Replacement of input/output cables of the digital control computers at Gentilly 2

During the 1990 annual outage at Gentilly 2 the Preventive Maintenance Program inspections on the digital control computers (DCCs) revealed an alarming degradation of cable insulation at several locations. It was found that approximately 20% of the cable connector assemblies inspected showed signs of degradation. These findings raised the concern of an increased risk of random short-circuit faults at the very heart of the station control system. Given the excellent reliability of the Gentilly 2 DCCs and their inherent design robustness, it was decided to proceed with the replacement of all of the complete cable connector assemblies within a reasonable time frame. It is planned to replace all assemblies of DCCX and DCCY during the 1991 annual outage. The degradation of the insulation was traced to a material incompatibility problem originating during cable manufacture. A migration of the plastifier contained in the PVC of the transparent sheaths, surrounding many of the cable conductors to terminal block connections, resulted in the chemical attack of the conductor insulation. This paper summarizes the problem identification and disposition process followed by Gentilly 2 Technical Unit personnel