Vol 58, No 3 (2016)

The possibilities of chemical identification of superheavy elements with the atomic numbers Z = 111 and 113 are discussed. The chemical identification of superheavy elements is preceded, as a rule, by model experiments on chemical isolation of light analogs of these elements. Thermochromatographic methods were developed for selective chemical isolation of carrier-free Ag, Au, In, and Tl radioisotopes from nuclear reaction products in the form of volatile chalcogenides and pnictides. Their deposition temperatures and enthalpies of adsorption on the quartz surface were determined. The prospects for using these results in designing experiments for chemical identification of elements 111 and 113 are analyzed.

Analysis of the published dependences of the HNO₃ distribution coefficient between the liquid and vapor in the system with water shows that these dependences are power functions with the exponent depending on the temperature (pressure) and emerge from the azeotropic point. The exponent is inversely proportional to the temperature, and its logarithm is directly proportional to the logarithm of the pressure. The pattern is preserved when a salting-out agent is present in the system and is described similarly when taking into account the hydration and hydrolysis of the cation and the degree of dissociation of sulfuric acid, as shown previously for atmospheric pressure. The dependences obtained are interpreted within the framework of the law of mass action (without activity coefficients) as dilution of the azeotropic compound HNO₃(H₂O)₂ with water with the formation of an associated ionic liquid.

The uranium content of some northern forest steppe soil samples taken in Chelyabinsk oblast was determined. The bulk analysis of the soils was performed. The uranium distribution in the soil profile was estimated, and the main forms of uranium occurrence, fractional distribution of uranium, and content of certain metals in the soils were studied.

The concept of closed nuclear fuel cycle, accepted in Russia, involves reprocessing of spent nuclear fuel (SNF). It ensures more complete utilization of natural nuclear resources, involvement of artificial fissile materials produced in the course of reactor operation into the fuel cycle, and minimization of the amount of radioactive waste (RW). Full-scale implementation of this concept is prevented by economical factors: The cost of the SNF reprocessing exceeds the cost of the reusable products, uranium and plutonium. Their recovery and sale allows, according to estimates made in the world, compensation of up to 50% of the SNF reprocessing cost. The paper discusses new methods and new approaches to the development of selective extraction and sorption processes for preconcentration, separation, recovery, and purification of valuable radionuclides present in SNF for their subsequent use in industry, nuclear medicine, and scientific research.

A technology for reprocessing mixed uranium–plutonium nitride fiel (MUPN) from BREST reactor is considered. The technology should ensure reprocessing of spent nuclear fuel with the storage time after irradiation of no more than 1 year, 10–15% content of fissile materials (FM), and burn-up of 10% of heavy atoms. The target product of the technology is a mixture of actinide oxides separated from fission products with the separation factor of ~10⁶. A PH (Pyro–Hydro) process was suggested for MUPN SNF reprocessing. It involves pyroelectrochemical fuel reprocessing with separation of U, Np, and Pu from the major fraction of fission products responsible for the heat release from the fuel and for the radiation load on process media, a series of hydrometallurgical operations for final purification of the target products (U–Pu–Np–Am), and radioactive waste (RW) management. The PH process is being developed since 2011 by the teams from the Bochvar High-Tech Research Institute of Inorganic Materials, Khlopin Radium Institute, and Research Institute of Atomic Reactors with active participation of the Leading Research Institute of Chemical Technology, Siberian Chemical Combine, and institutes of the Russian Academy of Sciences, primarily Frumkin Institute of Physical Chemistry and Electrochemistry and Vernadsky Institute of Geochemistry and Analytical Chemistry.

The kinetics of the accumulation of Er(III), Ho(III), Pr(III), Nd(III), and Yb(III) in the interfacial layer of the extraction system with HDEHP or TBP in a nonaqueous diluent (heptane, toluene, tetrachloromethane), responsible for the appearance of interfacial formations, was studied, and the process mechanism was suggested. Up to 30% of the initial amount of the extractable element in the aqueous phase can be accumulated in the dynamic interfacial layer (DIL) when using HDEHP as extractant, and up to 15%, in the systems with TBP. The time dependences of the accumulation of lanthanide di(2-ethylhexyl) phosphates are characterized by the presence of a horizontal plot, i.e., the process in this period is steady-state. The accumulation in DIL depends on the initial concentration of the extractable element, extraction reagent, and solution acidity. In systems with the more polar diluent, the accumulation of the rare earth element in DIL is smaller.

The presence of large amounts of ¹³⁷Cs and ⁹⁰Sr radionuclides in radioactive waste severely complicates its analysis for the presence of fuel matrix components. Labor-consuming procedures for determining uranium and plutonium radionuclides in soils and water are hardly applicable in this case. A rapid method based on these procedures was developed for determining fuel matrix components in both liquid and solid radioactive waste. The procedure was tested in the course of works on dismantling the MR reactor of the National Research Centre Kurchatov Institute. Samples of water, bottom slime, and deposits on the walls of ponds in the central room of the MR reactor and of deposits from the dismantled active drain system were analyzed.

The influence of the NO₉^-, SO₄^2–, HCO₃^–, and Ac^– anions on the efficiency of the sorption of bivalent metals by sulfonic cation exchangers was studied. The main method was elution of the Mg²⁺, Ca²⁺, and Co²⁺ cations with individual solutions of the corresponding sodium salts and their mixed solutions with sodium nitrate from the Dowex-50 ion-exchange resin at fixed temperatures. The exchange efficiency is influenced both by neutral complexes of the metal cations mainly with inorganic acid ligands and by the single-charged species. The latter species affect the efficiency of the ion-exchange waste reprocessing considerably more strongly. An increase in the temperature of the solution being treated leads to a significant shift of the peak position toward larger retention volumes, which indicates that it is appropriate to perform the water treatment on sulfonic cation exchangers at elevated temperatures. The first formation constant of the single-charged cobalt dihydrogen phosphate complex species at an ionic strength of 0 M was obtained: logK₁(CoH₂PO₄⁺) = 1.36.

The impact of a low-level radioactive sludge repository on the environment (surrounding soils, groundwater, surface waters) was substantiated by on-site observations in combination with data of experimental and thermodynamic modeling. The efficiency of natural geochemical barriers preventing the uranium release beyond the repository was evaluated. The main forms of uranium transfer and accumulation in waters and soils were revealed by experiments and on-site observations.