Partitioning of uranium in contaminated bottom sediments: The meaning of fractionation

Sequential extraction tests were used to study partitioning of U in the bottom sediments of two reservoirs that have been used for the temporary storage of nuclear waste at the "Mining and Chemical Combine" (Zheleznogorsk, Krasnoyarsk region, Russia). Various sequential extraction protocols were applied to the bottom sediment samples and the results compared with those obtained for laboratory-prepared simulated samples with different speciation and partitioning, e.g., U(VI) sorbed onto various inorganic minerals and organic matter, as well as uranium oxides. The distributions of uranium in fractions extracted from simulated and actual contaminated samples were compared to shed light on the speciation of U in the bottom sediments. X-ray absorption spectroscopy, X-ray diffraction, and scanning electron microscopy were also used to analyze the partitioning of U in contaminated sediments. We also compared the results obtained using the spectroscopic and microscopic techniques, as well as sequential extraction.

The plutonium isotopes and strontium-90 determination in hot particles by characteristic X-rays

This paper reports the developed non-destructive methods for the plutonium isotopes and strontium-90 content determination in hot particles and other samples. The proposed methods are based on the measurement of the characteristic X-rays accompanying the decay of these radionuclides. For hot particles of NPP accident origin, the proposed method's error limits are 10-15% for hot particles (samples) with activity above 100 Bq and 15-20% for hot particles (samples) with activity less than 100 Bq. For explosive particles, the determination accuracy is 10-15% for activity more than 5 Bq and 20-30% for 0.1-5 Bq activity. The accuracy of the proposed method for determining ⁹⁰Sr in samples with its specific content of more than 10⁴ Bq/sample is 5%, with ~10² Bq/sample its content is 15-20%. The cost of one sample measurement and the processing time of these methods are significantly reduced compared to traditional studies. The proposed methods are reasonably simple measurement methods and can be carried out even in the field condition. They open up new possibilities for the quick search and study of hot particles and environmental samples.

Speciation of Uranium and Plutonium From Nuclear Legacy Sites to the Environment: A Mini Review

The row of 15 chemical elements from Ac to Lr with atomic numbers from 89 to 103 are known as the actinides, which are all radioactive. Among them, uranium and plutonium are the most important as they are used in the nuclear fuel cycle and nuclear weapon production. Since the beginning of national nuclear programs and nuclear tests, many radioactively contaminated nuclear legacy sites, have been formed. This mini review covers the latest experimental, modeling, and case studies of plutonium and uranium migration in the environment, including the speciation of these elements and the chemical reactions that control their migration pathways.

Surface features on aged 238Pu-doped Eu-monazite

Several 238Pu-doped Eu monazite single crystals stored at ambient conditions are monitored for 15 years using Scanning and Transmission electron microscopy, spectroscopy, diffraction and optical microscopy. Despite preservation of high crystalline quality, mechanical cracking and formation of small flakes is observed. After several month of aging, a new phase appeared on surfaces of the crystals, which later formed a continuous shell of most crystallographic faces. Electron diffraction indicated that the shell consists of submicron Pu-containing rhabdophanes. Its formation likely occurs due to combined action of atmospheric moisture and recrystallisation of radiation damage in monazite domains adjacent to external and internal surfaces. Extent of the rhabdophane formation appears to be influenced by crystallography and Pu content of corresponding growth sectors of the parent monazite. Whereas macroscopic rhabdophanes and monazites are relatively stable against irradiation, formation of sub-microscopic particles is a point of concern for development of monazite-based ceramic forms for actinide immobilization.

Chemical alteration of 238Pu-loaded borosilicate glass under saturated leaching conditions

Highly radioactive 238Pu-doped and non-radioactive samples of borosilicate glass with chemical compositions and synthesis routine similar to SON68 glass were studied under static saturated leaching conditions in distilled water at 90 °C. Dramatic differences in behavior of the radioactive and model glasses were observed. On time scale of 4 months the radioactive glass is fully covered by mechanically unstable alteration layer, possibly consisting of aluminum hydroxides with small fraction of a separate secondary Pu bearing phase. The model glass remains virtually pristine. Addition of Eu3+ into the glass allowed examination of the glass radio- and photoluminescence and to assess changes or REE3+ impurity local environment during self-irradiation and leaching. Photoluminescence spectra suggest more ordered local environment of europium ions in the alteration “gel” than in the bulk glass. Peculiar behavior of the photoluminescence spectra excited at different laser power is observed for the alteration layer and is ascribed to optical bleaching of color centers.

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).

Multiscale Speciation of U and Pu at Chernobyl, Hanford, Los Alamos, McGuire AFB, Mayak, and Rocky Flats

The speciation of U and Pu in soil and concrete from Rocky Flats and in particles from soils from Chernobyl, Hanford, Los Alamos, and McGuire Air Force Base and bottom sediments from Mayak was determined by a combination of X-ray absorption fine structure (XAFS) spectroscopy and X-ray fluorescence (XRF) element maps. These experiments identify four types of speciation that sometimes may and other times do not exhibit an association with the source terms and histories of these samples: relatively well ordered PuO2+x and UO2+x that had equilibrated with O2 and H2O under both ambient conditions and in fires or explosions; instances of small, isolated particles of U as UO2+x, U3O8, and U(VI) species coexisting in close proximity after decades in the environment; alteration phases of uranyl with other elements including ones that would not have come from soils; and mononuclear Pu-O species and novel PuO2+x-type compounds incorporating additional elements that may have occurred because the Pu was exposed to extreme chemical conditions such as acidic solutions released directly into soil or concrete. Our results therefore directly demonstrate instances of novel complexity in the Å and μm-scale chemical speciation and reactivity of U and Pu in their initial formation and after environmental exposure as well as occasions of unexpected behavior in the reaction pathways over short geological but significant sociological times. They also show that incorporating the actual disposal and site conditions and resultant novel materials such as those reported here may be necessary to develop the most accurate predictive models for Pu and U in the environment.

