Одной из актуальных задач атомной энергетики является переработка отработавшего ядерного топлива. Такая переработка подразумевает отделение актиноидов от продуктов деления урана. Одним из методов переработки может стать плазменная масс сепарация. В ОИВТ РАН в последние 10 лет активно велись исследования, направленные на развитие различных аспектов, связанных с плазменной масс-сепарацией. В статье приведен обзор основных результатов этих исследований по четырем направлениям: численные расчеты и анализ схем сепарации; генерация плазмы буферного газа и создание потенциала в ней; источник плазмы для инжекции смеси разделяемых веществ; сепарация модельных веществ.

Plasma mass separation requires a lot of diagnostic techniques that not only demonstrate the separation effect but also show the efficiency of the process. During the test experiments, plasma flux to be separated may contain neutral particles that avoid the separation process due to their insensitivity to electromagnetic field. We present the diagnostics of the lost substance in experiments on plasma mass separation. The obtained data of the diagnostics helps determine the law of particle evaporation from the plasma source. We show that neutral flux is unable to distort the result of separation diagnostics. The presented approach can be used in experiments aimed at enhancing the separation effect and achieving target productivity for industry applications.

One of the relevant tasks of nuclear power industry is the reprocessing of spent nuclear fuel. Such processing implies the separation of actinides from uranium fission products. One of the processing methods can be plasma mass separation. In the last 10 years, research aimed at the development of various aspects related to plasma mass separation has been actively conducted at the Joint Institute for High Temperatures of the Russian Academy of Sciences. The article provides an overview of the main results of these studies in four areas: numerical calculations and analysis of separation schemes; generation of background plasma and formation of plasma potential distribution; plasma source for injection of a mixture of separated substances; and demonstration of the model substances separation.

The details of the charged particle separation by mass in the configuration with axial magnetic and radial electric fields are studied. The radial electric field, oriented to the discharge axis, is induced in a background reflex discharge with a hot cathode (−550 V, 8–14 A). The plasma source is based on a hot cathode arc discharge with independent metal vapor injection (18–21 V, 30 A) was situated at 18 cm from the axis. It was shown that the separated Ag + Pb mixture is transported across the magnetic field under the background discharge electric field. Effective separation is possible in such a system, while the separation coefficient increases from 4.9 to 6.2–8.4 when the mixture injection point is moved away from the background discharge axis from 18 to 23 cm. The effect of mixture injection on the plasma potential distribution is examined. It was shown that the presence of a plasma source of separated substances can cause a local (1–2 cm) distortion of the background plasma potential profile. Such distortion, as well as fluctuations of the background plasma potential, can significantly affect the width of the deposited spots of separated substances.

One of the alternative 'dry' methods for spent nuclear fuel (SNF) reprocessing is the plasma mass separation technique. This letter describes the first experiments that demonstrate the fundamental feasibility of a plasma mass separation approach in crossed electric and magnetic fields in collisionless mode. The Ag + Pb mixture was used to simulate the heavy (>235 u) and light (<150 u) components of the SNF. The Ag + Pb mixture was transformed into a plasma jet and ejected along the magnetic field. The action of the electric field caused the deposition of mixture components on the substrate in the form of localized spots. The estimated separation factor was of 35.

The review covers the results of predominantly experimental studies of stationary vacuum arcs with diffuse cathode attachment that burns in vapor of the cathode material with a current density of less than 100 A/cm 2 . Such discharges are of great interest for a number of technologies that require the formation of high-intensity plasma flows without a droplet fraction. The discharges on cathodes made of graphite, pure metals, and oxides, as well as mixed cathodes, are considered. The specificity of the processes on vacuum arc cathodes is characterized by the ratio of the fluxes of thermally vaporized atoms and thermionic electrons. The review presents the results of studies of cathode materials with an atom-electron ratio of ~10 –2 to ~10 8 . Data on the working cathode temperature, the current–voltage characteristic of the discharge, the heat flux from the plasma to the cathode, the plasma parameters, its radiation spectrum, and the ion energy in the cathode jet are presented. Depending on the cathode material, the working temperature ranged from 1.2 to 2.5 kK. An analysis of the features of the charge-transfer processes on various cathodes is also presented.

