ML060670138
| ML060670138 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 03/08/2006 |
| From: | Burgess B L, West K S NRC/RGN-III |
| To: | |
| References | |
| PNO-III-06-005A | |
| Download: ML060670138 (2) | |
Text
March 8, 2006PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE -- PNO-III 005AThis preliminary notification constitutes EARLY notice of events of POSSIBLE safety or publicinterest 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.FacilityLaSalle Unit 1Exelon Generation Co.Marseilles, IL Docket: 50-373 License: NPF-11Licensee Emergency Classification Notification of Unusual Event Alert X Site Area Emergency General Emergency Not Applicable
SUBJECT:
INDICATION FAILURE FOR THREE CONTROL RODS FOLLOWING REACTORTRIP (UPDATE)DESCRIPTION:At 12:23 a.m. CST on February 20, 2006, the Unit 1 reactor shut down automatically from6 percent power, and reactor instrumentation showed that three control rods failed to insert fullyinto the reactor core. There are 185 control rods which control reactor power level and whichare fully inserted to shut down the reactor. Because of the uncertainty of the position of the three control rods, the licensee declared a SiteArea Emergency under its emergency plan at 12:28 a.m. After determining that the reactor wasshut down (i.e. subcritical), the licensee terminated the emergency classification.The reactor remains shut down in a refueling outage.Region III (Chicago) initiated a special inspection to review the circumstances surrounding thecontrol rod indicator problem and the licensee's investigation and corrective actions.The Region III special inspection was concluded on February 27. The inspectors concludedthat the reactor operators' response and emergency notification classification to the event wereappropriate. The licensee's investigation determined that at least two of the three control rodswere fully inserted, but that the instrumentation did not record the position of the rods. Thelicensee's post event analysis determined that the reactor would have been safely shut down inthe unlikely situation where all three control rods remained fully withdrawn. The licensee is still investigating the position of the third control rod.CONTACTS:Bruce BurgessSteven West630/829-9629630/829-9601 PNO-III-06-005A-2-The uncertain control rod indication was due to friction between the control rods and the fuelchannels due to channel bowing or deformation. When inserted, the control rods were held in aposition slightly beyond the point where instrumentation would show a fully inserted indication.Fuel channel deformation is a known industry issue and the licensee had been following thevendor's recommendations addressing this phenomenon. Prior to the outage, the licensee hadidentified 73 fuel bundles meeting the criteria for potential channel bowing/deformation. Thelicensee has reevaluated its fuel plan and now plans to discharge all susceptible bundles to the spent fuel pool. Subsequent inspections are planned for specific fuel bundles discharged to thespent fuel pool to further evaluate the cause of the channel deformation/bowing.While the special inspection has been completed, the resident inspectors are continuing tofollow the licensee's ongoing root cause evaluation of the failure of the electro-hydraulic turbinecontrol system which led to the reactor shutdown. Further NRC inspection is also pl anned onthe rod worth minimizer to determine if the equipment provided control room operators withappropriate information regarding control rod position during the shutdown. The State of Illinois has been notified of this updated information.The licensee and the NRC issued a news release on this event. The information in thispreliminary notification has been reviewed with licensee management.