05000341/LER-2005-003
| Docket Number05 18 2005 2005 -0003 .000 06 29 2005 05000 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| Initial Reporting | |
| ENS 41714 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition |
| 3412005003R00 - NRC Website | |
Initial Plant Conditions:
Mode 1 Reactor Power 100 percent
Description of the Event
On May 18, 2005 during a review of the dedicated shutdown procedure (20.000.18), design and operating procedure deficiencies were identified relating to 10 CFR 50 Appendix R events. Battery charger 2C-1 is relied upon to feed post fire emergency shutdown loads. Although a circuit breaker supplying power to a battery charger 2C-1 was re-closed by procedure after a trip or loss of division 1 power, an additional action was required to return the battery charger to service. The battery charger 2C-1 contactor circuit logic requires the control switch first be returned to the off-reset position, before the contactor can be re-energized. That control switch and associated control wiring is located in the control room envelope that is evacuated in an Appendix R fire scenario.
Furthermore, the dedicated shutdown logic does not isolate this control switch circuitry from cables in the fire affected zone which is a requirement of the Appendix R circuit design.
In addition to the same issues identified for battery charger 2C-1, the dedicated shutdown procedure did not provide for reclosure of the circuit breaker feeding 480 volt power to battery charger 2C1-2 after a trip. The 480 volt power supply for charger 2C1-2 was also determined to be susceptible to spurious tripping of the supply breaker due to fire damage. Battery charger 2C1-2 is required to power 260VDC motor operated valves used by the standby feedwater system (SBFW) to provide reactor cooling water and to control reactor water level after a shutdown due to an Appendix R fire. In these scenarios, power is initially supplied by the associated battery 2PC, but the battery is not sized to provide power for the entire duration of the Appendix R event. Therefore, a safe shutdown was not assured using the dedicated shutdown panel [IL] during all Appendix R scenarios.
Balance of plant (BOP) battery 2PC [EI] is designed to operate for four hours without the chargers (or less depending on DC loads). Based on a review of the assumptions in the design calculation and the loads not shed from the battery by the dedicated shutdown procedure, engineering estimated that the battery could be expected to perform its intended function for approximately 2-1/2 hours after evacuation of the main control room due to an Appendix R fire with an attendant loss of division 1 power. This battery supplies the power to the dedicated shutdown panel, including the dedicated shutdown instrumentation, circuit isolation transfer relays, supervisory control for combustion turbine generator (CM) 11-1 [EK] and 120 KV (division 1) switchyard circuit breakers [FK], and SBFW flow control valves.
The affected Appendix R equipment was declared inoperable at the time of the event. Procedure changes have been made to incorporate the use of blocking devices in the battery contactors and to eliminate fire induced short circuit issues. Operators have been trained in the proper use of the blocking devices and the revised procedure to address this issue. These interim measures restore the ability to use dedicated shutdown panel to shutdown the plant from outside the control room with an attendant loss of offsite power.
Immediate notifications were made to the NRC in accordance with 10 CFR 50.72 on May 18, 2005 (EN 41714).
This event is being reported under 50.73(a)(2)(ii)(B), as an event or condition that resulted in the plant being in an unanalyzed condition that significantly degraded plant safety. There were no actual equipment failures.
Cause of the Event
The original design was deficient in that it did not ensure that the battery charger circuits were isolated from potential Appendix R fire areas. During the initial compliance strategy development in the mid 1980's, there was a lack of coordination between all of the parties involved in implementing the dedicated shutdown panel design for Appendix R scenarios. The procedure was deficient in that it only called for energizing one of two needed battery chargers and did not recognize that additional actions would be required after a loss of power to the chargers or fire induced shorts that could not be accomplished using the equipment as designed. Consequently, procedures and subsequent procedure revisions were written over the years that did not recognize or address these problems. Organizational and programmatic deficiencies contributed to the inadequate original design and the subsequent lack of coordination between the designers and site implementing groups.
Analysis of the Event
This event involves the ability to operate equipment from the dedicated shutdown panel under circumstances where a postulated Appendix R fire occurs that forces evacuation of the main control room and shutdown of the plant from the dedicated shutdown panel, concurrent with a loss of power to the BOP battery chargers. The BOP battery chargers provide the power to isolate required circuits from the fire affected zones, power the dedicated shutdown panel instrumentation, and power valves that need to operate to bring the plant to safe shutdown. Since the controls for the contactors supplying power to these chargers run through the fire affected zones, it must be assumed that the fire could cause the power loss to the BOP battery chargers. It is intended that a standby feedwater pump and other safe shutdown loads are operated from the dedicated shutdown panel under such conditions to achieve and maintain plant cold shutdown.
