RU2419900C1 - Method of plasma separation of spent nuclear fuel and device for its implementation - Google Patents

Abstract

FIELD: power industry. ^ SUBSTANCE: method and device are implemented when quasineutral axial symmetric multiple-component flow of plasma is obtained by means of plasma accelerator, during transportation of flow through azimuth device with transverse radial magnetic field, flow of plasma flow divided into masses through separating volume with stationary radial electric and homogeneous longitudinal constant magnetic fields, collection of ions of two groups of spent nuclear fuel (SNF) to ion receivers located on cylindrical surfaces. Ions of the third group of SNF are collected to annular end receiver. ^ EFFECT: group of inventions allows enlarging functional capabilities of plasma optic mass-separator owing to minimising negative impact of power and angular spreads of ions of various chemical elements in plasma flow and proper selection of the shape, quantity and location of receivers of groups of ions. ^ 2 cl, 7 dwg

Description

The invention relates to methods and devices for electromagnetic plasma separation of chemical elements, isotopes and can be used in the separation of elements or groups of elements from a multicomponent mixture, the production of stable and radioactive isotopes of chemical elements.

The invention relates to a promising priority area for the development of science and technology: "Technologies of nuclear energy, nuclear fuel cycle, safe handling of radioactive waste and spent nuclear fuel."

The main areas of application of isotopes and nuclear-pure substances are nuclear technology - fuel for nuclear power plants, structural materials in reactor engineering, moderators and neutron absorbers. In addition, these materials are in demand in the study of the structure and properties of substances by nuclear magnetic resonance, in the process of radiation sterilization, for modifying plants using radiation-induced mutations, isotope indicators (studying the distribution and pathways of a substance in a variety of systems), and in nuclear medicine .

Nuclear power plants (NPPs) currently provide more than 15% of global electricity production. The total capacity of 439 operating nuclear power plants is 372.2 GW. There are two main options for the nuclear fuel cycle - open and closed. In the first case, at the end of the working cycle, spent (irradiated) nuclear fuel (SNF) is placed in the SNF storage facility, after the necessary exposure, vitrified and the vitrified SNF is buried. A closed cycle involves the reprocessing of spent nuclear fuel, the production of uranium-plutonium (MOX) fuel from recycled material and its secondary use at nuclear power plants, the processing of radioactive waste, their storage, and geological disposal.

After using one ton of spent nuclear fuel in the reactor, approximately 960 kilograms of uranium remain. In addition, about 10 kilograms of plutonium is accumulated and about 30 kilograms of fragmentation radionuclides are formed. As a result of reprocessing spent nuclear fuel into the fuel cycle of a nuclear power plant, up to 97% of the starting material can be returned - not only ²³⁵ U and ²³⁸ U, but also isotopes of plutonium - a highly efficient fissile radionuclide - the products from which the fuel assemblies of MOX fuel are made. The reaction chain is explained by the following reaction chain: ²³⁵ U + n → ²³⁶ U + n → ²³⁷ U → (7 days) → ²³⁷ Np + n → ²³⁸ Np → (2.1 days) → ²³⁸ Pu; ²³⁸ U + n → ²³⁹ U → (23 min) → ²³⁹ Np → (2.3 days) → ²³⁹ Pu + shards + n → ²⁴⁰ Pu + n → ²⁴¹ Pu + shards + n → ²⁴² Pu + n → ²⁴³ Pu → (5 h) → ²⁴³ Am + n → ²⁴⁴ Am → (26 min) → ²⁴⁴ Cm.

The SNF composition can be clearly represented as the dependence of the yield of the decay product of primary nuclear fuel on the mass number - see Fig. 1, which shows the distribution of elements in spent nuclear fuel ( ²³⁵ U + thermal neutron cycle); peaks I, II - fission products, III - transuranic elements. Fission products include all elements from zinc to lanthanides and are concentrated at two peaks (Zr, Mo, Tc, Ru, Rh, Pd, Ag) and further (Xe, Cs, Ba, La, Ce, Nd). The greatest contribution to the activity of spent nuclear fuel with a three-year holding time is made by ¹³⁷ Cs + ^137m Ba (24%), ¹⁴⁴ Ce + ¹⁴⁴ Pr (21%), ⁹⁰ Sr + ⁹⁰ Y (18%), ¹⁰⁶ Ru + ¹⁰⁶ Rh (16%), ¹⁴⁷ Pm (10%), ¹³⁴ Cs (7%); the relative contribution of ⁸⁵ Kr, ¹⁵⁴ Eu, ¹⁵⁵ Eu is approximately 1% of each isotope. The most likely mass numbers of fission products (fragments) are 95 and 139 (peaks I and II in figure 1). Thus, spent nuclear fuel is a high-potential energy raw material (processing can save up to 30% of natural uranium) and a source of strontium, cesium, zirconium, niobium, ruthenium, yttrium, etc., for the manufacture of, for example, ionizing radiation sources widely used in various fields of human activity.

