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The IBR-2 (JINR) pulsed reactor is used in the field of solid state physics for experiments on extracted beams. It is predicted that the IBR-2 reactor will reach resource limits in 2032–2037. To keep and develop beam research at JINR, the development of a new pulsed neutron source has begun. According to estimates, the reactor will have average thermal power 12–15 MW, extracted by sodium coolant. At this power, the average flux density of thermal neutrons on the surface of the water moderator will reach 1014 sec–1·cm–2 and the peak density 5·1016 sec–1·cm–2, which is more than 10 times higher than the analogous parameters of the operating IBR-2 reactor. The new reactor is supposed to use neptunium-based fuel. The main characteristics and concept of the new reactor are presented.

The liquid–liquid extraction, recovery of Np(VI) and Np(V) from the solution of Na2CO3 by methyltrioctylammonium carbonate in toluene was investigated. By the graphic slope analyses method, as well as by recording of absorption spectra for obtained solutions and method of calculated determination of solution properties taking into account water activity, composition was established for the carbonate complexes of Np(VI) and Np(V) being extracted, which, depending on extraction conditions, can be expressed by the following formulae’s: (R4N)2[NpVIO2(CO3)2], (R4N)3[NpVO2(CO3)2], (R4N)6[NpVIO2(CO3)4], (R4N)2[NpVIO2(CO3)2]·2(R4N)2CO3, (R4N)5[NpVO2(CO3)3], (R4N)7[NpVO2(CO3)4], (R4N)3[NpVO2(CO3)2]·(1–2)(R4N)2CO3, where R4N is the quaternary ammonium cation. The results have been obtained in the experiments, has much interest both in the field of alkaline radioactive waste management and with respect to their usage for extraction of transuranium elements during reprocessing of alkaline radioactive waste, as well as for liquid–liquid extraction purification of uranium and plutonium from admixtures of fission products. These techniques are used within the framework of a new alternative method for reprocessing of spent nuclear fuel in carbonate media the CARBEX (CARBonate EXtraction) process.

Radioactive wastes are formed during the production of uranium-plutonium nuclear fuel at enterprises. In the present article the concentration ranges for uranium, plutonium, and neptunium in liquid and cemented wastes corresponding to different radioactivity classes are determined. The concentration ranges are determined for wastes formed in the production of nitride fuel for the initial load, as well as for waste formed on use of recycled uranium, plutonium, and neptunium in production. The effect of 241Am accumulation on the classification of radwaste is determined. The estimated cost of transferring the wastes formed on fabrication of mixed nitride fuel to the national operator for disposal is presented. The technological methods of reducing the cost of waste disposal, including the possibility of forming class-3 wastes for which surface disposal is admissible, are presented. The maximum concentration of plutonium and americium in liquid wastes at which the solidified forms of wastes correspond to class-3 is determined.

Microliter volumes are used in electrochemical detection and preconcentration of radionuclides to reduce the dose received by researchers and equipment. Unfortunately, there is a lack of analysis of radionuclides with coupled electrochemical techniques and microliter volume reactors. The goals of this work are (1) to develop a miniaturized micro-electrochemical quartz crystal microbalance (μeQCM) reactor for use in small volume (50–200 μL) electrogravimetric experiments and (2) to use this reactor to characterize the preconcentration of neptunium on carbon electrodes via electroprecipitation. We successfully deposited neptunium in the new μeQCM reactor and verified its operation. We found that preconcentration of neptunium on carbon coated electrodes was possible by chronoamperometry at − 1.6 VAg/AgCl. The mass shift of the resulting precipitate was indicative of the amount of neptunium on the electrode, although the correlation between the mass increase and activity of the preconcentrated material was not linear. Neptunium precipitate reduced electron transfer to the solution as evidenced by the increase in charge transfer resistance compared to bare electrodes.

In this study, a Boiling Water Reactor (BWR) modeling was done for the reactor core divided into square lattice 8 × 8 type using the Monte Carlo Method. Each of the square lattices in the reactor core was divided into small square lattices 7 × 7 type in groups of four. In the BWR designed in this study, modeling was made on fuel assemblies at pin-by-pin level by using neptunium mixed fuels as fuel rod, Zr-2 and SiC as fuel cladding, H2O as coolant. In fuel rods were used NpO2 and NpF4 fuels at the rate of 0.2%-1% as neptunium mixed fuels. In this study, the effect on the neutronic calculations as keff, neutron flux, fission energy, heating of NpO2 and NpF4 fuels in 0.2%-1% rates, and Zr-2 and SiC clads were investigated in the designed BWR system. The three-dimensional (3-D) modelling of the reactor core and fuel assembly into the designed BWR system was performed by using MCNPX-2.7.0 Monte Carlo method and the ENDF/B-VII.0 nuclear data library.

