Effect of irradiation dose rates on ethylene-propylene rubber for nuclear cables.

The effect of dose rates is the critical concern of irradiation testing in equipment qualification for polymeric materials used in nuclear power plants, and the rule 'the lower dose rates, the severer degradation' is always regarded as the truth due to the limited diffusion of oxidation. But it's obviously not economic and practical from the engineering point of view. In this paper, aiming at investigating such dose rate effects, gamma irradiation testing with multiple dose rates was performed on one domestically manufactured ethylene-propylene rubber that was intended for the nuclear cable insulations of the advanced pressurized water reactors in China. In detail, before and after testing, the mechanical, electrical and chemical properties were measured from the specimens, and their fractographs after tensile test were observed, and particularly the oxidation profiles on the whole cross sections of them were detected by the infrared microscope to quantitatively compare the degradation extent under different dose rates. Based on the results, the correlation among the dose rates, the measured properties, and the penetration depth of oxidation was clarified, the relevant degradation mechanisms were discussed, and a suitable dose rate for engineering practice was recommended. The effect of dose rate is the critical concern of irradiation testing in equipment qualification for polymeric materials used in nuclear power plants, and the rule 'the lower dose rate, the severer degradation' is always regarded as the truth due to the limited diffusion of oxidation. But it's obviously not economic and practical from the engineering point of view. In this paper, for purpose of investigating such dose rate effect, gamma irradiation testing with multiple dose rates was performed on one domestically manufactured ethylene-propylene rubber that was intended for use as the nuclear cable insulations in China. Before and after testing, upon the specimens, the mechanical, electrical and chemical properties were measured, the fractographs were observed, and particularly the oxidation profiles on the whole cross sections were detected to compare the degradation extent under different dose rates. The results indicated that the severest degradation was found occur at the intermediate dose rate instead of the lowest one due to the competing mechanisms between plasticizers volatilization and chain scission, seen in Fig. 1. But the oxidation penetration depth discovered indeed increases with the decrease of the dose rates, and even obeys roughly an arithmetic progression relation, as revealed in Fig. 2, from which the conventional concept that the degradation extent is inversely proportional to the dose rates is testified. Based on the results, the correlation among the measured properties, the penetration depth and extent of oxidation, and the dose rates were clarified, the relevant degradation mechanisms were discussed, and a suitable dose rate for engineering practice was recommended. Unlabelled Image • Irradiation testing with multiple dose rates was performed on one ethylene-propylene rubber to study the dose rate effect. • By infrared microscope, the dose rate effect based on the oxidation profile as extent and penetration depth was demonstrated. • Degradation of the measured mechanical, electrical and chemical properties was found influenced by the dose rate effect. • This paper will facilitate deeper understanding of the dose rate effect and the theories of diffusion-limited oxidation. [ABSTRACT FROM AUTHOR]