ML20086E428

AO 74-11:on 740705,both Plant Stack Monitoring Sys Failed Following Direct Lightning Strike During Severe Electrical Storm.Generator Turbine Tripped Causing Reactor Scram.Repair of Damaged Equipment Complete

ML20086E428
Person / Time
Site:	Vermont Yankee
Issue date:	07/08/1974
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20086E426	List: ML20086E418 ML20086E428
References
AO-74-11, VYV-3323, NUDOCS 8312070150
Download: ML20086E428 (3)

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)O ERMONT YANKEM NUCLMAR POWEN CORPOR ATION T>}$j ocvern Y GLVctJ OHOVc U1 HEL T lltJTI.AND, VElot O.N l' 0"3701 F4 E PL Y T O:

VYV-3323 e. o. nox is7 vERNON. PMONT oS354 July 8, 1974 Director ~~~>

Directorate of Regulatory Operations, Region I -

I United States Atomic Energy Co;maission .I 631 Park Avenue O h'  :

King of Prussia, Pennsylvania 19406 e

FIFERENCE: Operating License DPR-2S Dechet No. 50-271 Abnornal Occurrence No. A0-74 -11 (24 Hour Report)

Dear Sir:

s m As defined by Technical Specifications for the Vermont Yankee Kuclear Power Station, Section 6.7, we are reporting the following Abnormal Occurrence as A0-74-11 and confirming our telephone con-versation with "r. Gary 2nyder at 0930 on July 6, 1974.

At 1324 cr July 5, 1974, durin a ccvere electrica: ctorm in AL JI, cu lida ul u t. ., u lic a ou the tue of the plant ventilation stack were observed, both plant stack monitoring systems became inoperabic. This c::cceds the Limiting Condition of Operatien of Technical Specificatien J.9.B.l.a which requires that at least one of the two plant stack renitoring s'/stens shall be operable at all Lines.

The plant was operating at approximatcly 80% power at the time of the occurrence. Approxicately 30 seconds after the loss of the stack cenit ors another lightning strike resulted in a generator /

rurbine trip ubich caused a reactor scram. In addition to the loss of the stack monitoring systems, the perimeter fence monitor, the stack base fan, the process computer, nisec11cneous annunciating and indicatin3 circuits, four auxiliary equipment transforners and the instrumentation frca the site meteorological tower were rendered inoperable.

The A00 systen was kept in service until approximately 0400 en July 6, 1974. In an effort to mininize the stack release rate

'the turbine gland seal stesa pressure was inmediately reduced to

<1 psig in accordance with revised operating procedure and the

techanical vacuu

pu.? was not used until approximately 1700 on l July 6, 1974. During the period of time that the stack gas monitorn were inoperable, grab gas samples were taken at the etack on a periodic basis. The attached table sun.arizes the results of these gas canples. The stach cas monitors were declared fu1]y c,perabic f at 1835 on July 6, 1974. The naxiuun release rate follouing the shutdown was 111,J 19 pC1/sec and this was observed at 1707 on

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8312070150 740715 '

1 PDR ADOCK 05000271 y i d .5 S

PDR A),

ROW SENT REGION __/

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Directorate of Regulatory Operations, Region I i

July 8, 1974 *

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July 6, 1974. The Technical Specification limit at this time was determined to be 1,330,000 pC1/nec based on an IV of .06.

i i Repairing and testing of vital equipment and instrumentation j that was damaged as a result of the incident has been completed and l a plant startup is currently underway.

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l V.ry truly yours,  !

, i VERMONT YA'EEE NUCLEAR P0k'ER CORPORATION r

. B. U. Riley ,

Plant Superintendent wPu/sjp .

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C O STACK RELEASE RATES FOLLOWING Tile SilUTDOWN OF i

5 July 1974 4

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Date Titae Release Rate  !

7/5/74 1354 <3,000 pCi/sec 7/5/74 . 1444 <5,000 pCi/sce i 7/5/74 1531 <5,000 pCi/sce 7/5/74 1654 6,866 pCi/sec

{ 7/5/74 1751 11,881 pCi/sec 1

7/5/74 2003 15,981 pCi/sec 7/6/74 0803 3,284 pCi/sec 7/6/74 1308 15,941 pC1/sce J

7/6/74 1707 111,119. pCi/sec 7/7/74 1411 11,823 pC1/see i

j 7/B/74 0730 16,730 pCi/sec

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