ML20086D967

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

ML20086D967
Person / Time
Site:	Vermont Yankee
Issue date:	09/07/1973
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20086D971	List: ML20086D967 ML20086D972
References
AO-73-25, VYV-3017, NUDOCS 8312050704
Download: ML20086D967 (3)

Text

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VERMONT YANKEM NucLEau POWER CORPORATION  :

scvcNTY seven ovove srnccr RurtAxn, Veraioxr os;oi ,

VYV-3017 p. o. Box :57 VERNON. VERMONT oS354 September 7, 1973 2

0 + 4 Director Directorate of Licensing

$ {}[CilVED ,

SEP 101973 U.S. Atomic Energy Commission ~

g Washington, D.C. 20545 u.s. Amic tuna tomaission D, - REUlatM q

REFERENCE:

Opcrating License DPR-28 Mad satus Docket No. 50-271 g 1, Abnormal Occurrence No. A0-73-25 8 f

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Dear Sir:

4 I As defined by Technical Specifications for the Vermont Yankee w..-in,* u n. .a v genetnn c ,, inn A_7 , 1 ~ are v.n n .r t i n o tho fn110 wino nunu t audi vCeus. A cast.e des siv- I $- $.3 .

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 stach gas monitoring systems and the area gamma radiation monitor on the periueter fence became inoperable.

Since this instrumentation is required at all times as a Limiting i Condition for Operation by Technical Specifications Section 3.8. A.li j an orderly plant shutdown was initiated.

Subsequent to the above less of instrumentation, an apparent detonation in the Off-gas System caused suf ficient back pressure to fracture the air i 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 _ .

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an electrically induced " spike" on the mnitoring system power supplies '

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caused the trip relays to deenergize and activate the Reactor Protection i System. Prior to thia incider.t, the plant was operating at approximately 50% power.'

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, VERMONT YANKEC NUCLEAR POWCR CORPORATION l Directorate of hicensing September 7, 1973

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This act of nature resulted in the following events which occurred essentially simultaneously:

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

2. Stack Cas Monit oring System I and II tripped of f

3. Area gamma monitor at the perimeter fence tripped off

4. Panalarm system on CRP 9-6 and 9-7 inoperable (140 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 e maximum noble gas activity of 1x10-3 pC1/cc. The Turbine Building roof Louvers were closed at the time of the incident. Stack Gas Monitoring Syst ens I and II were returned to service at 1620. During the period of time in which the stack monitors were inoperabic, sampics taken at the stack indicated less than 50 pCi/sec. The perimeter fence monitor was restored to service at 1510.

n,,v , n <, eno o n ir n ~..n no v, nn eno ni v o,orent .. .p r . , vo nwc ..m c v pencon the " north" stack particulate filter was tested and met required efficiency for service, the of f-gas piping at the stack and in the Steam Jet Air Ejector Room was inspected and no damage was evident, the off-gas system was purged, the stack loop seals were checked, and the defective alarm system cards on Panels 9-6 and 9-7 were repaired. The plant returned to operation on September 1, 1973, without the IOG system in service.

. Following the rupture disc fracture, air samples were taken at the

'. s entrance to the Steam Jet Air Ejector Room and they indicated particulate i activity of 4.4x10-9 pCi/cc and a noble gas activity of <2x10-6 pCi/cc.

i Prior to plant startup, a site survey taken at ground level above the-of f-gas line showed no indication of leakage through the piping.

The Plant Operations Review Committee (PORC) met to review the incident and made the following recommendations:

1. The IJG, which was valved out of service on August 31, 1973, following this incident, should remain out of service until it can be ascertained that the system components are not a possible source of detonation.

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e-V VERMONT YAWKEE NUCLEAR POWER CORPORATION e

Directorate of Licensing September 7, 1973 Page 3

2. Investigate and determine the cause of the f ailure of the plant stack monitoring systems and the perimeter fence monitor.

3. Investigate and determine the cause of the failure of the l'analarm nystem on Pancis 9-6 and 9-7.

4. Test the plant grounding network for possible deterioration.

5. Determine if the design of the stack gas filter cartridge provides adequate grounding to the filter case and if not, purchase cartridges which will af ford a proper grounding feature.

In response to the above recommendations, the Nucicar Services Division will:

1. Investigate all instrument failures associated with this

2. Investigate the feasibility of performing a retest of the plant ground mat.

The indicated corrective recommendations are currently being pursued and will be completed in as timely a fashion as possible.

Very truly yours, VERMONT YANREE NUCLEAR POWER. CORPORATION B .W. Riley Plant Superintendent UFC/kbd 6

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