The design principles and parameters of a promising neutron source, based on the fission reaction of the isotope 237Np, for use in research in extracted beams are presented. Such a source can operate as a pulsing reactor or super-booster or as a super-booster multiplying the neutrons from the target of a proton accelerator by using a reactivity modulator. Owing to the threshold character of 237Np fission such a neutron source will possess significantly higher characteristics than a similar setup with plutonium, and in terms of utilization efficiency it will be the leading source in the world for research employing neutron spectroscopy.

A study for the quantitative actinide analysis by using a triple quadrupole ICP-MS/MS, Agilent 8900, was carried out. We confirmed the formation percentages of ionic species of each actinide in several kinds of collision/reaction cell modes. It was found that the dominant ions in oxygen gas mode were oxide ions, and the ratio of monoxide ion/dioxide ion increases with atomic number in the case of same oxygen gas flow rate. The percentages of actinide ion and oxide ions depend on the oxygen gas flow rate, and the number of oxygen attached on actinides increases with the oxygen gas flow rate.

The current trend in neutron-aided scientific research presupposes the development of new high-intensity pulsed sources. One variant of such an installation could be a pulsed reactor with a fissile-isotope core – 237Np. The present work is devoted to a study of the dynamics of power pulses of a neptunium reactor taking account of fast temperature feedback during pulse buildup. The problem is reduced to a simple model of a single frequency oscillator combined with the equation of single point kinetics of a reactor neglecting delayed neutrons. It is shown that on the basis of such an approximation, owing to feedback on the temperature of a fuel element the estimated energy of accidental power pulses decreases by almost a factor of 10 compared with a calculation neglecting fast feedback.

To evaluate the redox behavior of $${\text{VO}}^{2 + } / {\text{VO}}_{2}^{ + }$$ as a simulant of $${\text{NpO}}_{2}^{ + } / {\text{NpO}}_{2}^{2 + }$$ in boiling nitric acid solution, i.e., typical operating conditions for nuclear fuel reprocessing plants, oxidation rate measurements for VO2+ in boiling and non-boiling nitric acid solutions, thermodynamic calculations, and kinetic calculations were performed. The results indicated that the apparent oxidation rate of VO2+ to $${\text{VO}}_{2}^{ + }$$ is accelerated by a decrease in $${\text{NO}}_{2}^{ - }$$ and HNO2 concentrations owing to the boiling phenomena of nitric acid solution.

Herein, sorption of pentavalent neptunium from aqueous acidic solution was carried out onto 1st and 2nd generation of poly(amidoamine) dendrimer functionalized MWCNTs. The Np(V) sorption kinetics followed pseudo second order kinetics with rate constants of 1.4 × 10−4 and 6.84 × 10−4 g mg−1 min−1 for MWCNT–PAMAMG1 and MWCNT–PAMAMG2, respectively. The sorption of Np(V) onto MWCNT–PAMAMGn proceeded via chemisorption and the data fitted well to Langmuir isotherm model. MWCNT–PAMAMGn was found radiolytically stable up to 500 kGy dose of gamma radiation. Sodium carbonate was found to strip Np effectively from sorbent.

The solubility behavior of hexavalent neptunium (Np) was systematically investigated as function of [CaCl2] = 0.25–4.5 mol dm−3 [0.252–5.26 mol (kg H2O)−1] and pHm 8–12 (pHm = − log{m(H+)/mol (kg H2O)−1}) under oxidizing conditions adjusted by hypochlorite. As solubility limiting Np(VI) solid phase, hitherto unknown, non-stoichiometric calcium neptunates, Ca x NpO3+x (s,hyd), were identified by applying a wide range of analytical techniques including quantitative chemical analysis, powder XRD, Np L3-edge XANES, and SEM–EDX. The Ca:Np ratio in the equilibrium solid phase increased systematically with the pHm values in the batch solubility samples, and ranged between 0.60:1 and 1.66:1. For pHm > 10.5, the solubility of the calcium neptunates is around log{[Np]/mol (kg H2O)−1} ≈ − 6.1 ± 0.4 and does not show a strong dependence on [CaCl2]. For pHm

Solid-phase extraction of neptunium in pentavalent and hexavalent oxidation states from the acidic aqueous medium was investigated. The extraction of neptunium, carried out using N,N-dihexylamide functionalized multiwalled carbon nanotubes (MWCNT-DHA) showed high K d values. The sorption was found to follow Freundlich isotherm via chemical interaction between the amide functionality and neptunium. The time-dependent sorption study showed that the kinetics followed pseudo second order rate constants. MWCNT-DHA was found radiolytically stable up to 1000 kGy. The selectivity of MWCNT-DHA for the sorption of Np ion was found to be satisfactory. Citric acid was evaluated as the best strippants.

