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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]

Simple description: The semi-coke water slurries (SCWSs) were prepared by mixing semi-coke powders, water and five anionic dispersants (NNO, SLS, SH, PCE and NNO/PCE).The effects of different anionic dispersants on the concentration, rheological behavior and static stability of SCWS were investigated. The adsorption capacity and adsorption kinetics of anionic dispersants on the surface of semi-coke particles were analyzed. The SEM-EDS, surface tension, contact angle, zeta potential measurement, and the E-DLVO calculations were also used to reveal the dispersion mechanism of anionic dispersants in SCWS. The improvement of the slurrying performance of SCWS by anionic dispersant is due to the comprehensive effect of van der Waals forces, electrostatic repulsion, and hydrophobic interactions between semi-coke particles. A model of the interaction mechanism of the anionic dispersants and semi-coke particles was proposed. [Display omitted] • SCWSs were prepared by mixing semi-coke powders, water and five dispersants. • The slurrying performance of SCWS added with NNO/PCE dispersant was the best. • The adsorption kinetics of the dispersants on semi-coke was quasi-second-order equation. • The interaction mechanism between the dispersants and semi-coke particles was proposed. It is essential to prepare the semi-coke water slurry (SCWS) using semi-coke powder in China. The preparation of SCWS can not only alleviate the oil demand, but can also provide a new way to utilize semi-coke powder. In this work, the effects of sodium methylene naphthalene sulfonate (NNO), sodium lignosulfonate (SLS), sodium humate (SH), polycarboxylate (PCE), and compound anion-anion (NNO/PCE), on the slurrying performance of semi-coke water slurry (SCWS) were studied. The results showed that the anionic dispersants increased the concentration of SCWSs, and the slurry exhibited the pseudoplastic rheological behavior of shear thinning. Adding PCE and NNO/PCE in the SCWS could improve its stability and fluidity. The absorbed capacity the microstructure of the particles, surface tension, contact angle, as well as Zeta potential of semi-coke powder were impacted by the addition of anionic dispersants in the SCWS. The results showed that anionic dispersants were adsorbed on the surface of semi-coke by a single-molecular layer. The developments of molecular dynamics simulation indicated that all dispersants should be spontaneously adsorbed on the surface of semi-coke, and the addition of anionic dispersants could reduce the contact angle and surface tension of the semi-char particle surface, increase the hydrophilicity and enhance the electronegativity. Finally, extended Derjaguin–Landau–Verwey –Overbeek (E-DLVO) theory calculations showed that adsorption of dispersants could significantly increase the total interaction energy between semi-coke particles. Finally, a model of the interaction mechanism of the anionic dispersants and semi-coke particles was proposed in this paper. [ABSTRACT FROM AUTHOR]