ML20085H114

AO BFAO-50-260/7415W:on 740924,reactor & Turbine Bldg Ventilation Sys Operated for 14 H W/O Continuous Monitoring. Caused by Failed Voltage Regulator Zener Diode on Low Voltage Power Supply of Cam 2-RM-90-250

ML20085H114
Person / Time
Site:	Browns Ferry
Issue date:	10/04/1974
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Case E US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8308300188
Download: ML20085H114 (3)

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O TENNESSEE O

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October 4, 1974 { {5 ij 7 ,,

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& 0078 874 > n TCfE Mr. Edson G. Case a g.g Acting Director of Licensing noe 8

Office of Regulation gfgg s U.S. Atonic Energy Commission g / ru .g' b@

Washington, DC 20545

Dear Mr. Case:

TENNESSEE VALLEY AUTHORITY - BROWNS FERRY NUCLEAR PLANT UNIT 2 -

DOCKET NO. 50-260 - FACILITY OPERATING LICENSE DPR ABNOR!&L OCCURREUCE REPORT BFAO-50-260/7415W The enclosed report is to provide details concerning the unit 1 reactor and turbine building ventilation system which was operated for approxicately 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> without continuous monitoring as specified in Section 3.8.B.8 of the technical specifications and is submitted in accordance with Appendix A to Regulatory Guide 1.16, Revision 1, October 1973. This event occurred on Browns Ferry Nuclear Plant unit 2 on September 24, 1974.

Very truly yours, TENNESSEE. VALLEY AUTHORITY

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'4 7Y E. F. Thocas Director of Power Production Enclosure CC (Enclosure):

Mr. Nor=an C. Moseley, Director Region II Regulatory Operations Office, USAEC 230 Peachtree Street, NW., Suite 818 Atlanta, Georgia 30303 83083001gg 741004 l

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ABNORMtJ, OCCURRENCE REPORT 1

Report No.: BFAO-50-260/7415W Report Date: October 4, 1974 Occurrence Date: Septe ber 24, 1974 .

Facility: Browns Ferry Nuclear Plant units 1 and 2 .,

Identification of Occurrence The unit 1 reactor and turbina building ventilation system was operated for approximately 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> without continuous monitoring as specified in Section 3.8.B.8 of the techdical specifications. -

Conditions Prior to Occurrence Unit 1 was in the shutdown cooling mode during a planned outage. Unit 2 was in the startup test program at approximately 58-percent power.

Description of Occurrence At 0415 hours0.0048 days <br />0.115 hours <br />6.861772e-4 weeks <br />1.579075e-4 months <br />, all three channels of the unit 2 continuous air monitor (CR4) 2-RM-90-250 were reading downseale. Printed circuit boards were removed from the unit 1 CM41-RM-90-250 end were demaged when installed in the failed unit 2 CM4. The unit 1 CM4 was repaired, calibrated, and returned to service at 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br />. Likewise, the unit 2 CR4 was restored to service at 1740 hours0.0201 days <br />0.483 hours <br />0.00288 weeks <br />6.6207e-4 months <br />.

Designation o~f Antarent Cause of Occurrence The voltage regulator Zener diode failed on the low voltage power supply of the unit 2 CM4 2-RM-90-250. This malfunction apparently caused the alam card to fail and damaged the CM4 indicators.

Analysis of Occurrence These CM4 units are located on the refueling floor and serve to continuously monitor gaseous effluent from the unit turbine building, reactor building nones, and refueling floor. Short37 after the unit 2 CM4 failure, instrument personnel were called in to repair or replace the inoperable CM4. Enen the normal monitor is unavailable, when required, the technical specifications state that temcorarf monitors or other systems shall be used. An inoperable turbine building elevator prevented the substitution of the stare CM4 unit stored on the unit 2 turbine l floor. Upon arrival, the instrument mechanic borrowed the printed circuit boards from the operable unit 1 CM4 end installed them in the unit 2 CR4 to make it l operable within the allowable time 14-4t. . This was unsuccessful and damaged the l -borrowed printed circuit boards. This made both units 1 and 2 CM4 units inoperable.

Hourly grab samples were initiated at 0615 hours0.00712 days <br />0.171 hours <br />0.00102 weeks <br />2.340075e-4 months <br /> for unit 2 and at 0640 hours0.00741 days <br />0.178 hours <br />0.00106 weeks <br />2.4352e-4 months <br /> for l unit 1.

Subsequent maintenance revealed that a failed Zener diode on the unit 2 CM4 damcged the electrical co=ponents of the particulate / iodine, gaseous and alarm

's cards for both CM4nu its. Additionally, the local unit 2 channel indicators

. were d enged.

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2 Analysis of Occurrence (continued)

The analysis of grab sa=::les did not indicate crJ- significant change in the effluent activity. Also, the area radiation and air particulate ::enitors

- located in the turbine end reactor buildings operated below their alarm setpoints during this period. It was also noted that no fuel was stored on the refueling fleer. There vere no adverse effects on the health and safety l of the public as a result of the occurrence.

Corrective Action The present plant snare CMI has been =oved to the refueling floor of the reactor building and will nor-911y be kept at this location. An additional spare Cui {

will be purchased to help assure that a spare C1d1 is readi],y available.

Failure Data )

No previous failure of this type.

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