Information Notice 2014-03, Turbine-Driven Auxiliary Feedwater Pump Overspeed Trip Mechanism Issues
| ML13350A189 | |
| Person / Time | |
|---|---|
| Issue date: | 02/25/2014 |
| From: | Michael Cheok, Kokajko L Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| Popova A, NRR/DPR/PGCB, 301-415-2876 | |
| References | |
| IN-14-003 | |
| Download: ML13350A189 (6) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NEW REACTORS
WASHINGTON, DC 20555-0001
February 25, 2014
NRC INFORMATION NOTICE 2014-03:
TURBINE-DRIVEN AUXILIARY FEEDWATER
PUMP OVERSPEED TRIP MECHANISM ISSUES
ADDRESSEES
All holders of an operating license or construction permit for a nuclear power reactor issued
under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of
Production and Utilization Facilities, except those who have permanently ceased operations
and have certified that fuel has been permanently removed from the reactor vessel.
All holders of and applicants for a power reactor early site permit, combined license, standard
design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and
Approvals for Nuclear Power Reactors. All applicants for a standard design certification, including such applicants after initial issuance of a design certification rule.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of recent operating experience related to improper adjustments of control
mechanisms that led to inoperability of turbine-driven auxiliary feedwater (TDAFW) pumps.
Information from these events may apply to turbine-driven pumps in other systems such as
reactor core isolation cooling (RCIC) and high-pressure coolant injection (HPCI) systems. It is
expected that recipients will review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. However, suggestions contained in this IN
are not NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
Wolf Creek Generating Station, Unit 1
On January 13, 2012, during recovery from a loss of offsite power event at Wolf Creek
Generating Station, Unit 1, the TDAFW pump overspeed trip mechanism unexpectedly actuated
as operators were securing the pump. The licensee, Wolf Creek Nuclear Operating
Corporation, determined that the cause of the unexpected actuation was inadequate
engagement between the head lever and tappet nut on the overspeed trip mechanism
(reference Figure 1 on the next page). The preventive maintenance procedure for adjusting the
mechanism had been changed (specifically, removing steps that prescribed direct measurement
of the tappet nut engagement), and instead relied on visual inspection. A similar event occurred
on November 17, 2009, but corrective actions at the time did not adequately address the issue, making it likely that the conditions leading to the trip were present for an extended period of
ML13350A189 time. As a result of the latest event, the licensee implemented corrective actions that included
replacing the trip tappet nut, hand trip lever, and trip linkage spring. In addition, the licensee
developed a more precise method of measuring adequate engagement of the head lever to the
tappet nut. Additional information is available in NRC Augmented Inspection Team Follow-up
Report 05000482/2012009, dated August 6, 2012, and can be found on the NRCs public
website in the Agencywide Documents Access and Management System (ADAMS) under
Accession Number ML12227A919.
1Figure 1 Generalized depiction of a turbine overspeed trip mechanism
Palisades Nuclear Plant
On May 10, 2011, during surveillance testing on the TDAFW pump at Palisades Nuclear Plant, the pump tripped as a result of an unexpected actuation of the mechanical overspeed trip
mechanism. Entergy Nuclear Operations, Inc. (ENO), the licensee, determined that the cause
of the unexpected actuation was inadequate procedures that lead to poor preparation and
instruction related to maintenance and testing on the TDAFW pump overspeed trip mechanism.
1 Copyright © 2002. Electric Power Research Institute, EPRI TR- 1007461. Terry Turbine Maintenance
Guide - AFW Application. Reprinted with Permission. This resulted in failure to perform several vendor recommended maintenance activities on the
mechanism. To correct this issue, ENO revised the maintenance and post-maintenance testing
procedures to include these maintenance activities and verify the reliability of the overspeed trip
mechanism. Additional information is available in NRC Inspection Report 05000255/2012010,
dated July 31, 2012, and in Palisades Licensee Event Report 50-255/2011-004-01, dated
January 31, 2012. These documents can be found on the NRCs public website in ADAMS
under Accession Numbers ML12213A225 and ML12031A237, respectively.
Salem Nuclear Generating Station, Unit 1
On several occasions between April 26 and September 2, 2010, the thirteen TDAFW pump at
Salem Nuclear Generating Station, Unit 1, was found tripped. After consulting with the pump
vendor, PSEG Nuclear, LLC (the licensee) ultimately determined that the root cause was a
rounded head lever surface which resulted in an inadequate contact surface between the tappet
nut and head lever. This caused inadequate engagement between the head lever and the
tappet nut, making the overspeed trip mechanism overly sensitive. A contributing cause was
that a positive rod stop prevented adequate engagement between the head lever and tappet
nut. The rod stop mechanism had been installed on the TDAFW pump after initial installation of
the pump but was not referenced in any procedure or drawing. PSEG Nuclear, LLC,
determined that adjustments were made to the positive rod stop without using an approved
procedure. An additional contributing cause identified by the licensee was that the valves trip
solenoid was worn. The licensee implemented corrective actions that included removing the
positive rod stop mechanism from the TDAFW pump head lever and a weld build-up repair to
the head lever to restore the original design configuration. Additional information is available in
NRC Integrated Inspection Report 05000272/2010005 and 05000311/2010005, dated
February 8, 2011, and can be found on the NRCs public website ADAMS under Accession
Number ML110390451.
