05000255/LER-2002-002
| Palisades Nuclear Plant | |
| Event date: | 12-01-2002 |
|---|---|
| Report date: | 01-21-2003 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2552002002R00 - NRC Website | |
EVENT DESCRIPTION
On December 1, 2002, at approximately 2154 hours0.0249 days <br />0.598 hours <br />0.00356 weeks <br />8.19597e-4 months <br />, with the plant operating at 100% power, an automatic reactor [RCT] trip occurred on main generator [GEN] loss of load. The loss of load occurred when a transmission tower's [TWR] static line hanger [H] failed, allowing one of two static lines to contact a 345 KV transmission line, tripping the main generator. The static line also contacted the rear bus [BU] in the switchyard [FK] that supplies the plant non-1E 4160 volt startup transformers [XFMR]. The rear bus tripped on a fault-to-ground causing a loss of non-1E 4160 volt AC buses. Consequently, both main feedwater pumps [P;SJ] tripped, and the auxiliary feedwater system [BA] started automatically on low steam generator [SG] level, as expected.
The plant was maintained at or near normal operating pressure and temperature subsequent to the trip, on natural circulation, since startup power for primary coolant pumps [P;AB] was also lost.
The plant was returned to service on December 5, 2002.
This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in an automatic reactor trip and automatic actuation of the auxiliary feedwater system.
CAUSE OF THE EVENT
Inadequate preventive maintenance over a 30-year service life allowed mechanical wear of the hanger to the point of ductile failure. The additional mechanical load/force of the falling line caused a similar failure of the hanger and the pin/shoe connection on an adjacent tower. Evaluation of the event concluded that previous reviews of industry operating experience did not identify all hardware requiring inspections, which resulted in a lack of preventive maintenance activities.
SAFETY SIGNIFICANCE
The safety significance of this event was minimal. All safety systems functioned as expected during the plant trip.
CORRECTIVE ACTIONS
Authorization was obtained to operate without one static line on the section of 345 KV transmission line between the main power transformer and the switchyard. A new static line will be installed during the 2003 refueling outage, in accordance with original design.
The remaining static line was inspected and worn parts were replaced to prevent a similar event from occurring on this line. Also, the connections and conductors of the 345 KV lines were inspected with no anomalies identified.
Applicable industry operating experience is being re-evaluated and preventive maintenance activities for 345 KV components will be revised, as needed.
PREVIOUS SIMILAR EVENTS
A Consumers Energy hydro plant, Ludington Pumped Storage, had a failure of a static line hanger on October 14, 1995. The static line fell onto an arm of the tower that prevented it from contacting a conductor and creating an equipment trip. No incident report was distributed and Palisades' personnel were not previously aware of this occurrence.
PREVIOUS LERs None