05000237/LER-2004-006, Regarding Main Turbine Generator Rotor Cracks
| ML050330479 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 01/19/2005 |
| From: | Bost D Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVPLTR: #05-0001 LER 04-006-00 | |
| Download: ML050330479 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2372004006R00 - NRC Website | |
text
.1 Exelne.
Exelon Generation Company. LLC Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450-9765 www.exeloncorp.com Nuclear 10 CFR 50.73 January 19, 2005 SVPLTR: #05-0001 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Units 2 and 3 Facility Operating License Nos. DRP-19 and DPR-25 NRC Docket Nos. 50-237 and 50-249
Subject:
Licensee Event Report 2004-006, "Units 2 and 3 Main Turbine Generator Rotor Cracks" Enclosed is Licensee Event Report 2004-006, "Units 2 and 3 Main Turbine Generator Rotor Cracks," for Dresden Nuclear Power Station. 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."
Should you have any questions concerning this report, please contact Pedro Salas, Regulatory Assurance Manager, at (815) 416-2800.
Respectfully, Danny G. lst Site Vice resident Dresden Nuclear Power Station Enclosure cc:
Regional Administrator - NRC Region IlIl NRC Senior Resident Inspector - Dresden Nuclear Power Station
ZE
1%
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007
(-2004)Estimated
, the NRC may digis/chractrs fr eah blck)not conduct or spoonsor, and a person Is not required to respond to, fth digits/characters for each block)
Information MAIAfio.in.
- 3. PAGE Dresden Nuclear Power Station Unit 3 05000249 1 OF 3
- 4. TITLE Units 2 and 3 Main Turbine Generator Rotor Cracks
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NuMBER MONTH DAY YEAR YEAR S
EOUENT o.L REV MONTH DAY YEAR Dresden Unit 2 05000237 F ACILITY NAME DOCKET NUMBER 10 31 2004 2004 -
006 -
00 01 19 2005
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Checkall ihat apply) o 20.2201(b) 0 20.2203(a)(3)(i)
D 50.73(a)(2)(i)(C)
D 50.73(a)(2)(vii) 5 0 20.2201(d) al 20.2203(a)(3)(ii)
Dl 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
O 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B) 03 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL 0l 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x) o 20.2203(a)(2)(iii)
El 50.36(c)(2) 0 50.73(a)(2)(v)(A)
I 73.71 (a)(4) 000 o 20.2203(a)(2)(Iv)
E 80.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
E 73.71 (a)(5) 000 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) id 50.73(a)(2)(v)(C) 0 OTHER 0
20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B)
D 50.73(a)(2)(v)(D)
Specify In Abstract below
____or in NRC Form W6A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Indude Area Code)
Dresden Nuclear Power Station - George Papanic Jr.
(815) 416-2815CAUSE SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FATUER TOEPXFACTURER TO EPIX X
TB GEN G080 Y
NA
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION E YES (Ifyes, complete 15. EXPECTED SUBMISSION DATE) 0 NO DATE ABSTRACT (Limit to 1400 spaces, I.e., approximately 15 single-spaced typewritten lines)
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.
NRC FORM 360(6-2004)
PRINTED ON RECYCLED PAPER NRC FORM 366 (6-2004)
PRINTED ON RECYCLED PAPER (Ifmorespace Is required, useadditionalcopies of (If more space is required, use additional copies ofNRC Form 366A) (17)
The Unit 2 and Unit 3 cracks initiated in one of the two generator rotor shaft keyways under the turbine end coupling. The coupling is an interference fit to the shaft. The assessment of the metallurgical examination identified that each crack propagated at a 45-degree angle in a spiral fashion around the shaft with approximately 200 beach marks. The beach marks are indications where the cracks stopped and started again. The assessment concluded that intermittent oscillating torsional loads above the material fatigue endurance limit caused the crack propagation.
Dresden sent both Main Turbine Generator Rotors offsite for the inspections and to have the cracked end of the rotor shaft replaced with a new stub-shaft. A contributing cause to the reduced shaft material fatigue endurance limit was fretting. The ability of the shaft material to withstand fretting has been significantly increased by a redesign of the shaft keyway to eliminate stress risers and to increase shaft torsional capacity by an improved coupling shrink fit.
D.
Safety Analysis
The safety significance of the event is minimal. The Main Turbine Generator is not a safety related component and it is not credited in any Dresden accident analyses. Additionally, an engineering assessment concluded that Main Turbine Generator vibration levels would have exceeded operational limits prior to reaching critical crack size and the generator would have been removed from service prior to potential rotor failure. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.
E.
Corrective Actions
Dresden sent both Main Turbine Generator Rotors offsite for the inspections and to have the cracked end of the rotor shaft replaced with a new stub-shaft. A contributing cause to the reduced shaft material fatigue endurance limit was fretting. The ability of the shaft material to withstand fretting has been significantly increased by a redesign of the shaft keyway to eliminate stress risers and to increase shaft torsional capacity by an improved coupling shrink fit.
F.
Previous Occurrences
A review of Dresden Nuclear Power Station LERs identified no similar events. Additionally, a review of LERs from other nuclear plants did not identify any similar events.
G.
Component Failure Data
GE Main Turbine Generator Rotor shaft