Radionuclides migration behaviour

The potentially important role of colloidal species in the geochemical behaviour of the polyvalent actinides has nevertheless been stated by various authors (e.g., Kim 1991 Kersting et al. 1999). The present paper discusses the role of colloids on the release of radionuclides from a nuclear waste repositoiy with regard to the processes leading to (1) colloid generation and stability (2) radionuclide interaction with aquatic colloids and (3) colloid-borne radionuclide migration. 

Adsorption of complexes of radionuclides with inorganic or organic ligands (in particular complexes with humic substances) and of colloidal species of radionuclides may also markedly influence the migration behaviour. The predominant kind of interaction is physical adsorption. 

The main components of soils are sand, clay and humus. Whereas interaction between radionuclides and sand is rather weak, as in the case of sediments, sorption by clay minerals and reactions with the organic compounds in humus are most important for the migration behaviour of radionuclides. Cs+ ions are quite strongly bound in clay particles, as already mentioned. Ra + and 2i0pjj2+... 

The large number of measurements in various systems lead to the result that the interaction of radionuclides with solids is rather complex and depends on many parameters the species of the radionuclides in the solution, their properties and their dispersion, the components of the solid, the surface area of the particles, the nature of the sorption sites, the presence of organic substances and of microorganisms, and the interference or competition of other species. Therefore, an investigation of the behaviour of the radionuclides in the specific system of interest is unavoidable, if reliable information about their migration behaviour is required. 

M. Dozol, R. Hagemann, Radionuclide Migration in Groundwaters Review of the Behaviour of Actinides, Pure Appl. Chem. 65, 1081 (1993)... 

Maes N, Moors H, Dierckx A, Aertsens M, Wang L, De Canniere P, Put M. (2001). Studying the migration behaviour of the radionuclides in boom clay by electromigration. 3rd Symposium and Status ReportonElectrokineticRemediation EREM-2001).Schriftenreihe Angewandte Geologic Karlsruhe 63 35-1-35-21. 

The engineered barriers of a repository (waste form, container, clay buffer and backfill material and repository stmcmre) which will degrade with time due to various physico-chemical processes, strongly affect the geochemistry of fluids and rocks of the near field environment (redox properties, sorption properties, solubility limits, equilibrium chemistry, etc.) and determine the speciation and the subsequent migration behaviour of the radionuclides into the far field. Extensive... 

Dozol, M. Hagemann, R. 1993. Radionuclide migration in groundwaters review of the behaviour of actinides. Pure and Applied Chemistry, 65, 1082-1102. 

Another important feature of radiocesium partitioning in sediments is its apparently irreversible behaviour. It has generally been observed that Kd increases, and the exchangeability of radiocesium bound to aquatic particles decreases, with increasing contact time between the radionuclide and the particles (e.g. 1,2 J3). This observation has been interpreted as a slow migration of radiocesium from the frayed edge sites towards the deeper interlayer spaces between the illite layers, from where it cannot easily be released (3,14). It is, therefore, important to obtain rate parameters for this process in order to enable prediction of the long-term availability of radiocesium to the aqueous phase, and thus for further transport and uptake in the aquatic food chain. 

---