Partitioning and speciation of Pu in the sedimentary rocks aquifer from the deep liquid nuclear waste disposal

Plutonium partitioning and speciation was studied under the conditions of a liquid nuclear waste repository site. The dominating effect of corrosion products (Fe and Cr) oxides on plutonium partitioning was established in batch sorption tests at 150 ℃ and by using sequential extraction. Various techniques including Mössbauer spectrometry, XRD and TEM were used to characterize Fe/Cr oxide phases that form both precipitates and surface coatings which sorb plutonium. The sorption and speciation of plutonium was modeled thermodynamically using Pourbaix diagram that takes into account both surface complexation reaction and precipitation of insoluble PuO2.

[Molecular evolution: creation of nucleic acids capable of specific complex formation and possessing catalytic functions]

Method of designing nucleic acids capable of specific complex formation with arbitrary ligands (aptamers) and catalytically competent nucleic acids are described. The methods rely on generation of libraries of random nucleotide sequences, selection of molecules possessing the desired property from these libraries, and amplification of the selected molecules. Repeating of the selection and amplification procedures results in evolutional improvement of the molecule ability to accomplish the function under consideration. This molecular evolution approach opens up broad possibilities for investigation of mechanisms of molecular recognition of small ligands and biopolymers by nucleic acids and mechanisms of reactions catalyzed by ribozymes. Design of novel ribozymes and nucleic acids capable of specific binding to certain biopolymers may become an efficient approach for development of practically important compounds, biologically active compounds and affinity sorbents.

[Effect of transcription inhibitors on RNA synthesis in the polytene chromosomes of Drosophila melanogaster]

The inhibition of RNA synthesis by DRB (5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole) differs in different regions of D. melanogaster polytene chromosomes. In the majority of regions RNA synthesis is greatly inhibited, but in certain regions, including different development stage-specific puffs, it is still on. A case of transcription initiation in the heat shock puffs was also found. alpha-Amanitin considerably reduced RNA transcription in the majority of nuclei but some part of the nuclei are not affected at all. A combined action of alpha-amanitin and DRB exerts a considerably higher inhibitory effect.

[Combined effect of heat shock and ecdysone on the transcription of Drosophila melanogaster polytene chromosomes]

The combined action of ecdysone and temperature elevation (heat shock) on D. melanogaster polytene chromosome transcription has been investigated. It was shown that heat shock while blocking the transcription in ecdysone--induced puffs is not effective in decreasing their size. Thus we are able to observe chromatin decondensation without transcription. The indirect immunofluorescence using an antiserum directed against DNA/RNA hybrids revealed an intense fluorescence in the polytene chromosomes of heat shocked larvae both in the actively transcribed heat shock puffs and in ecdysone stimulated "primary puffs" with blocked transcription. Ecdysone introduced into the media during heat shock is unable to induce any puffs. On the other hand the hormone introduced into the media after temperature elevation (30' of heat shock + 1 hour of ecdysone stimulation) induces some of the "primary puffs". A new approach for cloning the genes inducible by ecdysone and other inducible loci as well has been developed using the data obtained.

[Quantitative analysis of the DNA content in salivary gland chromosomes of Chrironomus thummi in the larval and prepupal stages]

Relative DNA content during the polytenization of the salivary gland nuclei of Chironomus thummi was measured by cytophotometric and cytofluorometric methods. To estimate polyteny degree, DNA content was calculated in hemocyte and spermatocyte nuclei. Chromosome polytenization is associated with the 10th-12th replication rounds. There are 4-5 replication rounds in the 1st instar, 2-3 rounds in the 2nd instar, the 3rd and the 4th instars have 1-2 rounds each. From early postembryonic development, larvae already have salivary gland nuclei representing two polyteny classes (2-2-2-4c), this heterogeneity being retained in all instars. Approximate DNA content is 0.51-0.58 picogram per a diploid set.

Quantitative analysis of DNA content in the salivary gland chromosomes of Chironomus thummi at larval and prepupal stages

Relative DNA content during the polytenization of the salivary gland nuclei of Chironomus thummi was measured by cytophotometric and cytofluorometric methods. To estimate the degree of polyteny, the DNA content was calculated in hemocyte and spermatocyte nuclei. Chromosome polytenization is associated with 10 to 12 replication rounds. There are 4-5 replication rounds in 1st instar, 2-3 rounds in 2nd instar; 3rd and 4th instars have 1-2 rounds each. From early postembryonic development, larvae already have salivary gland nuclei representing two polyteny classes (2-3 - 2-4C); A similar heterogeneity is retained in all instars. The approximate DNA content is 0.51-0.58 picogram per diploid set.