Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
July 18, 1997
NRC INFORMATION NOTICE 97-53: CIRCUIT BREAKERS LEFT RACKED
OUT IN NON-SEISMICALLY
QUALIFIED POSITIONS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the potential that some safety-related circuit
breakers in their "racked-out" positions may not be seismically qualified. It
is expected 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 information notice are not
NRC requirements; therefore, no specific action or written response is
required.
Description of Circumstances
On June 13, 1991, during an in-house electrical distribution system functional
inspection, Ecovered that four circuit breakers in the 4160-volt
engineered safety features switchgear had been routinely positioned in a
racked-out configuration and seismic qualification for these circuit breakers
in this position was never performed. This problem was reported to the NRC by
the licensee for Arkansas Nuclear One, in accordance with Section 50.72,
"Immediate Notification Requirements for Operating Nuclear Power Reactors," of
Title 10 of the Code of Federal Regulations (10 CFR 50.72), in Event Number
(EN) 21189. On February 10, 1992, the licensee for Turkey Point, Units 3 and
4, reported in EN 22774 that its 4160-volt circuit breakers were not
seismically qualified in the racked-out position. Recently, licensees have
submitted a number of 50.72 reports on this issue: Susquehanna Steam Electric
Company (EN 31279); Comanche Peak Steam Electric Station (EN 31322); Three
Mile Island Nuclear Station (EN 31323); South Texas Project (EN 31362);
Oyster Creek Power Plant (EN 31325); Millstone Nuclear Power Station, Units
1, 2, and 3 (EN 31335, EN 31336, and, EN 31339); LaSalle County Station (EN
31780); Braidwood Station (EN 31799); Joseph M. Farley Nuclear Plant (EN
31807 and EN 31967); Clinton Power Station (EN 31873); and Grand Gulf Nuclear
Station (EN 32003).
9707150258. IN 97-53
July 18, 1997
Page 2 of 3
Discussion
With breakers in any position other than the seismically qualified racked-in
position, the Class 1E switchgear might not function as required for a
design-basis earthquake. Therefore, the plant is in a condition outside of
its design basis.
The root cause of these events was attributed to a lack of understanding of
the interaction between the seismic qualification status of equipment and
actual functional and/or operational configurations of equipment in the plant.
When the switchgear was seismically qualified, it was not understood that the
switchgear would be operated with the circuit breakers in the racked-out
position. Also, the seismically qualified circuit breaker positions were not
incorporated into plant operating procedures.
The term "racked-out" was defined to include any breaker position other than
the fully connected operating position. There are several intermediate
positions, depending upon the make and model of the switchgear, such as the
"test" position in which the primary contacts are disengaged but the secondary
contacts are in place so that the breaker can be tested. The "disconnect"
position has both the primary and secondary contacts disengaged but the
breaker is still in the switchgear cabinet and, in some cases, restrained.
The "removed" position is similar to the "disconnect" position but the breaker
is not restrained. These intermediate positions may not be seismically
qualified.
Because there are so many different makes and models of switchgear, a single
generic resolution of this concern is not likely. The licensees' corrective
actions following these events included restoring the affected breakers to
"racked-in" positions; evaluating the acceptability of various breaker
configurations for maintaining seismic qualification, modifying the
switchgear, and seismically qualifying the circuit breakers in all other
positions, if needed; reviewing seismic qualification procedures used to
procure new or replacement equipment to ensure that all anticipated modes of
operation are considered; verifying that other similar equipment is qualified
for all operating modes; developing training to enhance general awareness of
the effect that plant operating conditions and equipment status have on the
seismic qualification of the equipment; and physically removing those breakers
from the affected switchgear rooms. It should be noted that removal of the
circuit breaker from the switchgear will result in mass redistribution of the
switchgear. Mass redistribution of the switchgear may then change the
frequency of the switchgear and its dynamic response during a seismic event
and may invalidate the original seismic qualification of the switchgear.
Therefore, the situation must be evaluated to ensure that the removal of the
circuit breaker will not invalidate the original seismic qualification of the
switchgear.
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July 18, 1997
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This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
signed by S.H. Weiss for
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contact: Y. C. Li, NRR
301-415-2772
E-mail: ycl@nrc.gov