This paper reports an analytical method for rapid sequential separation of 210Po and actinides (Pu, Am and U) in air filter samples. An extraction chromatographic column TEVA + TRU was used in the separation of 210Po and actinides from the filter matrix, followed by its determination using alpha spectrometry. TEVA resin is widely used in the separation of plutonium and neptunium from the environmental samples, in this work potential application of TEVA in the sequential separation of 210Po and plutonium from filter matrix has been evaluated. This new method is simple, robust and can be performed formed in a day.

A procedure was developed for determination of Np using HR Sequential ICP-AES. Mutual interference and background free spectral lines of Np at 295.66, 297.43, 297.49, 302.64 nm were identified. The samples of higher concentration (10–20 µg/mL) of Np had been analyzed. Analytical values of 10–20 µg/mL samples were found to be in good agreement with the expected amounts. The concentration of Np between 2 and 4 μg/mL slightly affected as compared to higher concentration. In U/Pu, Np-295.66, 297.43 nm lines were monitored which showed noticeable enhancement of their intensities. The repetitive analyses showed that the precision was better than 2% RSD.

In order to understand the complex and dynamic neptunium process chemistry in the TBP-HNO3 system, the kinetics involved reversible redox reaction and extraction mass transfer was investigated. The results indicates that the mass transfer rate of Np(VI) is much faster than the redox reaction in aqueous solution. The concentrations of nitric acid and nitrous acid not only can change the Np(V) oxidation reaction and Np(VI) reduction reaction rate, but also can ultimately determine the distribution of neptunium extraction equilibrium. The variety of temperature can only influence the extraction equilibrium time, but cannot alter the equilibrium state of neptunium.

This work analyses the $$\alpha $$ decay properties of actinides. Geiger–Nuttall plots are presented for actinides. We have studied the competition between $$\alpha $$ decay and spontaneous fission and have identified the dominant decay mode. The results have been compared with experiments and they agree well with those of the experiments.

Studies of transuranic organometallic complexes provide a particularly valuable insight into covalent contributions to the metal–ligand bonding, in which the subtle differences between the transuranium actinide ions and their lighter lanthanide counterparts are of fundamental importance for the effective remediation of nuclear waste. Unlike the organometallic chemistry of uranium, which has focused strongly on UIII and has seen some spectacular advances, that of the transuranics is significantly technically more challenging and has remained dormant. In the case of neptunium, it is limited mainly to NpIV. Here we report the synthesis of three new NpIII organometallic compounds and the characterization of their molecular and electronic structures. These studies suggest that NpIII complexes could act as single-molecule magnets, and that the lower oxidation state of NpII is chemically accessible. In comparison with lanthanide analogues, significant d- and f-electron contributions to key NpIII orbitals are observed, which shows that fundamental neptunium organometallic chemistry can provide new insights into the behaviour of f-elements. Probing the chemistry of transuranic elements is notoriously challenging. Now, three neptunium(III) organometallic sandwich complexes have been prepared using a flexible macrocycle as ligand, and their molecular and electronic structures characterized, adding to our understanding of the behaviour of f-elements and suggesting that the lower oxidation state Np(II) may be chemically accessible.

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.

Recent nuclear forensics cases have focused primarily on plutonium (Pu) and uranium (U) materials. By definition however, nuclear forensics can apply to any diverted nuclear material. This includes neptunium (Np), an internationally safeguarded material like Pu and U, that could offer a nuclear security concern if significant quantities were found outside of regulatory control. This case study couples scanning electron microscopy (SEM) with quantitative analysis using newly developed specialized software, to evaluate a non-traditional nuclear forensic sample of Np. The results of the morphological analyses were compared with another Np sample of known pedigree, as well as other traditional actinide materials in order to determine potential processing and point-of-origin.

The objective of this study was to evaluate the spectral overlap for actinides and directly measure plutonium in uranium oxide and neptunium in uranium oxide matrix without an internal standard using laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). The system successfully measured 239Pu and 237Np with linear correlation coefficients (>0.99), relative standard deviations, limits of detections (0.026 and 0.111 wt% respectively) and percent biases reported. Each sample set was measured and analyzed within an hour which suggests a more rapid analytical technique than current methods used in nuclear safeguards to quantify plutonium and neptunium in a uranium matrix.

