Effect of colloids on transfer of radionuclides by subsurface water

Abstract

The fluid transfer of radionuclides in the geologic medium is considered under conditions when radionuclides are contained in fluids not only as solutes but also as colloids. The effect of colloidal transport of radionuclides on the rate of spreading of radioactive contamination in an underground medium is estimated, with assessment of this effect in mathematical models describing the transport of radionuclides by subsurface water. For this purpose, the exchange of radionuclides between subsurface water, colloid, and an immobile solid phase is considered, taking into account the precipitation of colloidal particles on both the immobile solid phase and other colloidal particles and their recurrent mobilization into the liquid phase. It is noted that, in real colloidal transfer, the heterogeneity of the geologic medium and colloidal particles in subsurface water is of great importance. The known models of colloidal transfer of radionuclides are evaluated on the basis of the analysis performed.

Radiochemistry

“…The contamination of ground water in areas near nuclear plants 265,266 or a nuclear accident 267 requires constant monitoring and from many parts of the world there is now much more information about the concentrations of uranium, 268,269 radon, 270,271 polonium-210, 269 in river, drinking 272 and mineral water. 273,274 The role of colloids in transporting radio-isotopes in ground waters 275,276 has been discussed. Sea water in the Barent's Sea has been monitored 277 for a range of radioisotopes and a study has been reported 278 of the distribution of caesium-137 in the Mediterranean.…”

Site-Specific Retention of Colloids at Rough Rock Surfaces

“…Colloid-borne migration of contaminants has been a major concern for many decades and plays a significant role in the context of safe disposal of radioactive waste in deep geological repositories. , It is well established that with possible damage of engineered barriers, radionuclides from the repositories will be released into the subsurface environment and they are expected to migrate at a higher rate on mobile colloids. Adsorption of contaminants was observed on humic substances, − bacteria, and mineral colloids .…”

Particulate Phases Possibly Conveyed from Nuclear Waste Repositories by Groundwater

“…A distinction between those two categories made by taking into account only the dimension criterion fails to be entirely satisfactory, although it is widely accepted and operationally useful. Opinions fail to be unanimous even as far as the dimensional boundary separating the two categories is concerned, so that according to various authors, the corresponding dimension may be 0.20 μm, 0.45 μm or 1 μm (Malkovsky & Pek, 2009a). In fact, the indicated values represent the pore dimensions of the filtering membranes which are used for separating the particles.…”

“…Besides the two already mentioned colloid groups, Malkovsky et al (2009) and Malkovsky & Pek (2009a) distinguish an additional third group, which they designate as "primary colloids". The latter are colloidal particles derived as a result of groundwater leaching the isolating materials utilized in the storage of low and intermediate level radioactive wastes, as well as of high-level radioactive wastes in geological disposal.…”

“…Entities formed by the coupling of colloidal particles with radionuclides and conveyed as such by groundwater, and which commonly are also termed radiocolloids, are classified in two large groups, according to their origin: (1) intrinsic-, eigen-colloids or "true" colloids; and (2) carrieror pseudo-colloids Malkovsky et al, 2009;Malkovsky & Pek, 2009a).…”