Remaining life prediction of class 1E cables by probabilistic reliability analysis

Class 1E cables are one of the most important components in nuclear power plants, since various aging and degradation stressors could produce immediate degradation or aging on the intended function over time and periodic maintenance or replacement is hard to conduct throughout the plants' lifetime. Hence, an effective condition monitoring technique is essential. Comparing with EAB(elongation at break) and other condition monitoring methods, IM(indenter modulus) is an ideal condition monitoring and aging trending technique for its non-destruction feature and good compatibility with EAB which is a good indicator of cable aging. To develop a combined method to build the relationship between IM and EAB and predict the remaining lifetime of class lE cables by probabilistic reliability analysis. A typical class IE cable used in Chinese units was accelerated aging at 399 K-360 Gy/h. Then EAB of both insulation and jacket and IM of jacket were tested. Relationship between IM and EAB was developed by linear regression and the standard deviation was acquired. The cable reliability at both 313 K and 338 K were analyzed by strength-stress interference theory and probabilistic analysis method. A combined method including IM testing and probabilistic reliability analysis was developed. The predicted lifetime of tested cable under 375 kGy radiation was 60 years and 35 years with 90% confidence at 313 K and 338 K respectively. The method developed in this study is effective, which could support on-line condition monitoring, system reliability analysis and remaining lifetime prediction of class lE cables. Predicted lifetime at different temperature indicated that temperature could be a significant aging stress on class IE cables. Also, the proposed methodology could loe extended to other aging stressors. (authors)