PNO-III-89-075, on 891122,startup Process of Reactor Was Terminated When Nuclear Instrumentation Showed That Reactor Was Approaching Criticality Sooner than Anticipated

PNO-III-89-075:on 891122,startup Process of Reactor Was Terminated When Nuclear Instrumentation Showed That Reactor Was Approaching Criticality Sooner than Anticipated

ML20198L764
Person / Time
Site:	Byron
Issue date:	11/21/1989
From:	Phillips M, Wright G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-89-075, PNO-III-89-75, NUDOCS 9710270140
Download: ML20198L764 (1)

PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-III-89-75 Date November 21, 1989 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public A 'erest significance. The information is as initially received without verification or luation, and is basically all that is known by the Region III staff on this date.

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Facility: Commonwealth Edison Co. Licensee Emergency Byron Unit 2 Classification: /A c ehleu. copI ,

Byron, IL 60407 Unusual Event Docket No. 50-455 A1ert Site Area Emergency (M T AN ' j General Eme gency X Not Applicab'e

Subject:

TERMINATION OF REACTOR STARTUP At approximately 9:50 p.m. on November 20, 1989, reactor operators began pulling control rods following a maintenance outage to repair a small leak from a pressurizer safety valve.

The startup process was terminated at 10:18 p.m. when nuclear instrumentation showed that the reactor was approaching criticality sooner than anticipated. Reactor operators moved all control rods to the fully inserted position. The licensee subsequently estimated that criticality would have been reached about 120 steps sooner in the control rod withdrawal procedure than estimated. (The point of criticality was not reached before the control rods were reinserted.)

The Senior Resident Inspector was in the control room monitoring startup at the time.

The criticality process is being reviewed by licensee nuclear engineers. A portion of the ical point which might not have appropriately claracterized the startup conditions.

Grepancy licensee doesmay havetobeen not intend resume caused by the startup activities until ituse of an identifies o)erating the cause of h tr.e difference between actual criticality point and the estimated point.

Region III (Chicago) and the resident inspectors will monitor the licensee's investigation.

Tha Senior Resident Inspector will be in the control room when startup activities resume.

The State of Illinois will be notified.

Tha Senior Resident Inspector notified Region III personnel of this incident at about 12:00 a.m. on November 21, 1989. This information is current as of 9:30 a.m.,

November 21, 1989.

CONTACT: M. Phillips (FTS 388-5530) G. Wright (FTS 388-5695)

DISTRIBUTION:

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