05000282/LER-2016-002

LER-2016-002, Listed System Actuation - Motor-Driven Cooling Water Pump Auto-Start

Prairie Island Nuclear Generating Plant, Unit 1
Event date:	1-29-2016
Report date:	3-25-2016
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
2822016002R00 - NRC Website

LER 16-002-00 for Prairie Island, Unit 1, Regarding Listed System Actuation - Motor-Driven Cooling Water Pump Auto-Start

ML16085A181
Person / Time
Site:	Prairie Island
Issue date:	03/25/2016
From:	Conboy T A Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-16-022 LER 16-002-00
Download: ML16085A181 (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 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.

Event Description

At 1110 CST on 1/29/2016, PINGP performed a planned overspeed trip test PMT of 22 DDCLP (EIIS Component Identifier P) in accordance with preventive maintenance procedure PM 3002-2-22, 22 DDCLP Diesel Minor Periodic Maintenance. During the overspeed trip test, 22 DDCLP tripped, and 121 MDCLP (EIIS Component Identifier P) auto-started on low pressure in the cooling water pump discharge header. This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in automatic actuation of an emergency service water system that does not normally run and that serves as ultimate heat sink.

Event Analysis

The PINGP Cooling Water (CL) System (EIIS System Identifier BI) is a shared system for Units 1 and 2 and 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 operation and shutdown, the CL System also provides this function for various safety-related and nonsafety-related components.

Five CL pumps are connected to a common pump discharge header that directs CL flow into two separate headers: three motor-driven pumps and two diesel-driven pumps. 121 MDCLP can function as a safeguards replacement when a diesel driven pump is taken out of service. In this configuration, the pump is aligned manually to the appropriate train of safeguards power and motor-operated valves are administratively disabled in accordance with technical specifications.

11 and 21 MDCLPs were running, and 121 MDCLP was not aligned as safeguards. Data from the Emergency Response Computer System (ERCS) showed that tripping 22 DDCLP resulted in a reduction of 8 psig in Loop A CL header pressure, 10 psig in Loop B CL header pressure, and over 1000 gpm in Loop B CL flow. 22 DDCLP developed a greater than normal discharge pressure while running at higher than normal speed during the overspeed PMT, and tripping the pump the higher speed caused a higher than expected change in pressure compared to stopping the pump from normal speed.

Operators correctly performed steps from plant operating and maintenance procedures intended to prevent an automatic start of 121 MDCLP. No inappropriate action was identified related to human performance. 121 MDCLP has auto-started on low pressure on previous occasions.

Pressure transients in the discharge header occur when stopping a DDCLP. Corrective actions taken since the last auto-start in April 2012 were effective in preventing auto-starts during monthly surveillance testing according to SP 1106A and SP 1106B, but they were not effective in this instance. Those corrective actions focused on running two MDCLPs and ensuring the pump discharge header was cross-connected to minimize the discharge header pressure transient when stopping a DDCLP. During this event, 22 DDCLP was running at an elevated speed, resulting in a larger transient when 22 DDCLP was stopped.

Safety Significance

121 MDCLP and other equipment operated as intended during the event. The low pressure transient was confined to the pump discharge header and did not result in below normal pressure in either cooling water Prairie Island, Unit 1 05000-282 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.

system header. Therefore, this event was of low safety significance since there was no loss of cooling water supply to safety-related or nonsafety-related system loads.

There was no radiological, environmental, nor industrial impact associated with this event, and the health and safety of the public were not affected. This event did not challenge nuclear safety as all plant systems nor Unit 2.

The likelihood of an automatic pump start during monthly surveillance tests (surveillance procedures SP 1106A, 12 Diesel Cooling Water Pump Monthly Test, and SP 1106B, 22 Diesel Cooling Water Pump Monthly Test) is low since no unexpected start has occurred on low pressure since April 2012 by requiring two MDCLPs are operating prior to stopping a DDCLP.

Cause

The cause of the 121 MDCLP auto-start was a low-pressure transient in the cooling water pump discharge header resulting from the trip of 22 DDCLP during planned overspeed PMT.

Corrective Action To eliminate a 121 MDCLP auto-start during the overspeed trip test PMT, PM 3002-2-22 and PM 3002-2-12, 12 DDCLP Diesel Minor Periodic Maintenance, were revised to ensure 121 MDCLP is running prior to performing PMT.

To eliminate a 121 MDCLP auto-start during SP 1106A, SP 1106B, and C35, these procedures will be revised to ensure 121 MDCLP is running or in pullout position when stopping a DDCLP.

Previous Similar Events

Previous instances of 121 MDCLP auto-start have occurred and determined to be caused by having only one MDCLP running prior to shutting down the DDCLP.

Access and Management System (ADAMS) Accession Number ML091390396). On 3/19/2009, 121 MDCLP auto-started when 12 DDCLP was tripped in accordance with procedure resulting in a transient of the cooling water system pressure. The momentary drop in pressure was large enough to auto-start the 121 MDCLP while it was aligned for safeguards service.

(ADAMS Access Number ML112840145). On 12/23/2010, 121 MDCLP was not aligned as a safeguards replacement pump and auto-started. The actuation of the 121 MDCLP was determined to be reportable under 10 CFR 50.73(a)(2)(iv)(A). Corrective actions to resolve the issue included performing a Cooling Water System review to determine methods and any single point vulnerabilities that can be performed to minimize the potential for auto-starts of a cooling water pump. Operating procedures were evaluated to determine if procedural or operation period changes can be made to reduce the likelihood of auto-starting a Cooling Water Pump.

Prairie Island, Unit 1 05000-282 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 Infocollects.Resource@nrc,gov, and to the Desk Officer, Office of Information and Regulatory Affairs, 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.

121 MDCLP auto-started while shutting down 22 DDCLP. The corrective action was to revise operating procedure C35 to ensure two MDCLPs are running prior to stopping the DDCLP.