WO2020106181A1 - Способ дезактивации элемента конструкции ядерного реактора - Google Patents
Способ дезактивации элемента конструкции ядерного реактораInfo
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- WO2020106181A1 WO2020106181A1 PCT/RU2019/000816 RU2019000816W WO2020106181A1 WO 2020106181 A1 WO2020106181 A1 WO 2020106181A1 RU 2019000816 W RU2019000816 W RU 2019000816W WO 2020106181 A1 WO2020106181 A1 WO 2020106181A1
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- electrode
- discharge
- inert gas
- cathode
- structural element
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/28—Treating solids
- G21F9/30—Processing
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
- G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
- G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes
- G21F9/004—Decontamination of the surface of objects with chemical or electrochemical processes of metallic surfaces
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
- G21F9/005—Decontamination of the surface of objects by ablation
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/007—Recovery of isotopes from radioactive waste, e.g. fission products
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/28—Treating solids
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/24—Generating plasma
- H05H1/26—Plasma torches
- H05H1/32—Plasma torches using an arc
- H05H1/34—Details, e.g. electrodes, nozzles
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Definitions
- the present invention relates to the field of nuclear engineering and can be used in nuclear energy technologies designed for the decontamination and safe handling of radioactive structural elements of nuclear power plants (NPP), in particular, for the surface decontamination of irradiated reactor graphite and metal structures in contact with the coolant.
- NPP nuclear power plants
- irradiated reactor graphite see, for example, patents RU 2546981, RU 2212074, EP1771865, US 9040014, which include heat treatment of reactor graphite in an inert and then in an oxidizing or reducing gas atmosphere with the release of gaseous compounds of radioactive isotopes and subsequent binding them in liquid or solid form.
- the method according to the patent RU 2212074 comprises isolating oxides of carbon isotope 14 C from the irradiated reactor graphite heated air purge mode at a temperature of 450 ° C to 530 ° C and subsequent chemical bonding.
- the disadvantages of these analogs include the impossibility to provide mainly surface cleaning of graphite (up to several microns in depth) due to the nonlocal nature of the thermal effect on the graphite surface due to its high thermal conductivity (deep layers are also heated). Another disadvantage is the formation of carbon oxides 14 C and other radio active isotopes in volatile form, which requires their further chemical bonding with an increase in the volume of generated radioactive waste in the liquid and solid phase.
- the disadvantages of the known processing methods include the need for preliminary dismantling and grinding of graphite blocks and structural elements of nuclear power plants with an initially high level of radioactivity, which worsens the radiation safety conditions of personnel and increases the complexity of the work.
- the method of plasma processing of graphite involves grinding it into fractions, followed by their placement in a plasma chemical reactor as consumable electrodes, which are then evaporated in a low-temperature plasma with an oxidizing agent. On the walls of the plasma-chemical reactor, the reaction products are precipitated in the dispersed phase in the form of an ash residue. Gaseous reaction products are removed from the reactor, carbon oxides are transferred to the liquid phase and sent for further disposal. The solid ash residue is recovered from the plasma chemical reactor for subsequent disposal.
- the disadvantages of the proposed method is the complexity of extracting the radioactive ash residue formed on the walls of the plasma chemical reactor, and the lack of a mechanism for the selective removal of contaminants with the highest concentration of radioactive isotopes.
- a known method for cleaning irradiated graphite bushings of a uranium-graphite reactor includes heating, gas treatment, transferring impurities to the gas phase, cooling the carbon material, while the process is continued until the graphite bush is completely evaporated.
- the disadvantages of the known method selected for the prototype is the need for disassembly and transportation of radioactive structural elements into the plasma-chemical chamber, which worsens the conditions of radiation safety of personnel, increases the complexity of the work.
- Another disadvantage of the method chosen for the prototype is the lack of a mechanism for the selective removal of contaminants with the highest concentration of radioactive isotopes.
- the task to which the proposed method is aimed is to create a technology for the decontamination of structural elements of a nuclear reactor by plasma spraying the surfaces of irradiated structural elements of a nuclear power plant and graphite masonry, which are predominantly contaminated with radioactive isotopes during operation, to knock these radionuclides from the surface together with surrounding atoms, deposition them to the cooled collector and subsequent extraction together with the collector.
