Vladimir G. Petrov

Radionuclide removal from aqueous solutions using potassium ferrate(VI)

The paper describes the effectiveness of uranium(VI) and europium(III) removal from aqueous solutions using potassium ferrate(VI) at different pH values. The removal of a mixture of alpha- and beta-emitting radionuclides (137Cs(I), 90Sr(II), 152Eu(III), 243Am(III), 239Pu(IV), 237+239Np(V), 238+233U(VI)) from synthetic fresh water and simulated seawater has been checked as well. There is an indication that potassium ferrate(VI) could be used as an effective scavenger for almost all investigated radionuclides except cesium.

Solubility and hydrolysis of Np(V) in dilute to concentrated alkaline NaCl solutions: formation of Na–Np(V)–OH solid phases at 22 °C

Abstract The solubility of Np(V) was investigated at T=22±2°C in alkaline NaCl solutions of different ionic strength (0.1–5.0 M). The solid phases controlling the solubility at different –log10 mH+(pHm) and NaCl concentration were characterized by XRD, quantitative chemical analysis, SEM–EDS and XAFS (both XANES and EXAFS). Aqueous phases in equilibrium with Np(V) solids were investigated for selected samples within 8.9≤pHm≤10.3 by UV-vis/NIR absorption spectroscopy. In 0.1 M NaCl, the experimental solubility of the initial greenish NpO2OH(am) solid phase is in good agreement with previous results obtained in NaClO4 solutions, and is consistent with model calculations for fresh NpO2OH(am) using the thermodynamic data selection in NEA–TDB. Below pHm~11.5 and for all NaCl concentrations studied, Np concentration in equilibrium with the solid phase remained constant during the timeframe of this study (~2 years). This observation is in contrast to the aging of the initial NpO2OH(am) into a more crystalline modification with the same stoichiometry, NpO2OH(am, aged), as reported in previous studies for concentrated NaClO4 and NaCl. Instead, the greenish NpO2OH(am) transforms into a white solid phase in those systems with [NaCl]≥1.0 M and pHm≥11.5, and into two different pinkish phases above pHm~13.2. The solid phase transformation is accompanied by a drop in Np solubility of 0.5–2 log10-units (depending upon NaCl concentration). XANES analyses of green, white and pink phases confirm the predominance of Np(V) in all cases. Quantitative chemical analysis shows the incorporation of Na+ in the original NpO2OH(am) material, with Na:Np≤0.3 for the greenish solids and 0.8≤Na:Np≤1.6 for the white and pinkish phases. XRD data confirms the amorphous character of the greenish phase, whereas white and pink solids show well-defined but discrepant XRD patterns. Furthermore, the XRD pattern collected for one of the pink solid phases match the data recently reported for NaNpO2(OH)2(cr). UV-vis/NIR spectra collected in 0.1–5.0 M NaCl solutions show the predominance of NpO2+ (≥80%) at pHm≤10.3. This observation is consistent with the Np(V) hydrolysis scheme currently selected in the NEA–TDB. This work provides sound evidences on the formation of ternary Na–Np(V)–OH solid phases in Na-rich hyperalkaline solutions and ambient temperature conditions. Given the unexpectedly high complexity of the system, further experimental efforts dedicated to assess the thermodynamic properties of these solid phases are needed, especially in view of their likely relevance as solubility controlling Np(V) solid phases in Na-rich systems such as saline and cement-based environments in the context of the safety assessment for nuclear waste disposal.

Testing a simple approach for theoretical evaluation of radiolysis products in extraction systems. A case of N,O-donor ligands for Am/Eu separation

In this paper, we studied the irradiation and ageing effect on the extraction properties of N,N′-diethyl-N,N′-di(p-hexylphenyl)-1,10-phenantroline-4,7-dichloro-2,9-dicarboxamide (1) and 2,5,9,12-tetra(n-hexyl)-benzo[f]quinolino-[3,4-b]-[1,7]-naphthyridine-6,8(5H,9H)-dione (2) towards Am(III) and Eu(III). DFT calculations were applied to estimate the probable ways of radiolysis for (1) and (2). Degradation products were identified by high-resolution ESI-MS. The interaction of (1) and (2) with the products of solvent radiolysis was established to be the most probable mechanism of ligand destruction.

Interaction of plutonium with iron- and chromium-containing precipitates under the conditions of reservoir bed for liquid radioactive waste

The behavior of Pu under the conditions of liquid radioactive waste (LRW) disposal in a reservoir bed was studied. The pH dependence of the Pu sorption is the same in the cases when the radionuclide is introduced together with the simulated LRW solution or after the precipitate formation. The composition and morphology of Fe,Cr-containing precipitates formed under the conditions simulating the radioactive waste disposal were determined. The solid phase was characterized by X-ray diffraction analysis and by transmission and scanning electron microscopy. The phase composition of the precipitates was determined in relation to the presence of acetate ions, Fe concentration in the solution, and storage time and temperature. The main phases formed are ferrihydrite, goethite, hematite, and grimaldiite.

