05000255/LER-2015-001
| Palisades Nuclear Plant | |
| Event date: | 09-16-2015 |
|---|---|
| Report date: | 11-10-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2552015001R00 - NRC Website | |
EVENT DESCRIPTION
On September 16, 2015, the plant was operating at approximately 85% power performing a coastdown in preparation for refueling outage 1R24. At approximately 0117 hours0.00135 days <br />0.0325 hours <br />1.934524e-4 weeks <br />4.45185e-5 months <br />, an anomaly within the digital electro-hydraulic (DEH) turbine control system [JJ] initiated a turbine [TRB] trip. As designed, the turbine trip actuated the reactor protection system [JC] to automatically trip the reactor [RCT] due to a loss of load. The auxiliary feedwater system [BA] started automatically, as designed, to recover steam generator [SG] levels.
No safety-related structures, components, or systems were inoperable at the start of the event that contributed to the event.
The Palisades DEH control system is based on the Westinghouse Distributed Processing Family (WDPF) MOD III that was installed in 1992.
CAUSE OF THE EVENT
The direct cause of the event is the turbine tripped due to actuation of the "DEH controller loss of power" turbine trip logic.
The cause for the turbine trip logic actuation was two-fold. Initially, there was a failure of a power supply [JX] module on a circuit board in the DEH turbine control system. Subsequent to the power failure on the circuit board, a second failure, either a loss of power to the overspeed protection control (OPC) distributed processing units (DPUs) or a loss of communications between the primary and backup OPC DPUs, occurred resulting in an actuation of the "DEH controller loss of power" turbine trip logic.
The root cause of the event is that the design of the DEH system contains unnecessary trip logic associated with turbine overspeed monitoring.
CORRECTIVE ACTIONS
The failed circuit board was replaced. A modification was implemented that removed the DEH system's trip logic for OPC loss of power and loss of communications.
ASSESSMENT OF SAFETY CONSEQUENCES
There were no actual consequences to general safety of the public, nuclear safety, industrial safety, or radiological safety for this event. The automatic reactor trip occurred as designed as a result of the turbine trip. The potential consequences of this event are considered to be of very low safety significance.
PREVIOUS SIMILAR EVENTS
None