Currently, the annual SNF reprocessing volume is about 5000 tons, while one light-water reactor with a capacity of 1000 MW produces about 25 tons of SNF annually (installed capacity as of January 2010 was 370394 MW). Thus, the main amount of SNF is put into storage without reprocessing, struggling with environmental problems and losing valuable products. The reason is the high cost and, therefore, the unprofitability of the chemical separation of SNF. The cost of chemical reprocessing of SNF, RW reprocessing and the cost of storing SNF account for 29.1% of the total costs of the nuclear fuel cycle.

The initial chemical state of the processed materials may be different: oxides, nitrides, metals and alloys. Chemical separation of spent nuclear fuel is carried out in the process of extraction, coprecipitation and adsorption of uranium and plutonium from aqueous solutions of their nitrates using organic solvents with further purification of uranium and plutonium [see, for example, Taylor Robin John, Dennis Ian Stewart, Walwork Andrew Lindsay. A method of processing spent nuclear fuel // RF patent No. 2182379]. Or, a separation is carried out, including the stage of fuel fluorination, with the conversion of uranium to uranium hexafluoride [for example, Babikov LG, Raspopin SP Method and installation for reprocessing spent nuclear fuel // RF Application No. 2007131674/06] followed by chlorination of uranium oxides in reducing conditions. Next, the “plutonium" and "uranium" fractions, as well as the fraction containing the fission products, are each isolated. The separation of SNF, for example, from three former US nuclear facilities (Hanford, Savannah River, Idaho National Laboratory; 379,000 m ³ SNF) using existing technologies is planned to be completed by 2028; it will cost about 200 billion dollars.

The present and future needs of human activity pose the problem of finding and industrial use of a new high-performance method for the separation of nuclear-pure substances, isotopes. An alternative to chemical technology can be plasma methods of separation of substances and installations for their implementation - magnetoplasma and plasma-optic mass separators. To date, to one degree or another, among plasma methods, separation of isotopes in plasma using selective ion-cyclotron heating, plasma centrifuges, separation of isotopes in the positive column of a gas discharge [Isotopes: properties, production, application. In 2 t. T. 1 / Ed. V.Yu. Baranova. - M .: FIZMATLIT, 2005. - 600 p.] And in a beam-plasma discharge [Skibenko E.I. Physical and technical aspects of creating devices for magnetoplasma separation of a substance into elements and their isotopes based on a beam-plasma discharge // Questions of atomic science and technology. Series: Vacuum, Pure Materials, Superconductors, 2009. - No. 6. - S. 67-85].

Separation of ions of spent fuel elements (material of complex composition) is possible into light and heavy mass groups of elements — partial separation, or element-wise separation — complete separation [Skibenko EI Physical and technical aspects of creating devices for magnetoplasma separation of a substance into elements and their isotopes based on a beam-plasma discharge // Questions of atomic science and technology. Series: Vacuum, Pure Materials, Superconductors, 2009. - No. 6. - S. 67-85]. In partial separation, the main task is to reduce the proportion of low- and medium-active elements in order to reduce the amount of waste for subsequent vitrification.

A known method of isotope separation and a device for its implementation [Skibenko E.I., Kovtun Yu.V., Egorov A.M., Yuferov VB Design and technological features of the conceptual design of an ion-atom separation device based on a beam-plasma discharge // Questions of atomic science and technology. Series: Physics of Radiation Damage and Radiation Materials Science, 2009. - No. 4. - S.286-292].

The known method is implemented in several stages:

1) preparation of the working substance in the required vapor phase state;

2) supply of a separable substance to the ionization zone;

3) creation in a vacuum (working) volume of a longitudinal magnetic field;

4) impact, in collisions with electrons, ionization of the working substance;

5) ionization of the working substance due to collective plasma processes;

6) heating of plasma ions of the working substance when a radial electric field, plasma and cyclotron oscillations occur in a beam-plasma discharge;

7) the spatial separation of “hot” (target) and “cold” ions of various masses during their rotation in crossed radial electric and longitudinal magnetic fields;

8) deposition of charged particles on ion receivers.

The signs of the known method, coinciding with the essential features of the proposed method are:

1) preparation of the working substance in the required vapor phase state;

2) supply of a separable substance to the ionization zone;

3) creation in a vacuum (working) volume of a longitudinal magnetic field;

4) impact, in collisions with electrons, ionization of the working substance;

5) spatial separation of ions of various masses;

6) the deposition of charged particles of various masses on various ion receivers (plates).

The disadvantages of this method are:

1) the heating mechanism of plasma ions of the working substance is not precisely defined: ions can receive energy both in the process of plasma rotation and drift in crossed electric and magnetic fields, and in resonant interaction with low-frequency oscillations excited by an electron beam, resulting in the separation efficiency of “cold "And the target ions are deteriorating, so the possibilities of plasma mass separators, from the point of view of their practical use, are narrowing;

2) the electric field necessary for ion rotation arises in the plasma as a result of electron heating and its value is determined by the electron temperature, which is set in an uncontrolled manner when electrons interact with vibrations whose frequencies are close to harmonics of the electron cyclotron frequency and the upper hybrid frequency, resulting in separation efficiency “Cold” and target ions deteriorate, therefore, the possibilities of plasma mass separators, from the point of view of their practical use, are narrowed I am.