Solubility and phase transformations of Np(V) hydroxide in solutions with different ionic strengths

New data on the solubility of neptunium(V) hydroxide in solutions with different ionic strengths are presented. The characteristics of the solid phases, which are in equilibrium with the supernatant, are described.

Slewing mirror telescope of the UFFO-pathfinder: first report on performance in space

To observe the early optical emissions from gamma ray bursts (GRBs), we built the Slew Mirror Telescope. It utilizes a 150 mm motorized mirror to redirect incoming photons from astrophysical objects within seconds and to track them as compensating satellite movements. The SMT is a major component of the UFFO-pathfinder payload, which was launched on April 28, 2016, onboard the Lomonosov satellite. For the first time, the slewing mirror system has been proven for the precision tracking of astrophysical objects during space operation. We confirmed that the SMT has 1.4 seconds of response time to the X-gamma-ray trigger, and is able to compensate for satellite drift and to track astrophysical objects with magnitudes from 7 to 18.

Research data supporting the publication: 'The effect of fission-energy Xe ion irradiation on dissolution of UO

Project: PhD work by A.J. Popel: ‘The effect of radiation damage by fission fragments on the structural stability and dissolution of the UO2 fuel matrix’. The Excel file ‘U_ICP-MS data’ with output ICP-MS data and calculations for water and acid dilutions supporting Figures 2 and 3 and ICP-MS results in the publication: A.J. Popel, V.G. Petrov, V.A. Lebedev, J. Day, S.N. Kalmykov, R. Springell, T.B. Scott, I. Farnan, The effect of fission-energy Xe ion irradiation on dissolution of UO2 thin films, J. Alloys Compd. 721 (2017) 586-592, https://doi.org/10.1016/j.jallcom.2017.05.084. The ICP-MS analysis was performed to measure 238U concentration in the extracted solutions. The data were generated on the 13-14th of October 2014 at the Department of Earth Sciences, University of Cambridge, Cambridge, UK, on a Perkin Elmer SCIEX Elan DRC II quadrupole ICP-MS. The data can be accessed through the University of Cambridge Data Repository.

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Here we report on a comparative analysis of laser techniques for detection and speciation of radionuclides and its complexes in the geosphere. The application of different methods is illustrated by the example of uranium(VI) speciation in aqueous environment and detection of trace elements on the ppm level in gases, which appear as a result of reprocessing of spent nuclear fuel.

thin films'

The participation of Am6p,5f electrons in the chemical bond in AmO2 was studied. Analysis of the structure of the AmO2 X-ray photoelectron spectrum (XPS) in the valence electron binding energy (BE) range (from 0 to ~35 eV), taking into account the results of relativistic calculation of the AmO8 cluster (D4h) reflecting the nearest surrounding of the Am atom in AmO2, showed that electrons of outer (from 0 to ~15 eV, OVMO) and inner (from ~15 to ~35 eV, IVMO) valence molecular orbitals (MO) noticeably contribute to the structure of the valence electron spectrum. The filled Am5f states appear in the AmO2 OVMO BE range. The atomic orbitals (AO) of Am6p electrons participate in the formation of not only IVMO but also OVMO. The filled Am6p3/2 and O2s AO participate in the IVMO formation to the greatest extent. The MO composition and sequent order was determined, and the quantitative MO scheme for AmO2 was constructed. The bonding and antibonding contributions of electrons of different MO in the AmO8 cluster were estimated. The MO scheme has fundamental significance not only for understanding the nature of the chemical bond in this dioxide, but also for interpreting the structure of other X-ray spectra of AmO2.

A Comparative Analysis of Optical Methods for Detection and Prediction of Radionuclides Migration in the Geosphere

Interaction of uranium dioxide with highly mobile radionuclides 237Np and 99Tc was studied under oxidative conditions. Sorption of these radionuclides at different pH was measured, and the mechanism of redox reaction occurring in the course of their sorption were determined. In alkaline solution, Np(V) is reduced on the UO2+x surface and is sorbed in the form of tetravalent species. In neutral solutions, Np is sorbed in the form of Np(V). This is due to the fact that the stoichiometry of the UO2+x surface corresponds to U4O9. In acid solution, U(VI) is leached to form surface UO2. Although the free surface area of a UO2+x sample is low, the Np distribution coefficients Kd at pH > 6 are relatively high: log Kd > 2. Unlike Np, Tc(VII) is not reduced on the UO2+x surface. However, the sorption capacity of uranium dioxide for Tc(IV) is high.