05000364/LER-2014-003
| Joseph M. Farley Nuclear Plant, Unit 2 | |
| Event date: | 11-15-2014 |
|---|---|
| Report date: | 01-13-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3642014003R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse - Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XXI.
DESCRIPTION OF EVENT
On 11/15/2014 Unit 2 was in Mode 2 and undergoing the reactor startup process following a refueling outage. At 0348 CST while withdrawing control rods during low power physics testing with control bank C at approximately 50 steps and the reactor subcritical, Digital Rod Position Indication (DRPI) for one of the control rods (M12) changed to 90 steps. The control room operators stopped withdrawing rods and entered the Abnormal Operating Procedure (AOP) for Malfunction of the Rod Control System. As directed by this AOP, the reactor trip breakers were opened at 0353 CST and all rods inserted as expected. Troubleshooting revealed that the issue was an indication problem, and control rod M12 had not been misaligned. The indication problem was determined to be caused by an invalid DRPI signal that was caused by a failure of the detector/encoder card associated with the M12 rod in the Data B cabinet. After replacement of the card all control rod indications returned to normal.
CAUSE OF EVENT
The invalid DRPI signal was caused by a failure of the detector/encoder card for control rod M12. This was an older DRPI card that was recently inspected and tested during this refueling outage and then subsequently failed. Therefore the failure is attributed to component aging.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT
The opening of the reactor trip breakers is reportable per 10 CFR 50.73(a)(2)(iv)(A) for manual actuation of the reactor protection system.
All required safety systems responded as expected. The control room operators entered the Abnormal Operating Procedure (AOP) for Malfunction of the Rod Control System. The plant remained stable at normal operating pressure and temperature.
This was determined to be an indication problem and the actual positions of the control rods were as required by Technical Specifications and by the procedure that was in use at the time for low power physics testing. When the reactor trip breakers were opened all control fully inserted. There was no impact to radiological safety, safety to the public, or safety of station personnel.
CORRECTIVE ACTION
The M12 DRPI detector/encoder card was replaced. The card will be sent to a vendor for failure analysis to determine the component on the card that actually failed. As an enhancement action, the AOP for Malfunction of the Rod Control System will be revised to assess rod position indication malfunction.
Internet e-mail to Intoccillect..Resourne0 me gm, and to the Desk Officer, Office of Information and Regulatory Maim, NE08-10202, (31a0-0104), Office of Management and Budget, Washngion, DC 20503. If a means u. xi to impose an Information collection do, a not display a currerily valid OMB control number, the NRC may not conduct or sponsor, and a person is not fagot /rW to respond to, the Irdennation collection.
I. FACILITY NAME 3. PAGE 6. LER NI 'WIER 2. DOCKET LiQUE NTIAL
NIIMBER
ADDITIONAL INFORMATION
Other system affected: No systems other than that mentioned in this report were affected by this report.
Commitment Information: This report does not contain any new licensing commitments.
Previous Similar Events:
A DRPI card failure in Farley Unit 1 in 2013 caused a similar indication problem for Control Rod P6 in Control Bank A. For that event the reactor trip breakers were not opened. This was because the condition was determined to be a Data B failure only when DRPI was selected for Data A and normal indication was restored.
This half accuracy mode of operation for DRPI met the Technical Specification requirements. Although this previous 2013 event was similar, no LER was required or submitted because the reactor protection system was not actuated. The AOP in effect in 2013 did not require opening the reactor trip breakers for a misaligned rod.
Subsequent to the 2013 event, and prior to the event for this LER, the AOP was revised to direct opening the reactor trip breakers for this situation.