|Reporting criterion:||10 CFR 50.73(a)(2)(iv), System Actuation|
|2472002003R01 - NRC Website|
- 1 DOCKET
- 2 SEQUENT
- 3 PLANT AND SYSTEM IDENTIFICATION
- 4 EVENT IDENTIFICATION
- 5 EVENT DATE
- 6 REFERENCES
- 7 PAST SIMILAR EVENTS
- 8 EVENT DESCRIPTION
- 9 DOCKET
- 10 SEQUENT REVISI
- 11 LER NUMBER
- 12 EVENT ANALYSIS
- 13 DOCKET
- 14 SEQUENT REVISI
- 15 IAL
- 16 EVENT SAFETY SIGNIFICANCE
- 17 DOCKET
- 18 SEQUENT REVISI
- 19 CORRECTIVE ACTIONS
- 20 PREVIOUS OCCURRENCES
FACILITY NAME (1) NUMBER (2) LER NUMBER6) PAGE (3)
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PLANT AND SYSTEM IDENTIFICATION
Westinghouse 4-Loop Pressurized Water Reactor
138 KV Ground Protection Trip Results in Auto Start of Emergency Diesel Generators
July 19, 2002
Condition Reporting System Number: 200207157
PAST SIMILAR EVENTS
On July 19, 2002 at approximately1413 hours
, with the plant operating at 100 percent steady state power, a loss of the Indian Point Unit 2 Buchanan 138-kV offsite power source occurred due to the actuation of ground protection controls for the 138/6.9-kV station auxiliary transformer. This 138-kV source is the preferred offsite supply to 6.9-kV Buses 5 and 6. As a result at1414 hours
, engineered safety feature (ESF) 480-V Buses 5A and 6A and associated required safeguards equipment became de-energized. Abnormal Operating Instruction (A0I) 27.1.1, "Loss of Normal Station Power," Revision 15 was entered. � With Buses 5A and 6A de-energized, 21, 23, 24, and 26 service water (SW) pumps became de-energized. This reduced the cooling water supply to both the essential and non-essential service water headers. However, because 480-V Buses 2A and 3A were unaffected by the loss of 138-kV offsite power source, 25 SW pump remained energized providing cooling on the essential service water header. Per Technical Specification 3.7.B.3, plant operation may continue for24 hours
if the entire 138-kV source of power is lost provided all three (3) emergency diesel generators (EDG) are operable. As designed, all three EDGs received an automatic start signal. However prior to this, 21 EDG had been declared inoperable in preparation for maintenance activities. At1429 hours
, operations personnel restored 21 EDG to operable status and re-energized Buses 5A and 6A by closing the output breakers from 21 and 23 EDGs. Once these EDGs were available, 22 SW pump was started to support operation on the non- essential service water header.
FACILITY NAME (1)
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EVENT DESCRIPTION (Continued) In accordance with AOI 27.1.1 operations personnel proceeded with the restoration of plant systems. At2107 hours
, the 138-kV feed to the station auxiliary transformer was restored. At2243 hours
, the limiting condition for operation (LCO) for Technical Specification 3.7.B.3 was exited. There were no inoperable structures, components, or systems, which contributed to the initiation of this event. Although 21 EDG had been declared inoperable prior to the event, this did not contribute directly to the loss of the 138-kV offsite power source.
This event was initiated by the actuation of ground protection controls for the 138/6.9-kV station auxiliary transformer. A fallen tree branch caused the grounding of the C-phase conductor on the station auxiliary transformer. This immediately resulted in the loss of the 138-kV offsite power source, the preferred supply to 6.9-kV Buses 5 and 6. A contract worker was electrocuted while trimming trees adjacent to the 138-kV feeder to the station auxiliary transformer. The worker had not been authorized to perform work in this specific area. Furthermore, the worker did not notify supervision of his intent to perform work in the area. This event was determined to be a human performance-related error. Contrary to existing station procedures, training, and management's expectations, a contract worker fatality occurred while performing unauthorized work activities.
