05000483/LER-2020-008, Reactor Trip Due to Main Generator Electrical Fault
| ML21049A109 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 02/18/2021 |
| From: | Bianco F Ameren Missouri |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ULNRC-06638 LER 2020-08-00 | |
| Download: ML21049A109 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4832020008R00 - NRC Website | |
text
MISSOURI February 18, 2021 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-000 1 Ladies and Gentlemen:
ULNRC-06638 10 CFR 50.73 CallawayPlant DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC COMPANY RENEWED FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 2020-08-00 REACTOR TRIP DUE TO MAiN GENERATOR ELECTRICAL FAULT The enclosed license event report is submitted in accordance with 10 CFR 50.73(a)(2)(iv)(A) to report a reactor protection system and auxiliary feedwater actuation.
This letter does not contain any new commitments.
Enclosure:
LER 2020-008-00 Senior Director, Nuclear Operations 8315 County Road 459 Steedman, MO 65077 AmerenMissouri.com
ULNRC-06638 February 1 8, 2021 Page 2 of3 cc:
Mr. Scott A. Morris Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission
$201 NRC Road Steedman, MO 65077 Mr. M. Chawla Project Manager, Callaway Plant Office ofNuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop O8B1A Washington, DC 20555-000 1
ULNRC-06638 February 18, 2021 Page 3 of3 Index and send hardcopy to QA File A160.0761 Hardcopy:
Certrec Corporation 6500 West Freeway, Suite 400 Fort Worth, TX 76116 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)
Electronic distribution for the following can be made via Tech Spec ULNRC Distribution:
F. M. Diya B. L. Cox F. 3. Bianco S. P. Banker R. C. Wink T. B. Elwood Corporate Oversight NSRB Secretary Performance Improvement Coordinator STARS Regulatory Affairs Mr. Jay Silberg (Pillsbury Winthrop Shaw Pittman LLP)
Missouri Public Service Commission
Abstract
on December 24, 2020 at 1235 with the reactor at approximately 90% rated thermal power, a main generator fault occurred hat led to a turbine trip and reactor trip. Safety systems functioned as required, induding actuation of the auxiliary eedwater system and a main feedwater isolation due to a valid feedwater isolation signal. Operations staff responded to he event in accordance with applicable plant procedures. The post-trip investigation indicated that a fault internal to the nain generator actuated the main generator protection system, which in turn caused the turbine trip and an automatic reactor trip since reactor power was above the P-9 setpoint.
orrective actions involve restoration of the main generator to its original design, including replacement of the connection ings. Generator support systems are being refurbished as necessary.U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 31504104 EXPIRES: 0813112023 (08-2020)
ES8mated buen response to comply with th mda)ory coflec8on request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br /> Reported
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- 1. FACILITY NAME I
- 2. DOCKEt NUWIBER I
- 3. LERNLRAB8 1
SEQUENTIAL 1;;
Callaway Plant, Unit No. I 05000-483 NUMBER NO.
2020
- - 008
- - 00 NARRATNE I.
DESCRIPTION OF STRUCTURE(S), SYSTEM(S), AND COMPONENT(S)
The systems and components affected by this eient indude the reactor protection system and the mn generator.
The reactor protection system at Callaway Plant initiates a unft shutdown, based on the values of Selected unit parameters, to protect against vidafing the core fuel design limfts and reactor coolant system pressure boundary design lhiifts during aitiUpated operafional occurrences and to assist the Engineered Safety Features systems in mitigating accidents.
The ma generator is a non-safety related componentthat converts the rotational Idnetic energy generated by the kirbke into elecbical energy. The turne receies high pressure steam from the main steam system and converts a poron of its thermal energy into rotational kinetic energy. The main generator has a number offfips in orderto protect this asset from irreparable damage. Internal to the main generator are connection rings that conned groups ofrdngs inthe stator in a sequential pattern to create a nusddal electrical wave form when subjectedto an decfficalfleld produced by the rotor. The main generatorwas onginally manufactured by General Electric as model number 180X732. EIIS System Code: TB; Function Code: GEN 2.
