05000306/LER-2015-002

LER-2015-002, 21 Feedwater Pump Lockout, Unit 2 Reactor Trip Due to Pressure Switch Failure

Prairie Island Nuclear Generating Plant Unit 2
Event date:	4-3-2015
Report date:	6-22-2016
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation
3062015002R01 - NRC Website

LER 15-002-01 for Prairie Island, Unit, Regarding 21 Feedwater Pump Lockout, Reactor Trip Due to Pressure Switch Failure

ML16174A434
Person / Time
Site:	Prairie Island
Issue date:	06/22/2016
From:	Northard S Northern States Power Company, Minnesota
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-16-053 LER 15-002-01
Download: ML16174A434 (6)

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by interne( e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

CONTINUATION SHEET

05000- 2 306 2015 002 01 On April 3, 2015, at 0652 CDT, the Unit 2 reactor was manually tripped while operating at 100 percent power, due to a lockout trip of 21 Main Feedwater Pump (245-261) as required by the Annunciator Response Procedure (ARP 47510-01 04) for the lockout alarm. This also resulted in a turbine trip as designed. The Operations crew entered the reactor trip emergency operating procedures and stabilized the unit in Mode 3 at normal operating pressure and temperature. All control rods fully inserted into the core following the trip. The Auxiliary Feedwater System (EIIS System Code - BA) actuated to start the Auxiliary Feedwater Pumps as designed on low narrow range Steam Generator level and provided makeup flow to the Steam Generator.

Steam Generator levels were returned to normal. The Auxiliary Feedwater Pumps were subsequently secured and returned to automatic. Steam Generators were being supplied by 22 Main Feedwater Pump and decay heat was removed by the condenser steam dump system. This event was entered into the Corrective Action Program (AR 01472846).

This event is reportable under 10 CFR 50.72(b)(2)(iv)(B), any event or condition that results in actuation of the reactor protection system (RPS) when the reactor is critical except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation, and 10 CFR 50.72(b)(3)(iv)(A), any event or condition that results in valid actuation of any of the systems listed in paragraph 10 CFR 50.72(b)(3)(iv)(B)(6), PWR auxiliary or emergency Feedwater system.

EVENT ANALYSIS

The PS-16012 was identified as a Mercoid, Model DSW-7223-153S1-10S pressure switch. A failure analysis was performed of the failed switch. The switch was disassembled and observations were made of the internal components. The results of this evaluation concluded that a C-clip that secures the linkage connecting the bourdon tube to the switch mechanism had fallen off the pin allowing the linkage to become disconnected from the switch mechanism. Wear was observed on the pin at the interface of the C-clip to the pin. The wear on the pin connected to the intermediate linkage was the cause for the switch failure.

There were no complications during the shutdown as all control rods fully inserted and Reactor Pressure Vessel pressure was maintained by normal means. All systems actuated as required. The Auxiliary Feedwater Pumps actuated as designed on low Steam Generator level. This is reportable under 10 CFR 50.73(a)(2)(iv) (A), any event or condition that results in manual or automatic actuation of any of the systems listed in paragraph 10 CFR 50.73(a)(2)(iv)(B)(1), RPS including: reactor scram or reactor trip, and in paragraph 10 CFR 50.73(a)(2)(iv)(B)(6), PWR auxiliary or emergency Feedwater system.

SAFETY SIGNIFICANCE

This event did not challenge nuclear safety as all plant systems responded as designed. The reactor was manually tripped in accordance with the annunciator response procedure. There were no radiological, environmental, or industrial impacts associated with this event and PINGP did not affect the health and safety of the public.

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

05000- 2 306 2015 002 01

CAUSE

The causal evaluation determined that pressure fluctuation within the system is resulting in the bourdon tube movement at a high frequency causing wear of the internal components of the pressure switch.

CORRECTIVE ACTION

• Immediate action to replace Pressure Switch PS-16012 per Work Order (WO) 00519920-01. Complete.

• Implement interim action monitoring plan for all Feedwater Pump suction pressure switches. Complete.

• Install pressure snubbers on the four Feedwater Pump suction pressure switches. Complete.

• [deleted]

PREVIOUS SIMILAR EVENTS

A LER historical search was conducted and no similar LER events at PINGP with the same apparent cause were identified in the last three years.