ML20086E636

AO 74-07:on 740509,spike Observed on Plant Stack Gas Recorder,Resulting in Stack Release Peak Greater than Allowed by Tech Specs.Caused by Steam Packing Exhauster Operation

ML20086E636
Person / Time
Site:	Vermont Yankee
Issue date:	05/15/1974
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20086E638	List: ML20086E636 ML20086E639
References
AO-74-07, AO-74-7, VYV-3271, NUDOCS 8312070462
Download: ML20086E636 (2)

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VERMONT YANKEE NUCLEAR POWER CORPORATION SEVENTY SEVEN OROVE STRECT RUTLAND, VEIO10NT 03701 VYV-3271 -m P. O. BOX 157 VERNON VERMONT o5354 l May 15, 1974 l

l Director Directorate of Regulatory Operations, Region I United States Atomic Energy Commission 631 Park Avenue

. King of Prussia, Pennsylvania 19406

REFERENCE:

Operating Licence DPR-28 Docket No. 50-271

• Abnormal Occurrence No. A0-74-07 (10 Day Report)

Dear Sir:

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As defined by Technical Specifications for the Vermont Yankee Nuclear Power Station, Section 6.7, we are reporting the following Abnormal Occurrence as A0-74-07.

At approximately 1212 on May 9, 1974, during a plant cooldown following a reactor manual scram, an apparent spike was observed on the plant stack gas recorder which resulted in a stack release peak of 0.450 Ci/sec. This incident was determined to be in violation of Technical Specifications, Section 3.8.C.l.a in that the maximum release rate of grcss radioactivity from the plant did exceed 0.08/Ey Ci/sec = (0.257 Ci/sec) for a period of ten seconds. Prior to

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the apparent spike, the release rate had been decreasing for approximately four minutes and was at a value of 0.135 Ci/sec. Immediately following the peak, the release rate was 0.120 Ci/sec. and continued on a steady downtrend for the following half hour.

The reactor manual scram was initiated as a result of turbine back pressure reaching the plant established administrative limit of five inches Hg Abs. This situation developed subsequent to automatic isolation of the Advanced Off-Gas System due to the loss of that system's condensate booster pumps. Breakers associated with these pumps were caused to open due to thermal overload protection. It was later established, through system testing, that operational requirements dictated the need for increasing the thermal protection settings based on amperage characteristics derived while testing. Upon completion of this change, the reactor was brought critical and the plant was phased to the system, grid at 0300 on May 10, 1974.

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VERMONT YANKEE NUCLEAR POWER CORPORATION Directorate of Regulatory OperatiUns l May 15,1974 l Page 2 l

l The annual average stack release rate since January 1,1974, and including this traasient is 2,252 pCi/sec. which is approximately 1%

of the allowable release rate. Analysis of recall data provided by the pressurized ion chamber located on the north perimeter fence indicated that the maximum exposure that occurred at that point based on a five minute average reading was 0.034 mr/hr above natural background.

Meteorological information at the time of the incident showed that the wind direction was from the southeast at fourteen miles per hour which provided good representative monitoring at the north perimeter fence.

. The Plant Operations Review Committee concluded that the initial increase in stack release was due to Steam backing Exhauster operation and recommended that applicable plant procedures be reviewed to address operation of that component during this type of incident. The committee, in reviewing the reason for the apparent spike, was unable to determine the precise cause.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION

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B.W. Riley T Plant Superintendent WFC/kbd l

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