ML20085G607

AO BFAO-50-259/7460W:on 741224,offgas Radiation Monitor Found Inoperable.Caused by Abnormal Leakage of Local Offgas Sample Flow Rotometer Due to Failure of O-ring to Seal properly.O-ring Reassembled

ML20085G607
Person / Time
Site:	Browns Ferry
Issue date:	01/03/1975
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Case E Office of Nuclear Reactor Regulation
References
NUDOCS 8308290209
Download: ML20085G607 (3)

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ABNORP.G OCCURREUC2 REPORT

• Report No.: EFAO-50-259/7h60W Report Date: January 3, 1975 Occurrence Date: December 24, 1974 .

Facility: Browns Ferry Nuclear Plant unit 1 Identification of Occurrence The unit 1 offgas radiation monitor was inoperable for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 55 minutes.

Conditions Prior to Occurrence Unit 1 was operating at 82-percent power.

Deceristion of Occurrence At 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br /> the offgas sa=ple flow abnormal alarm was received in the control room. The probles was isolated to the local offgas sarple flow rote =eter which was inspected and cleaned end returned to service at 1545 hours0.0179 days <br />0.429 hours <br />0.00255 weeks <br />5.878725e-4 months <br />. This action cleared the abnor- 1 flow slar= but at 1550 hours0.0179 days <br />0.431 hours <br />0.00256 weeks <br />5.89775e-4 months <br /> both the offgas radiation "high" and "high-high" alar =s were received in the control room. Although there was no significantly visibic change in related indications either upstrec= or downstrea= of the offgas system, reactor power was reduced to prevent auto =atic offgas isolation. At 2305 hourc the offgas radiation monitor was removed from service to eliminate a ca=ple Icak at the local offgas cc=ple flow rotometer,

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and unit 1 chutdown co=cnced. Corrective maintenance was completed and the offgas radiation =cnitor was restored to normal cervice at 0100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> on December 25.

Decis nation of Arnarent Cause An "0" ring in the local offgas sa=ple flow retometer failed to seal properly upon reascembly following initial inspection and cleaning. The resulting abnormal leakage caused an increased flow rate and a corresponding indicated activity increase of the offgas radiation tonitor due to an increase of short-lived radionuclides.

Analysis of Occurrence

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Two offgas grab ca=ples were co11ceted and analyzed, one at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> and another at 1955 hours0.0226 days <br />0.543 hours <br />0.00323 weeks <br />7.438775e-4 months <br />, which showed no significant change from previous offgas samples taken the day before. Investigation continued and at 2218 hours0.0257 days <br />0.616 hours <br />0.00367 weeks <br />8.43949e-4 months <br /> airborne

. activity was detected near the local offgas carple ficy rotometer which was found to be leaking. In cddition, dose rates at the detector chc=ber reflected increased radiation levels.

Under nor:..nl conditions the offgas monitor sample delay time is about 2 minutes.

s In this case the delay time was significantly reduced due to the increased offgas sample flow rate.

Thus, the offgas radiation monitor was monitoring a dispropor, tionate share of chort-lived radionuclides caucing a prc=ature actuation of the "high-high" offgas activity clarm. In addition,'the "high-high" offgas activity alar: setpoint was concervatively at 68 mr/hr which also contributer1 to the premature actuation of this ninrm.

8308290209 750103 PDR ADOCK 05000259 S PM

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.. TENNESSEE VALLEY AUTHORITY _ _ .

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.J l'.r. Edson G. Case -

/teting Director of Licensing p(, J '

Office of Ecgulation U.S. Atomic Energy Cor. mission Washingten, DC 20545

Dear IJr. Case:

TZ:i!TESSEE VALLEY AUTE03ITI - ERC'.C:S FERIX I;UCI2AR PIAI.T UIIIT 1 -

D00KET I:0, 50-259 - FACILITY OPERATII;G LICHISE DPR AIGOR'!.AL OcCURRr:CE REPC2T BFAO-50-259/7460'.i The enclosed report is to provide details concerning the unit 1 offgas radiation .onitor which was inoperable for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 55 minutes end is submitted in accor3cnce with Appendix A to Regulator-/ Guide 1.16, Revision 1, October 1973 This event occurred on Browns Ferry I!uclear Plut unit 1 on Decccber 24, 1974 Verf truly yours, TK;I:ESSEE VALIEY AUTi!ORITY

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(["T)irector of Power Production Enclosure CC (Enclosure):

I'.r. I!orman C. I:oseley, Director 4 Region II Regulc. tory Operations Office, USAEC

230 Peachtree Street, I.~I. , Suite 818 Atlanta, Georgia 30303 1

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An$h/sisofOccurrence(continued)

The co=bined stack release rate from both units 1 and 2 during this occurrence was less than 150 ue/see which is several decades below the allowable technical specification limit. Tnere was no adverse effect on the health and safety of the public as a result of this occurrence.

Corrective Action The offgas scrole flow rotometer "O" ring was reassembled correctly and the proper s:: role flow rate was confirmed. This corrective action was sufficient to clear the "high" and "high-high" clarm and to restore the offgas radiation monitor to its normal level of activity. ,

In addition, a design change will be considered to install a redundant offgas se=cle flow rotometer for each unit to prevent similar occurrences in the future.

Failure Data IIateplate: Fisher Porter

f. Tube Ilo.: FP1/4-23-6-3/61

. S/I: 69013Al-5 i ~

Range: 0-25 SCFH Air Fct G STP i

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