| dc.description.abstract | The final disposal of low-level radioactive wastes will be using concrete barriers. Due to the long service time, it is likely to encounter adverse environments and thus the service life of the concrete barrier needs be explored.
In this study, two concrete mixes possibly used for fabricating highly integrated containers, namely mixes C and M, were tested by ASTM C1556 standard procedures to determine their diffusion coefficient under the attack of chloride irons. The profile of chloride concentration at various depths was determined for concrete specimens at 28, 90, and 183 days of age after immersing in NaCl solution for 36 days. Then, Fick’s second law was used to obtain chloride diffusion coefficient and surface chloride content using non-linear regression technique. And the experimental data were used to estimate the change in diffusion coefficient with time for the two concrete mixes.
Also, based on AASHTO T259 test method, concrete specimens immersed in NaCl solution for about 4 years were determined for their apparent diffusion coefficient. And the results obtained from the two methods were compared in the study.
Finally, a computation scheme was developed to calculate the time required for chloride irons to penetrate 35 mm (approximately one-half of the thickness of containers) of the concrete barrier and reaching a concentration level of 0.05% by weight of concrete. The calculated results were compared and verified with those derived from Program Life-365, and found to be very similar. By using the computation scheme, the service life, in terms of resistance to chloride attack, of the two concrete mixes are both found to be more than 500 years.
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