IE Circular No. 79-05, Moisture Leakage in Stranded Wire Conductors


                              March 14, 1979 

MEMORANDUM FOR:     B. H. Grier, Director, Region I 
                    J. P. O'Reilly, Director, Region II 
                    J. G. Keppler, Director, Region III 
                    K. V. Seyfrit, Director, Region IV 
                    R. H. Engelken, Director, Region V 

FROM:               Norman C. Moseley, Director, Division of Reactor 
                    Operations Inspection, Office of Inspection and 


     The Draft Information Notice covering the above subject matter has been
upgraded to IE Circular status following consideration of several comments 
from NRR and IE Staff. The Circular is transmitted for issuance on March 20,
1979. This Circular should be issued to al holders of Reactor Operating 
Licenses or Construction Permits. Also enclosed is a draft copy of the 
transmittal letter. 

                                        Norman C. Moseley, Director 
                                        Division of Reactor Operations 
                                        Office of Inspection and Enforcement

1.   Draft Transmittal Letter
2.   IE Circular No. 79-05

V. D. Thomas, IE

(Transmittal letter for Circular 79-05 to each holder of an NRC Operating 
License or Construction Permit.) 

                                                      IE Circular No. 79-05 


The enclosed Circular 79-05 is forwarded to you for infomation. If there are
any questions related to your understanding of the suggested actions, please
contact this office. 

                                        (Regional Director) 

IE Circular No. 79-05 

                              UNITED STATES 
                          WASHINGTON, D.C. 20555 

                              March 20, 1979 

                                                      IE Circular No. 79-05 


Description of Circumstances: 

During a staff review of the results of environmental qualification test of 
certain electrical equipment, the phenomenon of water penetration between an
electrical conductor and its loosely fitting insulation sleeve was 
identified. The staff determined it to be prudent to investigate this 
phenomenon and initiated an equipment checkout test at Sandia Laboratories 
using a few typical conductors used in nuclear plants. 

The equipment checkout test for cable leaks performed at Sandia Laboratories
in August 1978, has shown that most stranded wire conductors, when subjected
to a differential pressure across the conductor ends, will leak steam or 
moisture through the interstices of the strands of wire. The test has also 
shown that solid conductors, under similar conditions, do not leak. 

Steam/moisture leakage through stranded conductors can occur during a Loss 
of Coolant Accident/Main Steam Line Break (LOCA/MSLB), if a differential 
pressure were to develop across the conductor ends; e.g., one end of the 
conductor is exposed to the accident environment (typically, in an unsealed 
junction box) and the other end is isolated from the environment (typically,
inside a sealed component such as a sensor/transmitter). 

In order to determine whether as-installed configurations exist in nuclear 
power plants which may result in degradation of safety-related functions due
to moisture leakage in stranded wire conductors, inspection visits by NRC 
personnel were made in October to two nuclear plants, (one under 
construction, and the other operating). During the inspections the detailed 
configuration of stranded conductor cables, and their terminations at 
splices, penetrations, junction boxes, transmitters, motors, motor 

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IE Circular No. 79-05                                       March 20, 1979 

operated valves, and valve limit switches were reviewed. Special attention 
was given to termination details of stranded conductors at the terminal 
blocks installed inside junction boxes and at the connections to the various
equipment. Additional infomation was provided by both licensees of the power
plants visited and by the Architect-Engineer regarding design and 
construction details of such equipment. Based on observations made during 
these site visits and information obtained, the following items have been 
identified as areas where the possibility of the steam/ moisture incursion 
phenomenon exists: 

1.   Terminal Blocks/Junction Boxes - Junction boxes in containment that are
     used to house terminal blocks where cables were terminated, usually 
     have dust tight and drip proof housings with vent and drain holes. 
     Cables terminated in this fashion are generally stranded conductor 
     type. The terminal blocks and cable terminations inside these boxes 
     will be exposed to the containment environment during normal operation 
     and a LOCA. No special provisions are generally made in the termination 
     of stranded conductors in terminal blocks/junction boxes to prevent 
     moisture or steam incursion. 
2.   Sensor Transmitters - Sensor transmitters such as Foxboro, Fisher and 
     Porter, Barton, etc. are typically contained in sealed housings that 
     are designed and constructed to maintain their internals isolated from 
     the environment during a LOCA. The electrical connection to the 
     transmitter is generally made with solid conductors which pass through 
     qualified pressure seal connectors. However, if stranded conductors are 
     used to make such connections, moisture incursion is a possibility. 
     With this configuration, a differential pressure can develop between 
     the exposed end of a cable in a terminal block or junction box and the 
     end terminated in a sensor transmitter. 
3.   Motors - The cable terminations at motors are normally housed in 
     terminal boxes which are not sealed and cables are brought into them by
     conduits which are open at, the other end. Hence, no differential 
     pressure will exist across the cable. However, 

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IE Circular No. 79-05                                       March 20, 1979 

     if the cable terminations at the motor are sealed and stranded 
     conductors are used to make such connections, then moisture incursion 
     is a possibility. 

4.   Electric Motor Operated Valves (MOV's) and Limit switches The cables 
     are brought into the housing of these components through open conduits 
     which were not designed to keep out the environment. Since these 
     components were qualified with the housings vented, steam/moisture 
     incursion does not appear to be of concern. 
These items were observed and no potential for steam/moisture incursion was 

1.   Splices - Qualified heat-shrink butt splices are used on terminations 
     in place of terminal blocks or connectors in several nuclear plants. 
     Where there are no interposing junction boxes or other possible 
     moisture entry points in a cable run between the penetration and the 
     equipment (and only splices are used), then moisture incursion into the 
     splice is not possible; i.e., if no differential pressure can exist 
     then moisture incursion is not possible. 
2.   Penetrations - The containment end and the end outside the containment 
     will experience a differential pressure during a LOCA event. However, 
     no leakage will occur across the conductor associated with the 
     penetration since the penetrations are designed, constructed, and 
     installed to prevent leakage. (The containment intergrated leak test 
     with all penetrations installed verifies this satisfactorily.) 

Based on the above observations, it is our view that qualification of Class 
IE equipment is generally done on a component basis. The "as-installed" 
configuration of the equipment and its interface connections have not been 
fully considered. In the case of sensor transmitters and connectors, the 
possible incursions of steam/moisture through the interstices of stranded 
conductors of a cable has not been specifically considered during LOCA 
qualification. However, NRC is only concerned if the steam/moisture 
incursion could affect the operation of the equipment. 

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IE Circular No. 79-05                                       March 20, 1979 

All holders of operating licenses or construction permits should be aware of
the potential problems of the types discussed above. Because cable 
termination details are plant specific, it is recommended that both 
licensees of operating facilities and holders of construction permits 
conduct a detailed review and analyses of their "as-installed" 
safety-related transmitters and connectors to ascertain the possibility of 
steam/moisture incursion through stranded conductors which could adversely 
affect the operability of safety-related equipment during a LOCA. If the 
possibility exists, then the facility should verify the qualification of the 
affected equipment for the service intended. 

No written response to this Circular is required. If you require additional 
information regarding these matters, contact the Director of the appropriate
NRC Regional Office. 

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