Information Notice 2010-23, In: Malfunctions of Emergency Diesel Generator Speed Switch Circuits
| ML102420002 | |
| Person / Time | |
|---|---|
| Issue date: | 11/01/2010 |
| From: | Mcginty T Division of Policy and Rulemaking |
| To: | |
| Beaulieu, D P, NRR/DPR, 415-3243 | |
| References | |
| IN-10-023 | |
| Download: ML102420002 (3) | |
ML102420002 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001
November 1, 2010
NRC INFORMATION NOTICE 2010-23:
MALFUNCTIONS OF EMERGENCY DIESEL
GENERATOR SPEED SWITCH CIRCUITS
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, 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.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees about recent examples of malfunctions of emergency diesel generator (EDG) speed
switch circuits. The NRC expects that recipients will review the information for applicability to
their facilities and consider actions, as appropriate, to avoid similar problems. 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
On October 22, 2009, with the Wolf Creek Generating Station in a refueling outage, the control
room annunciator for the A EDG actuated. The licensee took the A EDG out of service for
troubleshooting. The cause of the event was the actuation of the speed switch in the starting
circuit of the A EDG because of high alternating current (ac) noise on the direct current (dc)
supply circuit of the speed switch. The source of this electrical noise was traced to the
annunciator power supply within the EDG gauge board panel. The noise was more than the
filtering capacity of the capacitor installed on the dc feed to the speed switch. The licensee
replaced the annunciator power supply and the speed switch. It also established a preventive
maintenance activity to have the ac ripple voltage measured at the dc supply circuit. Additional
information appears in Wolf Creek Generating Station Licensee Event Report 50-482/2009-005, dated December 21, 2009, on the NRCs public Web site in the Agencywide Documents Access
and Management System (ADAMS) under Accession No. ML093640041.
San Onofre Nuclear Generating Station
On December 12, 2009, at San Onofre Nuclear Generating Station Unit 3, during the
performance of a test required by the technical specifications, the train A EDG failed to start
because a capacitor failed in one of the two dc-dc converter power supplies for the local panel annunciator. The failed capacitor caused excessive ripple voltage and spiking on the speed
switch circuits, causing the speed switch to change state prematurely, preventing the engine
from starting. Licensee corrective action included replacing the annunciator power supplies on
all the EDGs with more recently manufactured units. Additional information appears in San
Onofre Nuclear Generating Station Licensee Event Report 50-362/2009-002, dated
February 10, 2010, in ADAMS under Accession No. ML100470689.
DISCUSSION
Licensees are required to maintain EDGs in an operable condition as specified in the technical
specifications. The two events described above are recent examples of malfunctions of speed
switches on EDGs resulting from noise caused by degraded annunciator power supplies.
Industry operating experience during the last 7 years shows approximately 10 additional
examples where EDGs were rendered inoperable because of speed switch malfunctions. Three
of these events were caused by the inadequate filtering of electrical noise or ripple voltages.
The noise can be caused by the age-related degradation of noise-filtering capacitors in the
power supplies.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA by TQuay for/
Timothy J. McGinty, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: Vijay Goel, NRR
Joseph Giantelli, NRR
301-415-3730
301-415-0504 E-mail: vijay.goel@nrc.gov
E-mail: joseph.giantelli@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. annunciator. The failed capacitor caused excessive ripple voltage and spiking on the speed
switch circuits, causing the speed switch to change state prematurely, preventing the engine
from starting. Licensee corrective action included replacing the annunciator power supplies on
all the EDGs with more recently manufactured units. Additional information appears in San
Onofre Nuclear Generating Station Licensee Event Report 50-362/2009-002, dated
February 10, 2010, in ADAMS under Accession No. ML100470689.
DISCUSSION
Licensees are required to maintain EDGs in an operable condition as specified in the technical
specifications. The two events described above are recent examples of malfunctions of speed
switches on EDGs resulting from noise caused by degraded annunciator power supplies.
Industry operating experience during the last 7 years shows approximately 10 additional
examples where EDGs were rendered inoperable because of speed switch malfunctions. Three
of these events were caused by the inadequate filtering of electrical noise or ripple voltages.
The noise can be caused by the age-related degradation of noise-filtering capacitors in the
power supplies.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA by TQuay for/
Timothy J. McGinty, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: Vijay Goel, NRR
Joseph Giantelli, NRR
301-415-3730
301-415-0504 E-mail: vijay.goel@nrc.gov
E-mail: joseph.giantelli@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: ML102420002
TAC ME4083 OFFICE DE:EEEB
Tech Editor
DIRS:IOEB
BC:DIRS:IOEB
BC:DE:EEEB
NAME
VGoel
KKribbs
JGiantelli
JThorp
RMathew
DATE
9/23/10
9/10/10 (e-mail)
9/23/10
9/23/10
9/27/10
OFFICE D:DE
LA:PGCB:NRR
PM:PGCB:NRR
BC:PGCB:NRR
D:DPR:NRR
NAME
PHiland GWilson for CHawes
DBeaulieu
SRosenberg
TMcGinty (TQuay)
OFFICE 10/26/10
10/27/10
10/27/10
10/28/10
11/01/10
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