Known device [Skibenko E.I., Kovtun Yu.V., Egorov A.M., Yuferov VB Design and technological features of the conceptual design of an ion-atom separation device based on a beam-plasma discharge // Questions of atomic science and technology. Series: Physics of Radiation Damage and Radiation Materials Science, 2009. - No. 4. - S.286-292] contains:

1) vacuum volume;

2) a block of phase transformations;

3) electronic gun;

4) a magnetic system;

5) receiving plates;

6) the electron beam receiver.

Signs of a known device that matches the essential features of the claimed device are:

1) vacuum volume;

2) a block of phase transformations;

3) magnetic system;

4) receiving plates.

The disadvantages of the known device are:

1) the magnetic system is designed to create a longitudinal magnetic field, the intensity of which is sufficient to “magnetize” the target ions and amounts to B≤20 kG, which requires the use of high power electromagnets, therefore the possibility of plasma mass separators, from the point of view of their practical use, narrowing down; in the inventive device, the magnitude of the magnetic field should ensure magnetization of only electrons, therefore, B≤100 G and the required power of the electromagnets will be much less;

2) the presence of an electron gun to create plasma and excite plasma oscillations with an electric power of several MW, therefore the possibilities of plasma mass separators, from the point of view of their practical use, are narrowed; in the inventive device, such a gun is not needed, therefore, there are no costs of electric power.

A known method and device for the separation of spent fuel [Timofeev A.V. On the processing of spent nuclear fuel by the plasma method // Plasma Physics, 2007. - T.33, No. 11. - S.971-987].

The known method includes:

1) obtaining the atomic stream of the processed material;

2) ionization of the atomic stream;

3) the creation of an inhomogeneous magnetic field in the region of ion heating;

4) heating of ions;

5) the creation of an inhomogeneous magnetic field in the separation region;

6) separation of ions in an inhomogeneous magnetic field;

7) collecting separated groups of ions into spatially separated receivers.

The signs of the known method, coinciding with the essential features of the proposed method are:

1) obtaining the atomic stream of the processed material;

2) ionization of an atomic stream;

3) the creation of an inhomogeneous magnetic field in the separation region;

4) ion separation in an inhomogeneous magnetic field;

5) collecting separated groups of ions into spatially separated receivers.

The disadvantages of this method are:

1) the need for heating ions to energies of 0.35-1 keV before separation using an external generator of monochromatic high-frequency oscillations, which significantly increases the energy consumption for the separation of spent nuclear fuel;

2) the creation in the heating region of ions of a non-uniform magnetic field along the system with an induction varying from V _min ≤85B ₀ to V _max ≥155V ₀ (V ₀ is the resonant magnetic field for protons), with a maximum magnetic induction of V≤30 kG in a volume of about 1 m ³ , which requires high energy costs, so the possibilities of plasma mass separators, from the point of view of their practical use, are narrowing;

3) RF heating of spent nuclear fuel ions of various masses is difficult due to the asymmetry of heating of light and heavy ions; therefore, the possibilities of plasma mass separators are narrowing from the point of view of their practical use.

The known device [Timofeev A.V. On the processing of spent nuclear fuel by the plasma method // Plasma Physics, 2007. - T.33, No. 11. - S.971-987] includes:

1) block phase transformations;

2) an ionizer;

3) a chamber for heating ions when interacting with an external rf field;

4) a generator of monochromatic RF radiation;

5) the magnetic system of the RF heating chamber;

6) the magnetic system of the toroidal magnetic separator;

7) SNF ion receivers divided into 2 groups.

Signs of a known device that matches the essential features of the claimed device are:

1) block phase transformations;

2) an ionizer;

3) the chamber of the magnetic separator;

4) SNF ion receivers.

The disadvantages of the known device are:

1) the impossibility of receiving three groups of SNF ions (ions divided into 2 groups are received), which narrows the possibilities of plasma mass separators from the point of view of their practical use;

2) the presence of ions of mutual overlapping ions of a group of transuranic elements and a group of fission products (fragments), which narrows the possibilities of plasma mass separators from the point of view of their practical use.

The prototype of the proposed method and device is the method and device of plasma-optical mass separation (POMS-E) [Morozov A.I., Savelyev V.V. Axisymmetric plasmooptical mass separators // Plasma Physics, 2005. - T.31, No. 5. - S. 458-465].

The mass separation method (POMS-E) of the prototype includes:

1) obtaining a quasi-neutral axially-symmetric multicomponent plasma flow using a plasma accelerator - a stationary plasma engine;

2) the plasma stream is transported through an azimuthator, in which different pulses in the azimuthal direction are transmitted to different ions in a transverse radial magnetic field - mass separation is performed;

3) transportation of the plasma stream through a separating volume, in which a stationary radial electric field is created and which is placed in the region of a uniform constant magnetic field that magnetizes electrons, but practically does not affect the dynamics of ions;

4) collection of ions on ring ion receivers located in positions calculated along the length and radius of the separating volume.

