05000282/LER-2016-006

LER-2016-006, 121 Motor Driven Cooling Water Pump Auto Start

Prairie Island Nuclear Generating Plant
Event date:	12-18-2016
Report date:	2-15-2017
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
2822016006R00 - NRC Website

LER 16-006-00 for Prairie Island Nuclear Generating Plant, Units 1 and 2 Regarding 121 Motor Driven Cooling Water Pump Auto Start

ML17046A656
Person / Time
Site:	Prairie Island
Issue date:	02/15/2017
From:	Northard S Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-17-003 LER 16-006-00
Download: ML17046A656 (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.

2016 006 Prairie Island Nuclear Generating Plant 05000-282 00

DESCRIPTION OF EVENT

On December 18, 2016, at 0818 CDT, the Prairie Island Nuclear Generating Plant (PINGP) had a fire in the PINGP Switch Yard due to 8H8 Breaker-CT (Current Transformer) catastrophic failure. As the result of the 8H8 breaker fire, adjacent breakers 8H9, 8H7 and incoming lines from North Rochester (NRH) and Red Rock 2 (RRK2) were tripped and isolated from Bus 1 and Bus 2. Approximately 6 sec after the 8H8 CT catastrophic failure, automatic reclosing action to close the 8H7 breaker was initiated to place Red Rock 2 in service but failed. Approximately 15 sec after the 8H8 CT catastrophic failure, automatic reclosing action to close the 8H9 breaker was initiated to place North Rochester in service, which resulted in Bus 2 lock out (delay energized) due to relay 87B2S/345kV actuation. It was identified that this was a relay mis-operation.

At the time of the event, the non-safety related 11 Cooling Water (CL) pumps was running to supply load to the CL header. Low CL header pressure was caused by a trip of the Containment & Aux Building Chiller (ZX) System. The trip of the ZX system was caused by the electrical transient. The Containment Fan Coil Units CFCU's were aligned to the CL system for cooling. The Unit 2 CFCU's were aligned to the ZX system. When the ZX Chiller tripped, the Unit 2 CFCU's lost ZX flow, and automatically swapped to the safety related cooling of the CL system, as designed. This caused an increased demand on the CL system, which caused the 121 MDCLP to auto-start on low header pressure (at 80 psi) as designed.

EVENT ANALYSIS

The PINGP CL System2 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.

SAFETY SIGNIFICANCE

There was no radiological, environmental, or industrial impact associated with the 121 MDCLP auto-start, and the health and safety of the public were not affected. The auto-start of the 121 Motor Driven Cooling Water Pump did not challenge nuclear safety as all plant systems responded as designed; therefore, this event does not represent a safety system functional failure for Unit 1 or Unit 2.

'IEEE Component Code - P 2EIIS System Code - BI 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.

2016 006 Prairie Island Nuclear Generating Plant 05000-282 00

CAUSE

The cause of the 121 MDCLP auto-start was a low-pressure transient in the cooling water pump discharge header was caused by the trip of the ZX Chiller and the additional load on the CL system that reduced CL header pressure to the 121 MDCLP auto-start setpoint.

CORRECTIVE ACTION COMPLETED

When the ZX Chiller tripped, the Unit 2 CFCU's lost ZX flow, and automatically swapped to the safety related cooling of the CL system, as designed. Since the system operated as expected, thus there are no corrective actions.

PREVIOUS SIMILAR OCCURRENCES

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 ML 112840145). On 12/23/2010, the 121 MDCLP auto-started due to low header pressure. This low pressure condition was due to the failure of a header gasket on a non-safeguards chiller.

The gasket failure was due to an over-torque condition, gasket material, and the conditions under which the chiller was operating at the time of the failure. The 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.

Accession Number ML 12152A189). On 4/2/2012, while PINGP Unit 1 was operating at 100% power, 121 MDCLP auto-started while shutting down 22 DDCLP, this caused a low pressure condition in the header and the auto-start of the pump. The corrective action was to revise operating procedure C35 to ensure two MDCLPs are running prior to stopping the DDCLP.

Accession Number ML16085A181). On 1/29/2016, PINGP performed a planned overspeed post-maintenance test (PMT) of 22 Diesel Driven Cooling Water Pump in accordance with plant maintenance procedure. During the overspeed trip test PMT, 22 DDCLP tripped as expected and 121 MDCLP unexpectedly started automatically on low pressure in the cooling water pump discharge header.

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.

2016 006 Prairie Island Nuclear Generating Plant 05000-282 00 ML16281A208). On 8/21/2016, PINGP 2RY Transformer locked out. 121 Motor Driven Cooling Water Pump (MDCLP) stopped due to loss of power and then automatically restarted when sequenced by the load sequencer. The pump auto started on low pressure in the cooling water pump discharge header.