05000412/LER-2006-001, Regarding Turbine-Generator Trip Due to Loss of Generator Excitation Power Results in Reactor Trip
| ML061520195 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 05/24/2006 |
| From: | Lash J FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-06-091 LER 06-001-00 | |
| Download: ML061520195 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 4122006001R00 - NRC Website | |
text
-FENOC FirstEnergy Nuclear Operating Company James I. Lash Site Vice President 724-682-5234 Fax: 724-643-8069 May 24, 2006 L-06-091 Beaver Valley Power Station, Unit No. 2 Docket No. 50-412 License No. NPF-73 LER 2006-001-00 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 The following Licensee Event Report Supplement is submitted:
LER 2006-001-00, 10 CFR 50.73(a)(2)(iv)(A), "Turbine-Generator Trip Due to Loss of Generator Excitation Power Results in Reactor Trip."
Attachment c:
Mr. T. G. Colburn, NRR Senior Project Manager Mr. P. C. Cataldo, NRC Sr. Resident Inspector Mr. S. J. Collins, NRC Region I Administrator INPO Records Center (via electronic image)
Mr. L. E. Ryan (BRP/DEP)
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Abstract
On April 2, 2006, the Beaver Valley Power Station (BVPS) Unit No. 2 reactor tripped at 1402 hours0.0162 days <br />0.389 hours <br />0.00232 weeks <br />5.33461e-4 months <br /> due to a Main Generator Loss of Field Protection Trip. All safety systems functioned as designed. Both Emergency Diesel Generators (EDGs) automatically started due to a momentary under voltage condition caused by the initial Main Generator trip. Both EDGs ran unloaded. All three Auxiliary Feedwater System pumps started as expected on low steam generator levels. The plant was stabilized In Mode 3 with primary and secondary parameters returned to normal hot standby values.
The root cause of the generator trip has been determined to be less than adequate workmanship, manufacturing and/or disassembly inspections. Initial inspection by the vendor (post-trip) identified that the block which supports the field pole #1 and field pole #2 terminals was not present. With this block missing, the field pole connection is subject to Increased flexing during normal operation and also during maintenance activities. This increased flexing led to fatigue failure of the Exciter Field. With the open circuit resulting from the failed pole connection, the Main Generator tripped on loss of field. It was indeterminate if the support block was removed during one of the Exciter inspections/ disassemblies or never installed during the manufacturing process.
This reactor trip is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event which resulted in the valid automatic actuation of the Reactor Protection System, the Auxiliary Feedwater System, and the onsite emergency AC electrical power systems - Emergency Diesel Generators per 10 CFR 50.73(a)(2)(iv)(B).
The risk was determined to be very low safety significance.
NRC FORM 366 (6-2004)
(If more space Is required, use additional copies of (If more space Is required, use additional copies of (If more space Is required, use additional copies of NRC Form 366A)
SAFETY IMPLICATIONS (Continued) core damage probability for the event when considering the actual component unavailability that was present at the time of the reactor trip.
Based on the above, the reactor trip safety significance on April 2, 2006, was very low.
CORRECTIVE ACTIONS
- 1. The exciter field coil was replaced and a support block installed.
- 2. The existing main exciter preventative maintenance task is being revised to ensure that the proper details exist on disassembly and reassembly of the exciter field pole connectors.
- 3. A generator/exciter preventative maintenance template is being developed to include a mechanical inspection of the exciter which includes the exciter stator series lead connections and a verification of the presence of all the stator field lead support blocks.
Completion of the above and other corrective actions are being tracked through the BVPS corrective action program.
PREVIOUS SIMILAR EVENTS
A review found one prior BVPS Unit 1 and no prior BVPS Unit 2 Licensee Event Reports within the last ten years involving a main generator problem.
LER 1-99-010, "BVPS Unit 1 Manual Reactor Trip Due to Main Unit Generator Voltage Regulator Malfunction". This manual trip was initiated following cyclic field current variations observed in the control room, subsequently determined to be from a degraded voltage regulator logic drawer. The cause of this event was not similar to the cause of the Main Generator event on April 2, 2006.
COMMITMENTS
There are no new commitments made by FirstEnergy Nuclear Operating Company (FENOC) for BVPS Unit No. 2 in this document.
ON