Non-destructive diagnosis method of cable deterioration for nuclear power plant

The technique for the diagnosis of the deterioration of low voltage, cross-linked polyethylene insulation, vinyl sheath cables for nuclear power stations was examined. Attention was paid to the cable sheath material, and the accelerated deterioration test simultaneously by radiation and heat was carried out on vinyl, thus the accelerated deterioration curves were obtained. According to these accelerated deterioration curves, the acceleration factors were determined on dose rate and temperature, in this way, the synthesized deterioration curve peculiar to the material was obtained. Further in the various examinations on the nondestructive deterioration diagnosis technology, it was found that by sampling a small amount of a sheath material and carrying out its thermogravimetric analysis, the degree of deterioration of cables was able to be diagnosed nondestructively. By correcting the degree of deterioration in the elongation determined from the synthesized deterioration curve with that by the thermogravimetric analysis, the accuracy of the deterioration diagnosis and the prediction of the remainder of life can be heightened. (K.I.)