05000335/LER-2013-002
| St. Lucie Unit 1 | |
| Event date: | 11-12-2013 |
|---|---|
| Report date: | 01-13-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3352013002R00 - NRC Website | |
Description of the Event
On November 12, 2013 St. Lucie (PSL) Unit 1 was manually tripped due to a digital- electro-hydraulic (DEH) fluid leak from a cracked 14" Swagelok port connector tubing fitting in the turbine control system. Prior to the reactor trip, PSL Unit 1 was at 90% power ascending to 98% power following the SL1-25 refueling outage. Following the reactor trip, emergency operating procedures for standard post-trip actions and reactor trip recovery were successfully completed and the unit was stabilized in Mode 3. The reactor trip was uncomplicated.
Cause
A root cause analysis performed for this event identified the following causes:
Root Cause RC1: A change to the forcing frequency on the DEH cabinet caused the tubing connected to the differential pressure switch for the electro-hydraulic pump discharge filter to resonate and fail at a port connector due to high cycle fatigue.
The change in vibration occurred as a result of the replacement of the Unit 1 DEH pumps with a different forcing frequency.
Root Cause RC2: The tubing assembly was not adequately supported when CAJON tee connections were installed adjacent to the port connectors to allow testing in support of turbine test blocks. The mass of the CAJON tee connections installed adjacent to the port connectors resulted in the tubing being overstressed by the vibration created by the replaced DEH pumps.
Analysis of Safety Significance The DEH System is Quality Group D, non-seismic. The DEH System does not perform a safety function, and is not required to mitigate the consequences of a design basis accident; therefore it is considered Non-Nuclear Safety. All safety related systems functioned as designed. There were no safety system actuations as a result of the trip.
This reactor trip event is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) as a manual actuation of reactor protection system (RPS). This event had no significant safety consequence. Given the response of the plant and the actions taken, the health and safety of the public was not affected by this event.
Immediate Corrective Actions
1. Removed the CAJON tee connectors and port connectors and re-supported four similar tubing installations inside the DEH cabinet. COMPLETE
Corrective Actions
1. Update the engineering procedure for post-modification testing to inspect for vibration and inadequate support of adjacent tubing/piping after a change to a vibration inducing component (pump, fan, etc.) which changes its forcing frequency 2. Update the maintenance procedure for post-maintenance testing to inspect for vibration and inadequate support of adjacent tubing/piping after a change to a vibration inducing component (pump, fan, etc.) which changes its forcing frequency.
Similar Events A search and review of data in the St. Lucie Corrective Action Program Database addressing the past five years revealed no previous occurrences or similar events.
Failed Component(s) Swagelok 1/1" port connector (TBG) August 1989 Swagelok Catalogue Catalogue Number -401-PC Manufacturer Swagelok Company