ML20086D839

AO 73-05:on 730117,noble Gas Release Rate Exceeded Tech Spec Limit.Scram Resulted from Vessel Low Level Imposed by Feed Flow Transient Induced When Technician Returned Level Instrument Back to Svc After Surveillance Testing

ML20086D839
Person / Time
Site:	Vermont Yankee
Issue date:	02/26/1973
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086D841	List: ML20086D839 ML20086D847
References
AO-73-05, AO-73-5, VYV-2437, NUDOCS 8312050164
Download: ML20086D839 (4)

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, VERMONT YANKEE NUCLEAR POWER CORPORATION

/ M SCVENTY CcVEN OROVC STRCCT --

,' RUTLAND, Vautorr os701 VYV-2437 l P,O. BOX 157 N VERNON, VERMONT oS354 j

i February 26, 1973 1 -

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8 i I Director D " D MAR 2 1973>. El' Directorate of Licensing ,l.s. MDrc U,tur l C'N4 8 U.S. Atomic Energy Comnission Washington, D.C. 20545 $((M M 4

REFERENCE:

Operating License DPR-28 ro Docket No. 50-271 i Abnorma] Occurrence No. A0-73-05 0 .

Dear Sir:

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l As defined by Technical Specifications for the Vermont Yankee Nuclear

! Power Station, Section 6.7.B d, we are reporting the following Abnornal i Occurrence as A0-73-05.

. At approximately 1550 on January 17, during a plant cooldown following l a reactor scram from 100% power, the nobic gas release rate exceeded the j limit of .22 Ci/sec as specified in Section 3.8. A.2 of Technical Specification.

1 (See Attachnent #1) The limit was exceeded for a period of approximately j 26 minutes during uhich time the peak release rate was .416 Ci/sec. The I average release rate for the four preceding days at approximately 100% power was .076 Ci/sec.

The scram resulted from'a vessel low level which was imposed by a feed E

il flow transient induced when a technician returned a icvel instrument (0-400" Yarway - LI 2-3-73A) back to service after surveillance testing. This Yarway's

. Instrunent reference leg is common to and serves as the reference leg for the "A" feedwater systen IcVel transmitter (LT-6-52A) . Subsequent to the scram,

j which occurred at 1121, the initial off-gas transient was suppressed by s

j . clos _ing the Steam Jet Air Ejector suction valves. Neither valve could be

j inmediately opened'remotel ~fo1~16 wing closure and condenser vacuum decreased }

.? such that when the SJAEs were restored to service, at 1530, the high off-gas i flow resulted in an off-gas radiation icvel higher than anticipated. Although l}

the instantaneous release exceeded the limit, the three hour isolation of the

'! gas in the condenser resulted in a decrease in the total release.

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8312050164 730226 l! PDR ADOCK 05000271 -

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j OG VERMONT YAQ,dEu' NUCLEAR POWER CORPO

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/ Dir'ctorate e of Licensing

, , - February 26, 1973 .

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Average stock release rate since the beginning of plant power operations on 13 September 1972 and including this transient is 10,903 pCi/sec. Analysis of the release was made by our engineering group and resulted in the determin-ation that the maximum exposure that could have occurred off-site due to this '

incident was <1 mR. ,

The Plant Operations Review Committee conducted an indepth review of procedures governing the operation of the Off-Cas System and purging of the Off-Gas Sample System and recommended revisions to minimize peak stack gas release rates consistent with plant operational constraints.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION B.W. Riley '

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r VERMONT YA'IKEE SEQUENCE OF EVENTS 'I'I@ */lfr Cafet 82,28ff

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JANUARY 17, 1973

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1121 Reactor Scram to Water Level Manual Turbine Trip

+ Reactor Isolation At +50" Yarway .

RCIC btart

! Reactor Pressure.1070-950 B Relief Valve (Manual) l 1060-900 D Relief Valve (Manual) '

Reactor Building Vent Secured ,

HPCI Start SBGT System A,B Started Cleanup System Tripped On to Level +5" At Scram (Off For Next 24-ilours) .

1212 Vessel Level +25" Yarway, No Lo Level Problem Re-Open 11SIV ,

BPV Used For Cooldown .

1216 Secured llPCI and RCIC -

1218 IIPCI and RCIC In Normal Line-Up 1234 Off-Gas System Isolated (Timer Started At 1219) '

1236 becured SJAE

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1238 Closed SJAU Suction Valves

• 1239 Re-Start SJAE (Steam To SJAE Only, Suction Valves Remain Closed) ..

1255 Drywell to Pressure Alarm Closed 1257 Commenced Drywell Purge With SBGT 1302 Drywell Lo Pressure Alarm 1308 Secured Drywell Purg'c 1400 Oper. Vacuum Breaker To 3" Back Pressure And Re-Close .

1440 A SJAE Suction Valve (FCV 9) Failed To Open 1500 Switch To B SJAE, B SJAE Suction Valve (FCV 10) Failed To Open 1512 Reactor Building !!cating and Ventilation Returned To Normal

. 1515 Opened Torus outlet Purge Valve To Equalize Pressure (Inlet Valve Never Opened) 1530 Maintenance Opened B SJAE Suction Valve - Off-Gas Flow Indicator Pegs High 1550 . Secured Reactor Building Ventilation

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f 5616 Stack Gas Activity Exceeds Tech. Spec. Limit Stack Gas Activity Returns Below Tech. Spec. Limit ,

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N 1650 Started Reactor Building Vent On Normal ,

1700 Secured SBCT System, Both Trains 1710 Recommenced Cooldown With BPV's Slowly Duc To Stack Gas Release Rate Considerations 2030 Started Mechanical Vacuum Pump 2115 Broke Condenser Vacuuri To 6" lig. Absolute to Check !!ogger Operation '

To Stack For Release Rate 2125 Secured SJAE 2210 Gland Exhaust Vacuum Dropped To <5" 110 2 Started 2nd Gland Exhauster Turbine Building Airborne Radiation Levels Increased 2255 Placed Reactor On Shutdown Cooling (RllR) 1 Secured Steam Into Condenser '

Secured Scaling Steam ,

Broke Condenser Vacuum To 25" lig. Absolute

' ' ' 2327 Vented Vessel Via Main Steam Drain Valve-79 To Condenser secureo a utano r.xnauster e

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