- the technical result achieved by the present invention is that when plasma spraying the surface of structural elements of nuclear power plants and graphite masonry, as the most contaminated with radioactive isotopes, a significant decrease in the radioactivity of the processed structural elements of nuclear power plants, as well as concentration and a corresponding reduction in the volume of generated radioactive waste, is achieved.
- the specified technical result is achieved due to the fact that in the method of deactivating a structural element of a nuclear reactor, including processing a structural element of a nuclear reactor with low-temperature plasma while supplying a stream of chemically inert gas, according to the claimed solution, an electrode is supplied to the selected site on the surface of the structural element, a plasma discharge is ignited between the surface a structural element connected as a cathode and an electrode connected as an anode, select the discharge operating parameters that are effective for sputtering the cathode, atomize the cathode, cool the electrode and the gas line that removes the chemically inert gas from the discharge zone to a temperature sufficient to precipitate atomized atoms on the surface of the electrode and the line, after the cathode is sprayed to a predetermined depth, the electrode is moved to a new selected treatment site and the process is repeated until the entire surface of the deactivated structural element is completely treated ktsii.
- internal surfaces of the primary circuit of a nuclear reactor as well as its constituent pipelines and coolant circulation systems, can be used as structural elements.
- Argon or nitrogen are preferably used as the chemically inert gas.
- the electrode may be made of copper, or of aluminum, or of aluminum alloy, or of refractory metal, or of tantalum.
- the electrode and the gas line that removes chemically inert gas from the plasma discharge zone can be cooled by forced circulation of a liquid or gaseous refrigerant having a predetermined inlet temperature.
- the shape of the surface of the electrode is preferably chosen similar to the shape of the surface of the workpiece, so that the gap between the electrode and the workpiece is constant across the entire surface.
- the pressure of the supplied inert gas of the order of atmospheric or lower is preferably selected as the operating parameter of the discharge.
- the gap between the electrode and the surface is predominantly set so that it does not exceed 100 mean free paths of an electron at an inert gas operating pressure.
- the plasma discharge voltage can be set between the electrode and the surface in the range from 300 to 1000 volts.
- the plasma discharge current density in the range of 0.1 - 1 A / cm2 can be set as the working parameter of the discharge.
- the pulse-periodic regime of the plasma discharge can be selected as the working parameter of the discharge, and the pulse duration and duty cycle can be determined by the productivity of the process of mass transfer of atomized atoms to the anode and taking into account the cooling rate of the electrode.
- the temperature of the surface of the electrode and the line, sufficient for the deposition of atomized atoms, is preferably chosen equal to the temperature at which the pressure of saturated vapors of the deposited atoms is from 0.01 to 10 Pa.
- the atomization depth of the cathode is mainly controlled by the level of residual radioactivity after processing the site on the surface of a structural element of a nuclear reactor.
- the structural element of the nuclear reactor is treated with low-temperature plasma when a flow of chemically inert gas is supplied, and, unlike the prototype, in the proposed technical solution, an electrode is brought to the selected site on the surface of the treated structural element, and a plasma discharge is ignited between by the surface of the structural element as the cathode and the electrode as the anode, discharge parameters are selected for efficient cathode atomization, the electrode and gas line are cooled, which removes chemically inert gas from the discharge zone to a temperature sufficient to deposit atomized isotopes on the electrode and line surfaces, after the cathode is atomized to a predetermined depth, the electrode is moved to a new selected processing site and repeat the operation of the method until the entire surface of the decontaminated structural member is completely treated.
- the deposition of atomized surface atoms and radioactive isotopes is carried out on the surface of the cooled electrode in mass transfer mode. Spraying a surface with any geometry and any elemental composition is ensured by the formation of a near-surface cathode plasma layer with controlled energy of the bombarding ions. This allows decontamination at the nuclear power plant location until it is completely disassembled: the plasma source on the manipulator moves sequentially, step by step, on all internal surfaces of the reactor primary circuit, as well as on the surface of the graphite masonry, while surface atoms enriched in isotopes are transferred to the surface of the cooled metal electrode, which is made, for example, of copper or aluminum.
