PNO-III-88-086, on 881016,reactor Automatically Shut Down Following Loss of Offsite power.Diesel-driven Auxiliary Feedwater Pumps Maintained Steam Generator Level.Caused by Explosion & Fire in Substation & Carboard in Delay Relay

PNO-III-88-086:on 881016,reactor Automatically Shut Down Following Loss of Offsite power.Diesel-driven Auxiliary Feedwater Pumps Maintained Steam Generator Level.Caused by Explosion & Fire in Substation & Carboard in Delay Relay

ML20155J248
Person / Time
Site:	Braidwood
Issue date:	10/18/1988
From:	Forney W, Hinds J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-88-086, PNO-III-88-86, NUDOCS 8810250435
Download: ML20155J248 (2)

g ,

w PRELIMINARY N_0TIFICAT!0N OF EVENT OR UNUSUAL OCCURRENCE--PNO-III-88-86 Date October 18, 1988 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: Commonwealth Edison Company Licensee Emergency Classification:

Braidwood Unit I X Notification of an Unusual Event Braceville, IL 60407 Alert Site Area Emergency Docket No. 50-456 General Emergency Not Applicable

Subject:

LOSS OF 0FFSITE POWER At 8:19 p.m (CDT), October 16, 1988, while operating at 95 percent power, the reactor automatically shutdown following the loss of offsite power. Emergency diesel generators automatically started and loaded to the emergency busses. Diesel driven Auxiliary feedwater pumps maintained steam generator levels. All safety systems functioned as designed.

The licensee declared an unusual event at 8:56 p.m. (CDT), in accordance with its emergency classification system. The unusual event was terminated at 10:17 p.m. (CDT), af ter off-site power was restored.

T% loss of off-site power has been attributed to an explosion and possible fire in an

e. tectiical distribution system substation (off-site). Due to an electrical malfunction (pole disagreement) of the bus tie breaker to the off-site fceder line, the loss of off-site power feedback into the site distribution ring bus resulted in backup breakers opening, causing a loss of power to the System Auxiliary Transformer (SAT).

Upon loss of power to the SAT, the 6900 VAC power supplies to the reactor coolant pumps (RCPs) are designed to automatically fast transfer to the Unit Auxiliary Transformer thereby maintaining reactor coolant flow and preventing a reactur trip. An additional d: sign feature on the RCP power supply breakers, which aids in the fast transfer are ,

the over current (OC) trip time delay relays. In this case, the IC RCP time delay relay could not function due to a piece of cardboard inserted between the contacts of the relay, resulting in tripping the IC RCP from an instantancous OC signal. The loss of tN IC RCP resulted in a reactor trip on "RCP low flow above P-8." The reactor trip resulted in a main turbine generator trip and the loss of the Unit Auxiliary Transformer (UAT).

With the loss of the off-site feeder power, i.e. the SAT and the main turbine generator i.e. the VAT, the Unit Emer Emergency Safety Features (gency Diesel Generators auto started, closed in on theESF) buses, the unit on natural circulation cooling until forced cooling could be restored by starting a RCP from off-site power.  !

The licensee is investigating the cause of the pole disagreement malfunction on the off-site feeder line and the cause of the cardboard placement in the 1C RCP OC trip time delay relay.

Tha Unit is currently in the hot standby mode. Region III (Chicago) will continue to monitor the licensee's course of action.

The State of Illinois will be notified.

The Headquarters Duty Officer was first notified of this event at 10:19 p.m. (EDT),  ;

October 16, 1988. This information is current as of 9 a.m. (CDT), October 18, 1938.

O \

set w50435 8S1018

$d $ s8-096 PDC yyc/

s c

,, 2 PRELIMINARYNOTlFICATIONOFEVENTORUNUSUALOCCURRENCE--PNO-III-88-86DateOctober 18, 1988 CONTACT: s FTS 388-5575 FTS 388-5590 DISTRIBUTION:

WFN 1 MNBB 1WFN _EfW_ WFF 1 Chairman Zech XEDU WRT UIA E Com Roberts ARM 0! SLITP Comm. Carr 1WFN Mail To:

Com Rogers PA Resident Inspector Offices DCS(Original)

SECY OGC Resident Inspector 00T(Trans.Only)

OGC-H FAX T0: Nicholson Lane Regions CA INPO 2:SA NET Region I GPA NSAC 1 09 - Region II ACRS Licensee $ P.) - Region IV POR HQS. Operations Officer 3.W Region V Region III Rev. June 1988

_. _ __ . . _ . _.