Strontium transport modeling in high-concentrated nitrate solution in DEEP liquid radioactive waste repository.

This article focuses on modeling 90Sr migration in strong nitrate solutions in aquifers used for radioactive waste disposal. This type of radioactive waste disposal is typical only for the Russian Federation and is a unique object of study. The calculations are based on the laboratory study of strontium sorption in nitrate solutions on sandy, loamy and clayey rocks under biotic (with natural microbial communities obtained from Seversky repository) and abiotic conditions. To obtain a strontium sorption model, first, an ion exchange model in PHREEQC software is fitted to the experimental data both manually and automatically (using MOUSE software). Since real nitrate-ion concentrations at radioactive waste injection sites can reach values of hundreds of grams per liter, strontium Kd values are predicted for high ionic strength (for which no experimental study of strontium sorption efficiency has been carried out) with PHREEQC-model. The strontium transport models accounting for sorption and the nitrate reduction processes have been developed using two numerical software packages: the GeRa 3D hydrogeological simulation code and the PHREEQC reactive transport code. Reactive transport modeling under different conditions shows a high sensitivity to dispersion. A significant effect of sorption of nitrate ion on Sr sorption is shown and a relatively small contribution of microbial processes to strontium transport is noted for liquid radioactive waste injection sites.

Hypolimnion behavior of technetium in freshwater at various stages of eutrophication.

The article presents a study of various mechanisms of hypolimnion technetium behavior which occur at different stages of waterbodies eutrophication. Eutrophication stage was found to be positively correlated with the rate of 99Tc removal from water phase. The study identified a complex biogeochemical mechanism of technetium behavior. Planktonic phototrophic community plays a pivotal role in such a mechanism by ensuring fast oxygen consumption in hypolimnion. This creates favorable conditions for the active development of anaerobic bottom bacteria of sulfur and iron cycles given nutrients inflow. Sulfates and nitrates were discovered to have inhibitory effect on 99Tc biosorption by bottom sediments due to oxidizing conditions. Apart from the shift of redox potential of the medium to reducing values, the 99Tc removal and partial immobilization are also promoted by the presence of inorganic mineral phases of reduced sulfur and iron. These phases form a reducing barrier in the silt, thus preventing the oxidation and migration of technetium. We suggest the ways of stimulating in situ waterbody remediation by means of various additives, which will allow irreversible immobilization of technetium in silt once several growth periods have passed.

Activated carbon additives for technetium immobilization in bentonite-based engineered barriers for radioactive waste repositories.

Safe disposal of nuclear waste in a geologic repository will rely on natural geologic features and engineered barriers to greatly retard the movement of radionuclides from the repository. Clay minerals including bentonite are effective in retarding the migration of many radionuclides, but are ineffective for anionic radionuclides, of which pertechnetate is of particular concern owing to its relatively long half-life and the lack of natural isotopes that dilute it. Activated carbon is proposed as an additive material for reducing pertechnetate mobility in the nearfield. Activated carbon materials of different origins quantitatively sorb pertechnetate from aqueous solution under oxidizing conditions during the first day of contact, and sequential extraction showed that 73 % of this technetium is in the strongly bound fraction. X-ray photoelectron spectra (XPS) and extended X-ray absorption fine structure (EXAFS) spectra both demonstrated that no reduction of technetium occurred in the studied systems. The interaction of technetium with a composite material consisting of bentonite and activated carbon was studied at the first time. Effective technetium sorption was shown, with distribution coefficients (Kd) up to 740 cm3. g-1.

Speciation of actinides in groundwater samples collected near deep nuclear waste repositories.

Actinide binding to colloidal particles of different nature was studied under oxic and anoxic conditions of an underground nuclear waste disposal site using successive micro- and ultrafiltration techniques. According to the actinide redox speciation, under oxic conditions they were present in high oxidation states except for plutonium, for which a significant part was found in the tetravalent state. In case of the anoxic conditions, the share of An (IV) was proportional to the total U(IV) concentration. This indicated formation of intrinsic U(IV) hydroxocolloids, which bound other actinides. Formation of the intrinsic actinide colloids was proven by the secondary ion mass spectrometry (SIMS) with the submicron resolution. In contrast, under the oxic conditions uranium and plutonium were sorbed by natural colloids (amorphous hydrous ferric oxide and Mn oxides).

[Microbiological Aspects of Radioactive Waste Storage].

The article gives information about the microorganisms inhabiting in surface storages of solid radioactive waste and deep disposal sites of liquid radioactive waste. It was shown that intensification of microbial processes can lead to significant changes in the chemical composition and physical state of the radioactive waste. It was concluded that the biogeochemical processes can have both a positive effect on the safety of radioactive waste storages (immobilization of RW macrocomponents, a decreased migration ability of radionuclides) and a negative one (biogenic gas production in subterranean formations and destruction of cement matrix).

Khasan virus, a new ungrouped bunyavirus isolated from Haemaphysalis longicornis ticks in the Primorie region.

Strain LEIV-776P, possessing no haemagglutinating activity was isolated in 1971 in the Primorie region (U.S.S.R.) from Haemaphysalis longicornis Neumann 1091 tick. Complement fixation (CF) tests revealed no antigenic relationship with 24 antigenic groups of arboviruses or 21 ungrouped viruses isolated from ticks. The virus isolate contains RNA and is relatively sensitive to ether and sodium deoxycholate; it is pathogenic for suckling mice and two-week-old white mice by the intracerebral route, and replicates in primary cultures of chick and duck fibroblasts and green monkey kidneys and in a continuous line of pig embryo kidney cells without any cytopathic effect. According to electron microscopy, its size is 90-110 nm. Its morphological properties permit to classify it as a member of the family Bunyaviridae.