05000318/LER-2024-002-01, Automatic Reactor Trip Due to Main Turbine Loss of Load
| ML25024A089 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 01/24/2025 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25024A088 | List: |
| References | |
| LER 2024-002-01 | |
| Download: ML25024A089 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| 3182024002R01 - NRC Website | |
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Abstract
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 investigation for this event identified that Engineering personnel and their leadership failed to adequately exhibit technical conscience principles and the technical human performance behaviors Challenge and Questioning Attitude resulting in the cyclic fatigue of a single point vulnerability component that led to a plant trip.
(See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) Page 4 of 4 Following completion of the forced outage to effect repairs to the Exciter, Unit 2 was paralleled to the grid on 7/23/24.
The root cause investigation identified the following key corrective actions to address the identified root and contributing causes of the event:
Corrective Action to Preclude Repetition (CAPR): Implementation of recurring basis captured training that, when combined with management model oversight, reinforces excellence in Effective Technical Conscience Principles 3 & 5 and THU behaviors for station personnel - Engineering staff including FLS and above.
CAPR: Engineering Leaders perform a minimum of two documented Technical Conscience observations per week for a period of six months across the Engineering first line supervisor and above population.
Corrective Action
Rewind or replace the U2 Exciter.
Corrective Action
Implement a Preventative Maintenance (PM) Strategy for both Unit 2 and Unit 1 Exciter / Generator that fully aligns to the Constellation PM Template for the Exciter / Main Generator including a formal and documented assessment for completeness against Westinghouse (Unit 2) and General Electric (Unit 1) Best Practices and applicable EPRI documents.
Corrective Action
Perform a documented review of vendor issued Service Bulletins, Technical Notifications, and Industry issued OPEX for all Tier 1, Tier 2 and SPV systems from 1996 to present.
Document that each vendor Service Bulletin, Technical Bulletin and Industry Issued OPEX has been completely addressed or initiate IRs for all gaps / open recommendations that have not been completed for formal dispositioning.
G. PREVIOUS OCCURRENCES
A review of Calvert Cliffs events that preceded the July 18, 2024 Unit 2 automatic reactor trip 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