ML20085G607
| 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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D-ABNORP.G OCCURREUC2 REPORT
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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.
In this case the delay time was significantly reduced due to the increased offgas s 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
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4 l'.r. Edson G. Case p(, J '
/teting Director of Licensing 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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2 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
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