Need for condition monitoring and diagnosis of electric wires and cables used in nuclear power plants

Electric cables in nuclear power plants have to function even after serious events such as a loss-of-coolant accident (LOCA). In most cables, organic polymers that are very sensitive to radiation are used. Nevertheless, much attention was not paid until recently. Under these circumstances, the Japanese government started an extensive research project to examine the degradation behavior of safety-related cables at three different temperatures with three different dose rates. An interim report published recently revealed that some cables would be unable to function after the LOCA test. In this paper, a brief outline of the interim report is described. Categorization of all the causes of malfunctions occurred in electric apparatus in all the Japanese nuclear power plants for recent about 40 years, revealed that there has been only one case of a slight malfunction of cable caused by degradation of polymer insulation, indicating that we don't have to worry so much. It is still very important to establish a proper condition monitoring method in order to secure much higher reliability.