The signs of the known method, coinciding with the essential features of the proposed method are:

1) obtaining a quasi-neutral axially-symmetric multicomponent plasma flow using a plasma accelerator;

2) the plasma stream is transported through an azimuthator, in which different pulses in the azimuthal direction are transmitted to different ions in a transverse radial magnetic field - mass separation is performed;

3) the plasma stream is transported through a separating volume in which a stationary radial electric field is created and which is placed in the region of a uniform constant magnetic field that magnetizes electrons, but practically does not affect the dynamics of ions;

4) collecting ions at ion receivers located in positions calculated along the length and radius of the separating volume.

The disadvantages of the prototype method are:

1. Strict conditions for monoenergetic ion beam and angular spread of the stream at the exit of the accelerator, which limit the possibility of using the prototype method for practical purposes. The calculations in the above studies were made for the case of identical energies of ions of different masses at the exit from the plasma source and small (not more than ± 5 °) angular spreads of the velocities of the ions of the plasma stream. The ATON stationary plasma accelerator engine closest to these requirements [Morozov A.I., Bugrova A.I., Desyatskov A.V., Ermakov Yu.A., Kozintseva M.V., Lipatov A.S., Pushkin A .A., Kharchevnikov V.K., Churbanov D.V. Stationary plasma accelerator engine ATON // Plasma Physics. - 1997. - T.23, No. 7. - S.635-645] generates ions (xenon) with energies from several ionization potentials to eU _p , where U _p is the voltage between the cathode and anode, with an average energy of about E _cf ≈0.75 U _p . Ninety percent of the ion beam current lies inside the cone with a divergence angle of about 11 °. In most plasma sources, the longitudinal velocity spread is ΔV _z ~ V _z , which narrows the possibilities of plasma-optical mass separators from the point of view of their practical use.

2. The method does not allow collecting ions into receivers in the form of 3 groups, which is typical for SNF, which contains charged particles that differ significantly in mass, which narrows the possibilities of plasma-optical mass separators from the point of view of their practical use .

The device according to the prototype [Morozov A.I., Savelyev V.V. Axisymmetric plasmooptical mass separators // Plasma Physics, 2005. - T.31, No. 5. - S.458-465] includes:

1) plasma accelerator - stationary plasma engine;

2) azimuthator;

3) cathode;

4) a system for creating a magnetic field in a separating volume;

5) a system for creating a radial electric field in a separating volume;

6) ring receivers of the separated components of the ion beam, located in the positions calculated along the length and radius of the separating volume.

Signs of a known device that matches the essential features of the claimed device are:

1) plasma accelerator;

2) azimuthator;

3) cathode;

4) a system for creating a magnetic field in a separating volume;

5) a system for creating a radial electric field in a separating volume;

6) receivers of the separated components of the ion beam located in the positions calculated along the length and radius of the separating volume.

The disadvantages of the device of the prototype are:

1) the absence of a block of phase transformations, which narrows the possibilities of plasma-optical mass separators from the point of view of their practical use;

2) the possibility of ions of different masses falling on each of the receivers when using existing plasma accelerators as sources of ions of chemical elements, which narrows the possibilities of plasma-optical mass separators from the point of view of their practical use;

3) the stationary plasma engine has a cathode extended outside the limits of the plasma accelerator itself, which complicates the joining of the plasma accelerator and the azimuthator, requires modification of the plasma accelerator device, which narrows the possibilities of plasma-optical mass separators from the point of view of their practical use.

When creating a method for separating spent nuclear fuel and a device for its implementation, united by a single inventive concept, the task was to create as a result such a method and device in which all the positive qualities of the method and device of the prototype would remain and practical possibilities had been mastered in production to date plasma accelerators and separation of spent nuclear fuel into three fractions.

The technical result of the proposed method for the separation of SNF and a device for its implementation is to expand the capabilities of plasma-optical mass separators from the point of view of their practical use by minimizing the negative impact of energy and angular dispersion of ions of various chemical elements in the plasma stream and the correct choice of shape, number and position of the receivers groups of ions.

The technical result is achieved by the fact that in the method of plasma-optical separation of spent nuclear fuel, which includes obtaining a quasineutral axially symmetric multicomponent cylindrical plasma flow using a plasma accelerator, transporting the plasma flow through an azimuth transverse radial magnetic field, transporting the mass-separated plasma flow through the separating volume with stationary radial electric field and a uniform constant longitudinal magnetic field, magnitude which is sufficient for magnetization of electrons, while the ion paths are determined by the action of a radial electric field, the compensation of the space charge of the plasma stream, the collection of ions on the receivers, according to the invention, create a plasma stream containing ions of chemical elements that make up the spent nuclear fuel with atomic masses in the ranges from 85 to 106, 134 ÷ 155 and 235 ÷ 244; collection of ions is carried out in accordance with the selected three groups of spent nuclear fuel ions into 3 ion receivers, two of which are located on cylindrical surfaces with radii r ₁ for receiving ions of the third group and r ₂ for receiving ions of the first group with a length determined by the formula:

L _Zmax ≤6R,

Where

L _Zmax is the length of the cylindrical receivers, m;

R is the radius of the central path of the ion flow, m;

while the ions of the second group are collected at the end receiver.

