SVPLTR 06-0039, Retraction of Licensee Event Report 237/2005-003, Units 2 & 3 Offsite Power Sources Declared Inoperable Due to Low Voltage.

Retraction of Licensee Event Report 237/2005-003, Units 2 & 3 Offsite Power Sources Declared Inoperable Due to Low Voltage.

ML062200314
Person / Time
Site:	Dresden
Issue date:	07/31/2006
From:	Bost D Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 05-003-00, SVPLTR # 06-0039
Download: ML062200314 (2)

Text

ExeklJ n Exelon Generation Company, LLC Dresden Nuclear Power Station 65oo North Dresden Road Morris, IL 60450-9765 www.exeloncorp.com Nuclear 10 CFR 50.73 July 31, 2006 SVPLTR # 06-0039 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit Nos. 2 and 3 Renewed Facility Operating License Nos. DRP-19 and DRP-25 NRC Docket Nos. 50-237 and 50-249

Reference:

Retraction of Licensee Event Report 237/2005-003, "Units 2 and 3 Offsite Power Sources Declared Inoperable Due to Low Voltage" Letter from D. G. Bost (DNPS) to U.S. NRC, dated August 22, 2005, Licensee Event Report 237/2005-003, "Units 2 and 3 Offsite Power Sources Declared Inoperable Due to Low Voltage" Exelon Generation Company, LLC (EGC) is retracting Licensee Event Report (LER) 237/2005-003, "Units 2 and 3 Offsite Power Sources Declared Inoperable Due to Low Voltage" for Dresden Nuclear Power Station (DNPS). The LER was submitted in accordance with 10 CFR 50.73(a)(2)(v)(D), which requires reporting of 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.

Both sources of offsite power were declared inoperable on June 23, 2005, following notification to DNPS that the switchyard voltage for both Unit 2 and Unit 3 was below the required value necessary to ensure that offsite power would remain available following a postulated design basis accident.In July 2006, DNPS performed a reanalysis of the June 23, 2005 event. The reanalysis determined that the computer model used to determine the required switchyard voltage for the June 23, 2005 event conservatively assumed that the Reserve Auxiliary Transformers (RATs)were supplying all plant 4 kilovolt (kV) electrical loads and the second source of offsite power for each unit was based on a post unit trip. During normal plant operation the 4kV electrical loads are split between the RATs and the Unit Auxiliary Transformers (UATs). The reanalysis used the split bus configuration and the actual switchyard voltages at the time of the June 23, 2005 event. The reanalysis concluded that the voltages were greater than required, ensuring that the second source of offsite power for each unit would remain operable following a postulated design basis accident.

Therefore, there was no condition present on June 23, 2005, that could have prevented fulfillment of a safety function and this event is not reportable under 10 CFR Part 50.73(a)(2)(v)(D).

The associated 10 CFR 50.72 Emergency Notification System call was retracted on July 28, 2006.

Should you have any questions concerning this report, please contact Mr. James Ellis, Regulatory Assurance Manager, at (815) 416-2800.Respectfully, Danny G. Bost Site Vice President Dresden Nuclear Power Station cc: Regional Administrator

-NRC Region III NRC Senior Resident Inspector

-Dresden Nuclear Power Station