ML20086D972

AO 73-25:on 730831,during Electrical Storm in Which Direct Lightning Strike to Top of Plant Ventilation Stack Observed, Both Plant Stack Gas Monitoring Sys & Area Gamma Radiation Monitors on Perimeter Fence Became Inoperable

ML20086D972
Person / Time
Site:	Vermont Yankee
Issue date:	08/31/1973
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20086D971	List: ML20086D967 ML20086D972
References
AO-73-25, VYV-3002, NUDOCS 8312050707
Download: ML20086D972 (3)

Text

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) VERMONT Y ANKMIc NUCLEAR POWMR COIwOR ATION W

ScVENTY SEVEN OROVC STFtECT l(UTI.AND, VI:RMONT 03701 VYV-3002 "' '

P. O. DOX 157 VERNON, VERMONT o5354 August 31, 1973 United States Atomic Energy Commission Directorate of Regulatory Operations, Region I 631 Park Avenue King of Prussia, Pennsylvania 19406

REFERENCE:

Operating License DPR-28 Docket No. 50-271 Abnormal Occurrence No. A0-73-25 Gentlemen:

As defined by Technical Specifications for the Vermont Yankee Nuclear Power Station, Section 6.7.B.1, we are reporting the following Abnormal Occurrence as A0-73-25.and confirming our telephone conve rs ation with your office.

At 1445 on August 31, 1973, during a severe electrical storm in which a direct lightning strike to the top of the plant ventilation stack was observed, both plant stack gas monitoring systems and the area gamma radiation monitor on the perimeter fence became inoperable.

Since this instrumentation is required at all times as a Limiting Condition for Operation by Technical Specifications Secticn 3.8. A.1, an orderly plant shutdown was initiated.

Subsequent to the above loss of instrumentation, an apparent-detonation in the Of f-gas System caused sufficient back pressure to f racture the air ejector rupture disc, thereby degrading a boundary designed to contain radioactive materials as defined in Technical Specifications Section 1. A.5.

At 1500, a reactor scram occurred as a result of an Average Power Range Monitor high flux trip. Due to the fact that the flux recorders indicated a value lower than the scram setpoint, it. is presently felt that an electrically induced " spike" on the monitoring system power supplies caused the trip relays to deenergize and activate the Reactor Protection System. Prior to this incident, the plant was operating at approximately 50% power.

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• o o Directorate of Regulatory Operations August 31, 1973 Page 2 The cause of the instrument malfunction and apparent detonation is believed to have been the lightning strike. This act of nature resulted in the following events which occurred essentially simultaneously:

1. Interin off-gas system tripped of f due to loss of power

2. Stack Gas Monitoring System I and II tripped off

3. Area gamma monitor at the perimeter fence tripped off

4. Panalarm system on CRP 9-6 and 9-7 inoperable (approximately 100 cards)

5. Air ejector rupture disc fractured Following the incident, temporary repairs were made to the rupture

, disc to minimize gaseous radioactivity in the Turbine building. Air samples taken in the air ejector room of the Turbine Building indicated a maximum noble gas activity of lx10-3 pCi/cc. The Turbine Building roof louvers were closed at the tine of the incident. Stack Gas Monitoring Systems I and II were returned to service at 1620. During the period of time in which the stack monitors were inoperable, samples taken at the stack indicated less than 50 p C1/sec. The perimeter fence monitor was restored to service at 1510. -

Further investigation and evaluation of possible damage resulting from the incident is currently underway. Necessary repairs and testing are presently in progress and a plant startup is contemplated on September 1, 1973.

Very truly yours, VERMONT YANKEE NUCLEAR POWER C0hPORAT10N

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. UO. \7dw B.W. Riley O Plant Superintendent WFC/kbd .

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.* N/ Licensee: Vermont Yankee lear Power Corporation

11. D. Thornburg, oatt Docket No.- 50-271 Chief, FS6EB '

Abnonnal Occurrence: A0 73-25 to peam, an; en.o mmaa ai am RO:!IQ (5)

DR Central Files (1) cast The attached report from the subject licensee is Regulatory Standards '3)

Dir. of Licensing (13 i forwarded in accordance uith RO Manual Chnnter 1000 T O (tdarr,e and unto -

lee lllALS piMARPS RO Files The action taken by the licensee is considered bAft appropriate. Follouup will be performed during the next inspection as annronriate. conies of IhQL (r a n e ard br O etMARks Q ) - ~ ~, ~

the report have been foruarded to the PDR, Local A, . (? ) I t'h' D, L. Capiton, Senior PDR, NSIC, DTIE and State representatives. The Reactor Inspector, BWR Section licensee vill submit a 10 day written report to _

PHONE #00. DATE 9/17/73 Licensing.

WE OTHER TJDE Foft ACDit'ONAL REMARM.S clo : 1971 o - .4Fef t 1;

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