United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-84: Problems with Criticality Alarm Components/Systems

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
              OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
                          WASHINGTON, D.C.  20555 

                              December 26, 1991 


NRC INFORMATION NOTICE 91-84:  PROBLEMS WITH CRITICALITY ALARM 
                               COMPONENTS/SYSTEMS 


Addressees 

All Nuclear Regulatory Commission (NRC) fuel cycle licensees, interim spent 
fuel storage licensees, and critical mass licensees. 

Purpose 

NRC is issuing this notice to remind licensees of the importance of adequate 
reviews of plant modification, installation, maintenance, and response 
actions, to ensure that required criticality alarm systems meet their 
intended purpose.  It is expected that recipients will review this 
information for applicability to their facilities, distribute it to 
responsible staff, and consider actions, as appropriate, to avoid similar 
problems.  However, suggestions contained in this information notice do not 
constitute any new NRC requirements, and no written response is required. 

Description of Circumstances 

The following cases are recent events involving problems with licensee's 
criticality alarm systems that have been reported to, or discovered by, NRC. 

Case 1:  During a routine test of the criticality alarm system, a licensee 
discovered that several of the site's audible alarms ("howlers") did not 
actuate.  The licensee found that wiring to the alarms had been accidentally 
broken while other electrical cables were being pulled through the cable run 
that contained the criticality alarm wiring.  The licensee's system provided 
indication, prior to the next scheduled test, that some of the audible 
alarms had been disabled.  

Case 2:  Engineering drawings describing modifications at a licensed 
facility specified removal of "heat detectors (radiation)."  The licensee's 
review of the modification package did not recognize that it included 
removal, rather than relocation, of criticality alarm system detectors.  
When the specified detectors were removed no alarm was generated at the 
system monitoring panel.  Subsequent investigation disclosed that the alarm 
panel was wired in such a way that, although a "failure" light was activated 
at an intermediate panel (an unmanned location), a "loss of power/loss of 
detector" signal was not generated at the monitoring panel in a normally 
manned area. 


9112190113 
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                                                       IN 91-84 
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Case 3:  A licensee experienced an activation of the plant's criticality 
alarm system, but no criticality accident had actually occurred.  
Investigation found that the alarm had been generated when the 
uninterruptable power supply (UPS) circuit that powered the alarm system was 
turned off by means of a switch in the facility's main computer room.  The 
switch had been backfitted to the system to allow for cutoff of all power to 
the computer room in emergency situations and was not intended to affect 
power to the criticality alarm system.  The modification review associated 
with the addition of the switch did not identify the fact that the planned 
location was between the UPS source and the primary criticality alarm system 
circuit. 

Case 4:   During an electrical storm, the criticality safety alarms at only 
the Waste Treatment Facility (WTF) sounded because of a momentary power 
interruption.  Personnel in the WTF did not evacuate, but instead called 
Security, who then notified Radiation Control and Electrical Shop personnel.  
Electricians then entered the WTF to silence the alarms before obtaining 
clearance from Radiation Control.  An investigation of the incident 
determined that the personnel in the WTF did not evacuate in accordance with 
procedures required by 10 CFR 70.24, and that the electricians made an 
uncontrolled entry into the WTF to silence the alarms prior to getting 
clearance from Radiation Control. 

Case 5:   During a routine NRC inspection of a licensee's criticality 
accident monitoring system, the inspector found that:  (1) since 1970, no 
evaluation had been performed to demonstrate that the system provided 
adequate monitoring coverage for facility modifications or additions where 
large quantities of special nuclear material were being stored or used; (2) 
the licensee did not have a system to ensure that such technical evaluations 
were performed and documented; and (3) no program existed to limit the 
storage of intervening shielding materials between the neutron criticality 
detectors and the monitored areas. 

Case 6:   During maintenance, a licensee discovered that under design basis 
accident conditions (greater than 1 E+15 fissions) its criticality alarm 
system might not function as intended.  The alarm system used Geiger-Mueller 
detectors that could become electronically saturated in a high radiation 
field and not function.  As a result, the licensee declared an Unusual Event 
and discontinued transfers of fissile materials within the facility.  The 
licensee terminated the Unusual Event after connecting anti-saturation 
circuitry to the criticality alarm system. 

Discussion 

All licensees are reminded of the importance of maintaining operable 
criticality detection, monitoring, and annunciation capabilities, as well as 
procedures and training for response to criticality alarms.  As the 
forementioned cases indicate, a lack of detailed knowledge of the system's 
configuration and routing of detector or power circuits can result in 
failure to recognize the possible impact of installation, modification, or 
maintenance activities on the criticality alarm system.  Physical and 
electrical modifications have the 
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                                                       IN 91-84 
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clear potential to degrade or disable all or part of this important safety 
system.  Licensees should ensure that they have established a comprehensive 
testing program, both on a routine basis and after maintenance and 
modification activities, and a method of continuously monitoring the 
integrity of criticality alarm system lines and components, through line 
supervision, to preclude failure of criticality alarm system capabilities.  
These activities should include clearly written implementing procedures, and 
a training program to ensure appropriate implementation. 

This information notice requires no specific action or written response.  If 
you have questions about the information in this notice, please contact one 
of the technical contacts listed below or the appropriate regional office. 




                                   Richard E. Cunningham, Director 
                                   Division of Industrial and 
                                     Medical Nuclear Safety, NMSS 


Technical contacts:  Scott Pennington, NMSS 
                     (301) 504-2693 

                     Gerald Troup, RII 
                     (404) 331-5566 

Attachments:
1.  List of Recently Issued NMSS Information Notices
2.  List of Recently Issued NRC Information Notices 
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