North Anna Power Station, Unit 2
Following a reactor trip on December 25, 2007, the Unit 2 TDAFWP at North Anna Power
Station, Unit 2, automatically started but immediately tripped due to the actuation of the turbine
mechanical overspeed trip mechanism. The cause of the inadvertent trip of the pump was
determined to be inadequate engagement of the turbine trip mechanism head lever and tappet
nut. Virginia Electric & Power Company, the licensee, reset the turbine trip mechanism and
restarted the TDAFWP, which functioned properly for the remainder of the event. The cause of
the trip mechanism being inadequately set was that the maintenance procedure did not identify
some critical dimensional checks that should be performed when assembling the trip linkage.
The licensees corrective actions were to employ a more accurate method for obtaining critical
dimension checks. Additional information is available in NRC Integrated Inspection Report 05000339/2008002 and 05000339/2008002, dated April 30, 2008, and North Anna Licensee
Event Report 50-339/2007-004-01, dated May 29, 2008. These can be found on the NRCs
public website in ADAMS under Accession Numbers ML081220395 and ML081620437, respectively.
BACKGROUND
Related NRC Generic Communications
NRC IN 1988-067, PWR Auxiliary Feedwater Pump Turbine Overspeed Trip Failure, dated
August 22, 1988. This IN alerted addressees to an event involving the failure of the overspeed
trip mechanism as the result of damage to the tappet ball on the overspeed trip device.
NRC IN 1990-045, Overspeed of Turbine-Driven Auxiliary Feedwater Pumps and
Overpressurization of Associated Piping Systems, dated July 6, 1990. This IN alerted
addressees to potential problems with failures of the overspeed trip mechanisms of TDAFW
pumps that can result in turbine overspeed and overpressurization of the AFW systems.
NRC IN 1993-051, Repetitive Overspeed Tripping of Turbine-Driven Auxiliary Feedwater
Pumps, dated July 9, 1993. This IN alerted addressees to multiple instances of TDAFW pump
overspeed trips; the root causes of which were unknown.
DISCUSSION
This IN provides examples of recent operating experience involving inoperability of TDAFW
pumps where an invalid overspeed trip occurred without an actual overspeed condition present
at the time of the trip. The previous INs referenced above discuss events where actual
overspeed of the TDAFW pumps occurred as a result of the failure of the trip mechanisms to
actuate. All of these events resulted in the pump being inoperable. It is important to note that
improper adjustment of the overspeed trip mechanism can result in an inoperable pump. The
pump can become inoperable because of either the failure of the overspeed trip mechanism to
actuate when needed, or because of the overspeed trip mechanism actuating without an actual
overspeed condition.
The examples in this IN all involved the failure of licensee personnel to establish or follow
maintenance procedures as required by the NRC regulations and plant technical specifications.
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B, Criterion V,
Instructions, Procedures, and Drawings, states that nuclear power plants shall have
appropriate instructions, procedures, or drawings for activities affecting quality, and that these
activities shall be accomplished in accordance with these instructions, procedures, or drawings.
The examples in this IN, as well as the referenced INs, of improper adjustments of control
mechanisms that led to inoperability of pumps in nuclear power plants, illustrate the importance
of ensuring adequate procedures incorporating vendor guidance are established and followed
when setting and maintaining pump overspeed trip mechanisms.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA/
/RA/
Michael C. Cheok, Director
Lawrence E. Kokajko, Director
Division of Construction Inspection
Division of Policy and Rulemaking
and Operational Programs
Office of Nuclear Reactor Regulation
Office of New Reactors
Technical Contacts: Stanley J. Gardocki, NRR
Jesse Robles, NRR
301-415-1023
301-415-2940
E-mail: Stanley.Gardocki@nrc.gov Email: Jesse.Robles@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA/
/RA/
Michael C. Cheok, Director
Lawrence E. Kokajko, Director
Division of Construction Inspection
Division of Policy and Rulemaking
and Operational Programs
Office of Nuclear Reactor Regulation
Office of New Reactors
Technical Contacts: Stanley J. Gardocki, NRR
Jesse Robles, NRR
301-415-1023
301-415-2940
E-mail: Stanley.Gardocki@nrc.gov Email: Jesse.Robles@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ADAMS Accession Number: ML13350A189
- concurred via e-mail
TAC MF3142 OFFICE
NRR/DIRS/IOEB*
NRR/DSS/SBPB*
TECH EDITOR*
NRR/DIRS/IOEB
NRR/DSS/SPBP*
NRR/DSS
NAME
JRobles
SGardocki
HChernoff
GCasto
TMcGinty
DATE
01/06/2014
01/07/2014
12/17/2013
01/31/2014
01/07/2014
02/4/2014 OFFICE
NRO/DE/MEB
NRO/DCIP
NRR/DPR/PGCB*
NRR/DPR/PGCB
NRR/DPR/PGCB
NRR/DPR/PGCB*
NAME
TClark*
MCheok
APopova
TMensah
CHawes
SStuchell (A)
DATE
02/07/2014
02/11/2014
02/19/2014
02/19/2014
02/20/2014
02/20/2014 OFFICE
NRR/DPR
NRR/DPR
NAME
SBahadur
LKokajko
DATE
02/20/2014
02/25/2014 OFFICIAL RECORD COPY