One of the urgent tasks of the nuclear power industry today is reprocessing of spent nuclear fuel (SNF) and radioactive waste (RW), which is necessary to switch to a closed fuel cycle in order to use the reactor fuel resources to more extent by separating minor actinides for reuse of refabricated fuel. Another equally important driver for the creation and implementation of such technology is the environmental requirements aimed at reducing the disposal of radioactive waste and the scope of high-level waste transportation. It should be noted that any civil technology for SNF reprocessing must meet the requirement of non- proliferation of nuclear weapons, i.e. is obliged to prevent the release of plutonium, including by changing the operating modes of the equipment. There are promising hydrometallurgical and pyrochemical technologies developed at present day, as well as plasma processing methods. This report presents the engineering and physical fundamentals of plasma separation of SNF and RW. The potential advantages of plasma technologies for SNF or RW processing include a small amount of additional waste, the ability to adapt to different types of SNF and RW, and a possibility of implementing the technology into existing and designed material processing cycles and varying the processing scale from on-site to plant-size ones within large facilities. An important feature of plasma methods, i.e. insufficient selectivity for the separation of minor actinides from each other, shall also be mentioned. It is precisely such “crude” approach that ensures acceptable civilian processing technology, which satisfies the conditions for non-proliferation of nuclear weapons. The paper proposes an approach aimed to use the accelerating potential to overcome the energy and angular distribution of plasma ions at the entrance to the separation area and a potential well for the spatial separation of ions of different masses. It considers the physical principles of the plasma separation method and its main stages. There are provided experimental results achieved so far at a pilot facility for testing the plasma separation method. The results of calculations of ion trajectories and energy cost estimates are shown, demonstrating the prospects of the plasma method for process application. The process flow diagram of plasma processing and the steps to be taken to develop the technology are also discussed.

The paper presents a diffuse vacuum arc with heated cathode made of ceramic (CeO2) and metal (Cr) mixture, initiated and studied for the first time. Plasma sources of multicomponent mixtures are demanded for plasma based methods of rare-earths recycling and spent nuclear fuel reprocessing, which are currently under development. The discharge current-voltage characteristic was measured for different cathode temperatures (1950-2250 K); in the range of the arc current 30-100 A the voltage varied from 6 to 11 V. A cooling effect of the mixed cathode due to the thermionic emission at presence of the arc plasma was found; the effect reached about 150 W at the arc current of 30 A. The cooling effect and the current-voltage characteristic distinguish the discharge from the diffuse vacuum arcs with single-component cathodes made of cerium dioxide and chromium. The plasma parameters and optical emission spectra were analyzed for various cathode temperatures and arc currents (electron temperature was 0.4-0.6 eV, local particle densities in plasma near the cathode were in range 10(11)-10(13) cm(-3)). The study is of interest for plasma sources development and increase of their efficiency as well as for the tasks aimed at ionization of multicomponent mixtures.

A new concept of plasma separation of spent nuclear fuel components in a variable-cross-section chamber with a nonuniform magnetic field is proposed. Numerical simulation performed in axisymmetric geometry in the single-particle approximation have shown that, in a nonuniform magnetic field of <1.6 kG, at voltages of up to 100 V, and for a chamber radius varying from 20 cm to 60 cm over a distance of up to 1 m, spent nuclear fuel components can be spatially separated into three mass groups: actinides with masses of m ~ 240 amu, used for subsequent recovery of the fuel; fission products with $$m = 70{-} 160$$ amu; and light elements with $$m < 60$$ amu, which primarily include the structural materials and associated gases (nitrogen, oxygen). Separation of the latter two groups is important for practical use, because it potentially reduces the cost of the further treatment of separated radioactive waste.

The buffer plasma in plasma separator of substances must not lead to an additional ionization of ions to be separated, therefore it is needed to monitor its electron temperature. For this purpose an emission line-ratio method was used. In the paper optical diagnostic of argon rf-plasma (f approximate to 5 MHz) in magnetic field (130 and 650 G) was carried out. Argon pressure was of 5 mTorr. Corona model was used for the description of emission processes in plasma. Radial distribution of electron temperature was obtained using measured intensities of 763.5 and 811.5 nm argon emission lines. For data reprocessing the excitation from the ground state and metastable levels was taken into account. The obtained results are in agreement with data, measured from a double probe.