The technical result is achieved in that in a device for plasma-optical separation of spent nuclear fuel containing a plasma accelerator, an azimuthator, a separation volume, a system for creating a longitudinal magnetic field in a separation volume, a system for creating a radial electric field in a separation volume, a tracking electron source, according to the invention, a device additionally contains a phase transformation block, which provides the transfer of spent fuel into the vapor phase and steam supply to the plasma accelerator, two receivers ionics, moreover, the cathode of the plasma accelerator is aligned with the azimuthator, two receivers of the separated components of the ion flow of chemical elements of spent nuclear fuel are made in the form of cylinders of radii r ₁ and r _{2 of} length L _Zmax , determined by the formula:

L _Zmax ≤6R,

Where:

L _Zmax is the length of the cylindrical receivers, m;

R is the radius of the Central path of the ion flow, m,

and the third receiver is in the form of a ring located at the end of the separating volume directly behind the cylindrical receivers, and the radii of the cylinders of the receivers are made in accordance with the relations:

G (M _III.min , r ₁ ) = 0,

G (M _I.max , r ₂ ) = 0,

Where:

Where

M _III.min - the minimum mass of an ion from group III of transuranic elements of spent nuclear fuel, kg;

M _I.max is the maximum mass of an ion from group I of the lightest fission products of spent nuclear fuel, kg;

M ₀ is the mass of the central mass ion from group II, which does not have a radial velocity component, kg;

M is the mass of the ion, kg;

R is the average radius of the plasma stream, m;

r is the radius of ion motion, m;

r ₁ is the radius of the inner cylindrical ion receiver, m;

r ₂ is the radius of the external cylindrical ion receiver, m

The advantage of the proposed POMS-E option in comparison with the prototype is the possibility of practical implementation of the proposed method using already developed and mass-produced plasma accelerators as ion sources and the possibility of dividing SNF into 3 groups containing a set of chemical elements with significantly different mass numbers, which are ensured by combining cathode of a plasma accelerator with an azimuthator and a change in the number, design and spatial location of the receiver in groups of ions that differ in mass.

The general principle of constructing a process for plasma processing of spent nuclear fuel, including technological preparation in the phase conversion unit, obtaining a plasma of the working substance (SNF), separation of spent nuclear fuel in plasma, waste collection and disposal, is explained in the diagram given in the description of the invention (Fig. 7).

The inventive method of plasma separation of spent nuclear fuel and a device for its implementation are illustrated by the drawings shown in figure 1 ÷ 6.

Figure 1 shows the distribution of elements in spent nuclear fuel (nuclear cycle ²³⁵ U + thermal neutron): I, II - fission products (fragments), III - transuranium elements.

Figure 2 shows a diagram of the inventive device for plasma separation of spent nuclear fuel, designation of the analyzing fields and geometric elements necessary for calculating the device: 1 - block phase transformations, 2 - plasma accelerator type "accelerator with anode layer", 3 - azimuth, 4 - source electron tracking, 5 - a system for creating a longitudinal magnetic field in a separating volume, 6, 8 - cylindrical ion receivers, 7 - end ion receiver.

Figure 3 shows the dependence of the radius of the cylinder ℛ = r / R for collecting ions of spent nuclear fuel elements (R is the average radius of the plasma stream) on the mass of the target ion.

Figure 4 shows the trajectories of ions of extreme masses of groups I (85; 106), II (134; 155) and III (235; 244) obtained as a result of numerical calculation. The central mass of the second group is taken equal to 134. Given are the calculated values of the radii r ₁ and r ₂ .

Figure 5 shows the trajectories of ions of extreme masses of groups I (85; 106), II (134; 155) and III (235; 244), obtained as a result of numerical calculation. The central mass of the second group is taken equal to 139. The calculated values of the radii r ₁ and r _{2 are given} .

Figure 6 shows the trajectories of ions of extreme masses of groups I (85; 106), II (134; 155) and III (235; 244) obtained as a result of numerical calculation. The central mass of the second group is taken equal to 155. Given are the calculated values of the radii r ₁ and r ₂ .

The device contains (see Fig. 2) a phase transformation block 1, a plasma accelerator with an anode layer 2, an azimuthator 3 combined with the cathode of the plasma accelerator, an electronic tracking gun 4, a system for creating a longitudinal magnetic field 5, magnetizing electrons, but not affecting the dynamics ions, a system for creating a radial electric field, consisting of two cylindrical electrodes 6, 8, and receivers of the separated components of the beam 6, 7 and 8.

The following is a brief theoretical justification for the possibility of implementing the method and creating a device for this application.

Described in the works [Morozov A.I., Semashko N.N. On mass separation of quasineutral beams // Letters in ZhTF. 2002.Vol. 28. Issue 24. S.63-66; Morozov A.I., Savelyev V.V. Axisymmetric plasmooptical mass separators // Plasma Physics. 2005.V. 31. No. 5. S.458-465; Morozov A.I. Introduction to plasma dynamics. - M .: FIZMATLIT, 2008. - 616 pp.] The ideal focusing mode for POMS-E allows ions of the same mass, but emanating from an azimuthator with different radial velocities, to focus at a certain distance along the axis of the system. The radius of the rings on which focusing depends on the mass of ions. Such a regime is possible only if all the ions of the plasma stream are monoenergetic and if the oscillations of ions with different initial radial velocities are harmonious in the radial direction, which is certainly not true for currently existing plasma accelerators. We took into account the broadening of the focal rings due to both the angular spread of ions in the plasma stream and due to the non-monoenergetic energy of ions in the plasma stream. In addition, to ensure the possibility of practical implementation of the plasma-optical method of mass separation of spent nuclear fuel, the number, design, and geometric dimensions of the receiving electrodes of the mass separator were found. The motion of the separated ions was considered in the cylindrical coordinate system r, φ, Z in the one-particle approximation, when the ion flux was completely compensated by electrons.