- An electrode with a concentrated highly active precipitate is periodically removed and can either be compactly buried or used as a concentrate with a high degree of enrichment with the desired isotope (in particular, 14 C) for useful use in medicine.
- the proposed method requires only the cost of electricity and the supply of an inert gas (argon) with its recirculation. This method will allow you to preliminarily reduce the activity of all reactor structures before repair or final disassembly and disposal, to avoid the formation of a large volume of liquid radioactive waste, which will occur with competing methods of radiochemical decontamination, as well as additionally obtain some useful isotopes in significant quantities.
- the invention is illustrated by the following graphic materials.
- Figure 1 schematically shows a fragment of a vertical section of the active zone of a graphite nuclear reactor, as well as the formation scheme carbon isotopes of 14 C in collisions of neutrons with nitrogen atoms and subsequent diffusion of 14 C with the deposition and accumulation of graphite masonry on the surface.
- Figure 2 shows a diagram explaining the transfer of coolant radioactive isotopes from the core and their deposition on the surface of the structural elements of the primary reactor loop.
- Fig. 3 is a sectional view for explaining a general view of a sectional view of a plasma source device; for ease of understanding, the power source, gas supply lines, and electric voltage are not shown.
- FIG. 4 is a block diagram explaining in general terms the main elements of a plasma surface treatment plant.
- radionuclides formed in the active zone enter the coolant, are transferred as a result of its circulation, and settle on the inner surfaces of the metal structures of the reactor primary circuit, for example, VVER type.
- VVER type for example, VVER type.
- 14 C radionuclides are formed by neutron bombardment of gaseous nitrogen, blowing graphite masonry, and also settle on the masonry surface.
- the proposed method of plasma decontamination of structural elements of nuclear power plants is based on the ion sputtering of surface atoms in an inert gas plasma and the collection of atomized atoms on a removable substrate, followed by its extraction and burial.
- One example of the implementation of the proposed method is the purification of irradiated reactor graphite from 14 C, 60 Co, 134 Cs, 137 Cs and other radionuclides, among which the most active is the 14 C isotope, which has a half-life of 5730 years and produced in the process of operation in significant quantity.
- the main reaction leading to the formation of a carbon isotope of 14 C is the neutron capture reaction of 14 N (n, p) 14 C with a cross section of 1.8 barn, which occurs in a helium medium - a nitrogen mixture used to purge graphite masonry.
- the concentration of the gas mixture is ⁇ 10 19 cm 3
- the ratio of helium to nitrogen concentration is 6/4
- the nitrogen concentration is 0.4-10 19 cm 3
- the neutron fluence (full flux) for 30 years of operation of the reactor is 10 22 neutrons / cm 2 .
- the concentration of 14 C carbon accumulated in 1 cm 3 of space filled with a gas mixture over 30 years as a result of neutron capture of 14 N (n, p) 14 C is estimated by the formula:
- [ 14 C] [N 2 ] ⁇ s ( 14 N ( h , r) 14 C) ⁇ [F h ] (1)
- o ( 14 N (n, p) 14 C) is the neutron capture cross section, [N 2 ] - nitrogen concentration and [ ⁇ ⁇ ] - neutron fluence, while the value of the accumulated concentration [ 14 C] will be ⁇ 0.7-10 17 cm 3 .
- 4 C is determined by the formula:
- [ 14 ⁇ ] [ 13 ⁇ ] ⁇ quip ( 13 ⁇ ( ⁇ , êt) 14 ⁇ ) ⁇ [ ⁇ ⁇ ], (26) where [ 14 ⁇ ], [ 13 ⁇ ] and [ 12 ⁇ ] are the concentrations of carbon isotopes - 14, 13 and 12,
- FIG. 1 schematically shows the mechanism of formation in the gas phase and the deposition of carbon 14 C on the surface.
- Nitrogen atoms 1, colliding with neutrons 2 in a nitrogen-helium mixture filling the reactor space, are transformed as a result of reaction (1) into carbon isotopes 14 ⁇ - 3 and are deposited on the surfaces of graphite blocks 4, graphite rings 5, which surround the technological channel with a fuel assembly 6.
- the vertical arrows (from bottom to top) show the direction of supply of the nitrogen-helium mixture into the reactor space to cool the masonry.
