UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 March 26, 2007 NRC INFORMATION NOTICE 2007-09: EQUIPMENT OPERABILITY UNDER DEGRADED
VOLTAGE CONDITIONS
ADDRESSEES
All holders of operating licensees for nuclear power reactors, 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 of an event in which safety-related pump motors did not have adequate voltage at
the starter circuit to ensure operability under degraded voltage conditions and a related
deficiency involving a surveillance test procedure that specified an incorrect value for the
emergency diesel generator (EDG) minimum acceptable voltage. NRC staff expects 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
On August 17, 2006, the licensee for the Fermi 2 nuclear power plant declared all four EDGs
inoperable due to undersized control power transformers for each of the EDG service water
pumps. The concern was that the EDG service water pump motors did not have adequate
voltage at the starter circuit to ensure operability under degraded voltage conditions. The event
was caused by a design error that occurred in 1998 when a design change was prepared for
the replacement of motor control center buckets that did not account for the fact that the higher
inrush current of replacement contactors would necessitate installation of a larger control power
transformer. As part of the extent of condition review, the licensee also identified similar
concerns with the Division 1 EDG room ventilation fans. Subsequent analysis further revealed
a lack of a voltage margin on other potentially risk-significant components. The licensee
submitted a licensee event report (LER) to describe the event (LER 50-341/2006-004-00,
Agencywide Documents Access and Management System (ADAMS) Accession No.
ML0629302170).
During a special inspection of the above event, the NRC inspectors identified that the Division 1 EDG surveillance test procedure specified minimum required EDG voltage of 3740 volts which
was below the calculated minimum voltage required for component operability. As a result, the
surveillance test would not ensure that the Division 1 EDGs would support the operability of the
required components. To correct this deficiency, Fermi nuclear power plant established
administrative controls, pending procedure and technical specifications revision, to ensure that
future testing of the Division 1 EDGs would include a minimum required voltage acceptance
criterion of 3873 volts. (NRC Special Inspection Report 05000341/2006015, dated
November 7, 2006, ADAMS Accession No. ML0631204130).
BACKGROUND
Branch Technical Position PSB-1 of the Standard Review Plan (NUREG-0800) recommends
that the second level of undervoltage (degraded voltage) protection should be based on an
analysis of the voltage requirements of the Class 1E loads at all onsite system distribution
levels. The voltage levels at the safety-related busses should be optimized for the maximum
and minimum load conditions that are expected throughout the anticipated range of voltage
variations of the offsite power sources. Consequently, when powering the safety-related
busses from EDGs, the minimum required EDG steady state voltage must be greater than or
equal to the minimum established voltage for component operability.
DISCUSSION
It is important that EDG surveillance procedures specify a minimum EDG steady state voltage
that is greater than or equal to the calculated bus minimum voltage required for component
operability.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to one of the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA by TQuay for/
Michael J. Case, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: Amar Pal, NRR/DE
301-415-2760
E-mail: anp@nrc.gov
Omid Tabatabai, NRR/DIRS
301-415-6616 E-mail: oty@nrc.gov
Note: NRC generic communications may be found on the NRC public Website, 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 one of the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
/RA by TQuay for/
Michael J. Case, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts: Amar Pal, NRR/DE
301-415-2760
E-mail: anp@nrc.gov
Omid Tabatabai, NRR/DIRS
301-415-6616 E-mail: oty@nrc.gov
Note: NRC generic communications may be found on the NRC public Website, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
DISTRIBUTION:
IN FILE
ADAMS Accession Number: ML070390066 OFFICE EEEB:DE Tech Editor BC:EEEB:DE: IOEB:DIRS TL:IOEB:DIRS:
NAME APal CClark IJung OTabatabai JThorp
DATE 2/09/2007 2/07/2007 2/09/2007 2/08/2007 2/13/2007 OFFICE PGCB:DPR PGCB:DPR BC:PGCB:DPR D:PGCB
NAME CHawes CMH DBeaulieu CJackson TQuay for MCase
DATE 2/26/2007 3/6 /2007 3 /23/2007 3/26/2007 OFFICIAL RECORD COPY
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