In responding to this event Abnormal Operating Instruction (AOI) 27.1.1, "Loss of Normal Station Power," Revision 15 was entered. Prior to loading the EDGs onto their respective 480-V buses, AOI 27.1.1 requires operators to verify at least one SW pump on the essential header, component cooling water pump, and charging pump are running. After these items were verified, operations personnel re-energized Buses 5A and 6A by closing the output breakers from 21 and 23 EDGs. Once this was completed, 22 SW pump was started and other plant systems were restored in accordance with AOI 27.1.1 A post-event review indicates that the plant's response to the loss of the 138/6.9-kV station auxiliary transformer was per plant design. Timely operator response resulted in minimizing the amount of time that 480-V Buses 5A and 6A were de-energized. However, the need for improvement in the areas of procedure implementation, Technical Specification implementation, and control room log keeping were recognized.
Pursuant to 10 CFR 50.72 (b)(3)(iv)(A), an eight-hour report was made to the NRC on July 19, 2002 at1515 hours
(Event Number 39074).
FACILITY NAME (1)
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EVENT SAFETY SIGNIFICANCE
Industrial Safety This event adversely affected industrial safety. While performing unauthorized work activities, a contract worker fatality occurred. Due to the hazards associated with the station auxiliary transformer's location, the potential for additional injuries existed during the rescue efforts. Because of the controls put in place during the event, this potential was minimized.
Radiological Safety There were no direct or potential radiological safety implications from this event.
Nuclear Safety A post-event review indicates that the plant's response to the loss of the 138/6.9-kV station auxiliary transformer was per plant design. Power to the auxiliaries on 6.9-kV Buses 5 and 6 during "on line" plant operation is supplied by the station auxiliary transformer from the Buchanan 138-kV offsite power feeder. The alternate 13.8 kV feed remained unaffected during this event, and was available to power the plant vital equipment if needed. In addition, although 21 EDG was not in automatic, it was available and, in fact was started by the operators and loaded on to its respective bus as described previously. Therefore, except for this additional operator action, the plant was available to respond and did respond to the loss of the 138-kV offsite feed as designed. Based on the above, the conditional core damage probability was calculated to be 1.07 E-7 for this event. The previous discussion contained in Revision 0 of this report provided an instantaneous core damage frequency, and was very conservative in that it did not credit any power recovery, which was available during and following this event.
Indian Point, Unit 2 05000247 LER NUMBER) 6)
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As a result of this event, the following corrective actions were taken to reduce the probability of a similar event from occurring in the future.
1. Following the immediate rescue and equipment recovery activities, a stand-down of all station personnel involved with risk significant work activities was implemented. No risk significant work activities were permitted until such time that all station personnel attend a formal event briefing. The briefings were conducted on July 22, 2002 by senior station management and stressed the importance of ensuring that all personnel understood their work scope prior to initiating work activities. Also, the importance of accountability for all personnel to use appropriate safety equipment and to monitor their fellow employee's safety work practices were discussed. (Completed) 2. Additional "Danger-High Voltage" and "Danger-Fall Protection Required Beyond This Point" signs were placed at various locations. (Completed) 3. Placed signs requiring authorization by the plant manager for entry into the 138-kV and transformer yard areas. (Completed) 4. An additional Operations hold-off lock was placed on gate 209 (rear of EDG Building) in addition to the existing Security lock. (Completed)
A review of previous occurrences that involved the same underlying concern or reason as this event was performed. Three (3) recent occurrences were identified, and reported to the NRC in the following LERs:
Indian Point Unit 2 experienced an automatic reactor trip which was initiated by a main turbine trip on auto stop oil. The auto stop oil turbine trip was caused by a trip of over frequency relays actuated by a disturbance associated with the 345 Kv Bus W93. All three EDGs started and buses 2A and 3A were manually energized by 22 EDG.
hours, during surveillance testing of 480 volt Bus 3A undervoltage relays, with the reactor at 100 percent power, 480-volt Bus 3A was lost. This resulted in the automatic start of all three EDGs.
hours, during preparations for main turbine start-up and with the reactor at 6.5 percent power, a turbine trip occurred due to high water level in 21 Steam Generator. This event resulted in the initiation of the Auxiliary Feedwater System, which is an Engineered Safety Feature (ESF) actuation.