INfl1AL PLANT CONDITIONS:
Callaway was in MODE I at approximataly 90% rated thermal power at the time of this event. Power ascenon was in progress Idlowing a return to serve from a refueling outage that had ended on December 22, 2020. No major safety related systems were out of service.
3.
EVENT DESCRIP11ON:
On December 24, 2020 at 1235 with the reactor at approdmatdy 90% rated thermal power, the reactor automacalIy ffipped as a result ofa turbine trip caused by a main generatorfauft. Safety systems fUrdOned as expected. The Operaons ataff responded to the event in accordance with applicable plant procedures. An ENS notificalion (ENS 55049)was made for this event at 1514 hours0.0175 days <br />0.421 hours <br />0.0025 weeks <br />5.76077e-4 months <br /> on December 24, 2020.
Pnorto the eient, operators had been raising powarwhile returning the unftto service fUIoi4ng a refueling outage. The generator had been placed in service on December 22, 2020. Preceding the reactor ffip, annunciators associated wfth the generator mortonng instrumentation and generator auxiliary systemsware received. FdIoMng recalptof the annunciators, the reactor power ascension was stopped and non-licensed operators ware dispatched to irwesgate local annunciators and the operation of generator aLodliary systems. In addifion to the annunciators, indication of abnormal atator coding water system conckdvfty and decreasing man generator hydrogen pressure were observed. During the irwestigafion ofthe cause ofthe annundator the automafic reactortrip occurred as a result ofthe actuation of generator protecfive relaying.
The cause ofthe generatorfault was due to failure ofthe connection rings on the main generator stator. Both the collector end connection ring (i.e., phase ring) and the turbine end connection ring (i.e., serial nng)faled, resulting in an electiicel path from the generator atatorto ground. This electrical path resulted in a generator protecon fault that was detected by the generator neutral ground overcurrent relay resuWng in a generatorffip and turbinetrip. The underlying cause ofthe connecdon ring failure is still unde iwesgaon and wII be determined dunng the course ofthe generator disassembly and repair.
Per plantdesign, an awdliaryfeedwater system actuation occurred as expected in response to the reactor ffip. Also, Consistent wh plant responseto a readortdp from a high powarleiel, a main feedwater isolation signal was generated.
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NRC FORM36M U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 31504104 EXPIRES: 0813112023 (08-2020)
Estimated burden p response to comp Ydtth this mada1ory collection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br /> Reported
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LICENSEE EVENT RE RT (LER; en esumate tse Ubrary, aid teformatlon Colections Branch (T-6 AWN), U.S.
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- 1. FACILITY NAME a DOCKEr Nl.BER
- 3. LERNLNBB YEAR Callaway Plant, Unit No. I 05000-483 NUNBER NO.
2020
. 008
- - 00 5.
PREViOUS SIMILAR EVENTS
No previous occurrences of a main generatorffip due to an electncal fault internal to the generator have occurred at Cailaway Plant Three occurrences of a reactortrip of a similar nature dueto main generator protective relaying actuation are identified and summarized below.
On Jtiy 26, 2013, a turbine ffip occurred when &eCtIiCaI faults caused damage to the isophase bus in the auxiliary transformer and main generator neutral connecon box. Theturbine trip resulted in a readorffip. See LER 2013-008. (Ameren Missouri letter ULNRC-06042, ML13268M 12).
On December 3, 2014, aturne frip occurred when the main generator exdtation fransfomierfaufted to ground. The turbine ffip resufted in a readorbip. See LER2OI4-006. (Ameren Missoun letter ULNRC-06178, ML15033A215).
On September 27, 2020, a turtne hip occurred due to a main generatorfauft that was the result of a piece of a laminated-style fledte link located in an isophase bus dud becoming detached and causing a phase-to-ground frnit The turne ffip resulted in a readorthp. See LER 2020-006. (Ameren ssoud letter ULNRC-06620, M120330A266).Page 4 of 4