Resolution of Generic Safety Issues: Item B-9: Electrical Cable Penetrations of Containment ( NUREG-0933, Main Report with Supplements 1–34 )
Some prototype electrical penetration failures have occurred to date. In addition, failures of low voltage penetration modules have occurred at a licensed facility. It was originally postulated that failures of the low voltage penetration modules were due to electrical short-circuits caused by the collection of moisture in fissures (cracks) in the epoxy insulator/sealant. However, results of laboratory analysis indicated that failures were caused by heating of the conductors at the connection splices within the penetration module. The heating resulted from high contact resistance due to epoxy intrusion into an area of the conductor splice which was not insulated during the manufacturing process. The accumulation of carbon deposits over a period of time, resulting from the heating process, created a conductive path (short-circuit) between adjacent conductors in the penetration module. This item is documented in NUREG-0471.3
An evaluation of the standards and guides related to electrical penetrations was conducted by ORNL for the NRC. A draft report169 was prepared by ORNL and transmitted to the NRC on December 13, 1978. This report stated that existing requirements contained in IEEE 317-197681 and Regulatory Guide 1.6382 provided adequate guidance for the design of containment electrical cable penetrations.