- the gap between the surface of the graphite masonry blocks and the process channel with the fuel assembly is approximately 1 mm (this is the thickness of the gas layer above the surface).
- the enrichment of the entire surface of the graphite block with a cross section of 25x25x60 cm is 5-10 19 atoms of 14 C, which is an order of magnitude higher than the volume enrichment of graphite with the 14 C isotope the result of neutron bombardment during operation.
- additional surface contamination of the graphite masonry with the 14 C isotope can be caused by the penetration and intercalation of gaseous nitrogen between the graphene layers forming the surface layers of graphite, followed by the conversion of intercalated nitrogen atoms to 14 C at neutron bombardment.
- the proposed method will find application to remove radioactive contaminants of the primary reactor loop (in particular, VVER or RBMK type), which occur due to the precipitation of active isotopes in the form of insoluble sediment on the internal surfaces of the primary circuit during the circulation of the coolant.
- radioactive contaminants of the primary reactor loop in particular, VVER or RBMK type
- the causes of radioactive contamination of the coolant can be distinguished: neutron irradiation of coolant impurities, oxides of structural materials resulting from corrosion processes, as well as the violation of the tightness of fuel assemblies with the subsequent ingress of radioactive elements into the coolant.
- the heat transfer medium of radioactive isotopes and their deposition on the surfaces of the elements of the primary reactor loop are illustrated in FIG. 2.
- radioactive isotopes 7 (indicated by asterisks) is formed in the area of the fuel assemblies in reactor 8. Further, these radionuclides are dispersed due to the circulation of the coolant (the direction of circulation is indicated by dashed arrows) through the steam separator 9, main circulation pump 10, turbine 11, generator 12, a capacitor 13, a feed pump 14, contaminating the surfaces of these elements of the primary circuit. To complete the picture in figure 2. The direction of movement of the water of the 2nd cooling circuit to the spillway 15 and the direction of the water from the reservoir 16 are shown. The radionuclides deposited on the surfaces cannot penetrate deeply into structural elements and pipelines, because they are made of high strength stainless steels, so the decontamination method due to plasma spraying the deposited surface layer of contaminants is effective.
- the method is as follows.
- the processing of a structural element of a nuclear reactor with low-temperature plasma is carried out by supplying a stream of chemically inert gas, which is discharged from the treatment zone using a gas line.
- Argon or nitrogen, chemically inert gases that do not enter into chemical reactions with atomized atoms, are predominantly used as a chemically inert gas.
- the deactivated surface of the structural element is chosen as the cathode, and the electrode serves as the anode.
- Deactivated structural elements can be the surfaces of the irradiated graphite masonry of a nuclear reactor, the inner surfaces of the primary circuit of a nuclear reactor, as well as its constituent pipelines and coolant circulation systems.
- An electrode is brought to the selected site on the surface of the structural element, a plasma discharge is ignited between the electrode and the surface of the structural element, and the cathode surface is sprayed.
- the operating parameters of the discharge are selected based on the conditions of effective atomization of the cathode.
- the operating parameters of the discharge ensuring effective atomization of the cathode surface
- a number of indicators are selected that depend on each other, while the pressure of the supplied inert gas is chosen on the order of atmospheric or lower, the gap between the electrode and the surface is chosen so that it does not exceed 100 mean free paths of the electron at an inert gas operating pressure, the plasma discharge voltage is also established between the electrode and the surface in the range from 300 to 1000 Volts, and the plasma discharge current density in the range of 0.1 - 1 A / cm2.
- the pulse periodic mode of the plasma discharge can be selected as the working parameter of the discharge, and the pulse duration and duty cycle can be determined by the productivity of the process of mass transfer of atomized atoms to the anode and taking into account the cooling rate of the electrode.
- the electrode may be made of copper, aluminum or an aluminum alloy, as well as of refractory metal or tantalum.
- an electrode made of refractory metal it is possible to maintain the temperature of the electrode high enough to condense less volatile atomized atoms on the surface of the electrode, and more volatile - on the surface of the gas line that removes chemically inert gas.
- the shape of the surface of the electrode is preferably chosen similar to the shape of the surface of the workpiece, so that the gap between the electrode and the workpiece is constant across the entire surface.
