05000318/LER-2024-002, Automatic Reactor Trip Due to Main Turbine Loss of Load
| ML24260A142 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 09/16/2024 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24260A140 | List: |
| References | |
| LER 2024-002-00 | |
| Download: ML24260A142 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| 3182024002R00 - NRC Website | |
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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APP ROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/202 (0 4 202 4 ) Esbmated burden per response to comp y ,*, th this ma n datory coilecbon request 80 hours Reported lesso n s
/ ~-,**:*~**\\ LICENSEE EVENT REPORT (LER) learned are incorporated mto the licensmg process and fed back to mdusl,y Send comments regard*ng b u rden esbmate to the FOIA Library and lnformabon Co l!ections Branch (T-6 A10M) U S Nuclear Regu lnfoco ects.Resource@nrc gov and the 0MB reviewer atory
'; ~ ~11 } (See Page 2 for required number of digits/characters for each block) Commission . Washington DC 20555-0001 or by ema I to l~., ~- al or.IS Office ..... (See NUREG -1022 . R 3 for of lnformabon and Regulatory Affairs (3150-0104) Attn Desk Officer for the Nuclear Regulatory instruction and guidance for completing this form Comm1ss1on 725 17th to respond to. a collection of Information unless the document requesbng or requ ring the co llStreet NW. Wash ngton . DC 20503 The NRG may not conduct or sponsor and a person is ection htl(! //www nrc gov/readmg-rm /doc-collectionslnuregs /staff/sr1022/r31) not required displays a currently valid 0MB control number
- 1. Facility Name [gJ 050 2. Docket Number 3.Page Calvert Cliffs Nuclear Power Plant, Unit 2 052 05000318 1 OF 4
- 4. Title Automatic Reactor Trip Due to Main Turbine Loss of Load
- 5. Event Date 6. LER Number 7. Report Date 8. Other Facilities Involved
Month Day Year Year Number No. Month Day Year 050 Sequential Revision Facility Name Docket Number
07 18 2024 2024 002 00 09 16 2024 Facility - - 052 Name Docket Number
- 9. Operating Mode 1 - Power Operation 110. Power Level 100
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 10 CFR Part 20 20.2203(a)(2)(vi) 10 CFR Part 50 50. 73(a)(2)(ii)(A) 50. 73(a)(2)(viii)(A) D 73.1200(a) 20.2201(b) 20.2203(a)(3)(i) 50.36(c)(1 )(i)(A) 50. 73(a)(2)(ii)(B) 50. 73(a)(2)(viii)(B) 73.1200(b) 20.2201(d) 20.2203(a)(3)(ii) 50.36(c)(1 )(ii)(A) 50. 73(a)(2)(iii) 50. 73(a)(2)(ix)(A) 73.1200(c) 20.2203(a)(1) 20.2203(a)(4) 50.36(c)(2) [gJ 50. 73(a)(2)(iv)(A) 50.73(a)(2)(x) 73.1200(d) 20.2203(a)(2)(i) 10 CFR Part 21 50.46(a)(3)(ii) 50. 73(a)(2)(v)(A) 10 CFR Part 73 D 73.1200(e) 20.2203(a)(2)(ii) D 21.2(c) 50.69(g) 50. 73(a)(2)(v)(B) 73.77(a)(1) 73.1200(f) 20.2203(a)(2)(iii) 50.73(a)(2)(i)(A) 50. 73(a)(2)(v)(C) 73.77(a)(2)(i) 73.1200(9) 20.2203(a)(2)(iv) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D) 73.77(a)(2)(ii) 73.1200(h) 20.2203(a)(2)(v) 50. 73(a)(2)(i)(C) 50. 73(a)(2)(vii)
D OTHER (Specify here, in abstract , or NRC 366A).
- 12. Licensee Contact for this LER Licensee Contact Phone Number (Include area code)
Michael J. Fick, Regulatory Assurance Manager 410-495-6714
- 13. Complete One Line for each Component Failure Described in this Report
Cause System Component Manufacturer Reportable to IRIS Cause System Component Manufacturer Reportable to IRIS 8 TL EXC W120 y
- 14. Supplemental Report Expected Month Day Year
- 15. Expected Submission Date No [gJ Yes (If yes , complete 15. Expected Submission Date) 11 15 2024
- 16. Abstract (Limit to 1326 spaces , i.e., appr o x imately 13 single-spaced typewritten Im es)
On July 18, 2024 at 1524, Calvert Cliffs Nuclear Power Plant Unit 2 incurred an uncomplicated automatic reactor trip from 100 percent power due to a Main Turbine Loss of Load trip initiated by the Reactor Protection System (RPS). The Loss of Load trip was the result of an internal Main Generator Exciter failure that led to a loss of field on the Main Generator that in turn led to a load reject trip from the Main Turbine. The direct cause of the Exciter failure was a failed stationary field pole electrical connection. An engineering analysis performed to determine the failure mechanism for the stationary failed field pole electrical connection identified cyclic fatigue as the cause for the failure. Impacted Exciter components were replaced and an extent of condition inspection on the other field pole electrical connections was performed prior to returning the Exciter to service. The root cause evaluation for this event is still in progress at this time.
NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO . 31 50-01 04 EXPIRE S: 04/30/2027 (04 2024 )
Eshmaled burden per response to campy w ilh lh1s mandatory collechon requesl 80 hours Reported lessons learned are incorporaled inlo the l'cens ing process and fed back to industry Send commenls LICENSEE EVENT REPORT (LER) regarding burden es11mate to !he FOIA. Library. and lnformahon Collechons Branch (T-6 A 1 OM) U S Nuclear Regulatory Comm ssion Wash ington . DC 20555-0001 or by email to CONTINUATION SHEET lnfocollects.Resource@nrc .gov . and the 0MB reviewer al. 0MB Office of lnformal1on and Regulalory Affairs. (3150-0104). Attn: Desk Officer for the Nuclear Regulatory Commiss ion . 725 171h Street NW (See NUREG-1022 , R.3 for instruction and gu idance for completing this form W ashington . DC 20503. The NR C may not c o nd uc l o r sponsor . and a person is nol required to http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3 D respond to . a co llection of informat,on unle ss the documen t requesting or requiring !he collection displays a currently valid 0MB control number .
- 1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER 050 YEAR SEQUENTIAL REV NO.
NUMBER Calvert Cliffs Nuclear Power Plant , Unit 2 0 052 05000318 002 00 2024 -
NARRATIVE PLANT AND SYSTEM IDENTIFICATION
Calvert Cliffs Nuclear Power Plant, Unit 2, is a Combustion Engineering Pressurized Water Reactor with a licensed maximum power level of 2737 megawatts thermal. The Energy Industry Identification System code used in the text is identified as [TL].
A. CONDITION PRIOR TO EVENT
Unit: 2 Date: July 18, 2024 Power level: 100 Mode : Unit 2 was in Mode 1 when the event occurred .
B. DESCRIPTION OF EVENT
At 1524 on 07/18/2024, the Control Room received an alarm on Unit 2 for Main Generator Loss of Field / Out of Step. In response to receipt of this unexpected alarm , the Unit 2 Control Room Operators identified erratic reactive load swings on both Unit 1 and Unit 2 as indicated on Control Room panel indications. As the Operators were retrieving the associated alarm manual response manual and commencing detailed monitoring activities, the Unit 2 reactor was automatically tripped (scrammed) by RPS due to a Loss of Load actuation .
The Unit 2 Control Room staff implemented immediate post trip actions and successfully responded to an uncomplicated reactor trip.
During troubleshooting activities to determine the cause of the Unit 2 Loss of Load trip, a local inspection of the Unit 2 Exciter identified a failed stationary field pole connection . The failed stationary field pole connection was identified at this time as being the direct cause for a loss of field / loss of excitation on the Main Generator which led to a Main Generator lockout that resulted in a load reject trip of the Main Turbine and the subsequent RPS Loss of Load automatic trip.
C. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES
July 18, 2024
- 15 :23:34: Unit 1 and Unit 2 begin to experience reactive load swings as identified on the site's three 500KV high line reactive load trends (identified during post-trip data review).
- 15:24 :43: Generator lockout/ loss of field indication was received on the Unit 2 Plant Computer .
- 15 :24 :43 : Turbine load reject indication was received on the Unit 2 Plant Computer.
- 15 :24:44: RPS initiates an automatic trip for Unit 2.
- 18:33: The Shift Manager completes Event Notification #57233 to satisfy the requirements of 1 0CFR50. 72(b)(2)(iv)(B).
