05000306/LER-2024-001, Reactor Trip and Auto-Start Actuation of Auxiliary Feedwater Due to Loss of Suction to the 22 Main Feedwater Pump

Reactor Trip and Auto-Start Actuation of Auxiliary Feedwater Due to Loss of Suction to the 22 Main Feedwater Pump

ML24121A043
Person / Time
Site:	Prairie Island
Issue date:	04/29/2024
From:	Borgen T Northern States Power Co, Xcel Energy
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-Pl-24-015 LER 2024-001-00
Download: ML24121A043 (1)

LER-2024-001, Reactor Trip and Auto-Start Actuation of Auxiliary Feedwater Due to Loss of Suction to the 22 Main Feedwater Pump

Event date:
Report date:
3062024001R00 - NRC Website

text

1717 Wakonade Drive fl Xcel Energy Welch, MN 55089

April 29, 2024 L-Pl-24-015 10 CFR 50.73

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

Prairie Island Nuclear Generating Plant Unit 2 Licensee Event Report 2024-001-00

Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM "), hereby submits Licensee Event Report (LER) 50-306/2024-001-00 per 10 CFR 50.73(a)(2)(iv)(A).

Summary of Commitments

T his letter makes no new commitments and no revisions to existing commitments.

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Timothy P. Borge Plant Manager, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota

Enclosure

cc : Administrato r, Region Ill, USNRC Project Manager, Prairie Island, USNRC Resident Inspector, Prairie Island, USNRC State of Minnesota ENCLOSURE

PRAIRIE ISLAND NUCLEAR GENERATING P LANT LICENSEE EVENT REPORT 50-306/2024-001-00

3 pages follow

Abstract

At 11:42 on March 03, 2024, with Prairie Island Nuclear Generating Plant Unit 2 operating at 29 percent power, the Unit 2 Reactor automatically tripped due to a Turbine trip caused by a loss of suction to the 22 Main Feedwater (FW) Pump. The loss of 22 Main FW Pump 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. All systems responded normally post trip.

The cause of the event is currently under evaluation and will be provided later, along with corrective actions, as a supplement to this LER.

This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) due to a Reactor Trip and a valid Pressurized Water Reactor Auxiliary Feedwater actuation.

Plant Operating Conditions Prior to the Event:

Unit 1 - Mode 1, 100 percent Power Unit 2 - Mode 1, 29 percent Power.

EVENT DESCRIPTION

At 11:42 on March 03, 2024, with Prairie Island Nuclear Generating Plant Unit 2 operating at 29 percent power, 22 Main Feedwater (FW) [SJ] Pump experienced a loss of suction, resulting in the automatic actuations of Auxiliary Feedwater (AFW) [BA] and the trip of the Main Turbine [TA] and subsequently the Reactor.

During power ascension the 21 and 22 Condensate (CD) [SD] Pumps were running along with the 22 Main FW Pump.

Per normal startup procedure, a Condensate Polishing [SF] filter demineralizer (F/D) was being placed into service to improve the chemistry of the FW system by removing ionic and particulate contaminants from the condensate water. The suction pressure on the 22 Main FW Pump dropped below the trip set point causing the automatic trip of the 22 Main FW pump. With the 21 Main FW Pump off, the loss of the 22 Main FW Pump caused an automatic start of both the 21 Turbine Driven AFW Pump and 22 Motor Driven AFW Pump.

This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) due to a Reactor trip and an AFW actuation.

Unit 1 was not affected during this event and remained at 100 percent power.

ASSESSMENT OF SAFETY CONSEQUENCES

All systems responded normally post trip. Decay heat was removed via the AFW system. Secondary steam control mechanism was controlled by the steam generator Pressurizer Power Operated Relief Valves (PORVs).

The health and safety of the public and site personnel were not impacted during this event.

CAUSE OF THE EVENT

The cause of Unit 2 Turbine Trip and subsequent Unit 2 Reactor Trip was a loss of suction to the 22 Main FW Pump.

Initial troubleshooting determined the cause of loss of suction to the 22 Main FW Pump was that CV-39140, Condensate Filter Demineralizer System Main Bypass Valve, [SF] the bypass for the full-flow filter demineralizer, failed to operate as expected while placing 22 F/D in service.

The direct cause of this event is being investigated and will be provided in the supplement to this LER.

CORRECTIVE ACTIONS

The station is currently investigating the cause(s) of the event. Additional corrective actions will be provided in the supplement to this LER.

The condensate polishing system was not used during subsequent startup of Unit 2 to prevent reoccurrence until the direct cause of this event had been determined. Steam Generator blowdown was used to remove iron and contaminates prior to startup.

At 07:00 on March 08, 2024, Unit 2 entered Mode 1 and was placed online.

PREVIOUS SIMILAR EVENTS

The review of the similar past events will be provided in the supplement to this LER.

ADDITIONAL INFORMATION

All times are in Central Daylight Time

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].