Information Notice No. 85-09: Isolation Transfer Switches and Post-fire Shutdown Capability
SSINS No.: 6835
IN 85-09
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
January 31, 1985
Information Notice No. 85-09: ISOLATION TRANSFER SWITCHES AND POST-FIRE
SHUTDOWN CAPABILITY
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This information notice is to alert recipients of potential deficiencies in
the electrical design of isolation transfer switches installed outside the
control room at many nuclear power plants. The transfer switches provide
electrical isolation of certain shutdown circuits from the control room and
other essential fire areas during post-fire accident conditions. It is
expected that recipients will review the information for applicability to
their facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities. However, suggestions contained in
this notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Description of Circumstances:
During a recent NRC fire protection inspection at the Wolf Creek facility,
it was discovered that a fire in the control room could disable the
operation of the plant's alternate shutdown system. Isolation transfer
switches of certain hot shutdown systems would have to be transferred to the
alternate or isolated position before fire damage occurred to the control
power circuits of several essential pumps and motor-operated valves at this
facility. If the fire damage occurred before the switchover, fuses might
blow at the motor control centers or local panels and require replacements
to make the affected systems/components operable. This situation existed
because the transfer scheme depended on the existing set of fuses in the
affected circuit and did not include redundant fuses in all of the alternate
shutdown system circuits. For most of the transfer switches, the situation
would not cause a problem because the desired effect after isolation is the
deenergization of power. In instances where the system/component has to be
operable or where operation might be required to override a spurious
actuation of a component (such as a motor-operated valve), replacement of
fuses may have become necessary. In such cases, troubleshooting/repair would
be required to achieve or maintain hot shutdown.
8501300138
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IN 85-09
January 31, 1985
Page 2 of 2
Discussion:
At the Wolf Creek facility, where the concern was discovered, the transfer
switches at the remote shutdown panel had redundant fusing. The only
transfer switches identified as a concern were those at other local stations
that mainly involve support systems operability or correction of spurious
operations. The facility is either modifying existing switches or installing
new switches for certain components so that redundant fusing will exist with
a new (different) set of fuses switched into the circuit when the switch is
placed in the isolated mode. Alternate shutdown procedures also are being
revised so that shutdown could be achieved under fire conditions which
result in immediate evacuation of the control room and control room circuit
damage that causes maloperation of equipment prior to isolation outside the
control room.
This situation may exist at other facilities and may involve the shutdown
panel and other local stations that are needed for alternate shutdown
capability. This could include the switches and other circuits on the
alternate/remote shutdown panel. Operability of the hot shutdown systems,
including the ability to overcome a fire or fire suppressant induced
maloperation of hot shutdown equipment and the plant's power distribution
system, must exist without repairs, including replacement of fuses. Section
III.G.1 of Appendix R to 10 CFR 50 addresses fire protection of safe
shutdown capability. Meeting this requirement for the affected circuits will
ensure that redundant fuses are part of the transfer schemes.
No specific action or written response is required by this information
notice. However, if you have any questions regarding this notice, please
contact the Regional Administrator of the appropriate NRC regional office or
the technical contact listed below.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: W. T. LeFave, NRR
(301) 492-9470
V. D. Thomas, IE
(301) 492-4755
Attachment: List of Recently Issued IE Information Notices
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