International audience; A new protocol designed for the rapid determination of U, Th, Pu, Np, Am and Sr in up to 500 mL of river water samples has been developed. The new method employs chromatographic separation, using TEVA, TRU and Sr resins, coupled to an inductively coupled plasma mass spectrometry and to a gas proportional counting (GPC). Excellent figures of merit characterized by recoveries and accuracies exceeding 80 and 90 %, respectively and detection limits below emergency thresholds are obtained. The new GPC methodology for the quantification of radiostrontium led to accurate results even with activity ratios (A89Sr/A90Sr) as high as 95. © 2016, Akadémiai Kiadó, Budapest, Hungary.

A new procedure was developed for the separation of uranium, thorium, plutonium, neptunium and americium based on extraction chromatography using the N,N,N′,N′-tetraoctyldiglycolamide sorbed onto Amberchrom CG-71 (available as DGA resin® from Triskem International). Radioactive waste samples were wet ashed, actinides were preconcentrated by coprecipitation with ferrous hydroxide. The dissolved precipitate was loaded from a reductive media on the column and the actinides were sequentially eluted changing the nature and the acidity of the eluents, the oxidation states of the given actinides, the concentration of the complexing agent, and the temperature. Alpha sources were prepared by micro-coprecipitation from the strip solutions without further processing. High recoveries and decontamination factors were obtained in each alpha source.

Recently a Np-237 target (26 mg) was analyzed for trace Pu isotopes (approximately 300 ppb). This work describes the chemistry required for a Np/Pu separation sufficient for Thermal Ionization Mass Spectrometry (TIMS), as well as the Pu purification from other potential contaminants. A point source was prepared from the purified Pu fraction and the atom ratios were measured via TIMS. The Pu isotopics provide a picture of the Np target’s irradiation history, which will also be discussed.

An ICP-AES based methodology was developed for the determination of 22 trace metallic constituents (Ca, Co, Cr, Pb, Cu, Fe, Ga, In, Mg, Mn, Na, Ni, Sr, Zn, Eu, Sm, Gd, Dy, B, Be, Cd and Ag) in high purity neptunium matrix alongwith simultaneous determination of Np. Np 295.660 nm line was found to have the best analytical performance. The spectral interference of Np on other analytes have been investigated which includes identification of interference free line, evaluation of correction factor and tolerance level of neptunium. Presence of U, Th, Zr and Pu on the determination of Np has also been studied. The method was validated using synthetic samples.

The radiolytic changes in oxidation state for solutions of initially Np(V) and/or Np(VI) were investigated by gamma-irradiation in conjunction with UV/Vis spectroscopy of the aqueous phase. Samples were irradiated in varying concentrations of nitric acid, and with or without the presence of 30 % TBP in dodecane. At short irradiation times Np(V) was oxidized to Np(VI), even in the presence of the organic phase. Upon the radiolytic production of sufficient amounts of nitrous acid, reduction of Np(VI) to Np(V) occurred in both phases. This was accompanied by stripping of the previously extracted Np(VI). Nitric acid concentrations of 6 M mitigated this reduction.

Select anthropogenic radionuclides were measured in lichen reference material, BCR 482. This material was originally collected in Axalp, Switzerland in 1991 and is composed of the epiphytic lichen Pseudevernia furfuracea. Samples from three separate bottles of BCR 482 were analyzed for uranium, neptunium, and plutonium isotopes by inductively coupled plasma mass spectrometry and analyzed for 137Cs by gamma-ray spectrometry. The isotopic composition of the radionuclides measured in BCR 482 suggests contributions from both global fallout resulting from historical nuclear weapons testing and more volatile materials released following the Chernobyl accident.

The concentrations of 237Np, 239Pu and 240Pu were determined in lichen samples (Usnea arizonica) that were collected from ten locations in New Mexico between 2011 and 2013 using isotope dilution inductively-coupled plasma mass spectrometry (ID-ICP-MS). The observed isotopic ratios for 237Np/239Pu and 240Pu/239Pu indicate trace contamination from global and regional fallout (e.g. Trinity test and atmospheric testing at the Nevada Test Site). The fact that actinide contamination is detected in recent lichen collections suggests continuous re-suspension of fallout radionuclides even 50 years after ratification of the Limited Test Ban Treaty.

During recent decades, the search for possible repositories for high-level nuclear waste has yielded large amounts of sorption data for actinides on different minerals. Clays and clay minerals are of special interest as potential host-rock formations and backfill materials, by virtue of their good retardation properties. Neptunium (Np) is one of the actinides which is considered in long-term scenarios due to its long-lived nuclide 237Np (t1/2 = 2.1 × 106 y). Because neptunium sorption is heavily dependent on the experimental conditions, comparison of sorption data from different experiments is challenging. Normalizing reported data with respect to the surface area of the sorbent enables conversion of conventional distribution coefficients (Kd) to normalized (Ka) values, which improves comparability among the results of different experiments. The present review gives a detailed summary of sorption data of Np on clays and clay minerals and examines critically the applicability of the Ka approach.

