United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-17: Fire Safety of Temporary Installations or Services

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                               March 11, 1991 


Information Notice No. 91-17:  FIRE SAFETY OF TEMPORARY 
                                   INSTALLATIONS OR SERVICES 


Addressees: 

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose: 

This information notice is intended to alert licensees to the fire hazards 
that may arise because of inadequate engineering design and supervisory 
control of electrical and mechanical systems temporarily installed to 
support operational or maintenance activities at commercial nuclear power 
reactors.  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 do not constitute NRC requirements; therefore, no specific action or 
written response is required. 

Description of Circumstances: 

On December 3, 1990, a fire occurred in the personnel access airlock between 
the Unit 1 reactor building and the drywell at the Brunswick Steam Electric 
Plant.  Unit 1 was in a refueling outage and was defueled at the time.  The 
fire lasted approximately two hours.  Both the inside and outside doors of 
the airlock were open to accommodate the passage of numerous cables and 
hoses in support of refueling outage activities in the drywell.  The fire 
spread along cables to just inside the drywell, but drywell damage was 
limited to smoke and soot deposits.  Most of the cables and hoses in the 
airlock were destroyed and permanent airlock components were damaged.  No 
significant effects were observed in the reactor building.  The fire was 
caused by the overheating of electrical cables from the combined effects of 
excessive current and insufficient heat dissipation.  These cables were 
supplying power to resistive heaters used for post-weld heat treatment 
(PWHT) of recirculation system piping welds and were rated at 100 amps (free 
air installation).  At the time of the fire, two PWHT circuits were carrying 
approximately 150 to 170 amps each.  The licensee had arranged 72 cables 
that supplied power to 36 PWHT circuits on a temporary fire-retardant wood 
cable tray along with numerous other lines and cables, such as welding 
leads, hydraulic hoses, drop cords, thermocouple lines, 


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                                                            IN 91-17
                                                            March 11, 1991
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air hoses, and closed circuit television cables.  All were enclosed in 
individual plastic sleeves for contamination control.  Also passing through 
the airlock were miscellaneous other lines, cables, and ventilation ducts, 
such that personnel could not gain access through the airlock.  Initially, 
the licensee had installed the cables and lines in an orderly manner, with 
cables neatly bundled.  However, the bundling and use of plastic sleeves to 
control contamination significantly reduced the ability of the PWHT cables 
to dissipate heat.  The guidance in the Institute of Electrical and 
Electronic Engineers (IEEE) Standard S-135 and the National Electric Code 
(Articles 400 and 630) indicates that the cables should have been derated by 
approximately 50 percent because of the spacing between them.  The 
combination of excessive current and inadequate spacing resulted in the 
cables carrying over three times the recommended rated current.  The 
licensee and the NRC staff concluded that the temporary services passing 
through the airlock were not properly engineered.  Following the orderly 
initial installation of temporary services through the airlock, additional 
cables and hoses were pulled through in a haphazard manner wherever they 
would fit.  Services no longer needed could not be easily removed because of 
the tangling and interference from other lines.  These factors resulted in a 
disorganized, congested, and confined space that further restricted the heat 
dissipation of the PWHT cables and, once the fire started, seriously 
hampered efforts to extinguish it. 

Discussion: 

The use of temporary services at power reactor facilities is routine, 
especially in support of maintenance and other activities during outages.  
In view of the magnitude and complexity of some temporary services, proper 
engineering and, once installed, maintenance of the design basis become 
significant.  

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 NRR project manager.  




                                   Charles E. Rossi, Director 
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation 


Technical Contact:  D. J. Nelson, RII 
                    (919) 457-9531 


Attachment:  List of Recently Issued NRC Information Notices 
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Page Last Reviewed/Updated Tuesday, November 12, 2013