Bulletin 79-27: Loss of Non-Class-1-E Instrumentation And Control Power System Bus During Operation
SSINS No.: 6820
Accession No.:
7910250499
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
November 30, 1979
IE Bulletin No. 79-27
LOSS OF NON-CLASS-1-E INSTRUMENTATION AND CONTROL POWER SYSTEM BUS DURING
OPERATION
Description of Circumstances:
On November 10, 1979, an event occurred at the Oconee Power Station, Unit 3,
that resulted in loss of power to a non-class-1-E 120 Vac single phase power
panel that supplied power to the Integrated Control System (ICS) and the
Non-Nuclear Instrumentation (NNI) System. This loss of power resulted in
control system malfunctions and significant loss of information to the
control room operator.
Specifically, at 3:16 p.m., with Unit 3 at 100 percent power, the main
condensate pimps tripped, apparently as a result of a technician performing
maintenance on the hotwell level control system. This led to reduced
feedwater flow to the steam generators, which resulted in a reactor trip due
to high coolant system pressure and simultaneous turbine trip at 3:16:57
p.m. At 3:17:15 p.m., the non-class-1-E inverter power supply feeding all
power to the integrated control system (which provides proper coordination
of the reactor, steam generator feedwater control, and turbine) and to one
NNI channel tripped and failed to automatically transfer its loads from the
DC power source to the regulated AC power source. The inverter tripped due
to blown fuses. Loss of power to the NNI rendered control room indicators
and recorders for the reactor coolant system (except for one wide-range RCS
pressure recorder) and most of the secondary plant systems inoperable,
causing loss of indication for systems used for decay heat removal and water
addition to the reactor vessel and steam generators. Upon loss of power, all
valves controlled by the ICS assumed their respective failure positions. The
loss of power existed for approximately three minutes, until an operator
could reach the equipment room and manually switch the inverter to the
regulated AC source.
The above event was discussed in IE Information Notice No. 79-29, issued
November 16, 1979.
NUREG 0600 "Investigation into the March 28, 1979 TMI Accident" also
discusses TMI LER 78-021-03L whereby the RCS depressurized and Safety
Injection occured on loss of a vital bus due to inverter failure.
Actions to Be Taken by Licensees
For all power reactor facilities with an operating license and for those
nearing completion of construction (North Anna 2, Diablo, Canyon, McGuire,
Salem 2, Sequoyah, and Zimmer):
.
IE Bulletin No. 79-27 November 30, 1979
Page 2 of 3
1. Review the class-1-E and non-class 1-E buses supplying power to safety
and non-safety related instrumentation and control systems which could
affect the ability to achieve a cold shutdown condition using existing
procedures or procedures developed under item 2 below. For each bus:
a) identify and review the alarm and/or indication provided in the
control room to alert the operator to the loss of power to the
bus.
b) identify the instrument and control system loads connected to the
bus and evaluate the effects of loss of power to these loads
including the ability to achieve a cold shutdown condition.
c) describe any proposed design modifications resulting from these
reviews and evaluations, and your proposed schedule for
implementing those modifications.
2. Prepare emergency procedures or review existing ones that will be used
by control room operators, including procedures required to achieve a
cold shutdown condition, upon loss of power to each class 1-E and
non-class 1-E bus supplying power to safety and non-safety related
instrument and control systems. The emergency procedures should
include:
a) the diagnostics/alarms/indicators/symptom resulting from the
review and evaluation conducted per item 1 above.
b) the use of alternate indication and/or control circuits which may
be powered from other non-class 1-E or class 1-E instrumentation
and control buses.
c) methods for restoring power to the bus.
Describe any proposed design modification or administrative controls to
be implemented resulting from these procedures, and your proposed
schedule for implementing the changes.
3. Re-review IE Circular No. 79-02, Failure of 120 jolt Vital AC Power
Supplies, dated January 11, 1979, to include both class 1-E and
non-class 1-E safety related power supply inverters. Based on a review
of operating experience and your re-review of IE Circular No. 79-02,
describe any proposed design modifications or administrative controls
to be implemented as a result of the re-review.
4. Within 90 days of the date of this Bulletin, complete the review and
evaluation required by this Bulletin and provide a written response
describing your reviews and actions taken in response to each item.
Reports should be submitted to the Director of the appropriate NRC Regional
Office and a copy should be forwarded to the NRC Office of Inspection and
Enforcement, Division of Reactor Operations Inspection, Washington, D.C.
20555.
If you desire additional information regarding this matter, please contact
the IE Regional Office.
.
IE Bulletin No. 79-27 November 30 1979
Page 3 of 3
Approved by GAO B180225 (R0072); clearance expires 7/31/80. Approval was
given under a blanket clearance specifically for identified generic
problems.
Page Last Reviewed/Updated Tuesday, March 09, 2021