This paper presents the numerical simulation results of characteristics and efficiency of separation of uranium ion fluxes and its fission products in the process of the plasma separation. The movement of beams of heavy (238 u) and light (160 u) single-charged ions in vacuum and in helium buffer plasma has been investigated at a pressure of 10 mtorr, magnetic fields 0.8-1.2 kG and electrical potentials up to 1 kV. The interaction between the ion beams and their interaction with the buffer plasma has been taken into account. The numerical simulation of plasma has been conducted in a drift-diffusion approximation. It has been shown that the presence of buffer plasma in the area of ion fluxes and occurring compensation of their space charge can greatly improve the separation efficiency compared to the separation of ion fluxes in vacuum.

This paper outlines the requirements for a source of buffer plasma, which is necessary for elaboration of plasma separation method of substances and following foundations development of plasma reprocessing technology of spent nuclear fuel and radioactive waste. Such source is implemented on the basis of a helicon discharge, allowing plasma generation in a cylindrical volume with characteristic dimensions on the order of 1 m and bounded by metal walls. At plasma-forming gas (argon) pressure of 1 mTorr, radial profiles of density n(e) and temperature T-e of electrons were obtained for various magnetic field magnitudes (0-200 G) and RF power (up to 6 kW) using double probe and optical methods. The typical value of T-e amounted to eV units and n(e) was about 10(12) cm(-3).

Diffused vacuum arc with consumable hot cathode is one of the most perspective plasma sources for the development of spent nuclear fuel (SNF) plasma reprocessing technology. In this paper, studies of the discharge on cerium oxide cathode are continued. Cerium oxide simulates evaporation and ionization processes of the uranium dioxide-the main component of the most common SNF nowadays. Current-voltage characteristic of the arc at currents from 30 to 120 A was registered. Cathode temperature changed in range of 2.1-2.4 kK. With the help of Langmuir probe electron temperature was measured and plasma density was evaluated within the interelectrode gap and above the anode. The data of cerium oxide thermionic characteristics were obtained. Obtained discharge properties were compared with gadolinium arc characteristics which were studied earlier.

Spatial distribution of electrical potential formation in background plasma involving the magnetic field is one of the important challenges for the plasma separation method of spent nuclear fuel that is currently being developed. This is required for spatial separation and compensation of space charge of the ionized flows of substances with different masses; such flows are injected into the background plasma along the magnetic field lines. This paper studies the mutual influence of the argon reflex discharge and the lead plasma jet injected into this discharge. The lead plasma jet is formed by the plasma source based on arc discharge with the hot cathode and the induction evaporation of the plasma forming substance. This study demonstrates the possibility of the lead plasma jet ion deflection by the radial electric field formed in the reflex discharge plasma. The experimental data show that the lead plasma jet has a significant effect on the spatial distribution of reflex discharge electric potential. Whereby, the volume occupied by reflex discharge plasma is much greater than the volume occupied by the lead plasma jet.

A diffuse (spotless) vacuum arc was investigated on a hot cathode made from cerium dioxide. The discharge is obtained in the following range of current, voltage, and cathode temperature of I = 15–150 A, Va = 9–14 V, and Tc = 2.1–2.4 kK. The main characteristics of the plasma flow in space behind the anode with a hole were determined: it was found that the electron temperature at the working parameters lies in the range of 0.4–1 eV, the ions are predominantly singly charged, the average charge of the outgoing heavy particles reaches 0.9 e (elementary charge), and the most probable kinetic energy of the ions does not exceed 9 eV. Potentially found regimes of vacuum arc operation are promising for use in the work on implementation of the plasma method for spent nuclear fuel and/or radioactive waste reprocessing.

The optical diagnostics of an inductively coupled RF discharge in a magnetic field is considered. The radiative processes in the plasma are described by an extended corona equilibrium model. The temperature distribution of plasma electrons over the radius of the separator chamber is obtained using the line-ratio method for argon spectral lines (763.5/811.5, 451.1/811.5, 425.9/811.5 nm) and taking into account the excitation of levels from both the ground and metastable states. The results are compared with the data obtained by the electrostatic probe method.