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| Report date | Site | Event description | |
|---|---|---|---|
| 05000249/LER-2004-006 | 19 January 2005 | Dresden | Dresden Nuclear Power Station, Units 2 and 3, had been experiencing increasing trends in vibration levels on both Main Turbine Generators, bearings 9 and 10 since May 2004. Numerous efforts and reviews during the summer and fall of 2004 were not successful in resolving the vibration. Dresden Unit 3 entered a refueling outage in October 2004 and as part of the outage scope, the Main Turbine Generator was inspected. On October 31, 2004, the inspection identified that the Unit 3 Main Turbine Generator Rotor had a crack in the shaft near the rotor coupling. This finding resulted in the decision to remove Unit 2 from service and conduct an inspection of its rotor shaft. On November 1, 2004, a crack was identified on the Unit 2 rotor shaft. The Unit 2 crack was in the same general location and similar configuration as the Unit 3 crack. These events are being reported as a Voluntary Licensee Event Report in accordance with the guidance contained in NUREG 1022, Revision 2, "Event Reporting Guidelines 10 CFR 50.72 and 50.73. The root cause of these events was determined to be intermittent oscillating torsional loading on the generator rotor, which produced a torsional fatigue failure mode. The cause of the intermittent oscillating torsional loading is indeterminate. The cause and source of the intermittent oscillating torsional loading will be investigated through analytic modeling and data acquisition during plant operation. |
| 05000249/LER-2004-005 | 29 November 2004 | Dresden | On September 29, 2004, at 1235 hours (CDT), with Unit 3 at approximately 100 percent power in Mode 1, it was discovered that 3 of the 4 Unit 3 Isolation Condenser Time Delay Relays exceeded their Allowed Value specified in Technical Specification 3.3.5.2, "Isolation Condenser (IC) System Instrumentation." The event was discovered while performing Surveillance Procedure DIS 1300-08, "Sustained High Reactor Pressure Time Delay Relay Calibration." This event identified that two independent channels of the time delay portion of the Unit 3 Isolation Condenser Initiation Logic were inoperable and is being reported under 10 CFR 50.73(a)(2)(vii), "), "Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system." Additionally, this event is being reported under 10 CFR 50.73(a)(2)(i)(B), "Operation or condition prohibited by Technical Specifications." The Isolation Condenser Time Delay Relays were previously calibrated on June 16, 2002 by using a stopwatch. The root cause of the event was due to an ineffective extent of condition review for a corrective action associated with a 1996 event in which stopwatches were determined to not be sensitive enough for calibration checks on components with limited margin. The corrective action to prevent recurrence was to use a strip chart recorder for calibrating the Isolation Condenser Time Delay Relays. |