05000306/LER-2024-002, Reactor Trip and Auto-Start Actuation of Auxiliary Feedwater Due to High Negative Neutron Flux Rate Trip
| ML24354A316 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 12/19/2024 |
| From: | Currier B Northern States Power Company, Minnesota, Xcel Energy Inc |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-PI-24-050 LER 2024-002-00 | |
| Download: ML24354A316 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| 3062024002R00 - NRC Website | |
text
fl Xcel Energy December 19, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant, Unit 2 Docket No. 50-306 Renewed Facility Operating License No. DPR-60 1717 Wakonade Drive Welch, MN 55089 L-Pl-24-050 10 CFR 50.73 Prairie Island Nuclear Generating Plant Unit 2 Licensee Event Report 2024-002-00 Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), hereby submits Licensee Event Report (LER) 50-306/2024-002-00 per 10 CFR 50. 73(a)(2)(iv)(A).
Summary of Commitments lier ma c
ommitments and no revisions to existing commitments.
Bryan C rrier Plant Manager, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:
Administrator, Region Ill, USNRC Project Manager, Prairie Island, USNRC Resident Inspector, Prairie Island, USNRC State of Minnesota
ENCLOSURE PRAIRIE ISLAND NUCLEAR GENERATING PLANT LICENSEE EVENT REPORT 50-306/2024-002-00 3 pages follow
Abstract
Prairie Island Nuclear Generating Plant, Unit 2
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Reactor Trip and auto-start actuation of Auxiliary Feedwater due to High Negative Neutron Flux Rate Trip 10 29 2024 2024 002 00 12 19 2024 Mode 1 100
Nathan Fedora, Senior Nuclear Regulatory Engineer 612-342-8971 X
At 10:23 Central Daylight Time on October 29, 2024, with Prairie Island Nuclear Generating Plant Unit 2 operating at 100 percent power, Unit 2 experienced an automatic Reactor Trip. This led to an auto-start actuation of Auxiliary Feedwater. Operators responded to the event in accordance with approved procedures and safely placed the plant in Mode 3. While performing a test of the Control Rod Drive System, Bank C Group 2 control rods fully inserted unexpectedly, and the automatic Reactor Protection System tripped on a High Negative Neutron Flux Rate Trip. Troubleshooting identified the most likely cause of the control rods fully inserting and causing the High Negative Neutron Flux Rate Trip to be back plane connectors in the 22AC power cabinet for the Control Rod Drive System being outside the desired tolerance criteria. The pins were reformed within specifications. Additionally, five regulation cards and two phase control cards in 22AC power cabinet were replaced with new cards to ensure any undetected issues with the cards would be resolved. Page of
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
052 050
CAUSE OF THE EVENT
The cause of the Unit 2 Reactor Trip was Bank C Group 2 control rods fully inserting thus causing an automatic RPS trip on High Negative Neutron Flux Rate Trip.
Extensive troubleshooting activities took place, and the most likely cause of the control rods fully inserting and causing the High Negative Neutron Flux Rate Trip was the back plane connectors of the control card cage in the 22AC power cabinet that were found outside the desired tolerance criteria.
All of the control cards of the 22AC power cabinet were tested and found fully functional.
CORRECTIVE ACTIONS
Corrective action was taken to reform the pins of the back plane connectors in the control card cage of the 22AC power cabinet to original Westinghouse specifications, and they were re-measured satisfactorily.
The Control Rod Drive System had its original gripper regulation cards and lift regulation cards. Because the original equipment manufacturer no longer makes the original cards, an engineering change was developed and all five regulation cards in 22AC power cabinet were replaced with the new regulation cards to ensure any undetected issues with the cards would be resolved. In addition, the stationary phase control card and movable phase control card for Bank C Group 2 control rods were replaced.
While initial inspection and testing of the control cards found them to be fully functional, troubleshooting could not rule out an undetected failure mode with regulation cards in the 22AC power cabinet. Since a specific failure mode was not able to be identified, additional forensics testing is planned for the original regulation cards and phase control cards that were removed.
At 10:35 Central Standard Time on November 10, 2024, Unit 2 was placed online.
PREVIOUS SIMILAR EVENTS
There were no previous similar events in the past three years.
ADDITIONAL INFORMATION
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
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Prairie Island Nuclear Generating Plant, Unit 2
- - 306 2024 002 00