PNO-III-98-051, on 981029,Prairie Island Unit 1 Automatically Tripped from 100 Percent Power Due to Negative Flux Rate Reactor Flux Rate Trip Signal.Nrc Resident Inspectors Are Monitoring Licensee Investigation & Repair Activities

PNO-III-98-051:on 981029,Prairie Island Unit 1 Automatically Tripped from 100 Percent Power Due to Negative Flux Rate Reactor Flux Rate Trip Signal.Nrc Resident Inspectors Are Monitoring Licensee Investigation & Repair Activities

ML20155E404
Person / Time
Site:	Prairie Island
Issue date:	11/02/1998
From:	Michael Kunowski, Vegel T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-98-051, PNO-III-98-51, NUDOCS 9811050034
Download: ML20155E404 (1)

- . . -. -- - , . - . . - . - - . . - - . . --

. November 2, 1998 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-III-98-051 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is t known by Region III staff (Lisle, Illinois) on this date. )

Facility Licensee Emergency Classification Northern States Power Co. Notification of Unusual Event Prairie Island 1 Alert Welch, Minnesota Site Area Emergency Dockets: 50-282 General Emergency X Not Applicable

Subject:

UNIT 1 SHUTDOWN TO REPAIR 60 CONTROL R0D DRIVE CABLES On October 29, 1998. Prairie Island Unit 1 automatically tripped from 100 percent power due to a negative flux rate reactor trip signal. The signal was. generated when a control rod dropped into the reactor core after two fuses blew in the control circuitry for the rod. All safety systems responded to the trip as designed.

As of November 2,1998, the licensee preliminarily determined that the cause for the blown fuses and subsequent control rod drop was a fault in a control rod drive power. cable, but is conducting further troubleshooting to ensure that the control rod drive mechanism itself is not in need of repair. Because this is the third instance in 2 years of a dropped control rod, the licensee has decided to replace power cables for  ;

all of the control rod drives and the cables for the control rod position indicating system a total of about 60 cables.

In' addition, while the reactor is shut down, the licensee will be l

conducting selected maintenance activities, including the repair of a  ;

minor leak on a steam generator manway cover that was discovered during a  !

L containment inspection. Unit l's shutdown is expected to last approximately 2 weeks. ,

p NRC resident inspectors are monitoring the licensee's investigation and repair activities. 1 Prairie Island Unit 2 was unaffected by the tri) of Unit 1 and remains at

)

100 percent power. The State of Minnesota will 3e notified. The information in this preliminary notification has been reviewed with

licensee management.

L The licensee notified the NRC Operations Center of this event at 1:00 a.m. (CT) on October 30, 1998. This information is current as of 9:00 l a.m. (CT) on November 2, 1998.

L

Contact:

Tony Vegel Mike Kunowski

(630)829-9872 (630)829-9618 4

b 1{gL

}

9811050034981102{

PDR I&E PNO-III-90-051 PDRr' t

(yl l

l vouovo l

L .. 1