PNO-II-88-018, on 880309,unit Tripped from 21% Power Resulting in Feedwater Isolation Which Caused Steam Generator Levels to Decrease

PNO-II-88-018:on 880309,unit Tripped from 21% Power Resulting in Feedwater Isolation Which Caused Steam Generator Levels to Decrease

ML20148F204
Person / Time
Site:	Catawba
Issue date:	03/10/1988
From:	Brian Bonser NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To:
References
PNO-II-88-018, PNO-II-88-18, NUDOCS 8803280089
Download: ML20148F204 (2)

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/?f /SSO 3//0/8Y March 10, 1988 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PN0-II-88-18 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verifi-cation or evaluation, and is basically all that is known by the Region 11 staff on this date.

FACILITY: Duke Power Company Licensee Emerger y Classification:

Catawba Units 1 and 2 Notification of Unusual Event Docket No. 50-413 and 50-414 Alert Rock Hill, South Carolina Site Area Emergency General Emergency X Not Applicable

SUBJECT:

AUGMENTED INSPECTION TEAM O!SPATCHED An Augmented Inspection Team was dispatched at 10:00 a.m. (EST) today to the Catawba nuclear power plant, operated by Duke Power Company near Rcck Hill, South Carolina, to review events associated with inadvertent introduction of raw service water into tWo of the Unit's four steam generators and clogging of two of the auxiliary feedwater flow control valves, causing flow degradation to the steam generators.

On March 9,1988, at 6:25 p.m. (EST), the unit tripped from 21 percent power. The trip occurred when the feedwater regulating valve to the B steam generator, which was being placed under automatic control, failed open. This caused a feedwater swing which resulted in the D steam generator being fed to the high-high level, resulting in a feedwater isolation which caused steam generator levels to decrease. l Tha # steam generator reached the low-low level, causing the reactor trip.

Both motor driven auxiliary feedwater pumps and the turbine driver auxiliary feedwater purrp started automatically. Th A train auxiliary feedwater pump suction changed over to the nuclear service water system (a safety grade system).

The licensee is investigating a possible malfunction of the pressure switches on the A train supply header, which normally operate on a 2/3 logic with a four-second time delay.

The normally throttled A train flew control valves to the A and B steam generators became partially clogged when service water was passed through them, causing a degradation in flow, Unit 1 declared an Unusual Event today at 12:50 p.m. (EST), after declaring both trains of auxiliary feedwater inoperable and determining that required flow rates could not be assured from the service water system should certain postulated events occur. Unit 1 is being taken to Mode 4 (hot shutdown). The licensee reports that Asiatic clams were the cause of the clogging on the two flow control valves on Unit 2 which were taking suction from the service water system. The licensee believes that there is a potential for a similar occurrence on Unit 1, leading to the decision to declare an Unusual Event.

The States of North Carolina and South Carolina have been informed.

Both the licensee and the NRC are prepared to respond to media inquiries. .a

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The NRC received initial notification of this event by telephone from the licensee to the headquarters Incident Response Center at 10:15 p.m. (EST) on March 9.

This information is current as of 2:00 p.m. (EST) on March 10.

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