05000298/LER-1979-030, Forwards LER 79-030/03L-0

Forwards LER 79-030/03L-0

ML19210F011
Person / Time
Site:	Cooper
Issue date:	11/20/1979
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19210F012	List: 05000298/LER-1979-030, Forwards LER 79-030/03L-0 05000298/LER-1979-030-03, /03L-0:on 791021,while Pumping Water from Torus to radwaste,drywell-to-torus Differential Pressure Dropped Below Tech Specs.Caused by Nitrogen Pressure Forcing Water from Downcomers to Flow to Torus
References
NUDOCS 7912130387
Download: ML19210F011 (2)

LER-1979-030, Forwards LER 79-030/03L-0

Event date:
Report date:
2981979030R00 - NRC Website

text

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COOPER NUCLEAR STATloN P.o. BOX 98, BRoWNVILLE, NEBR AS KA 68321 Nebraska Publ.ic Power D. tr. t TELE ~oNE sm n.3.n is ic CNSS790595 November 20, 1979 Mr. K. V. Seyfrit U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.2 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occurrence that was discovered on October 21, 1979. A li-censee event report form is also enclosed.

Report No.:

50-298-79-30 Report Date:

November 20, 1979 Occurrence Date: October 21, 1979 Facility:

Cooper Nuclear Station Brownv111e, Nebraska 68321 Identification of Occurrence:

Operation in a degraded mode as permitted by a limiting condition for operation established in Section 3.7.E.2 of the Technical Specifications.

Conditions Prior to Occurrence:

The reactor was at a steady state power of approximately 927. of rated thermal power.

Description of Occurrence:

While pumpi.ng water from the suppression chamber to the radioactive waste system, the drywell to suppression chamber differential pres-sure suddenly dropped to approximately 1.0 psid.

Designation of Apparent Cause of Occurrence:

The cause of the occurrence was a high differential pressure be-tween the drywell and the suppression chamber forcing all the water out of the downcomers allowing nitrogen to flow from the drywell to the suppression chamber.

1552 249 4003 s

//

7912130 N 9

a Mr. K. V. Seyfrit November 20, 1979 Page 2.

Analysis of Occurrence:

Technical Specifications require the drywell to suppression chamber differential pressure be maintained at >1.47 psid. This is ac-complished by maintaining the drywell pressure 1.55 to 1.57 psig with the nitrogen pressurizing system and pumping nitrogen from the suppression chamber to the drywell to maintain the differential pressure 1.50 to 1.55 psid.

This differential pressure forces most of the water out of the downcomers to minimize the stress on the torus during an accident that would pressurize the drywell. This differential pressure allcws approximately 4 to 16 inches of water in the downcomers, depending upon the differential pressure and the water level in the torus.

At the time of the occurrence, the nitrogen pressurizing system had automatically raised the drywell pressure to the high end of its allowable band. At this same time water was being pumped from the suppression chamber lowering the water level and the pressure in that area.

This caused sufficient differential pressure forcing all the water out of the downcomers allowing nitrogen to flow from the drywell to the torus, reducing the differential pressure to 1.0 psid.

This occurrence presented no adverse consequences from the stand-point of public health and safety.

Corrective Action

The differential pressure was restored to >l.47 psid within approx-imately 8 minutes. The instruction letter being used for the evolution was reviewed and changed to insure that in the future during this evolution the water level is maintained at the high end of the allowable band and the differential pressure at the low end.

Additionally, a copy of the engineering evaluetion of the occurrence was routed to all licensed operating personnel.

Sincerely, e

L. C. Lessor Station Superintendent 1552 250 Cooper Nuclear Station LCL:cg Attach.