PNO-III-86-061, on 860622,reactor Tripped as Result of Signal Showing MSIV Not Fully Open.Caused by Failed Relay in MSIV Circuitry Giving Incorrect Indication.Relay Replaced & Tested

PNO-III-86-061:on 860622,reactor Tripped as Result of Signal Showing MSIV Not Fully Open.Caused by Failed Relay in MSIV Circuitry Giving Incorrect Indication.Relay Replaced & Tested

ML20206J117
Person / Time
Site:	La Crosse File:Dairyland Power Cooperative icon.png
Issue date:	06/23/1986
From:	Boyd D, Guldemond W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-86-061, PNO-III-86-61, NUDOCS 8606270006
Download: ML20206J117 (2)

PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-III-86-61 Date June 23, 1986 #

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 known by the Region III staff on this date.

Facility: Dairyland Power Cooperative Licensee Emergency Classification:

LACBWR Notification of an Unusual Event Genoa, WI 54632 Alert Site Area Emergency Docket no: 50-409 XX General Emergency Not Applicable h

Subject:

REACTOR TRIP AND WATER LEVEL INSTRUMENTATION PROBLEM At 10:10 a.m. (CDT), June 22, 1986, while operating at 98 per cent power, the reactor tripp:d as a result of a signal showing the Main Steam Isolation Valve (MSIV) was not fully open. (Subsequent investigation identified the cause of the trip to be a failed relay in the MSIV circuitry which gave an incorrect indication that the MSIV was not fully open. The relay has been replaced and tested.)

Initially all systems functioned normally, but when the MSIVs closed, as designed when reactor pressure reached 1000 pounds per square inch, some erratic reactor vessel water level indications occurred:

1. The wide range water level monitor went full scale high. The wide range monitor failure was later found to be caused by the parting of a sensing line. This line was isolated and repaired.

2. One of the three narrow range water level monitors dropped to a reading of negative 30 inches, while the other two remained at positive 18 to 20 inches, which is the normal level following a reactor trip. The zero point for these indicators is 3 feet above the top of the core. The low level signal on the one monitor initiated the high pressure core spray system and started the emergency diesel generator. The negative 30 inch level indication then returned to normal levels--agreeing with the other two indicators--and the levels on all three increased to reflect the water added by the core spray system. Core spray was terminated after about 5 minutes of operation.

3. The wide range monitor remained in service and after the broken sensing line was isolated, the monitor indicated a water level of 2 inches above the core. The licensee determined the monitor was out of calibration--apparently caused by the pressure surge when the sensing line parted. After recalibration, the wide range monitor agreed with the level DISTRIEUTION:

H. St. ED0 NRR E/W Willste Mail: ADM:DMB Chairman Palladino PA IE NMSS D0T:Trans only Comm. Zech ELD OIA RES Comm. Bernthal AE00 Comm. Roberts Comm. Asselstine SP M l. Regional Offices ACRS SECY INP0 it/ 3 NSAC M ,1 l

CA RIII Res~ident Offi  :

PDR Licensee: _SV '

(Corp. Office - Reactor Lic. Only) 4 l 401 8606270006 860623 Region III I N-I!I-86-061 PDR Rev. November 1985

PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-III-86-61 Date June 23, 1986 shown on the three narrow range monitors.

4. In addition, during the time when the conflicting readings were observed, an operator entered containment and checked a direct reading reactor water level instrument (a feature unique to the LACBWR plant). Its level measurement confirmed that there was sufficient water in the core.

The licensee continues to investigate the event. Restart of the plant is on hold, pending the outcome of this review. An NRC inspector was dispatched and is on site, monitoring the licensee's activities.

The State of Wisconsin will be informed.

Region III (Chicago) was notified of this event about 10:25 a.m., June 22, 1986. This '

information is current as of 11 a.m., June 23, 1986. )

{ f CONTACT: [Y Boyd FTS 388-5546 W. Guldemond FTS 388-5574 i

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