ML19259D519

Environ Incident 50-289/75-07:on 750815,water Discharged from Mechanical Draft Cooling Tower Below Ambient River Temp.Caused by Operator Switching to Cooling Tower Fan W/Greater Cooling Capacity & Lack of Proper Temp Monitoring

ML19259D519
Person / Time
Site:	Three Mile Island
Issue date:	08/22/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
GQL-1418, NUDOCS 7910240781
Download: ML19259D519 (4)

Text

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FILE: 88Y LTR TWX RPT OTHER FROM: Metropolitan Edison Co. DATE OF DOC D ATE R EC'D Reading, Penna

• 8-22-75 8-26-75 XXXX I R.C. Arnold XXX ORIG CC OTHER SENT NRC POR TO: SENT LOCAL PDR M J.P. O'Reilly NONE INPUT NO CYS REC'D DOCKET NO:

CLASS UNCLASS PROPINFO 50-289 1

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ENCLOSURES:

DESCRIPTION: -

Enviro. Incident # 75-07, on 8-15-75, ccn- r< .

cerning Excessive Cooling of Mechanical Draft C.I Cooling Tower (MDCT) discharge.......

( 1 cy. Ltr. rec'd) .

PLANT N AME: Three Mile Island # 1 hJ VCR 8-27-7),

FOR ACTION /INFORMATION

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a2 -4 Mr. J. P. O'Reilly, Director

, Office of Inspection and Enforcement, Region 1 U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406 .

Dear Mr. O'Reilly:

Operating License No. DPR-5]

Docket No. 50-289 Three Mile Island Nuclear Station Unit 1 Environmental Incident Report No. 50-289/75-07 In accordance with the Environmental Technical Specifications for Three Mile Island Nuclear Station Unit 1, we are reporting the following Environmental Incident:

(1) Raporting Number: E.I. 50-289/75-07 .

(2a) Report Date: August 22, 1975 (2b) Incident Date: August 15, 1975 (3) Facility: Three Mile Island Nuclear Generating Station Unit 1 (TMI-1)

(4) Identification of Incident:

Excessive cooling of Mechanical Draf t Cooling Tower (MDCT) discharge, is a violation of the Environmental Technical Specifications.

paragraph 2.1.a (1) , and constitutes violation of a Limiting Concition for Operation.

(5) Conditions Prior to Occurrence: 1459 293 The reactor was at Steady State Power with major plant parameters as follows:

Core: 100%

S086

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• Page 2 Elec.: 823 MWe RC Flow: 140 x 10 lb/hr RC Pressure: 2155 psig RC Temp.: 579 F PRZR Level: 240 in.

PRZR Temp. : 650 F (6) Description of Incident:

o On August 3rd, water with a temperature 5.5 F below the ambient river tempersture (90 F at the time) was discharged from the Mechanical Draf t Cooling Tower at TMI-1. This temperature drop occurred when the Control Room Operator switched from the "A" Cooling Towcr fan to the "C" f an, which has a slightly greater cooling capacity. This action was taken as a precaution against conflicting temperature differential readings on the computer and Control Room (AT) recorder; however, the cooling occurred more rapidly than had been anticipated. Within about 30 minutes after it was realized that a limiting condition had been exceeded, the Control Room Operator changed the fan combination to restora the temperature differential to within the allowable range.

(7) Designation of Apparent Cause of Incident:

Procedure, in that the procedure governing MDCT operation did not provide enough guidance on switching cooling tower fans.

Personnel, in that the Control Room Operator failed to properly monitor the efiluent temperature and AT recorder af ter fan switching to insure that they had stabilized. Had this been done the decreasing effuent temperature might have been observed and there would thus have been a greater opportunity to take i==ediate corrective action.

Material, as a possible contributing cause of the occurrence, in that the computer and AT recorder readings appeared to differ by as much as 2 F, which presented a confusing choice to the Control Room Operator.

(8) Analysis of the Incident:

It is believed that the negative temperature differential of this report i did not cause any environmental damage in that the condition lasted only a .ahort time and was not so severe as to greatly alter the ambient temperature of the river.

(9) Corrective Action:

The only im=ediate corrective action taken was to restore the temperature differential to within the allowable range by changing the cooling tower fan combination.

1459 294

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Page 3 At a meeting held imediately af ter the incident was reported, the Plant Operations Committee (PORC) reviewed and gave its approval of this action. In addition, they recomended to the Station Superintendent that the following long-term corrective actions be taken:

a. Add a section *to the procedure governing MDCI operation to provide better guidance on the switching of fans. .

b. Caution all Control Room Operators to use the AT recorder when adjusting the temperature differential and to monitor effluent temperature and temperature differential when switching fans or performing other evolutions which will affect these parameters.

Jc. Check the various temperature indicating instruments to insure that they are reading within their design tolerances.

. The Station Superintendent concurred with these recommendations and has

.taken the necessary steps to insure their implementation.

-(10) Failure Data:

Although the present incident did not result directly from a material

' failure, E.I. 's 74-1 and '74-8 (reports dated May 31, and July 24, 1974,

. respectively) both involved excessive negative temperature differentials and to some extent both involved material (instrument / alarm) failures.

Sincerely, Signed: R. C. ARNOLD R. C. Arnold Vice President RCA:JFV:pa ec: Director Division of Reactor Lic :nsing U.S. Nuclear Regulatory Comission Washington, D.C. 20555 File 20.1.1/7.7.3.11.1 1459 295 e

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