLY notice of events of POSSIBLE safety or ouolic interest slanificance. Tne information oresented is as initially received witnout verificat1on or evaluation and is basically all tnat is known by IE staff on tnis cate.

Facility: Metropolitan Edison Company Three Mile Island, Unit 2 Middletown, Pennsylvania Docket Number 50-320

Subject:

NATUPAL CIRCULATION TRANSIENT 5etween 5:00 p.m. and 7:00 p.m. on September 22, 1979, the first indications of anticipated natural circulation flow variations through the "A" loop steam generator were observed. This loss of stable natural circulation flow has been expected to occun as a result of diminishing heat input from the core. The "A" loop has been the primary means of decay heat removal since the enset of natural circulation on April 27, 1979. Prior to the transient the "A" loop differential te ;erature was 7.30F with the "A" Hot Leg Temperature (T h ) 3t 157 gcF. The

ean dif'erential temperature (inci ative of a lower than ner:31 pretransient n.n ioop ih ceaked at 160.c.a.r. .he /.;o-r nan loop flow.) was 1:.r-- :sr.en11e the n i differer.tiai ;c perature re-establishec at approxirately 2:00 a. . , September 7 ,. , 't c-

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The highest reading inc:re therroccuple ;eaked at 237.SCF aith a pretransient reacing Of 235.70F. A similar but less noticeable transient occurred between 7:00 p.m., September 23,1979, and 1:00 a.m. on September 2',1979. These -

trar.sients are expected to continue.

"edia ' :erest is expectec beca.se of c:n:inuing sensitivity to Trree "ile

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Distribution: Transmitted H St //d5I Chairman Hendrie Commissioner Bracfore S. J. Chilk, SECY Commissioner Kennedy Commissioner Ahearne C. C. Kammerer, CA Commissioner Gilinsky ACRS (For Distribution) _

Transmitted: MNBB //o7 P. Bldg //to IE:XOOS //00 (IE:HQ Dist.

L. V. Gossick, EDO~ H. R..Denton, NRR H. L. Ornstein, EDO R. C. DeYoung, NRR J. J. Fouchard, PA R. J. Mattson, NRR Landow //27 (6 min /page' N. M. Haller, MPA D. Vassallo, NRR J. J. Cummings, 0IA R. G. Ryan, OSP D. Eisenhut, NRR H. K. Shapar, ELD SS Bldg //of JMAIL)

W. J. Dircks, NMSS R. Minogue, SD Region II //75' S. Levine, RES IE:XOOS 4 _. s Region III

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