. После выхода из азимутатора движение иона по радиусу происходит при сохранении момента

под действием центробежной силы и силы со стороны радиального электрического поля E_r(r)=-E₀(R/r), направленного к оси. По оси Z движение ионов происходит по инерции с постоянной скоростью V_ZA, равной скорости ионов на выходе азимутатора.In the POMS-E scheme, an annular plasma flow with isotope ions of different masses first flies along the Z axis through the annular azimuth gap with an average radius R, in which a radial magnetic field B _r = const = B exists along the entire width Δ of the azimuth slit (along the Z axis) _R. In this case, the azimuthal velocity acquired by the ion after passing through the azimuthator is determined by the mass of the ion and is equal to

. After exiting the azimuthator, the ion moves along the radius while maintaining the moment

under the action of centrifugal force and the force from the side of the radial electric field E _r (r) = - E ₀ (R / r) directed to the axis. On the Z axis, the movement of ions occurs by inertia with a constant speed V _ZA equal to the speed of ions at the output of the azimuthator.

. Определим центральную массу

, как массу такого иона, который, вылетев из азимутатора с нулевой радиальной скоростью, будет всегда находиться на радиусе r=R. Тогда уравнение движения иона с произвольной массой М по радиусу будет таким:The ion motion along the radius after the azimuthator can be described by the equation

. Define the central mass

as the mass of such an ion, which, having flown out of the azimuthator with zero radial velocity, will always be at a radius r = R. Then the equation of motion of an ion with an arbitrary mass M along the radius will be as follows:

. Тогда из (1) следует, что

, где Е - полная энергия иона - кинетическая плюс потенциальная. Потенциальную энергию вычислим, интегрируя уравнение (1). Постоянную интегрирования выбираем из того факта, что в момент вылета из азимутатора полная энергия Е равна начальной кинетической энергии радиального движения

, U(R)=0.Equation (1) can also be written in terms of the potential energy U (r):

. Then it follows from (1) that

where E is the total energy of the ion - kinetic plus potential. We calculate the potential energy by integrating equation (1). The integration constant is chosen from the fact that at the time of departure from the azimuthator, the total energy E is equal to the initial kinetic energy of the radial motion

, U (R) = 0.

Then:

Where

The shape of the potential wells G (r), as can be seen from (2), when the oscillation period T of particles of different masses in the wells is the same, is far from parabolic.

- координата дна потенциальной ямы для иона массой М=М₀-δМ). Уравнение колебаний при этом будет таким:We introduce the variable x = r / R. For small deviations from the bottom of the well, the function G (x) is equal to:

- coordinate of the bottom of the potential well for an ion of mass M = M ₀ -δM). The equation of oscillation will be as follows:

, а V_φA0 - азимутальная скорость иона центральной массы. Решение уравнения (3) в общем случае описывает ангармонические колебания. Запишем это решение в первом приближении, учитывая только первую, основную гармонику, отражающую зависимость частоты от амплитуды колебаний:Where

, and V _φA0 is the azimuthal velocity of the ion of central mass. The solution of equation (3) in the general case describes anharmonic oscillations. We write this solution as a first approximation, taking into account only the first, fundamental harmonic, which reflects the dependence of the frequency on the amplitude of the oscillations:

.where a is the amplitude of the oscillations, φ is the initial phase,

.

для иона массы М=М₀-δМ амплитуда определяется величиной

, если выполнено условие

, которое означает, что максимальная полная энергия

много больше величины приращения потенциальной энергии от дна потенциальной ямы до уровня U=0. При противоположном условии можно показать, что перекрытия фокусных колец вообще нет. Учтем, что

. Именно при таком соотношении скорость вылета иона из азимутатора вдоль Z, равная

, будет слабо изменяться для ионов разных масс, находящихся вблизи M₀, так как в этом случае ∂V_ZA/∂M(M=М₀)=0. Тогда a₀=α,

. Для ионов обеих масс получаем одинаковые частоты колебаний

и одинаковые периоды колебаний

, где

.For a monoenergetic plasma flow with ion energy W _{0, the} boundaries of the focal rings are determined by ions with maximum vibration amplitudes, i.e. with maximum radial velocities V _rmax = α (M ₀ / M) ^1/2 V ₀ , where V ₀ = (2W ₀ / M ₀ ) ^1/2 , α is the angle of divergence of the plasma flow. For a central mass ion, the maximum amplitude of oscillations will be equal to

for a mass ion M = M ₀ -δM, the amplitude is determined by

if the condition

which means that the maximum total energy

much larger than the increment of potential energy from the bottom of the potential well to the level U = 0. Under the opposite condition, it can be shown that there is no overlap of the focal rings at all. We take into account that

. It is with this ratio that the ion escape velocity from the azimuthator along Z equal to

, will vary slightly for ions of different masses located near M ₀ , since in this case ∂V _ZA / ∂M (M = M ₀ ) = 0. Then a ₀ = α,

. For ions of both masses we get the same oscillation frequencies

and identical periods of oscillation

where

.

