Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No. 6835
IN 85-77
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
September 20, 1985
Information Notice No. 85-77: POSSIBLE LOSS OF EMERGENCY NOTIFICATION
SYSTEM DUE TO LOSS OF AC POWER
Addressees:
All holders of a nuclear power plant operating license (OL) or a
construction permit (CP).
Purpose:
This information notice is provided to alert licensees to the possibility
that modifications to plant telephone systems may result in a change in the
vulnerability of the Emergency Notification System (ENS) and other plant
telephones to losses of ac power, It is expected that recipients will review
the information for applicability to their facilities and consider actions,
if appropriate, to preclude similar problems occurring at their facilities.
However, suggestions contained in this information notice do not constitute
NRC requirements; therefore, no specific action or written response is
required.
Description of Circumstances:
On January 8, 1984, the Palisades Nuclear Plant interrupted its offsite
power supply for maintenance activities. Subsequently all ac power from the
emergency diesel generators was lost. (This event is described in detail in
Information Notice No. 84-42.) As a result of the ac power problems, all
onsite telephones were rendered inoperable for approximately 3 hours, except
for two offsite-powered pay telephones. Loss of the ENS and normal
communications significantly hampered the notification process.
On May 7, 1985, Quad Cities Unit 1 was operating at 90% power. The Unit 2
auxiliary transformer was inadvertently shorted while the unit was shut down
with its associated emergency diesel generator out for maintenance. This
caused the loss of offsite ac power to Unit 2 and a voltage transient in
Unit 1 that subsequently caused that unit to scram about 15 minutes later.
Unit 1 retained offsite ac power. One division of Unit 2 was promptly
powered by autostart of the swing emergency diesel generator, and the other
division was powered within about 20 minutes by crosstie to a 4kV bus of
Unit 1. When the licensee attempted to notify the NRC Emergency Operations
Center over the ENS, the circuit repeatedly disconnected. The Quad Cities
plant also was unable to receive incoming calls from the NRC over commercial
telephone lines.
8509180410
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IN 85-77
September 20, 1985
Page 2 of 3
These incidents indicate that the provisions of IE Bulletin 80-15 were not
maintained at the affected facilities at the times of the events. The bulle-
tin required verification that all ENS station packages that use onsite ac
power were connected to a safeguards instrumentation bus backed up by auto-
matic transfer to batteries and an inverter or an equally reliable power
source. At the time the bulletin was issued, both plants had ENS packages
that were powered by the local telephone company, making them independent of
ac power sources at the plant sites.
Discussion:
The installation of the ENS requires a station package ,that operates on 110
Vac. In some cases, the station package is located at the local telephone
company which supplies the required power for normal operation and emergency
power for operation during abnormal situations. However, in many cases, the
ENS package is located at the site and is served by ac power provided by the
plant.
Earlier incidents involving loss of offsite power led to losses of emergency
notification capabilities at the Davis-Besse facility on October 15, 1979,
and at the Indian Point Unit 2 on June 3, 1980. These incidents prompted the
issuance of IE Circular 80-09 and IE Bulletin 80-15. The bulletin contained
a list of those stations with ENS packages powered by the telephone company
and a list of those stations with ENS packages powered at the plant site. At
that time, both the Palisades plant and the Quad Cities plant had-ENS pack-
ages with power supplies provided by the telephone company.
Subsequent changes to provide additional circuits in the telephone system at
the Palisades plant resulted in the ENS and commercial telephone system
packages being powered at the plant site. Power was supplied. from a bus
supported by an emergency diesel generator. However, the modification was
not controlled within the licensee's formal modification process and was
thus completed without formal review. The modified ENS power supply was not
backed by batteries and an inverter, as previously provided by Bulletin
80-15, and was not independent of the station's commercial telephone service
as reflected in the licensee's Emergency Plan.
During the incident at Palisades on January 8, 1984, the unit was
intentionally powered from a single emergency diesel generator on the 1C
2400-V bus to allow isolation of a faulty switchyard breaker. The unit was
defueled, and the other diesel was inoperable due to maintenance. When the
running diesel subsequently overheated and tripped, the station was without
ac power with the exception of preferred ac. Although some other buses were
repowered by offsite ac within an hour, difficulties in closing the breakers
to the 1C and 1E 2400-V buses resulted in the extended loss of all
telephones except for two pay telephones powered by the telephone company.
The 1E bus was repowered after about 3 hours by successfully closing the
breaker to the offsite source. This provided partial restoration of the
telephone service. However, the ENS telephones on the 1C bus were not
restored for 6 hours, when they were finally jumpered to an energized
source.
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IN 85-77
September 20, 1985
Page 3 of 3
At the Quad Cities plant, the local telephone company abandoned the copper
wire cables that were in use in 1980 and installed a fiber optics communi-
cations system in its place. Because the fiber optics cable does not provide
for electrical power transmission, the fiber optics package at the plant had
to be provided with an onsite power source. Similarly, the site package for
the ENS had to be shifted to onsite power. The licensee powered the fiber
optics package from an instrument bus in Unit 2 and the ENS from an
instrument bus in Unit 1. These buses are supported by emergency diesel
generators, but the power supplies to the communications packages are not
backed up by batteries and an inverter in accordance with Bulletin 80-15.
During the event on May 7, 1985, when the Unit 2 instrument bus powering the
fiber optics package lost power, both the ENS and normal PBX telephones be-
came inoperable. The Unit 1 bus supporting the ENS package remained powered
by an offsite ac source through the switchyard, but could not communicate
through the unpowered fiber optics system. Once power was restored to the
Unit 2 bus through a crosstie, the ENS circuit repeatedly disconnected as
the licensee attempted to make emergency notifications.
These events illustrate the need for careful review of changes to plant
telephone equipment to ensure that the reliability of the ENS is not com-
promised. In those cases where offsite communications power that is supplied
by the telephone company is replaced by an onsite power source, it is impor-
tant to consider the reliability of the power sources for all segments of
the ENS transmission path. Those plants that already supply the ENS from an
onsite safeguards instrumentation bus should be, aware that the introduction
of a fiber optics connection by the local telephone company still may
compromise the ENS if the plant-end fiber optics package is not similarly
powered.
No specific action or written response is required by this information
notice. If you have any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this
office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: S. Long, IE
(301) 492-7159
R. Priebe, IE
(301) 492-4333
Attachment: List of Recently Issued IE Information Notices
