05000220/LER-2005-004
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. | |
| Event date: | 12-19-2005 |
|---|---|
| Report date: | 02-17-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2202005004R00 - NRC Website | |
I. Description of Event
On December 19, 2005, at 1509 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.741745e-4 months <br />, National Grid (NG) Regional Control notified the Nine Mile Point Unit 1 (NMP1) Control Room that a Traveling Operator had noted abnormal readings on one of the 115 KV off-site power lines (Line 4) and suggested the indication could be the result of an open phase. The James A. Fitzpatrick Nuclear Power Plant (JAF) Control Room was contacted and an investigation revealed a failure of the bus bar connector on the "A" phase of Line 4 in the JAF switchyard. The unknown failure had existed from November 29, 2005, to December 19, 2005. Line 4 was declared inoperable as of November 29, 2005, arid removed from service for repairs. The failure was not flagged by any alarms at NMP1, JAF or NG installations and was not noted by Control Room operators at NMP1 or JAF.
During the time that the unknown failure existed, NMP1 exceeded the Technical Specification (TS) 3.6.3.b, "Emergency Power Sources," allowed out-of-service time for inoperable off-site power line. Line 4 was inoperable for longer than the allowed out-of-service time of 7 days. Additionally, during that time, NMP1 exceeded the TS 3.6.3.c allowed out-of service time for inoperable diesel-generator power system on two occasions. After Line 4 became inoperable on November 29, 2005, Emergency Diesel Generator (EDG) 102 was already inoperable for planned maintenance and was restored to operable status 4 days later, on December 3, 2005, at 0406 hours0.0047 days <br />0.113 hours <br />6.712963e-4 weeks <br />1.54483e-4 months <br />. Thus, TS 3.6.3.c allowed EDG out-of service time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> was exceeded. On another occasion, on December 12, 2005, at 1612 hours0.0187 days <br />0.448 hours <br />0.00267 weeks <br />6.13366e-4 months <br />, EDG 103 was declared inoperable and restored to operable on December 13, 2005, at 1718 hours0.0199 days <br />0.477 hours <br />0.00284 weeks <br />6.53699e-4 months <br />, which is another instance of non compliance with TS 3.6.3.c.
Line 4 was restored to operable status on December 20, 2005, at 1512 hours0.0175 days <br />0.42 hours <br />0.0025 weeks <br />5.75316e-4 months <br />.
11. Cause of Event The underlying cause of failure to identify the Line 4 deviation is a functional design deficiency regarding the adequacy of Control Room indications and alarms. Because of the "ring bus" design of off-site power to JAF, and NMP1 and alarms and indications, there was no interruption of power to either unit and no alarm to alert personnel of the abnormal situation. There is ampere loading indication for both off-site lines at NMP1, but the typical operating value falls in an uncalibrated and unmarked area of the meter.
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III. Analysis of Event
This event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications....
There were no actual safety consequences associated with this event. The most risk significant time period was during the overlapping of Line 4 out-of-service concurrent with EDG 102 out-of-service. Prior to taking EDG 102 out of service, the risk assessment of the maintenance activities resulted in the following risk management actions being taken:
- The redundant EDG was verified operable and no elective testing or maintenance activities were scheduled on the redundant (operable) EDG
- No elective testing or maintenance activities were scheduled in the 115 kV switchyard or on the 115 kV power supply lines and transformers which could cause a line outage or challenge offsite power availability
- The NMP1 diesel driven firewater pump (DFP) was verified operable as a feedwater makeup source to the NMP1 reactor pressure vessel (RPV)
- The Nine Mile Point Unit 2 DFP and cross-tie to NMP1 were verified operable as a feedwater makeup source to the NMP1 RPV.
The incremental core damage probability for Line 4 being unavailable for the duration of the event was calculated as 8.7E-8.
Based on the above, the event did not pose a threat to the health and safety of the public or plant personnel.
IV. Corrective Actions
A. Action Taken to Return Affected Systems to Pre-Event Normal Status On December 20, 2005, at 1317 hours0.0152 days <br />0.366 hours <br />0.00218 weeks <br />5.011185e-4 months <br />, NMP1 was notified by the JAF that repairs were complete. The same day, at 1512 hours0.0175 days <br />0.42 hours <br />0.0025 weeks <br />5.75316e-4 months <br />, Line 4 was returned to service and declared operable based on the plant process computer indications.
B. Action Taken or Planned to Prevent Recurrence NOTE: There are no NRC regulatory commitments in this Licensee Event Report.
Corrective actions have been developed such that, when completed, a similar failure will be accompanied by an alarm and will be clearly visible on the control panel indications. These actions include:
- Implement a plant process computer alarm modification for low amperage on all 3 phases of off-site power lines.
- As a compensatory measure, amperage readings from the plant process computer of 3 phases of both off-site power lines will be verified and logged twice each shift until the corrective action (alarm modification) is implemented.
V. Additional Information
A. Failed Components:
None
B. Previous similar events:
None C. Identification of components referred to in this Licensee Event Report:
Components IEEE 805 System ID�IEEE 802.A Function 115 kV Offsite Power FK� N/A Emergency Diesel Generators EK DG AIM