05000282/LER-2021-002, Loss of Electrical Bus Results in 121 Motor Driven Cooling Water Pump Auto Start
| ML21347A972 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  (DPR-042, DPR-060) |
| Issue date: | 12/13/2021 |
| From: | Domingos C Northern States Power Company, Minnesota |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-Pl-21-044 LER 2021-002-00 | |
| Download: ML21347A972 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2822021002R00 - NRC Website | |
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fl Xcel Energr December 13, 2021 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant, Units 1 and 2 Docket Nos. 50-282 and 50-306 Renewed Facility Operating License Nos. DPR-42 and DPR-60 1717 Wakonade Drive Welch, MN 55089 L-Pl-21-044 10 CFR 50.73 Prairie Island Nuclear Generating Plant (PINGP) Unit 1 Licensee Event Report 2021-002-00 Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), hereby submits Licensee Event Report (LER) 50-282/2021-002-00 per 10 CFR 50.73(a)(2)(iv)(A).
If you have any questions about this submittal, please contact Carrie Seipp, Senior Regulatory Engineer, at 612-330-5576.
Summary of Commitments ew commitments and no revisions to existing commitments.
Christopher P. Domingos Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure (1) cc:
Administrator, Region Ill, USNRC Project Manager, Prairie Island, USNRC Resident Inspector, Prairie Island, USNRC State of Minnesota
ENCLOSURE 1 PRAIRIE ISLAND NUCLEAR GENERATING PLANT LICENSEE EVENT REPORT 50-282/2021-002-00 3 pages follow
Abstract
On October 17, 2021, the Prairie Island Nuclear Generating Plant (PINGP) 2RY Transformer was de-energized when operations personnel opened the 2RSY Reserve Auxiliary Transformer 34.5KV B Disconnect Switch instead of closing the 2RSX Reserve Auxiliary Transformer 34.5KV B Disconnect Switch during restoration of the 2RX Transformer in the substation. The de-energization of 2RY caused a loss of power to the Unit 2 4.16 KV Bus 23. This led to an auto-start of 121 Motor Driven Cooling Water Pump on a sensed low header pressure.
This event is reportable under 10CFR 50.73(a)(2)(iv)(A) due to a valid Emergency Service Water system actuation.
Outage Shutdown Safety Assessment and Probability Risk Assessment remained green during the event and recovery actions.
The cause of the de-energization of 2RY was individual errors during hard match and concurrent verification.
The corrective action implemented required all substation switching to be identified as high risk with field supervisor oversight required.
EVENT DESCRIPTION
On October 17, 2021, the Prairie Island Nuclear Generating Plant (PINGP), Unit 1 was in Mode 1 (Power Operation) at 100 percent power and Unit 2 was in Mode 6 (Refueling) at 0 percent power. The 2RY Reserve Auxiliary Transformer was supplying Safety Related 4.16 KV Bus 25 and the Non-Safety Related 4.16 KV Buses 23 and 24. At 1601 CDT, the 2RY Reserve Auxiliary Transformer was de-energized when operations personnel opened the 2RSY Reserve Auxiliary Transformer 34.5KV B Disconnect Switch instead of closing the 2RSX Reserve Auxiliary Transformer 34.5KV B Disconnect Switch during restoration of the 2RX Reserve Auxiliary Transformer in the substation. The de-energization of 2RY caused a loss of power to the Unit 2 Buses 23, 24, and 25. Automatic reenergization of Bus 25 via CT12 Transformer, the other offsite power source, occurred.
Bus 23 supplies power to Non-Safety Related 21 Cooling Water (CL) pump, which was supporting all the CL system loads.
Following the trip of 21 CL Pump, 121 Motor Driven Cooling Water Pump (MDCLP) auto started on a sensed low header pressure. The 121 MDCLP is designed to start automatically if CL header pressure drops to 80 pounds per square inch gauge (psig).
EVENT ANALYSIS
121 MDCLP The 121 MDCLP is a part of the PINGP CL System (EIIS CODE: BI). The CL system is a ring header which is shared by Units 1 and 2 that provides a heat sink for the removal of process and operational heat from safety-related components during a design basis accident or transient. During normal and shutdown operation, the CL system also provides this function for various safety-related and non-safety related components. The CL system consists of a common CL pump discharge header for five CL pumps: two non-safety related pumps, two safety related Diesel Driven Cooling Water Pumps (DDCLP), and 121 MDCLP that can be aligned as replacement for either DDCLP by realigning its power supply and administratively disabling the CL pump discharge header valves to direct flow to the appropriate train.
The total Cooling Water (CL) system operating flow rates were in the range that operation of only one CL pump for both Units was desired. The ring header valves were open and 121 MDCLP was not aligned as a replacement for either DDCLP. The trip of 21 CL Pump resulted in a reduction in header pressure to the 121 MDCLP auto start setpoint.
This event is reportable per 10CFR 50.73(a)(2)(iv)(A) due to a valid Emergency Service Water system actuation.
Human Performance PINGP Non-Licensed Operators (NLOs) were performing their first-time evolution of the tasks of restoring the 2RX Reserve Auxiliary Transformer in the switchyard during the Unit 2 Refueling Outage. After successful closure of the 2RSX Reserve Auxiliary Transformer 34.5KV A Disconnect Switch, the NLOs opened the 2RSY Reserve Auxiliary Transformer 34.5KV B Disconnect Switch instead of closing the 2RSX Reserve Auxiliary Transformer 34.5KV B Disconnect Switch.
ASSESSMENT OF SAFETY CONSEQUENCES
Outage Shutdown Safety Assessment (SSA) and Probability Risk Assessment (PRA) remained green during the event and subsequent recovery actions.
The auto start of 121 MDCLP did not challenge nuclear safety as the Cooling Water system responded as designed. This event does not represent a safety system functional failure for Unit 1 or Unit 2.
CAUSE OF THE EVENT
The cause of the de-energization of 2RY was individual errors during hard match and concurrent verification.
Page 3 of 3 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Prairie Island Nuclear Generating Plant, Unit 1 05000282 YEAR SEQUENTIAL NUMBER REV NO.
2021
- - 002
- - 00
CORRECTIVE ACTIONS
The corrective action implemented required all substation switching to be identified as high risk with field supervisor oversight required.
PREVIOUS SIMILAR EVENTS
No previous similar events have occurred at PINGP in the prior 3 years.