- isotopes are sprayed, and therefore the atomized isotopes are deposited on the surfaces of the failed electrode and gas line by cooling the latter. That is, they cool the electrode and the gas line, which removes the chemically inert gas from the discharge zone, to a temperature sufficient to deposit atomized atoms on the surface of the electrode and the line after the cathode is sprayed to a predetermined depth. After that, the electrode is moved to a new selected treatment site and the process is repeated until the entire surface of the decontaminated structural member is completely treated.
- the electrode and the gas line which removes chemically inert gas from the plasma discharge zone, can be cooled by forced circulation of a liquid or gaseous refrigerant having a predetermined inlet temperature, while creating such a temperature distribution along the length of the gas line, which removes chemically inert gas and atomized atoms from the plasma discharge zone, that atomized atoms with different evaporation temperatures will condense in different sections of the pipeline.
- the temperature of the surface of the electrode and the line, sufficient for the deposition of atomized atoms, is preferably chosen equal to the temperature at which the pressure of saturated vapors of the deposited atoms is from 0.01 to 10 Pa.
- the atomization depth of the cathode is controlled by the level of residual radioactivity after processing the site on the surface of the structural element of a nuclear reactor.
- FIG. 1 A general view of a device for implementing plasma surface spraying, collection and removal of radionuclides is shown in FIG.
- the discharge is ignited between the treated surface — the cathode (K) and the positively charged cooled copper (or aluminum) electrode — the anode (A).
- An inert gas argon, xenon, helium, neon
- a glow discharge occurs as a result of applying voltage between the electrodes (A) and (K), fast electrons generated in the discharge 18 collide with inert gas atoms 19 and lead to the formation of positively charged inert gas ions 20.
- the distribution of potential V along the length of the discharge gap d is presented on the right side of FIG.
- sputtering occurs when a chemically inert gas is supplied to the discharge gap, the discharge is ignited, and the spray products 21 are pumped out, at which they are deposited on the cooled electrode (A). It is advisable to use argon as a chemically inert gas, as it is cheaper and has the necessary electrophysical properties, as well as nitrogen.
- the applied voltage between the surface to be treated and the electrode for igniting a discharge in argon should be at least 100 V.
- the sputtering speed of the cathode material V p which characterizes the thickness of the removed material layer per unit time at a given ion current density, is:
- V P K ⁇ j ⁇ MJe ⁇ N a ⁇ p (3)
- e is the electron charge, C
- p is the density of the material, g / cm 3
- j is the ion current density, A / cm 2
- M s the mass of atoms of the material (carbon), g / mol
- N a - Avogadro number, mole 1 or
- Atomized atoms from the treated surface diffuse in the argon atmosphere from the cathode to the substrate (anode), in our case, diffusion is described by the one-dimensional Laplace equation with boundary conditions at the cathode and anode:
- n (x) is the concentration of atomized atoms of the treated surface (cathode)
- F is the flux density of atomized atoms leaving the cathode
- D is the diffusion coefficient of atomized atoms in an inert gas medium
- the solution to equation (4) is the function:
- n (x) F ⁇ (dx) / D (5) showing a linear decrease in the concentration of atomized atoms from the cathode to the anode, while the flux density of atomized atoms leaving the cathode is maintained along the entire length of the gap between and is equal to the atomic flux density reaching the collector .
- the optimal experimental conditions for ignition of the discharge vary over a wide range: pressure and composition of the working chemically inert gas or working mixture (Ar, Xe, Kg, N2, etc.), the distance between the working electrode and the surface to be treated, the magnitude of the applied voltage, the current density in the discharge.
- the discharge can be ignited in a stationary or pulse-periodic mode, depending on the state of the sprayed surface and the required energy input into the plasma, while the period and duration of the pulse can vary widely to achieve the optimal gas temperature in the discharge gap.
- cool the electrode and the gas line which removes chemically inert gas from the plasma discharge zone, by forcing the circulation of a liquid or gaseous refrigerant (for example, water or liquid nitrogen vapor) having a predetermined inlet temperature.
