ML19341A666

Forwards LER 80-048/03L-0

ML19341A666
Person / Time
Site:	Cooper
Issue date:	12/16/1980
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19341A667	List: ML19341A666 ML19341A669
References
CNSS800733, NUDOCS 8101270649
Download: ML19341A666 (2)

Text

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1 COOPER NUCLEAR STATloN Nebraska Public Power District

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CNSS800733 December 16, 1980 gg 1 g N D ~TT h 1 g .b  ; W Mr. K. V. Seyfrit, Director.

U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance wich Section 6.7.2.B.2 of the Technical Specifications for Cooper Nualear Station and discusses a reportable occurrence that was disco.xted on November 21, 1980. A licensee event report form is also enc'.osed.

Report No.: 50-298-80-48 , -m ,

Report Date: December 16, 1980 (. ,

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Occurrence Date: November 21, 1980 (~ , , .y',]

Facility: Cooper Nuclear Ststion ;h y Brownville, Nebraska 68321

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~ . '. A Identification of Occurrence: . ~l A condition leading to operation in a degraded mode permitted .)y a limiting condition for operation established in Section 3 7.A.5.b" of the Technical Specification.

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Conditions Prior to Occurrence: ,'dV The reactor was in the "Run" mode at approximately 55% of rated thermal power. -

Description of Occurrence:

Technical Specification 3.7.A.5.b was not met in that the oxygen concentration in the primary containment was not reduced to less than 4% within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> subsequent to placing the reactor in the "Run" mode. The actual time required to reduce the containment oxygen concentration below 4% was 26 hours3.009259e-4 days <br />0.00722 hours <br />4.298942e-5 weeks <br />9.893e-6 months <br /> and 55 minutes.

Designation of Apparent Cause of Occurrence:

The root cause of this occurrence is unknown. After the torus was initially purged with nitrogen to approximately 5% oxygen, the torus oxygen concentration increased to greater than 10% while the drywell was being purged. Upon completion of the drywell purge, insufficient time remained to repurge the torus,

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-mv' eene-6 Mr. K. V.-Seyfrit December 16, 1990

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. Analysis of Occurrence:

The oxygen concentration is maincained below 4% (by volume) to aid in the control of combustible gases in containment following a LOCA per Technical Specification 3.7.A.5.a. -NRC Regulator- Guide 1.7 establishes a flammable limit for oxygen at greater 2n 5% (by 4 volume). At the time cf the event, the oxygen concentracion was 3.5% in the drywell r.nd 4.1% in the torus. This would result in an average concentratica in eae torus of 4.1% following a LOCA when all noncondensibles would be purged from the drywell to the tcrus. '

This would have resulted in a concentration in containment below the fla=mable limit. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> limit for purgiag has no basis other than to insure timely inerting upon startup. The additional

' 2.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> does not significantly degrade from overall reactor safety. Thus, this occurrence presented no adverse consequences to the public health and safety. Further hydrogen control could also have been obtained in the event it was needed with the installed 1.tmospheric Containment Atmospheric Dilution (ACAD) System.

Corrective Action:

The torus was purged to less than 4% oxygen as quickly as possible.

This action negated the action statement in the LCO for shutdown within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The evaluation of the incident is complete, while no exact cause for this event can be defined, the applicable procedures are being reviewed and revised as needed. This revision will attempt to provide more definitive guidance to the operator during the purging evaluation in order to reduce the potential for recurrence of events of this type. This event will be reviewed with all control room operators.

Sincerely,

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L. C. Lessor Station Superintendent Cooper Nuclear Station LCL:cg Attach.

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