抄録
Safety-related cables used at PWR plants in Japan must pass the environmental qualification test in accordance with IEEE Std.323 and 383. IEEE Std.383 describes the method of accelerated aging of cables that corresponds to the aging during in-service period. However, IEEE Std.775,etc. raise questions about the testing process in which (1) conditions for the accelerated thermal aging are estimated by extrapolating the activation energy, which is evaluated by the Arrhenius plot obtained in relatively high temperature range, (2) irradiation at high dose rate (<10kGy/h) is permitted, and (3) irradiation is carried out sequentially after the thermal aging test. Based on these background, we obtained the Arrhenius plot in relatively low temperature range to evaluate the activation energy using cables with insulation material such as ethylene propylene rubber, silicone rubber and polyvinyl chloride. And we experimented variety of simultaneous exposure tests to be exposed irradiation of 10-100Gy/h and thermal condition of 60-120degree, and presented at ICONE9 a part of the evaluation result of data obtained from these tests. After these study, the date of the activation energy at low temperature range was improved, because of getting the more advanced thermal aging data and the data of simultaneous radiation aging late. We also revised "the master curve" based on the method of "superposition of time dependent data" described in IEC 1244-2,and established the method to determine the accelerated aging conditions under various environmental conditions of existent plant according to this method. In addition, we conducted LOCA exposure test after the low acceleration simultaneous aging test simulating the natural aging at the existent plant, and as a result, we identified almost correctly the critical value of in-service period o cables made of each insulation material before the accident assumed in the design, from the result of cable soundness judgment based on the test specified in IEEE Std.383. Consequently, we could determine the control value of "elongation at break" at the nondestructive aging diagnosis of cable that was presented at ICONE7. At present, we have been confirming the long-term soundness of cable by applying our cable condition monitoring method (non-destructive aging diagnosis method, "the master curve") in several PWR plants.