The criterion for the absence of suppression of focal rings for the two masses under consideration has the form x ₀ <x ₁ and gives the condition for the angular divergence of the plasma flow:

, угол α<25°.which is weak enough. For example, when

, angle α <25 °.

.Let us now consider the broadening of the focal rings due to the nonmonoenergetic nature of the plasma flow (ions with energies W <W ₀ are present in the plasma flow), and the ion vibrations in potential wells will be considered harmonic with the oscillation period T ₀ . An ion of central mass M ₀ with energy W ₀ after an azimuthator takes off at a speed

.

, что и приводит к уширению фокусного кольца. Критерий отсутствия пересечений фокусных колец после необходимых вычислений дает условиеThe focal plane is located at a distance Z _Ф = T ₀ V _ZA0 / 2. An ion with lower energy W = W ₀ -ΔW when moving along the Z coordinate reaches the focal plane with a time delay of

, which leads to broadening of the focal ring. The criterion for the absence of intersections of the focal rings after the necessary calculations gives the condition

As ΔW / W → 3/8, the right-hand side of inequality (6) tends to zero. Therefore, under the condition ΔW / W> 3/8, ion separation in the Z _Φ plane becomes impossible. For plasma accelerators, this condition is usually realized.

,

. Ионы массой М₀ проходят на торцевой приемник ионов. Требование, чтобы ионы М₀ не пересекали при своем движении цилиндрические поверхности радиусами r₁ и r₂, дает условие

, где ξ=V_X/V₀<1, V_X - потоковая скорость ионов, причем V_X≥V_φA0, иначе большая часть ионов не пройдет через азимутатор. Длина приемников ионов определится так:

.For POMS-E, we offer a new scheme for receiving separated ions: particles with mass M ₁ can be collected on a cylindrical surface of radius r ₁ , particles of mass M ₂ can be collected on a surface of radius r ₂ . We note specifically that on cylinders of radii r ₁ and r _{2 there} will be ions of masses M ₁ and M _{2 of} any energy. The radii r ₁ and r _{2 are} determined by the equations: G (M ₂ , r ₂ ) = 0; G (M ₁ , r ₁ ) = 0. For an ion with a central mass of M ₀ = (M ₁ + M ₂ ) / 2, δM = (M ₁ -M ₂ ) / 2, M ₁ = M ₀ + δM, and M ₂ = M ₀ -δM. At δM / M ₀ << 1 we obtain approximate formulas for determining the radii of the receiver cylinders:

,

. Ions of mass M ₀ pass to the end ion receiver. The requirement that the ions M ₀ do not intersect during their movement cylindrical surfaces of radii r ₁ and r ₂ gives the condition

, where ξ = V _X / V ₀ <1, V _X is the ion flow rate, and V _X ≥V _φA0 , otherwise most of the ions will not pass through the azimuthator. The length of the ion receivers is determined as follows:

.

The POMS-E plasmooptical mass separator thus modified is called a POMS-E-3 mass separator.

Note that the larger the mass of M, the smaller will be the radius of reflection of the ion; the smaller the mass M, the greater the radius of reflection. As already mentioned (see Fig. 1) for SNF there are three peaks in the distribution of elements by mass with the most probable masses: M _I.HB = 95, M _II.HB = 139 and M _III.HB = 239. The cylindrical receiver of all ions with M _III ± δM _III (δM is the mass dispersion near the most probable for the corresponding peak) must be located at a radius R _min , which is determined from the equation G (M _III -δМ _III , R _min ) = 0, while all the particles of peak M _I will fall on the cylinder R _min , since all particles with masses M> M _III- δM _III have reflection points at a distance less than R _min . The cylindrical receiver of all ions with M _I ± δM _I must be located on a radius R _max , which is determined from the equation G (M _I + δМ _I , R _max ) = 0, while all particles of the peak containing M _I will fall on the cylinder R _max since all particles with masses M <M _I + δM _I have reflection points at a distance exceeding R _max . For the purposes of SNF separation, the POMS-E-3 plasma-optic mass separator is ideally suited: all transuranium elements (peak III ions — FIG. 1) will be collected on a receiving electrode with a radius r ₁ . A large radius (r ₂ ) receiver will receive all ions corresponding to peak I; on the end receiver - elements of peak II. Transuranic elements are transferred after isolation for the manufacture of MOX fuel. The "minor" elements, already partially separated at the first stage of mass separation, can be further separated either using the same reconfigured POMS-E-3, or transferred to an electromagnetic mass separator.

The inventive method is implemented as follows.