In order to understand the equilibrium state, conversion process and mechanism of Np(V)/Np(VI) in nitric acid solution, the redox kinetics of neptunium with nitrous and nitric acids was studied spectrophotometrically by an nonlinear fitting method. The rate equation of the redox reaction was acquired. Apparent activation energy of forward reaction and reverse reaction are approximately the same of 80 kJ/mol. Varying the concentrations of nitric and nitrous acids will change the reaction rate of forward and reverse reaction in different degrees. As a result, the equilibrium state of Np(V)/Np(VI) is altered, but it is not influenced by temperature.

We prepared neptunium chloride complexes electrochemically and performed spectroelectrochemical measurements of neptunium ions in LiCl–KCl eutectic melts at 450 °C, where the neptunium concentrations studied were in the range of 0.1–1 mM. We observed a highly absorbing f–d transition band of Np3+ at 383 nm, which was used to determine an formal potential of the Np4+|Np3+ redox couple (E°′ = 0.45 V vs. Ag|Ag+) with a solution of concentration as low as ~0.1 mM. This result agreed well with the value (E°′ = 0.42 V vs. Ag|Ag+) determined by cyclic voltammetry with a ~15 mM solution.

Microbial processes can affect the environmental behavior of priority radionuclides, and understanding these reactions is essential for the safe management of radioactive wastes and can contribute to the remediation of radionuclide-contaminated land. Underlying mechanisms that can control radionuclide solubility in biogeochemical systems can range from biosorption and biomineralization process, through direct (enzymatic) and indirect redox transformations. The mechanisms of enzyme-mediated reduction of problematic actinides, in principal, uranium (U), but including neptunium (Np), plutonium (Pu) and Americium (Am), are described in this review. In addition, the mechanisms by which the fission products technetium (Tc), cesium (Cs), and strontium (Sr) are removed from a solution by microorganisms are also described. The present review discusses the status of these microbiological processes, and the potential for cost-effective and scalable in situ remediation of radioactive waste.

We have developed a new chromatographic method to efficiently separate and isolate neptunium (Np) and protactinium (Pa), based on the selective extraction of protactinium by primary alcohols. The effectiveness of the new technology is demonstrated by efficient separation of 233Pa from parent radionuclide 237Np, using a hydrochloric acid mobile-phase medium. Our new approach reproducibly isolated 233Pa tracer with a yield of 99 ± 1 % (n = 3; radiochemical purity 100 %) and enabled chemical recovery of 237Np parent material of 92 ± 3 % (radiochemical >99 %) for future 233Pa tracer preparations. Compared to previous methods, the new approach reduces radioactive inorganic and organic waste; simplifies the separation process by eliminating cumbersome liquid–liquid extractions; and allows isolation of radiochemically-pure fractions in less than 1 h.

Examples of synchrotron-based investigations, chosen to illustrate various themes of research and development related to the nuclear fuel cycle, are summarised: (1) XAFS studies into the coordination chemistry of actinide versus lanthanide complexed with partitioning ligands to evaluate performance of separations, (2) high energy resolution X-ray emission measurements for characterizing electronic structure as a tool for fundamentally understanding actinide bonding and reactivity, and (3) investigation of processes leading to neptunium retention in a granite column tracer study using three dimensional imaging techniques.

Radiochemical separation of americium, neptunium and plutonium was tested on model solution of evaporator concentrate sample for isolation of each of them for alpha-spectrometry analysis. A good chemical separation of radionuclides of interest from the matrix and interfering radionuclides is required, once the relatively small difference in alpha-particle energy makes it difficult to spectrometrically separate the peaks. This paper describes use of the molecular recognition technology product AnaLig®Pu-01 gel from IBC Advanced Technologies, Inc. to effectively and selectively pre-concentrate, separate and recover americium, neptunium and plutonium from model solution of evaporator concentrate samples from Nuclear Power Plant which belong to the most difficult matrices to analyse. The method is suitable for analysing highly contaminated samples of radioactive waste in a relatively short time. For counting the alpha activity of 241Am, 239,240Pu, 238Pu and 237Np ORTEC 576A alpha-spectrometer equipped with ULTRATM ion implanted silicon detectors (600 mm2 active area) was used. The spectra were processed by using the Alpha-visionTM 32-bit emulation software from the EG&G ORTEC company.

