Deterioration behavior of ethylene propylene rubber in LOCA simulation environment by simultaneous method and successive method

The most important problems in the LOCA simulation environment test on the electric wires and cables for nuclear power plants are the propriety of using more practical successive method instead of simultaneous method for assuring the safety, and the method of setting up the testing condition of successive method which gives the equivalent deterioration to that of simultaneous method. The authors carried out the comparison of simultaneous method and successive method using the deterioration curves by measuring the change of the tensile properties of ethylene propylene rubber (abbreviated hereafter as EPR) in course of time during the exposure to steam at 120 deg C. The specimens were the sheets of about 1 mm thickness of standard EPR and flame retardant EPR. The irradiation was carried out by Co-60 gamma ray up to 1.5 MGy. The exposure was made by chemical spray and by heating with 120 deg C saturated steam and steam containing air. The tensile strength and elongation, the change of weight and the change of insulation resistance were measured. When the elongation was used as a criterion for evaluation, the deterioration by simultaneous method was able to be nearly simulated by successive method, but the change of the strength under the air containing atmosphere was much severer than by simultaneous method. (Kako, I.)