05000364/LER-2014-001
| Docket Number | |
| Event date: | 01-11-2014 |
|---|---|
| Report date: | 03-12-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 3642014001R00 - NRC Website | |
Westinghouse - Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX].
Description of Event
On January 10, 2014 at 0919 CST, while operating in Mode 1 at 100 percent power, Farley Nuclear Plant (FNP) Unit 2 voluntarily entered 24-hour Required Actions of Technical Specifications 3.3.1 (Reactor Trip System Instrumentation) and 3.3.2 (Engineered Safety Feature Actuation System Instrumentation) in order to perform periodic logic testing of the B- Train Solid State Protection System (SSPS)[CABI per surveillance procedure FNP-2-STP- 33.0B, "Solid State Protection System Train B Operability Test". During this testing, unexpected test results were encountered at two logic test switch [HS] positions, C-22 and D-1. FNP immediately organized an Issue Response Team to coordinate troubleshooting efforts. FNP was unable to resolve the unexpected test results prior to the expiration of the Required Actions, resulting in the shutdown of Unit 2 to Mode 3 on January 11, 2014 at 1453 CST. This shutdown is reportable under 10 CFR 50.73(a)(2)(i)(A), 'The completion of any nuclear plant shutdown was cooled down to Mode 5 on January 12 at 2045 CST to further comply with Technical Specification Required Actions.
A subsequent inspection of the connector pins for the Safeguards Driver circuit card at location A516 identified a stray "termi-point clip" electrical connector (CON] making contact with pins 16 and 17. The termi-point clips are utilized In the FNP SSPS system to secure circuitry wiring to circuit board connector pins. A search of accessible portions of the cabinet resulted in the identification of a second stray termi-point clip on pin 43 of the Universal Logic card at location A407. No other foreign material was identified in the cabinet.
Following removal of the two termi-point clips a successful logic test of the B-Train SSPS per procedure FNP-2-STP-33.013 was completed on January 13, 2014 at 1845 CST. The 8-Train SSPS was returned to operable status and a plant startup was commenced with Mode 2 being entered on January 14, 2014 at 1003 CST. Unit 2 returned to full power on January 15, 2014 at approximately 2300 CST.
Cause of Event
A root cause investigation determined that the direct cause of the B-Train SSPS logic test failure was foreign material in the form of a stray terms-point clip that caused an intermittent short between pins 16 and 17 of the Safeguards Driver card at location A516. The logic card at location A407 is associated with nuclear instrument intermediate range trip circuitry. Due to a lack of a history of any intermediate range trip logic errors or other issues associated with this location, the stray termi- point clip at this location is not suspected of having caused any electrical shorts. A review of the maintenance history for the B-Train SSPS failed to identify a specific work activity or time period when the foreign material was introduced into the cabinet.
The root cause of this event was determined to be that FNP leadership did not appropriately manage the risk associated with past indeterminate SSPS failures.
Safety Assessment The intermittent short caused by the stray termi-point clip may have resulted in numerous B-Train component actuations not occurring in the event of an automatic safety injection. However the manual B-Train safety injection actuation capability remained unaffected by the short. Initiation of manual safety injection is an immediate operator action in the emergency response procedures that is directed by procedure and performed by a single action from the main control board. Both automatic and manual reactor trip functions of B-Train SSPS were unaffected by the short.
The redundant A-Train SSPS and A-Train components actuated by SSPS remained operable for the duration of declared inoperability of the B-Train SSPS. Additionally there was no plant event during the inoperability period that called for an SSPS actuation. Unit 2 remained within Technical Specification limits at all times.
Corrective Action To address the extent of condition from this event, non-intrusive foreign material inspections of the Unit 2 A-Train SSPS cabinet and both trains of Unit 1 SSPS cabinets are being performed at the next opportunity (when each train of SSPS is disabled during scheduled surveillance testing) and more thorough and intrusive foreign material inspections of the SSPS cabinets will be performed during the next refueling outage for each unit.
FNP implemented FME controls for electrical cabinets in 2003 and strengthened these procedures in 2007 with the inclusion of a checklist to document FME breeches and closeout inspections.
During the root cause investigation, the FME procedure (NMP-MA-009) and completed FME breech checklists for work in SSPS cabinets were reviewed. This review determined that current FME practices are sufficient to preclude uncontrolled introduction of FME during work activities.
To prevent reoccurrence, troubleshooting procedures will be revised to establish a practice of performing component validation during troubleshooting and to establish a practice to address timely issue resolution when the direct cause of a failure was not validated during initial troubleshooting.
Additional Information
Previous FNP Licensee Event Reports were reviewed from 2008 to present with no reports being identified related to failures of the SSPS of either train on either unit.