Aging and condition monitoring studies of composite insulation cables used in nuclear power plants

Abstract

Five composite ethylene propylene rubber/chlorosulfonated polyethylene (EPR/CSPE) insulated cables, a single composite cable with EPR/Neoprene, and a single Kerite insulated cable used in US nuclear power plants (NPP's) were evaluated. All of the cables had a CSPE outer jacket. To study the rate of degradation these cables were thermally aged at 110 and 120 degC until embrittlement of the composite insulation and/or outer jacket occurred. The degradation of the composite insulation and outer jackets was assessed by measuring elongation at break and indenter modulus. Both the indenter modulus and elongation values of the composite insulation and outer jacket exhibited excellent superposition when shifted using the time-temperature superposition principle. Regardless of whether or not the EPR insulation was bonded or non-bonded to the CSPE or Neoprene composite jacket thermal induced hardening and fusion of the composite jacket with EPR insulation was the cause for loss of flexibility of the composite wires. The aging rate of the composite insulated wires were not affected by the aging mode, namely, whether the composite wires were aged as a complete cable or with the jacket removed. However, the aging rate of the composite insulation and the outer jacket varied between different cables. Threshold indenter modulus values for successful loss of coolant accident (LOCA) performance for each of the composite insulation and outer jacket was correlated with the thermal aging periods of the studies available in the literature. Close correlation was found between the thermal aging periods used for satisfactory LOCA performance and the time to reach 50% elongation of the composite insulation. Indenter modulus values of the composite insulation and outer jacket when the composite insulation decreases to 50% elongation is also provided