ML20085L918

AO BFAO-7415W:on 740312,during Startup,Rod Sequence Control Sys Automatically Removed from Operation at 26% Thermal Power.Caused by Wrong Setting of first-stage Pressure Switches.Switches Reset

ML20085L918
Person / Time
Site:	Browns Ferry
Issue date:	03/22/1974
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085L916	List: ML20085L918 ML20085L926
References
AO-BFAO-7415W, NUDOCS 8311070020
Download: ML20085L918 (3)

Text

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/ TENNESSEE VALLEY AUTHO AITY MKH.

CHATTANOOGA, TENNESSEE l. e 37401 L #~.

50-259 2%J March 22, 1974 $$5[sQ 1/r. John F. O' Leary, Director Directorate of Licensing Office of Regulation U.S. Atomic Energy Co=cission  ;

Washington, DC 20545

Dear Mr. O'Learf:

TENNESSEE VALLEY AUTIiORITY - BROWS FERRY UUCLEAR PLAIrf UNIT 1 -

DOCKET no. 50-259 - FACILITY OPERATING LICENSE DPR ABNORI'AL OCCURRE'!CE REPORT BFAO-7417<T The enclosed report is to provide details concerning the rod sequence control r/ stem that was automatically re=oved from operation at 26-percent ther"1 power which occurred on 3rowns Ferry Duclear Plant unit 1 on 2hrch 12,1974, and is submitted in accordance with Appendix A to Regulator / Guide 1.16, Revision 1, October 1973 Very truly yours, .

TEICIESSEE VALISY ALTdORITY Q l 1%,

?[a E. F. Thomas b (4 Director of Power Production 2  % < L dt ' H

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CC (Enclosure): \$ (, 4',

Mr. Norman C. !bseley, Director Region II Regule. tory Operations Office, USAEC Q W' I"Q 5

- - - - 230 Peachtree street, Inr., Suite 818 Atlanta, Georgia 30303 O ,

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8311070020 740723 1

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ABNORMAL OCCURRENCE REPORT Report No.: BFAO-74174 Report Date: Parch 22, 1974 Occurrence Date: March 12, 1974 .

Facility: Browns Ferry Nuclear Plant unit 1 Identification of Occurrence The rod sequence control system (RSCS) was automatically removed from operation at 26-percent thew power. . .

Conditions Prior to Occurrence ,

The reactor was undergoing normal startup following a load rejection test from.

75-percent ther=al power on March 11, 1974 Description of Occurrence Technical specifications require the RSCS to be operable whenever the reactor is in the startup or run modes below 30-percent rated power. During a hot startup on March 12, 1974, the RSCS was automatically re=oved from service at 26-percent thermal power and re=ained inoperable for, a period of 40 minutes. No control rods were r.oved while the RSCS was inoperable.

Analysis of Occurrence Two turbine first-stage pressure switches are used as a sensing device to deter =ine -

the 30-percent power operability of the RSCS. Both switches must operate to remove the RSCS from service. The unique relationship between turbine first-stage pressure and reactor the.-.a1 power is affected by a number of factors which affect turbine-generator perfor=ance and unit efficiency. In this instance, the setting of the pressure switch was determined on October 31,~1973, when the feedwater heaters were not'in service. Investigation.following r,he occurrence shews that the first-stage pressure with heaters in service and with heaters out of service varies significantly for equivalent thermal power conditions.

This variance accounts for the RSCS being recoved from service at 26-percent-power. The rod sequence control system restricts withdrawals and insertions of the control rods to prespecified. sequences established to -assure.that the

==4mm individuel control rod worth before withdrawal shall.be less than 1.25-percent delta K. Its purpose is to assure that the results of a control N C rod drop accident will not exceed a max 4== fuel energy content of 280 calories -

- per gre::1 Technical specifications require that the reactor shall be immediately shut down if the RSCS is inoperable when required. "I= mediately" is defined in the technical specifications as ". . . as 'soon as practicable considering the safe operation of the unit and the importance of the required action." lHad the.

l- operator either withdrawn or inserted control rods-with the RSCS out of service,'

t he would have been in violation of the intent of the -technical specification.

1 No unsafe consequences could result from not moving control rods during the brief period the RSCS was out of- service. There was no controlled way to reduce

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I I reactor power below the 26-percent point without moving' control rods, since the c .

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Analysis of Occurrence (continued) recirculating puros were on mini =m speed. The only way the operator could have shut down the plant would have been to scrc=. This was not warranted by the situation and not required by the technical specifications under the definition of "ir::nediately."

Corrective Action A determination of first-strSe pressure with the feedwater heaters in service has been cade and the pressure switches set to this value with conservatism.

i JRC: BAH O

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