Diffusion behavior of THO, Sr, Cs, and Am through concrete and its chemical degradation

To understand the transport processes in a repository silo for radioactive waste, the diffusion behavior of tritium (THO), strontium (Sr), cesium (Cs), and americium (Am) through concrete was investigated using a through-diffusion setup. The concrete and groundwater used in this study were sampled from the waste repository site. The diffusivity of the nuclides was obtained by a linear curve fitting of the diffused concentration data against time. After 18 months, the concrete coupons and solutions were recovered from the experimental setups. A sequential chemical extraction was carried out with the recovered coupons to determine the types of sorption involved in the nuclides diffusion processes. The THO transported freely through the concrete pores without sorption. The sorption of Sr and Cs was reversible, whereas that of Am was highly irreversible with a very low diffusivity. After a year in the diffusion test, some precipitate and suspended matter were observed. The precipitates were analyzed with SEM, EDS, and XRD. Identified as calcium carbonates and magnesium compound, they are likely formed by the chemical degradation of the concrete.