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HomeNRC LibraryDocument CollectionsGeneral CommunicationsInformation Notices1993

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                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                            WASHINGTON, D.C.  20555

                                 June 18, 1993


NRC INFORMATION NOTICE 93-47:  UNRECOGNIZED LOSS OF CONTROL 
                               ROOM ANNUNCIATORS 


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 problem of unrecognized loss of
control room annunciators.  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

Callaway

On October 16, 1992, while the Callaway Plant was operating at 100 percent
power, approximately 75 annunciators on the main control board illuminated. 
After verifying that the annunciators were not valid, the shift supervisor
(SS) notified the plant manager and the engineering duty officer of the
condition and requested instrumentation and control (I&C) technicians to begin
repairs.  The I&C technicians found that one of four field power supplies for
the annunciators had failed.  The failed power supply was replaced and the
annunciators appeared to return to normal.  Two minutes later, while removing
jumper cables installed during the replacement, an electrical short occurred. 
In the control room, 371 of the 463 main control board annunciators
illuminated and remained lit.  The I&C technicians inspected the power
supplies and determined that the output fuses for all four field power
supplies had blown.  The blown fuses resulted in the loss of all main control
board annunciators.  This was not recognized by the plant staff.

Callaway procedure EIP-ZZ-00101, "Classification of Emergencies," describes
those conditions which constitute entry into established emergency action
levels (EALs).  The procedure states that, for an initiating condition of
"Most or All Alarms (Annunciators) Lost," the proper emergency classification
is an Alert.  



9306150062.

                                                                 IN 93-47
                                                                 June 18, 1993
                                                                 Page 2 of 3


Approximately one hour after the loss of all annunciators, the blown output
fuses were replaced and power was restored to the annunciator system.  Plant 
personnel verified that power was available to the annunciators by depressing
test switches in the control room.  However, this did not test the annunciator
logic circuitry and, as a result, the operating crew was unaware that 
164 annunciators with re-flash capability were completely inoperable. 
Apparently, the short that blew the output fuses in the field power supplies
also blew fuses in eight annunciator logic power supplies.  Later, while
investigating problems with the annunciators, the I&C engineer found and
replaced the blown fuses in the eight logic power supplies and an appropriate
test was performed.  However, there was not an approved procedure for this
test nor was it properly documented.  By 7:37 p.m. on October 17 the main
control board annunciators had been restored to fully operable status.

Because the SS failed to recognize that all of the main control board
annunciators were inoperable after the four field power supply output fuses
had blown, an Alert was not declared on October 17, 1992.  On October 19, the
licensee determined that an Alert should have been declared and notified State
and local authorities and the NRC of the event.

Inspection of this event by an NRC Augmented Inspection Team (AIT) found the
following weaknesses: (1) insufficient knowledge of the annunciator system by
the plant staff, (2) poor communications and inadequate teamwork, (3) lack of
a questioning attitude, and (4) inadequate work performance.  Contributing to
the insufficient knowledge of the annunciator system was the failure to have
an off-normal operating procedure or other procedure that addressed loss of
annunciators.

Salem Unit 2

On December 13, 1992, control room operators at Salem Unit 2 Nuclear Station
discovered that the overhead annunciators had been inoperable for about 
90 minutes.  The inoperable condition was detected when an alarm printer
printed a change in alarm status which was not reflected by the overhead
annunciators.  The operators reset the annunciator system and restored it to
operable status within two minutes.  Subsequent inspection of the event by an
NRC AIT identified several weaknesses that contributed to the problem.  The
operators were not adequately trained to verify proper operation of a recently
installed micro-processor based annunciator system.  The new system was not
designed with annunciation as a priority task and therefore it did not
indicate a critical mispositioned switch.  Attempts by the operators to enter
files, despite a procedure caution, contributed to locking up the system.  The
plant staff delayed in notifying plant management and the NRC.  The licensee
did not have a procedure to deal with the loss of annunciators.  The AIT
concluded that the overall knowledge of the system was inappropriate for a
system that, if lost, required the declaration of an Alert.  
.

                                                                 IN 93-47
                                                                 June 18, 1993
                                                                 Page 3 of 3


Discussion

Although plant annunciators are not considered safety related, they are
important for the safe operation of a nuclear power plant.  Further, an 
unrecognized loss of annunciators may increase the difficulty of diagnosing
problems in plant operations and equipment.  In order for plant operators to
recognize and respond properly to a loss of annunciators, it is important to
have clear procedures, appropriate training, and effective communications
between operators and plant support personnel.  For the events described
above, an off-normal operating procedure that clearly stated required actions
would have significantly aided the operators to diagnose the extent of the
problem, take necessary response actions, and make required notifications.

Loss of annunciator events were covered by the emergency classification
procedures of both licensees, premised upon guidance of Appendix 1 of 
NUREG-0654/FEMA-REP-1, "Criteria for Preparation and Evaluation of
Radiological Emergency Response Plans and Preparedness in Support of Nuclear
Power Plants," (November 1980).  The NRC recently issued Revision 3 to
Regulatory Guide 1.101, "Emergency Planning and Preparedness for Nuclear Power
Reactors" (August 1992).  That revision endorsed NUMARC/NESP-007, Revision 2,
"Methodology for Development of Emergency Action Levels," (January 1992), as
an acceptable alternative.  With respect to loss of annunciators, the 
NUMARC/NESP-007 guidance provides an alternative delineation of thresholds for
declaring an Unusual Event, Alert or Site Area Emergency.  

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.


                                            ORIGINAL SIGNED BY


                                         Brian K. Grimes, Director
                                         Division of Operating Reactor Support
                                         Office of Nuclear Reactor Regulation

Technical contacts:  Bruce L. Bartlett, RIII
                     (314) 676-3181

                     Rolf A. Westberg, RIII
                     (708) 790-5776

                     Scott A. Boynton, NRR
                     (301) 504-2926

Attachment:  
List of Recently Issued NRC Information Notices
.
```

*Page Last Reviewed/Updated Thursday, March 29, 2012*

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