In the block of phase transformations, spent fuel is converted to a vapor state, for example, as a result of evaporation by an electron beam. Next, the working vapor is introduced into a plasma accelerator with an anode layer, where a quasineutral axially symmetric multicomponent cylindrical plasma stream with an average radius R is formed, which is transported through an azimuth transverse radial magnetic field. In the magnetic field of the azimuthator, ions are separated by mass and then transported through a separating volume with a stationary radial electric field and a uniform constant longitudinal magnetic field that magnetizes electrons, but does not affect the dynamics of ions. In the separating volume, the volumetric charge of the plasma stream is compensated. The collection of ions of chemical elements that make up the spent nuclear fuel, divided by mass numbers into 3 groups: M _I in the range from 85 to 106, M _II - 134 ÷ 155, M _III - 235 ÷ 244, is carried out on 3 ion receivers of length L _Zmax ≤6R, two of which are arranged on cylindrical surfaces of radii r ₁ - for receiving ions of M _III and r ₂ - for receiving a group of ions M _I, M and group _II ions collected on a receiver end.

The inventive device operates as follows.

In the phase transformation unit 1 (see FIG. 2), the spent nuclear fuel, which is predominantly in solid form, is vaporized, for example, by means of an electron beam, and fed to a plasma accelerator with an anode layer 2, where the vapor is ionized. At the output of the plasma accelerator, a multicomponent plasma flow is formed, which enters the azimuthator 3, combined with the cathode of the plasma accelerator 2, in which the ions of the SNF plasma flow acquire an azimuthal velocity different for ions of different masses. After azimuthator 3, the plasma stream enters the separation volume formed by the longitudinal magnetic field creation system 5, the radial electric field creation system — electrodes 6 and 8, the receivers of the separated SNF elements 6, 7, and 8. In the separation volume, the spatial separation of the SNF ions into 3 groups : M _I in the range of mass numbers of 85 to 106, M _II - 134 ÷ 155 M _III - 235 ÷ 244 which fall respectively on two cylindrical receiver 6 and 8 radii r ₁ and r ₂ and a length L _Zmax ≤6R and an end ring receiver 7 located directly about behind cylindrical receivers. Examples of calculations of SNF ion trajectories for various central masses M ₀ (134, 139 and 155) are shown in FIGS. 5, 6, 7. The radius of the inner cylindrical receiver can be selected in the range 0.596R ÷ 0.6765R; the length of the cylindrical receivers (position of the end receiver) does not exceed 2.5R (R is the average radius of the plasma stream).

Claims (2)

1. A method for plasma separation of spent nuclear fuel, including obtaining a quasi-neutral axially symmetric multicomponent cylindrical plasma flow using a plasma accelerator, transporting a plasma flow through an azimuth transverse radial magnetic field, transporting a mass-separated plasma flow through a separating volume with a stationary radial electric field and uniform constant longitudinal magnetic field, the magnitude of which is sufficient to magnetize the electron new, the ion paths are determined by the action of an electric field, the compensation of the space charge of the plasma stream, the collection of ions on the receivers, characterized in that they create a plasma stream containing ions of chemical elements that make up the spent nuclear fuel with masses from 85 to 106, 134 ÷ 155 235 ÷ 244 and picking up ions are produced in accordance with the selected ions in three groups of spent nuclear fuel on the receiver 3 ions, two of which are arranged on cylindrical surfaces of radii r ₁ - for at ma ions of the third group and r ₃ - ions for receiving a first group of length determined by the formula
L _Zmax ≤6R,
where L _Zmax is the length of the cylindrical receivers, m;
R is the radius of the Central path of the ion flow, m,
while the ions of the second group are collected at the end receiver. 2. A device for plasma separation of spent nuclear fuel containing a plasma accelerator, an azimuthator, a separating volume, a system for creating a longitudinal magnetic field in a separating volume, a system for creating a radial electric field in a separating volume, a source of tracking electrons, characterized in that it further comprises a phase transformations, providing the conversion of spent nuclear fuel into the vapor phase and steam supply to the plasma accelerator, two ion receivers, and the plasma cathode of the accelerator with the anode layer is combined with the azimuthator, two detectors of the separated components of the ion beam of spent nuclear fuel chemical elements are made in the form of cylinders of radii r ₁ and r _{2 of} length L _Zmax , determined by the formula
L _Zmax ≤6R,
where L _Zmax is the length of the cylindrical receivers, m;
R is the radius of the central trajectory of the ion flow, m, and the third receiver is in the form of a ring located at the end of the separating volume directly behind the cylindrical receivers, and the radii of the cylinders of the receivers are made in accordance with the relations
G (M _III.min, r ₁ ) = 0;
G (M _I.max , r ₂ ) = 0,
Where

where M _III.min is the minimum mass of an ion from group III of transuranic elements of spent nuclear fuel, kg;
M _I.max - maximum mass of an ion from group I of the lightest fission products of spent nuclear fuel, kg;
M ₀ is the mass of the central mass ion from group II, which does not have a radial velocity component, kg;
M is the mass of the ion, kg;
R is the average radius of the plasma stream, m;
r is the radius of ion motion, m;
r ₁ is the radius of the inner cylindrical ion receiver, m;
r ₂ is the radius of the external cylindrical ion receiver, m

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