The extraction behavior of Pu(III), Pu(IV), Np(IV) and Np(V) with di(chlorophenyl)-dithiophosphinic acid (DCPDTPA) in toluene from nitric acid solutions was studied systematically. In aqueous solution with high nitric acid concentration, the extraction capability (represented by distribution ratio D) for Pu and Np in different valences with DCPDTPA comes as D Np(IV) > D Pu(IV) > D Np(V) > D Pu(III). A new radiochemical procedure for Np/Pu separation based on DCPDTPA extraction was proposed and tested with simulated samples. The recoveries of Np and Pu are as high as 80 % after the whole separation procedure, with the decontamination factor of trivalent lanthanide fission product element (e.g. Eu) greater than 1.5 × 104. The decontamination factor of Pu–Np is 2.0 × 103, while the decontamination factor of Np–Pu is greater than 4.8 × 103 after additional purification.

A method was developed for the determination of 237Np with liquid scintillation counting (LSC) in the batch experiment of neptunium sorption onto bentonite. Before we use the pulse shape analysis (PSA) technique to discriminate α/β emission, a new approach was developed to set the optimum PSA by measuring a mixed α/β emitters sample and a background sample. The mathematic treatment of neptunium spectrum indicated that at the selected PSA-level of 38 approximately 86 % of the total α emission is detected, which is suitable for the determination of samples in the batch sorption experiments. Moreover, we confirmed that, at mass to volume radio 0–10 g/L the bentonite suspension in samples has a little impact on LSC determination. Thus, sorption percentage can be easily obtained by counting equivalent amount of suspension and supernatant from the same sample. Therefore, 237Np samples of batch sorption experiments could be detected with LSC quickly and effectively.

In this study, a flow-based electrochemical detection system coupled to a solid-phase extraction column was developed for the determination of neptunium in the presence of Pu(IV). Np(V) in the sample solution was completely oxidized to Np(VI) via electrolysis using a column electrode composed of carbon fibers. The column electrode effluent was then loaded onto a TEVA® column, and subsequently onto a UTEVA® column using 3 mol L−1 HNO3. Pu(IV) was retained on the TEVA column and separated from Np(VI), while Np(VI) was retained on the UTEVA column. Np(VI) was eluted from the UTEVA column with 0.01 mol L−1 HNO3 and then introduced directly into a flow-through electrolysis cell. An electrochemical amperometric method with a working potential of +0.1 V (vs. Ag/AgCl) was used to detect Np(VI). The current produced due to the reduction of Np(VI) was continuously monitored and recorded, and the Np concentration was calculated from the peak area. The relative standard deviation of 10 analyses was 2.4 % for an Np solution (0.50 mg L−1) containing 1.0 μg Np. The detection limit, which was determined to be three times the standard deviation, was 35 μg L−1 (70 ng Np).

To elucidate the sorption behaviors of radionuclides in multi-mineral systems and the mutual effects of minerals on this sorption, we carried out the sorption and desorption experiments of neptunium(V) on Na-montmorillonite-based two-mineral phasic systems (montmorillonite–calcite, montmorillonite–apatite). In the montmorillonite–calcite system, the sorption on the montmorillonite moiety decreased with increasing calcite content due to interference by the calcium ions dissolved from the calcite moiety, while no accumulation of Np to the calcite was observed. Total sorption of Np on the montmorillonite–apatite system was larger than that on apatite-free Na-montmorillonite, but the sorption on the montmorillonite moiety in this system was less than that on apatite-free Na-montmorillonite. Under weakly acid and neutral pH conditions, Np accumulated on the apatite moiety in a short period. At final pH 4 or less, though the pH condition was sufficient to dissolve the apatite moiety completely, the sorption very slowly increased with time and the increased Np was unexchangeable with 1 M KCl solution. This increase of the unexchangeable sorption cannot be explained by the knowledge accumulated so far.

An improved PUREX process in Tc separation is introduced in this paper. Experiments including we did and done by other investigators are cited in this paper to testify the feasibility of the process. The scheme of this process is as follows: First, to extract U, Pu and most Tc, Np into the organic phase, so the concentration of Tc in the high level liquid waste (HLLW) may be very low, which can alleviate the burden of Tc treatment in HLLW vitrification. Second, in the Pu and Np separation stage to reduce or complex Pu and Np using acetohydroxamic acid, this step separates Pu and Np from the organic phase. Next, to separate Tc from U, it can be realized easily by reducing Tc to lower valance using reductant such as hydrazine or quadrivalence U. By this technology, we may resolve the problems caused by Tc remained in the HLLW such as a long time surveillance of HLLW condensate or the risk of Tc transferring into the biosphere, and meanwhile the over-consumption of reductant in the U/Pu splitting stage can be avoided.