NRC FORM 366A (04 202 4 ) Page_2_ of _4_
NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0 104 EXPIRE S: 04/30/2027 (0 4-02-202 41 Estimated burden per respo nse to comply with this mandatory co llection request 80 hours Reported lessons learned are incorporated into the licensing process and fed back to industry Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA. Library. and Information Co llections Branch (T-6 A10M). U S Nuclear Regulatory Commission. Washington. DC 20555-0001. or by email to CONTINUATION SHEET lnfocollects Resource@nrc.gov. and the 0MB reviewer at: 0MB Office of Information and Regulatory Affairs (3150-0104) Attn: Desk Officer for the Nuclear Regulatory Comm ,ssion. 72517th Street NW (See NUREG-1022 , R.3 for instruction and guidance for completing this form Wash ington DC 20503. The NRC may not conduct or sponsor . and a person 1s not required to http://www . n re. gov I reading-rm/doc-collections/nu regs/staff /sr1 022/r3D respond to. a co llection of infonmation unless the document requesting or requiring the collection displays a currently valid 0MB contro l number
- 1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER 050 YEAR SEQUENTIAL REV NUMBER NO.
Calvert Cliffs Nuclear Power Plant, Unit 2 052 05000318 2024 -
002 00
NARRATIVE D. CAUSE OF EVENT
The method of discovery for this event was self-revealing and is documented in the site's Corrective Action Program (CAP) under IR 04788102. The direct cause cited for the Unit 2 automatic trip is the loss of an Exciter stationary field pole electrical connection resulting in a complete loss of excitation on the Main Generator. The current root cause is identified as cyclic fatigue to the point of failure on the Exciter stationary field pole electrical connection. The cyclic fatigue is attributed to a combination of long-term vibration of the Exciter and long-term out of specification Exciter air temperature.
The root cause evaluation for the Unit 2 main turbine loss of load trip due to the failure of the exciter electrical connection is still in progress at the time of this Licensee Event Report (LER) submittal; therefore, a supplement to the LER will be submitted following completion of the associated CAP product.
E. SAFETY ANALYSIS
The subject event satisfies the criteria in NUREG-1022, Revision 3, for any event or condition that resulted in manual or automatic actuation of any of the systems listed in 1 0CFR50. 73, paragraph (a)(2)(iv)(B).
Specifically, for this event, the Reactor Protection System actuated. Therefore, this event is reportable pursuant to 10CFR50.73(a)(2)(iv)(A). The resultant automatic trip was uncomplicated and there were no safety consequences as a result of the event. All safety systems functioned and operated as designed.
F. CORRECTIVE ACTIONS
During the forced outage following the July 18, 2024 Unit 2 automatic trip, the following immediate actions were taken prior to restarting the unit:
- Two Exciter stationary field poles were replaced - the stationary field pole that experienced the failed connection and the adjacent stationary field pole that had indications of a partial failure at the corresponding connection location. The two connection locations for the replaced stationary field poles are connected to one another by a jumper (metal bar). The jumper was determined to not be impacted by the failure and was reused.
- An extent of condition inspection of the remaining Exciter stationary field poles was performed and no other issues or concerns were identified.
Following completion of the forced outage to effect repairs to the Exciter, Unit 2 was paralleled to the grid on 7/23/24.
As part of the continuing root cause evaluation, corrective actions will be developed as appropriate to address the identified root and contributing causes of the event.
NRC FORM 366A (0 4-02-2024) Page_3_ of _4_
NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2027 (0 4-02-2024 ]
Estimated burden per response to com ply with tl11s mandatory co llection request 80 hours Reported lessons learned are *ncorporated into the lic ens in g process and fed back to industry Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOI A. Library. a n d Information Collections Branch (T-6 A 10M). U S.
Nuclear Regulatory Comm issio n. Wa shin gton. DC 20555-0001. or by email to CONTINUATION SHEET lnfocollects.Resource@nrc.gov . and the 0 MB reviewer at: 0MB Office of Information and Regulatory Affairs. (3 150-0104) Attn: Desk Offic er for the Nu c lear Regulatory Commission. 725 17th Street NW .
(See NUREG-1022, R.3 for instruction and gu idance for completing this form Washingto n. DC 20503. The NRC may not conduct or spons o r. and a perso n is not required to http ://www .nrc .g ov/read in g-rm/doc-colleclions/nure gs/staff/sr1022/r3D respond to. a col lection of informat ion un less the document requ esting or requiring the collection displays a currently va id 0MB contro l number .
- 1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER 050 YEAR SEQUENTIAL REV NUMBER NO.
Calvert Cliffs Nuclear Power Plant, Unit 2 052 05000318 2024 -
002 00
NARRATIVE G. PREVIOUS OCCURRENCES
A review of Calvert Cliffs' events was performed. No events were identified from this review that involved a reactor trip due to a failure of a Main Generator Exciter.
H. COMPONENT FAILURE DATA
Component IEEE 803 IEEE805 FUNCTION ID SYSTEM ID Exciter EXC TL
NRC FORM 366A (04 2024 ) Page_4_ of _4_