- a liquid or gaseous refrigerant for example, water or liquid nitrogen vapor
- the deposition and reverse evaporation rate of a given type of atoms is determined by the pressure of saturated vapors of this substance; therefore, the temperature of the surface of an electrode or a section of a line designed to deposit specified atomized atoms can be chosen in the range in which the pressure of saturated vapors of the deposited atoms is, for example, 0 01 - 10 Pa.
- the electrode is made of refractory metal (for example, tantalum Ta) so that its temperature can be kept high enough due to the plasma energy or an additional heating source (for example, 2000 ° C) in order to condense more volatile atomized atoms (Co, Cs, etc.) no longer on the surface of the electrode, and on the surface of the colder sections of the gas line, which removes chemically inert gas.
- refractory metal for example, tantalum Ta
- isotopes of 14 C, 40 Co, 41 Ca, 137 Sr, 137 Cs can be selectively obtained by deactivating radioactive contaminated elements of nuclear power plants.
- a plasma source with a size of 10> ⁇ 10 cm moves on the manipulator step by step, covering all points of the inner surfaces of the reactor primary circuit, as well as along the surface of the graphite masonry, while surface atoms enriched in isotopes are transferred to the surface of the cooled collector (anode) and the exhaust gas line .
- Radiation detectors can also be mounted on an additional manipulator to control the degree of decontamination of treated surfaces.
- FIG. 1 A block diagram of a surface treatment device whose operation is based on the proposed method is shown in FIG.
- the discharge module 22 and its parameters are controlled remotely using a computer 23, the parameters of the ignition of the discharge are set and monitored using a power supply 24, a key 25, and a current meter 26.
- An electrode with a concentrated highly active precipitate is periodically removed and can be either compactly buried or used as a concentrate with a high degree of enrichment with the desired isotope (in particular, 14 C) for useful use in medicine.
- One example of the invention is the ignition of a direct current plasma discharge in argon at a pressure of P ⁇ 0.1 atm, the collector (anode) is installed at a distance of 2 mm above the surface of deactivated graphite.
- the operating voltage at the discharge gap is set by the power supply in the range of 300-1000 V, necessary for ignition of the discharge, and then is adjusted to the optimal value, necessary for the stability of the discharge and to achieve the desired current density.
- the sputtering coefficient of graphite by argon ions with an energy in the range of 100-500 eV (ion energy after passing through the cathode plasma layer) is 0.03-10, 1 [4].
- the rate of atomization of carbon by argon ions will be 0.75-10 5 cm / s, and it will take ⁇ 13 s to spray a graphite layer 1 ⁇ m thick.
- the thickness of surface contamination of graphite blocks due to the deposition of 14 C from a nitrogen-helium mixture to the surface, as well as the conversion of 14 C of intercalated nitrogen in the surface layer of graphite does not exceed 1 ⁇ m.
- about 1000 seconds will be required for plasma processing of the surface of a graphite block with dimensions of 25x25x60 cm and a surface area of 7250 cm 2 with a plasma electrode of 100 cm 2 to a depth of 1 ⁇ m.
- the total surface area of the graphite masonry of the RBMK type reactor is about 1.4-10 8 cm 2 , and the total time for processing the surface layer with a thickness of 1 ⁇ m of the entire graphite masonry of the RBMK reactor (while using 10 devices based on the proposed method at the same time) is approximately 2-10 6 s, those. about 1 month.
- Another example embodiment of the invention is the ignition of a direct current plasma discharge in argon at a pressure of P ⁇ 0, 1 atm, the collector (anode) is installed at a distance of 2 mm above the deactivated surface of steel (iron).
- the operating voltage at the discharge gap is set by the power supply in the range of 400-600 V.
- the sputtering coefficient of iron atoms with argon ions with an energy in the range of 100 - 500 eV is 0.2–10.0 [4].
- the rate of atomization of iron by argon ions will be 7-10 5 cm / s, and it will take time ⁇ to ⁇ 1 ⁇ m of a steel layer with precipitated impurities with a thickness of 1 ⁇ m from a selected site 1.3 s
- a third embodiment of the invention is the ignition of a plasma discharge of a direct current in an argon medium at a pressure of P ⁇ 0, 1 atm, the collector (anode) is installed at a distance of 2 mm above the deactivated surface of stainless steel (chrome).
- the operating voltage at the discharge gap is set by the power supply in the range of 400-600 V.
