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).

ML070390066
IN 2007-09

Page 2 of 3

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. 
IN 2007-09

Page 3 of 3

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.