ENS 44748
ENS Event | |
|---|---|
19:30 Jan 1, 2009 | |
| Title | Two Emergency Diesel Generators Declared Inoperable Due to Component Failure |
| Event Description | EVENT DESCRIPTION: During return to service testing for Emergency Diesel Generator (EDG) #3, it was noted that the fuel rack limiting cylinder was not returning to its non-limiting position. The fuel rack limiting cylinder is designed to limit the stroke distance of the fuel rack assembly during the initial EDG start sequence. Once the EDG is at rated speed, ~10 seconds, the fuel rack limiting cylinder should return to its non-limiting position. Failure of this component to operate as expected may have prevented EDG #3 from fulfilling its safety function during the postulated Loss of Off Site Power and/or Loss of Coolant Accident conditions. As a result, EDG #3 remains inoperable.
During performance of subsequent surveillance testing on the remaining EDG's (#1, #2, and #4), in accordance with Technical Specifications, a similar condition as described above existed on EDG #4. EDG's #1 and #2 did not exhibit the same behavior and therefore, these EDG's remained operable during this sequence of events. Consequently, EDG #4 was declared inoperable at 1430 on 1/01/09. Failure of this component to operate as expected may have prevented EDG #4 from fulfilling its safety function during the postulated Loss of Off Site Power and/or Loss of Coolant Accident conditions. The concurrent failure of this component on EDG #3 and EDG #4 may have prevented on-site emergency power to Emergency busses 3 & 4 and thus the fulfillment of a safety function needed to mitigate the consequences of an accident. INITIAL SAFETY SIGNIFICANCE EVALUATION: Plant operation is being maintained within the limiting conditions of the license expected. However, transient analyses relating to accident mitigation could have been impacted due to the inability to ensure emergency on-site power supply to Emergency busses 3 & 4. Off-site power and the grid have been stable during the time period both EDG's were inoperable. CORRECTIVE ACTIONS: The fuel rack limiting cylinder for EDG #4 was repaired and EDG #4 was restored to Operable on January 1, 2009 at 1755 EST. Actions required per technical specifications for 2 EDG's were exited within the required time frame. Repair efforts are in progress for EDG #3. The licensee informed the NRC Resident Inspector.
On January 1, 2009, at 2106 hours0.0244 days <br />0.585 hours <br />0.00348 weeks <br />8.01333e-4 months <br />, the Control Room Shift Manager made a notification (i .e. Event Number 44748) to the NRC Operations Center in accordance with 10 CFR 50.72 (b) (3) (v) (D) (i.e., any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident). The notification was made due to two Emergency Diesel Generators (EDGs) being declared inoperable. During return to service testing for BSEP's EDG 3, it was noted that the fuel rack limit cylinder was not returning to its non-limiting position in a timeframe consistent with prior observations. The fuel rack limit cylinder is designed to limit the stroke of the fuel rack during the initial EDG start sequence, preventing too much fuel from being provided to the engine cylinders on initial start. Once the EDG is at half-rated speed (i.e., in approximately 5 to 8 seconds), the fuel rack limit cylinder should be released to return to its non-limiting position. Failure of this component to operate as expected may have prevented the EDG from fulfilling its safety function during the postulated Loss of Off-site Power (LOOP) and/or Loss of Coolant Accident (LOCA) conditions. As a result, EDG 3 was conservatively declared inoperable due to the potential for the unexpected response of the fuel rack limit cylinder to impact Design Basis Accident (DBA) transient loading criteria. During performance of subsequent surveillance testing on the remaining EDG's, (i.e.,1,2, and 4), in accordance with Technical Specifications, a similar condition was identified on EDG 4. EDGs 1 and 2 did not exhibit the same behavior and therefore, these EDGs remained operable during this sequence of events. Consequently, EDG 4 was also conservatively declared inoperable at 1430 on January 1, 2009. The concurrent failure of this component on EDG 3 and EDG 4 may have prevented the onsite emergency power from fulfilling its intended safety function needed to mitigate the consequences of an accident. Basis for Retraction Further investigation has demonstrated that both EDG 3 and EDG 4 were fully operable. The EDG 3 evaluation concluded that the fuel rack limit would remain in effect for approximately seven (7) seconds after the diesel output breaker closed during a LOOP loading event or a design basis LOOP/LOCA loading event. After that, the fuel limit cylinder would not have limited the governor response in any way. The generator capacity during the first seven seconds of load acceptance at the fuel rack limited position would be sufficient to ensure proper acceleration of the 480-volt design basis loads and the Nuclear Service Water pump. These are the only loads expected to start during the first seven seconds of the EDG loading. The generator frequency response during the acceleration of these loads would be well within the EDG design limits. The Residual Heat Removal and Core Spray pumps are sequenced onto the EDG at 10 seconds and 15 seconds, respectively, following the closure of its output breaker and are not affected by the fuel limiter impairment. The EDG 4 evaluation is bounded by the above analysis. Therefore, the fuel rack limiter impairment would not have prevented either EDG 3 or EDG 4 from fulfilling their intended safety function. On this basis, this event is not reportable under 10 CFR 50.72(b) (3) (v) (D). Investigation of this condition is documented in the corrective action program in Nuclear Condition Report (NCR) 312876. The NRC resident was notified of this retraction. R2DO (Musser) has been notified. |
| Where | |
|---|---|
Brunswick  North Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+1.6 h0.0667 days <br />0.00952 weeks <br />0.00219 months <br />) | |
| Opened: | C. Dunsmore 21:06 Jan 1, 2009 |
| NRC Officer: | Steve Sandin |
| Last Updated: | Mar 2, 2009 |
| 44748 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Brunswick with 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
WEEKMONTHYEARENS 559972022-07-16T00:20:00016 July 2022 00:20:00
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