The plant design includes provisions that provide a defense-in-depth approach to fire protection. This includes minimizing the susceptibility to fire through the use of fire retardant cables, automatic suppression systems, and limits placed on the amount of transient combustible material allowed in fire zones. These provisions minimize the chances of a fire that would result in using the alternative shutdown system. The plant is walked down monthly to ensure that combustible material is not allowed to accumulate. Fire detection, fire protection systems, and a trained fire brigade are available to mitigate the consequences of plant fires. Detection and suppression equipment is maintained and tested in accordance with industry and Technical Requirement Manual specifications to ensure a high degree of reliability.
In summary, this event involves only those postulated scenarios requiring evacuation of the main control room during an Appendix R fire concurrent with a loss of power to BOP battery chargers. For scenarios during which power is not lost to the BOP battery chargers, the dedicated shutdown procedures and equipment would have performed as intended. The alternative shutdown design is one of several defense-in-depth measures taken to mitigate the consequences of plant fires. The effect of this event on plant risk has been evaluated, and it has been determined to be of very low safety significance. Therefore, the health and safety of the general public was not adversely affected by this event.
Corrective Actions
The dedicated shutdown procedure has been revised to address the issues identified in this report. It incorporates steps that require the manual blocking of contactors that supply power to both 2C-1 and 2C1-2 battery chargers.
Blocking devices specific to this application have been fabricated and staged in the vicinity of the battery charger contactors. The operating staff has been trained on the proper use of the blocking devices and the revised procedure. These interim measures address both the inability to access the battery charger controls from the control room and the possibility of fire induced short circuits. Operations personnel reviewed the entire dedicated shutdown procedure to ensure that similar issues were not contained in other sections of the procedure.
This event is documented and evaluated in the Fermi 2 corrective action program, CARD 05-23111. Permanent design and procedural changes are being developed under this CARD to address the problems identified in this LER. The interim measures discussed above will be replaced by permanent design and procedure changes. The design changes are in progress with a planned completion in mid-August 2005. Installation of the design changes and completion of the associated procedure modifications will follow, commensurate with established priorities and processes of the Fermi 2 corrective action program. Any further corrective actions identified as a result of these evaluations will be tracked and implemented by the corrective action program.
Additional Information
A. Failed Components: None B. Previous LERs on Similar Problems:
be assured under all postulated scenarios described in the Updated Final Safety Analysis Report (UFSAR).
Under certain conditions where Combustion Turbine Generator (CTG) 11-1 (the dedicated Appendix R alternate AC source) or other station CTGs (11-2, 11-3 or 11-4) are operating in parallel with the grid, availability of the dedicated alternate AC source cannot be assured. Actions to address the potentially affected Appendix R scenarios were put in place on March 7, 2005, when the deficiencies were identified.
Additional scenarios were identified and additional corrective actions are being evaluated within the plant's corrective action program. The cause of these problems was determined to be a lack of coordination, dating back to the mid-1980's, between all of the parties involved in implementing the use of CTG 11-1 as the Alternate AC source for Appendix R scenarios involving a loss of offsite power. Root Cause analysis and corrective actions were in progress at the time of the current event. The current LER's BOP battery charger issue was identified during the performance of corrective actions for LER 2005-002.
result of the regional electric grid disturbance that affected several eastern and central states and portions of Canada and that led to blackout conditions in a large portion of the United States. Combustion Turbine Generator (CTG) 11-1 did not initially start in response to this event. The causes of the CTG 11-1 failure to start were an improper trip setpoint for the battery powered inverter and a failure to start the DC fuel oil pump due to a starter contact sticking open against its arcing horn. The improper inverter setpoint occurred because the inverter was not properly integrated into the overall system design during a 1996 modification / refurbishment. CTG 11-1 related corrective actions focused on entering the proper inverter setpoint into the design database, periodically testing the low voltage trip setpoint, maintenance to the sticking contactor, and the performance of periodic black start tests on CTG 11-1.