05000255/LER-2003-003
| Palisades Nuclear Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2552003003R00 - NRC Website | |
EVENT DESCRIPTION
On March 25, 2003, at 1116 hours0.0129 days <br />0.31 hours <br />0.00185 weeks <br />4.24638e-4 months <br />, with the plant in Mode 6, a loss of offsite power occurred while installing a signpost. The signpost penetrated a buried conduit, damaging a control power cable associated with both offsite power feeds. As a result, the safety-related and non-safety related buses de-energized, which caused a loss of shutdown cooling [BP] flow. The emergency diesel generators [DG;EK] started and loaded safety-related buses, as expected. An Alert was declared at 1126 hours0.013 days <br />0.313 hours <br />0.00186 weeks <br />4.28443e-4 months <br />. Shutdown cooling flow through the core was restored in approximately 20 minutes.
The Alert was downgraded to an Unusual Event at 1231 hours0.0142 days <br />0.342 hours <br />0.00204 weeks <br />4.683955e-4 months <br />. The Unusual Event was exited on March 27, 2003, at 1737 hours0.0201 days <br />0.483 hours <br />0.00287 weeks <br />6.609285e-4 months <br />, when offsite power was fully restored.
This occurrence is reportable in accordance with 10 CFR 50.73(a)(2)(v)(B) as an event that prevented the fulfillment of the safety function of a system needed to remove residual heat, and in accordance with 10 CFR 50.73(a)(2)(iv)(A), as an event that resulted in automatic actuation of the emergency AC electrical power system.
ANALYSIS
Two offsite power feeds from the switchyard [FK] to the plant were being maintained operable.
Some of the control circuits involving both of these offsite power feeds were routed in the same cable.
While installing a signpost in the main parking lot, a conduit was penetrated, damaging the cable containing the control circuits for both offsite power feeds. This caused a spurious actuation of several relays. Actuation of these relays resulted in the opening of breakers, interrupting power from the switchyard to the plant.
The de-energized safety-related buses resulted in loss of power to the operating low pressure safety injection (LPSI) pump [P;BP] that was providing shutdown cooling flow. The emergency diesel generators started and loaded as designed. The LPSI pumps are not automatically re-energized from the emergency diesel generator under these circumstances. Shutdown cooling flow was restored in approximately 20 minutes, when operators manually started a LPSI pump, with an emergency diesel generator supplying power to the pump's bus.
CAUSE OF THE EVENT
There was no written process for controlling excavating/trenching/piercing the ground. Additionally, NMC missed an opportunity in May 2002 to identify the lack of procedural controls when an inadequate evaluation was performed for a previous event.
CORRECTIVE ACTIONS
A plant policy was issued prohibiting all digging and landscaping activities without appropriate approval and oversight.
The damaged cable was repaired, and the control circuits for one of the two offsite power feeds were relocated to a separate cable.
A procedure is being written to control excavating/trenching/piercing activities.
SAFETY SIGNIFICANCE
All safety systems functioned as designed. Primary coolant system temperature increased from approximately 92°F to 104°F. The average hourly heat-up rate limit specified in Technical Specification 3.4.3 was not exceeded. Fuel integrity was not challenged.
PREVIOUS SIMILAR EVENTS
Palisades has had several instances where equipment or cabling was damaged as a result of excavation/digging/trenching activities; however, none have caused a loss of offsite power.