- the sputtering coefficient of chromium atoms by argon ions with an energy in the range of 100 - 500 eV is 0, 12 -10, 6 [4].
- the rate of atomization of iron by argon ions will be 4 10 5 cm / s, and for atomization of a layer of steel with precipitated impurities 1 ⁇ m thick from a selected site of the structural element of the 1st reactor loop, thus ⁇ 2 s will be required.
- a fourth embodiment of the invention is the ignition of a plasma discharge of direct current in a nitrogen atmosphere, the collector (anode) is installed at a distance of 2 mm above the deactivated surface of graphite.
- the operating voltage at the discharge gap is set by the power supply in the range of 400-600 V.
- the atomization coefficient of carbon atoms by N + nitrogen ions with an energy in the range of 100 - 500 eV is 0.2–10.5 [6]
- the atomization coefficient of carbon atoms by nitrogen ions is 1 g + with an energy of 150 eV is 0.5, which is an order of magnitude higher than the sputtering coefficient of argon ions [7].
- the rate of spraying and transfer of material to the collector under conditions of prevailing N2 + ions, as well as the decontamination performance increases by an order of magnitude.
- the contaminated surfaces of the primary structures of the reactor contain a number of radionuclides that can be sufficiently selectively collected for subsequent useful use, for example, for the production of radioisotope energy sources, fire safety sensors, applications in nuclear medicine and as isotopic indicators.
- the selective separation of various radioactive atoms sprayed in an inert gas medium (argon, xenon) from contaminated surfaces can be achieved by controlling the collector temperature (by changing the energy input into the plasma gap and the corresponding heating electrodes) and the temperature distribution along a gas line that discharges an inert gas.
- the temperature of the electrode and the adjacent section of the outlet gas line are maintained at about 2200 ° K, then only carbon atoms, including the 14 C isotope, will be deposited in this region, and other atoms will move further along the outlet gas line along with a stream of heated inert gas. As the gas stream moves along the discharge line, the inert gas and the atomized atoms carried by it will cool. In the section of the exhaust gas line, where the gas temperature reaches a value of about 1700 ° K, the deposition of Co atoms from the flux, including the isotope 60 Co, will begin.
- the cesium and its isotope 137 Cs sprayed from the treated surface (half-life of 30 years, specific activity of 9 10 2 Bq / g in reactor graphite) will begin to condense (at At this temperature, the density of saturated cesium vapor Cs is 10 1 Pa).
- the exhaust gas line is disassembled into segments with selectively separated isotopes, and they can be used for their intended purpose.
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CN201980043442.5A CN112655056A (zh) | 2018-11-21 | 2019-11-14 | 核反应堆结构元件的去污方法 |
EP19888171.6A EP3886117A4 (en) | 2018-11-21 | 2019-11-14 | METHOD FOR DEACTIVATING A STRUCTURAL ELEMENT OF A NUCLEAR REACTOR |
BR112020026838-0A BR112020026838A2 (pt) | 2018-11-21 | 2019-11-14 | Método para descontaminar um elemento estrutural de um reator nuclear |
CA3105179A CA3105179A1 (en) | 2018-11-21 | 2019-11-14 | Method for decontaminating a structural element of a nuclear reactor |
EA202092704A EA202092704A1 (ru) | 2018-11-21 | 2019-11-14 | Способ дезактивации элемента конструкции ядерного реактора |
JP2020573545A JP2022511216A (ja) | 2018-11-21 | 2019-11-14 | 原子炉の構造要素の汚染を除去する方法 |
KR1020207037556A KR20210094460A (ko) | 2018-11-21 | 2019-11-14 | 핵 원자로 구조 요소에 대한 오염 제거 방법 |
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US20210272715A1 (en) | 2021-09-02 |
BR112020026838A2 (pt) | 2021-08-24 |
CA3105179A1 (en) | 2020-05-28 |
EA202092704A1 (ru) | 2021-08-09 |
CN112655056A (zh) | 2021-04-13 |
KR20210094460A (ko) | 2021-07-29 |
EP3886117A4 (en) | 2022-07-20 |
JP2022511216A (ja) | 2022-01-31 |
RU2711292C1 (ru) | 2020-01-16 |
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