It was established that heating to 90 °C of nitrate solutions of U, Np and Pu in the presence of hydrazine hydrate results in the formation of hydrated dioxides of these elements. On ignition under inert or reducing conditions in the temperature range of 280–800 °C hydrated uranium dioxide transmogrify into crystalline UO2. On ignition in air atmosphere UO2·nH2O turns into UO3 at 440 °C and into U3O8 at 570–800 °C. It was shown that thermolysis of the solution containing a mixture of uranium, neptunium and plutonium nitrates at 90 °C in the presence of hydrazine hydrate allows one to prepare hydrated dioxides (U, Np, Pu)O2·nH2O which on heating to ~300 °C transmogrify into crystalline product of UO2, NpO2 and PuO2 solid solution. The technique of preparation of solid solutions of U and Pu dioxides is very promising as simple and effective method of production of MOX-fuel for.

One of the primary aims of the actinide community within nanoscience is to develop a good understanding similar to what is currently the case for stable elements. As a consequence, efficient, reliable and versatile synthesis techniques dedicated to the formation of new actinide-based nano-objects (e.g. nanocrystals) are necessary. Hence, a “library” dedicated to the preparation of various actinidebased nanoscale building blocks is currently being developed. Nanoscale building blocks with tunable sizes, shapes and compositions are of prime importance. So far, the non-aqueous synthesis method in highly coordinating organic media is the only approach which has demonstrated the capability to provide size and shape control of actinide-based nanocrystals (both for thorium and uranium, and recently extended to neptunium and plutonium). In this paper, we demonstrate that the non-aqueous approach is also well adapted to control the chemical composition of the nanocrystals obtained when mixing two different actinides. Indeed, the controlled hot co-injection of thorium acetylacetonate and uranyl acetate (together with additional capping agents) into benzyl ether can be used to synthesize thorium/uranium mixed oxide nanocrystals covering the full compositional spectrum. Additionally, we found that both size and shape are modified as a function of the thorium:uranium ratio. Finally, the magnetic properties of the different thorium/uranium mixed oxide nanocrystals were investigated. Contrary to several reports, we did not observe any ferromagnetic behavior. As a consequence, ferromagnetism cannot be described as a universal feature of nanocrystals of non-magnetic oxides as recently claimed in the literature.

Model and real solutions are used to study and monitor the dissolution and extraction operations in the reprocessing of spent fuel AM(B) based on uranium oxide or uranium-molybdenum alloy (alloy OM-9, 9% molybdenum) with a sublayer of mass 12% comprised of Ca, Mg or the alloy Cu–Mg individually and in a batch with VVER-440. Batching of different types of spent fuel or their solutions should be done for in order to clarify them.

Although the physiological impact of the actinide elements as nuclear toxicants has been widely investigated for half a century, a description of their interactions with biological molecules remains limited. It is however of primary importance to better assess the determinants of actinide speciation in cells and more generally in living organisms to unravel the molecular processes underlying actinide transport and deposition in tissues. The biological pathways of this family of elements in case of accidental contamination or chronic natural exposure (in the case of uranium rich soils for instance) are therefore a crucial issue of public health and of societal impact. Because of the high chemical affinity of those actinide elements for phosphate groups and the ubiquity of such chemical functions in biochemistry, phosphate derivatives are considered as probable targets of these cations. Among them, nucleotides and in particular adenosine mono- (AMP) and triphosphate (ATP) nucleotides occur in more chemical reactions than any other compounds on the earth's surface, except water, and are therefore critical target molecules. In the present study, we are interested in trans-plutonium actinide elements, in particular americium and curium that are more rarely considered in environmental and bioaccumulation studies than early actinides like uranium, neptunium and plutonium. A first step in this strategy is to work with chemical analogues like lanthanides that are not radioactive and therefore allow extended physical chemical characterization to be conducted that are difficult to perform with radioactive materials. We describe herein the interaction of lutetium(III) with adenosine AMP and ATP. With AMP and ATP, insoluble amorphous compounds have been obtained with molar ratios of 1:2 and 1:1, respectively. With an excess of ATP, with 1:2 molar ratio, a soluble complex has been obtained. A combination of spectroscopic techniques (IR, NMR, ESI-MS, EXAFS) together with quantum chemical calculations has been implemented in order to assess the lutetium coordination arrangement for the two nucleotides. In all the complexes described in the article, the lutetium cation is coordinated by the phosphate groups of the nucleotide plus additional putative water molecules with various tridimensional arrangements. With AMP 1:2 and ATP 1:1 solid-state compounds, polynuclear complexes are assumed to be obtained. In contrast, with ATP 1:2 soluble compound, the Lu coordination sphere is saturated by two ATP ligands, and this favors the formation of a mononuclear complex. In order to further interpret the EXAFS data obtained at the Lu LIII edge, model structures have been calculated for the 1:1 and 1:2 ATP complexes. They are discussed and compared to the EXAFS best fit metrical parameters.

