05000237/LER-2006-002
| Dresden Nuclear Power Station | |
| Event date: | 04-06-2006 |
|---|---|
| Report date: | 06-05-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2372006002R00 - NRC Website | |
Dresden Nuclear Power Station (DNPS) Unit 2 is a General Electric Company Boiling Water Reactor with a licensed maximum power level of 2957 megawatts thermal. The Energy Industry Identification System codes used in the text are identified as [XX].
A. Plant Conditions Prior to Event:
Unit: 02� Event Date: 04-06-2006 �Reactor Mode: 1� Mode Name: Power Operation Power Level: 97 percent Reactor Coolant System Pressure: 1000 psig
B. Description of Event:
On April 6, 2006, at approximately 1039 hours0.012 days <br />0.289 hours <br />0.00172 weeks <br />3.953395e-4 months <br /> (CDT), with Unit 2 at approximately 97 percent power, DNPS Instrument Maintenance (IM) technicians were installing a new High Pressure Coolant Injection System (HPCI) [BG] temperature recorder 2-2340-9 when an energized recorder electrical lead was accidentally shorted to a recorder mounting bracket screw. A consequence of this electrical short was the transfer of the Essential Service System (ESS) to its emergency power supply from Motor Control Center (MCC) 28-2 and the trip of ESS circuit 16. This resulted in HPCI being declared inoperable due to a loss of its automatic function from the loss of power to its flow controller and signal converter. However, the system was available due to control room personnel being able to manually control system operation.
An ENS call was made on April 6, 2006, at 1344 hours0.0156 days <br />0.373 hours <br />0.00222 weeks <br />5.11392e-4 months <br /> (CDT) for the above-described event. The assigned ENS event number was 42481.
The HPCI was declared operable on April 6, 2006, at 1850 hours0.0214 days <br />0.514 hours <br />0.00306 weeks <br />7.03925e-4 months <br /> (CDT).
This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident." HPCI is a single train system and is credited in mitigating the consequences of an accident.
C. Cause of Event:
On April 6, 2006, two DNPS technicians were continuing with the work to replace the HPCI temperature recorder. The work for this day consisted of installing the new recorder in the control room panel. The installation consisted of mounting, rewiring, and testing of the recorder. Both technicians were involved with the removal of the old recorder two days prior to this event. A pre-job brief was conducted which included a discussion on working with hot leads and the necessity to tape the adjacent terminals and metal as a human performance tool to prevent a short condition.
The recorder was mounted, thermocouples wires were landed, and the neutral and ground power leads were landed and taped off as discussed in the pre-job brief. The next step was to land the hot power lead.
While a technician was attempting to land the hot power lead, the lead came in contact with the mounting bracket screw for the recorder, which caused a short to ground. The event occurred following the technicians return from a morning break. A self-checking drill was not performed when returning to the job site. Failure to perform the self-checking drill and a lack of attention to detail resulted in the technicians not noticing that the mounting bracket screw was only 1/4" away from the power lead terminal. Had the technicians noticed the close proximity of the mounting screw and taped it off, the event would have been prevented. During the evolution all correct safety attire was worn and no one was injured.
D. Safety Analysis:
The safety significance of the event is minimal. Technical Specification (TS) 3.5.1, ECCS - Operating," allows Unit 2 to remain at power for 14 days with an inoperable HPCI if the Isolation Condenser System (IC) is operable. Unit 2 was in compliance with TS 3.5.1 during this event as the IC was operable and HPCI was inoperable for approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. ESS circuit 16 supplies power to the HPCI signal converter and the flow controller. As a result of the power being lost, HPCI would not automatically ramp to full speed to supply the required injection flow to the reactor vessel.
Although the automatic function was affected, the control room personnel maintained the ability to manually control the turbine speed to achieve the required system injection flow. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.
E. Corrective Actions:
Corrective actions addressed the human performance issues through discussions of this event with the IM technicians during department training sessions and the evaluation the technicians during out of-the-box training for proper use of human performance tools. These corrective actions reinforced the need for self-checking and the use of tape on adjacent metal components when working with energized electrical leads.
F. Previous Occurrences:
A review of DNPS Licensee Event Reports (LERs) for the last three years identified two LERs associated with human performance.
dated June 11, 2004. This LER reported on the failure of technicians to reconnect electrical leads after a surveillance was stopped. The corrective actions from this LER address the control of action associated with activities not completed in their entirety. This event and associated corrective actions are not similar to and would not have prevented this event.
Estimated," dated July 18, 2003. This LER reported a calculation error and ineffective implementation of previous corrective actions to implement an appropriate setpoint. This event and associated corrective actions are not similar to and would not have prevented this event.
G.� Component Failure Data:
NA