ML19291C280

Deficiency Rept 79-07:on 800116,during Prototype Testing, Isolation Block Valve Failed to Fully Close Under Design Flow Conditiions.Cause by Manufacturer Error in Determining Size of Valve Operator.Valve Operator Will Be Modified

ML19291C280
Person / Time
Site:	Catawba
Issue date:	01/16/1980
From:	DUKE POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19291C272	List: ML19291C271 ML19291C280
References
NUDOCS 8001230268
Download: ML19291C280 (1)

Text

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Duke Power Company Catawba Nuclear Station Units 1 & 2 Report Number: IE-79/06-SDD-413/414 Report Date: January 15, 1980 Facili ty: Catawba Nuclear Station, Units 1 & 2 Identification of Deficiency: Refueling Water Storage Tank (RWST) Capacity Description of Deficiency:

On December 17, 1979, Mr J R Wells and Mr R E Miller advised Mr Milt Hunt, NRC, of the following design deficiency. During Duke's review of tank safety related level setpoints, it was discovered there was insufficient tank height between RWST low level and the tank overflow nozzle to store the water volume needed for safe shutdown of Containment Spray Pumps.

Originally it was assumed the RWST outflow would be self-venting, providing usable volume from the top of the outlet nozzle to the overflow nozzle. Calcu-lations for incipient air entrainment, along with good engineering practice for vortex prevention and the effect of instrumentation inaccuracy have shown the need for additional storage volume.

Analysis of Safety Implications:

The RWST is the source of water for the Emergency Core Cooling System and Con-tainment Spray System pumps during the injection mode of operation following a loss of coolant accident (LOCA). Catawba Nuclear Station has employed automatic switchover of the resideal heat removal (RHR) pumps to the containment recircu-lation sump.

After the automatic switchover level of the tank is reached and switchover of the RHR pumps is initiated, the centrifugal charging pumps and safety injection pumps are manually realigned for recirculation, also. Containment spray pumps continue to take suction from the RWST until a tank " empty" level alarm is reached.

At this level, sufficient water must remain such that a maximum of 10,000 gallons can be pumped out via the containment spray pumps. If sufficient volume does not exist, air entrainment in the tank outlet piping could possibly cause damage to the containment spray pumps and/or system piping. Such damage would preclude use of the containment spray system for long term recirculation.

Corrective Action:

In order to provide more than sufficient water to preclude possible air en-trainment, a 450 turned-down elbow with vortex preventer will be added on the outlet nozzle inside the tank. The resulting suction elevation will be 24" lower than the present design, assuring sufficient water volume to safely shut down the containment spray pumps.

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Appropriate design documents have been revised to effect the necessary hardware changes which will be completed prior to system pre-operational testing.

This problem is not applicable to other Duke stations.

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