Information Notice 2005-20, Electrical Distribution System Failures Affecting Security Equipment
| ML051920213 | |
| Person / Time | |
|---|---|
| Issue date: | 07/19/2005 |
| From: | Hiland P NRC/NRR/DIPM/IROB |
| To: | |
| Tabatabai O, NRR/DIPM/IROB, 415-6616 | |
| References | |
| IN-05-020 | |
| Download: ML051920213 (6) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 July 19, 2005 NRC INFORMATION NOTICE 2005-20: ELECTRICAL DISTRIBUTION SYSTEM
FAILURES AFFECTING SECURITY EQUIPMENT
ADDRESSEES
All holders of operating licenses for power reactors, except those who have permanently
ceased operations and have certified that fuel has been permanently removed from the reactor.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform
addressees about the adverse impact of electrical distribution system failures on security
systems. The NRC anticipates that recipients will review the information for applicability to their
facilities and consider taking actions, as appropriate, to avoid similar issues. However, no
specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
On June 14, 2004, a ground fault occurred on a 230kV transmission line at a location some
distance from the Palo Verde Nuclear Generating Station. A failure in the protective relaying
prevented the immediate isolation of the ground fault from the local grid and caused a loss of
offsite power and reactor trips of all three Palo Verde units. The Unit 2 Train A emergency
diesel generator (EDG) started but did not complete the load sequencing process due to a
failed diode in the exciter rectifier circuit. As a result the Train A engineered safeguards feature
busses deenergized, causing the loss of some security equipment. Other aspects of this event
were previously discussed in NRC Information Notice 2005-15, Three-Unit Trip and Loss of
Offsite Power at Palo Verde Nuclear Generating Station, issued on June 1, 2005.
On June 29, 2004, a complete loss of security power occurred while operators were
troubleshooting the security power distribution system at the Watts Bar Nuclear Plant. An
operator opened a panel door and removed a subpanel cover to verify the system parameters
for an uninterruptible power supply (UPS). The operator then reattached the subpanel cover
but did not verify that the latching screw adequately secured the subpanel cover to the outer
panel frame. Subsequently, when the operator closed the panel door, the subpanel cover
rocked off of the latching mechanism and nicked a ribbon cable, causing a short to ground and
the eventual loss of all security power.
On January 14, 2005, water intrusion into the central alarm station (CAS) master electrical
distribution panel resulted in arcing in the vicinity of the power supply circuit breaker to the CAS
at the Millstone Power Station. The ensuing fire caused a loss of electrical power to multiple
security systems. Although the security EDG was available during the event, the electrical fault
and fire also prevented the licensee from transferring loads to the EDG.
On February 8, 2005, a short circuit and fire occurred in an outdoor cable tray at the Turkey
Point Nuclear Plant, resulting in the loss of some plant security equipment. The fire also
resulted in the loss of the normal power supply to a security UPS; however, all security systems
powered by the UPS remained energized. On February 17, 2005, a second event occurred at
Turkey Point when a component of the security UPS overheated and started a fire. Operators
immediately opened circuit breakers at the UPS, causing all security systems serviced by the
UPS to be lost.
DISCUSSION
Failures of electrical distribution systems that supply electrical power to plant security systems
can cause significant, prolonged outages of equipment normally relied on by security personnel
to provide intrusion detection and access control and to respond to security incidents. In all of
the events described above, the affected licensees implemented compensatory security
measures in response to the security system degradations. Other licensees are reminded to
consider these types of failures when developing and reviewing security procedures for
responding to degraded equipment.
Licensees are also encouraged to ensure that security equipment undergoes preventive
maintenance and is subject to corrective action programs similar to programs for safety-related
equipment. In addition, licensees should consider taking actions to identify single points of
failure which may not have been recognized in the original design of or modifications to these
systems .
CONTACT
This information notice does not require any 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/
Patrick L. Hiland, Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: F. Paul Peduzzi, NSIR Robert J. Stransky, NSIR
301-415-5734 301-415-6411 E-mail: fxp1@nrc.gov E-mail: rjs3@nrc.gov
NRR Project Manager: Omid Tabatabai, NRR
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.
ML051920213 DOCUMENT NAME: E:\Filenet\ML051920213.wpd
OFFICE OES:IROB:DIPM TECH EDITOR DNS:NSO:NSIR DPR:IRD:NSIR
NAME OTabatabai PKleene FPPeduzzi RStransky
DATE 07/11/2005 07/11/2005 07/12/2005 07/12/2005 OFFICE SC:DNS:NSO:NSIR TL:C:IROB:DIPM SC:OES:IROB:DIPM C:IROB:DIPM
NAME BWestriech EJBenner MJRoss-Lee PHLiland
DATE 07/12/2005 07/12/2005 07/19/2005 07/19/2005