United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-01: Cable Damage caused by Inadequate Cable Installation Procedures and Controls

                                UNITED STATES
                          WASHINGTON, D.C.  20555 

                              January 3, 1992 

                               INSTALLATION PROCEDURES AND CONTROLS 


All holders of operating licenses or construction permits for nuclear power 


The U.S. Nuclear Regulatory Commission is issuing this information notice to 
alert addressees to the possibility that inadequate cable installation 
procedures and quality control could cause safety-related cables to fail.  
It is expected that the 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 

In June 1989, the Tennessee Valley Authority (TVA) removed the cables from a 
conduit in the reactor protection system of the Watts Bar Nuclear Plant, 
Unit 2, to inspect for damage.  TVA selected this conduit in response to an 
employee's concern that a welding arc that struck the conduit during 
construction may have damaged cables in the conduit.  When the cables were 
removed, TVA found significant damage in the insulation of some cables.  
This damage was not attributed to heat generated by the alleged welding arc.  
The damage was principally attributed to the pulling stresses exerted during 
the initial installation of the cables.  Some of the cables had insulation 
removed down to the conductors.  To assess the extent of cable damage and 
determine the scope of its investigation, TVA removed more cables from 
conduits that constituted the most difficult pulls (worst case) and found 
varying degrees of damage that it attributed to pulling stresses. 

To fill a conduit at Watts Bar, personnel used pull cords to pull more 
cables through the conduits over the top of existing cables.  This practice 
is called "pull-by."   This practice can cause damage to the existing cables 
from the 


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                                                          January 3, 1992 
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sawing action of the pull cords and the friction of cables as they are 
pulled over existing cables.  The University of Connecticut, under contract 
for TVA, evaluated damaged cables and determined the cause of damage to have 
been cable pull-bys.  Usually such damage would be minimized by using the 
proper and  adequate amounts of lubricants, controlling pulling tension, 
choosing appropriate pull cords, limiting the distance between pull points, 
and minimizing the number and angle of bends allowed in the conduit.  
Industry standards provide no specific guidance for performing multiple 
pulls of cables in conduits. 

TVA instituted programs to assess the adequacy of cable installation at all 
its nuclear facilities and take appropriate corrective actions.  At Watts 
Bar, TVA replaced cables in conduits which exceeded a calculated threshold 
value of side wall bearing pressure (SWBP) and performed high-potential 
(hi-pot) tests on a number of other cables in conduits with SWBP below the 
calculated threshold value.  The hi-pot test voltage was 240 Vdc per mil of 
insulation thickness (based on the minimum qualified thickness) not to 
exceed 80 percent of the factory's test voltage.  Before conducting the 
testing, TVA flooded the segments of conduits with the highest SWBP values 
with water to establish a continuous electrical ground at the external 
surface of the cable.  TVA did not flood conduits with shielded cables 
because the shield provided adequate ground. 

At the Sequoyah and Browns Ferry Nuclear Plants, TVA performed hi-pot tests 
on cables in a smaller sample of conduits with high SWBP values.  TVA did 
not replace, but included in the test sample, cables at these plants that 
exceeded the threshold SWBP values of Watts Bar because it had not used the 
very abrasive nylon cord (parachute cord) at these plants that was 
extensively used at Watts Bar.  This cord was used as pull cord and seemed 
to have caused the more severe damage to cables.  Though TVA observed some 
failures during the hi-pot testing, it attributed none of the failures to 
the effects of cable pull-bys.  

Discussion of Safety Significance 

The damage identified in the reactor protection system cables at Watts Bar 
demonstrates that the safety function of safety systems could be lost if 
damaged cables are located in harsh environments.  Such cable damage can be 
caused by the pulling stresses exerted during cable installation.  If 
moisture enters the affected conduits, it can cause cables to short, which 
could cause the common mode loss of safety function of systems whose 
performance is required to mitigate the consequences of an accident. 

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                                                          January 3, 1992 
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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 Office of Nuclear 
Reactor Regulation (NRR) project manager. 

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

Technical contact:  H. Garg, NRR 
                    (301) 504-2929 

Attachment:  List of Recently Issued NRC Information Notices 

Page Last Reviewed/Updated Friday, May 22, 2015