High-level nuclear waste containing long-lived radionuclides must be reliably contained in a deep underground storage facility. Its safety will be ensured by a system of artificial engineered barriers and the surrounding geological environment. Backfill is one of the least studied barriers, and it is often considered in conjunction with a bentonite buffer. However, it has its own tasks: fixing the position of the buffer and waste container, stabilizing tunnels and galleries, decreasing their permeability and thermal conductivity, maintaining groundwater Eh and pH to reduce the solubility and enhance the sorption of radionuclides, and preventing their migration as colloids on bentonite particles derived from the buffer erosion. Clays, bentonite, zeolites, cement, and a mixture of bentonite and crushed rock were proposed previously as potential backfill materials. One of the requirements to the backfill is its compatibility with the geological environment, which is met by the crushed rocks around the repository. High sorption properties of such rocks for radionuclides significantly reduce the radionuclide washout by water from the repository into the biosphere.
Recent advances in the fundamental chemistry of technetium carbonyl compounds on the macroscopic and tracer levels and in the field of search for and development of new radiopharmaceuticals based on 99mTc carbonyl compounds are summarized. A comparative analysis of the results is made, and the scientific approaches used in the basic and nuclear medical research are compared. The directions that seem promising are outlined.
The possibility of replacing potentially hazardous perfluorooctanoic acid (PFOA) by nonfluorinated analogs in the technology of low-water decontamination using liquefied Freon HFC-134a was demonstrated. The efficiency of the radionuclide extraction from the fabric surface with formulations based on PFOA and on alkylbenzenesulfonic acid (ABSA) was compared. The emulsion formation in the PFOA–water–Freon and ABSA–water–Freon systems was detected; it favors the radionuclide extraction from the fabric surface. The optimum reactant concentrations in the system were determined.
The extraction of U(VI), Th(IV), and lanthanides(III) from nitric acid solutions using solutions of a complex of diphenyl(dibutylcarbamoylmethyl)phosphine oxide (L) with hydrogen di(2-ethylhexyl) sulfosuccinate (HSSu) in organic solvents was studied. Actinide and lanthanide(III) ions are extracted from nitric acid solutions with solutions of this complex via a cation-exchange mechanism. The stoichiometry of the extracted complexes was determined, and the effect of the organic diluent on the extraction of metal ions into the organic phase was examined. The conversion of CMPO to a complex with HSSu leads to a significant increase in the degree of extraction of U(VI), Th(IV), and Ln(III) ions from nitric acid solutions.
Intermolecular interactions in the known mono-, bi-, tri-, and tetranuclear manganese, technetium, and rhenium carbonyl halides were analyzed using the method of molecular Voronoi–Dirichlet polyhedra. The topology of transition metal (M) sublattices in dimeric carbonyl halides [MХ(CO)4]2 was examined in terms of the Voronoi–Dirichlet polyhedra. This analysis has proved that such complexes with X = Cl or Вr are isostructural but differ from the related iodides, which, in turn, are isostructural to each other irrespective of the kind of M. Similar pattern is observed for mononuclear complexes [MХ(CO)5]. The size effect is considered as the main cause of the change in the crystal structure in going from X = Cl and Br to X = I. No convincing evidences of specific intermolecular interactions involving halide ligands (halogen bonds) have been found.
