ISSUES WITH APPROACHES FOR SIMULATING AGING OF NUCLEAR POWER PLANT CABLE MATERIALS

Over the past 20 y, the International Electrotechnical Commission and the International Atomic Energy Agency have published several Technical Documents describing recommended methods for carrying out accelerated radiation plus temperature aging of cable materials in nuclear power plants. These methods include the power law method, the time-dependent model, the dose to equivalent damage approach, and the simplified method approach. Because of the expected and observed changes in chemistry that occur as aging conditions transition radiation–temperature space, we highlight issues with the time-dependent and simplified method approaches by showing that they do not simulate the chemistry occurring under ambient conditions. The DED approach and a recent modification, the Matched Accelerated Conditions approach, can handle the changes in chemistry for many important cable materials and therefore offer more confident accelerated simulations. Problems with the power law method are then briefly described. Also discussed are the significant issues that occur when trying to simulate the aging of semicrystalline cable materials that show inverse-temperature effects. For these materials, degradation rates under radiation can increase as the aging temperature drops below ∼60 °C, in temperature regions where typical ambient aging conditions occur. A possible approach for dealing with such materials is suggested.