Three radionuclide-spiked salt solutions have been prepared that simulate a range of typical compositions in Savannah River Site waste solutions. The Savannah River National Laboratory performed a series of tests with the three salt solutions designed to determine the propensity of ammonium molybdophosphate (AMP) to bind some of the common analytes such as the actinides (Pu, Am, Np, U), strontium, or the elements (Ag, As, Ba, Cd, Cr, Hg, Pb, Se) regulated by the Resource Conservation Recovery Act (RCRA). The results of the tests indicate that within the protocol conditions, AMP exhibited no appreciable affinity for plutonium, neptunium, uranium and strontium. AMP showed a possible minor affinity for americium; however, the data is not as clear due to continued americium solubility changes during the duration of the experiment. Of the eight RCRA elements studied, AMP exhibited affinity for only silver under our experimental conditions.

This paper describes a method for the separation and purification of 90Sr from PUREX–HLLW employing solvent extraction and precipitation techniques. 30 % TBP in n-dodecane was used for the removal of residual uranium, plutonium and neptunium from HLLW. Trivalent actinides and lanthanides were subsequently removed using N,N,N’,N’-tetra(2-ethylhexyl) diglycolamide (TEHDGA, 0.20 M in 30 % isodecyl alcohol and n-dodecane). 90Sr was selectively extracted from actinides and lanthanides depleted HLLW using 0.3 M TEHDGA in 5 % isodecyl alcohol and dodecane. Loaded strontium was stripped using 0.01 M HNO3 and further purified by radiochemical precipitation technique after adding Fe and natural strontium as carriers. Based on the experimental results, a flow-sheet was formulated and mCi levels of 90Sr recovered.

An ICP-MS analytical method as an alternative to the current radiochemical method was developed to analyze trace level 237Np in bulk plutonium materials. In this method, 237Np is determined together with a suite of trace elements during a single analysis using one dissolution solution. Method validation was achieved through precision examination, spike recovery study, detection limit determination, comparison of results with the radiochemical method, and laboratory intercomparison studies on Pu metals. The ICP-MS method significantly reduced the analysis cost, the sample amount, consumption of chemicals and waste generation, as well as the sample turnaround time.

In order to co-recycle neptunium, uranium and plutonium using the PUREX process, numerical simulations were used to investigate the behaviors of neptunium in the first solvent extraction cycle. Counter-current extraction experiments using a miniature mixer-settler were performed to verify the simulation. Calculated results based on experiments show that the concentrations of nitric and nitrous acid, saturation of uranium, flow ratio and residence time have important effects on the pathway of neptunium, and accumulation of neptunium may appear with the presence of uranium and plutonium.

A case study for dissolution and assay of neptunium oxide is presented in this paper. A simple analytical method for completely dissolving neptunium oxide is described. Addition of 12 M HNO3 is sufficient to dissolve neptunium oxide without precipitate formation. Various analytical chemistry methods were evaluated for neptunium assay including controlled potential coulometry, gas proportional counting/alpha spectrometry, gamma spectrometry using a high purity germanium detector, inductively coupled plasma-mass spectrometry, and isotope dilution-inductively coupled plasma-mass spectrometry. The precision and uncertainty of each analytical method is discussed.

The irradiation of aqueous nitric acid solutions generates transient, reactive species that are known to oxidize neptunium. However, nitrous acid is also a long-lived product of nitric acid irradiation, which reduces neptunium. When we irradiated nitric acid solutions of neptunium and measured its speciation by UV/Vis spectroscopy, we found that at short irradiation times, oxidation of Np(V) to Np(VI) occurred due to reactions with radicals such as •OH, •NO3 and •NO2. However, at higher absorbed doses and after a sufficient amount of nitrous acid was produced, reduction of Np(VI) to Np(V) began to occur, eventually reaching an equilibrium distribution of these species depending on nitric acid concentration. Neptunium(IV) was not produced.

Spectrophotometric investigations have been carried out on the disproportionation of Np(V) to form Np(IV) and Np(VI) in 1.1 mol⋅L−1 solutions of tributyl phosphate (TBP) and in N,N-dihexyl octanamide (DHOA) in n-dodecane medium. The Np(V) was found to coordinate with Np(IV) in 1.1 mol⋅L−1 TBP solution in n-dodecane to form a mixed valence “cation–cation” complex by bonding through an axial oxo group on Np(V). By contrast, this interaction was less prominent in the case of 1.1 mol⋅L−1 DHOA solutions. The effect of 1-octanol, added as phase modifier, on the disproportionation behavior of Np(V) was also investigated. An attempt was made to calculate the disproportionation/reduction rate constants for Np(V) under the conditions of these studies. Absorbance measurements on the Np stripped from organic phases revealed the occurrence of Np(V) in the aqueous phase.