RU2371792C2 - Method and plant for recycling of spent nuclear fuel - Google Patents

Abstract

FIELD: fuel systems. ^ SUBSTANCE: invention is related to recycling of return nuclear fuel (RNF) and materials of blanket region (BR) of fast breeder reactors (FBR) for their multiple use with the possibility to adjust content in creation of a new fuel composition. Initial chemical state of processed material may vary: oxides, nitrides, metals and alloys. Method represents a combination of serial processes of chemical transformation of radiated nuclear fuel (RNF): fluoridation with gaseous fluorine and extraction of main uranium mass; transition of fluoridation remains into oxides (pyrohydrolysis); - chlorination of oxides in recovery conditions with group separation of plutonium chlorides, uranium (left in process of fluoridation) and fission products. Further "plutonium" and "uranium" fraction, and also fraction containing fission products (and, possibly, minor-actinides), are used each separately in various processes according to available methods. Earlier produced uranium hexafluoride, with low boiling fluorides of fission products, is cleaned from the latter and used, according to objectives of processing, also by available methods. Using waterless processes with application of salt melts, suggested version makes it possible to realise continuous highly efficient processes of fuel components production, moreover, it is stipulated to carry out preparation stages in continuous mode. Plant for processing of spent nuclear fuel containing uranium and plutonium includes three serially installed devices: fluoridiser; pyrohydrolysis device; chlorinator-condensator-granulator device. Two last devices are of flame type. The last of devices represents a pipe with a central element, in which lines of inlet product and reagents supply are installed. In lower part there is an expansion in the form of pear with a flame burner along its axis, and medium part has a row of conical shelves inside, between which there are nozzles with pipelines for chlorides outlet. Nozzle for chlorides outlet is also arranged in lower point of pear-like part. Nozzle for exhaust of non-condensed gases is provided in upper part. Granulator is arranged as reservoir with low boiling incombustible liquid, and to produce drops, capillaries are provided at pipeline ends. ^ EFFECT: highly efficient method for processing of spent nuclear fuel of practically any composition from thermal reactors and fast breeder reactors, blanket region of fast breeder reactors and some other types of reactors with the possibility to produce several other types of fuel compositions. ^ 19 cl, 3 dwg

Description

The invention relates to the field of nuclear energy, in particular to the regeneration (reprocessing) of recycled nuclear fuel (SNF) and materials of the reproduction zone (3B) of fast neutron reactors (RBN) for their repeated use with the possibility of adjusting the composition when forming a new fuel composition. The initial chemical state of the processed materials may be different: oxides, nitrides, metals and alloys.

The classical (water) method for processing spent nuclear fuel [Chemical technology of irradiated nuclear fuel. Ed. V.V.Shevchenko. - M., Atomizdat, 1971] is widely known and, along with advantages, has two major disadvantages:

- a large amount of liquid waste (high costs of their transfer to a less dangerous state);

- low radiation resistance of the applied aqueous and organic media (inability to work with low-cooled SNF, additional fire and explosion hazard).

Known fluoride-gas method of processing spent nuclear fuel [Jonke A.A. Reprocessing of nuclear Reactor Fuels by Processes, based on Volatilization, fractional Distillation and selective Adsorption. Atomic Energy Review, V.3, No. 1, 1965], which consists in the fluorination of crushed oxide SNF, the conversion of the total amount of U and Pu together with many elements - fission products (PD) into volatile low boiling fluorides (NFC). Next, U and Pu are freed from these NKF (carry out their cleaning). Further, together or separately purified hexafluorides U and Pu can be used in different scenarios:

- enrichment of the isotope ²³⁵ U;

- Separate processing into dioxides (including the method of pyrohydrolysis);

- joint conversion to fuel (MOX, including the method of pyrohydrolysis).

The method is characterized by high productivity at the head stage (fluorination, separation of uranium and other NKF from non-volatile high-boiling fluorination “residues” (VKOF)), the ability to conduct correction of uranium isotope composition without intermediate transformations, followed by conversion of uranium hexafluoride by pyrohydrolysis into dioxide suitable for production fuel rods both according to the technology of vibration compaction (granular) and by the “tablet” technology (“cannon”).

The disadvantages of the discussed method:

1) thermal and radiation instability of plutonium hexafluoride, which lead to the formation of deposits of solid PuF ₄ in the equipment and piping used, which complicates their maintenance, reduces productivity and increases the radiation hazard;

2) the thermodynamic properties of uranium and plutonium fluorides are such that the equilibrium of PuF ₆ + UF ₄ → PuF ₄ + UF _{6 is} strongly shifted to the right, that is, only after complete conversion of uranium to the gas phase is it possible to transfer plutonium to the gas phase, moreover, to completely transform plutonium into hexafluoride requires a significant excess of fluoride.

A variant can be implemented in which plutonium is not fluorinated to hexafluoride, leaving it in the total amount of VKOF in the form of PuF ₄ ; for this, some fraction of uranium (a fraction of a percent) is not transferred to the gas phase. Then, uranium hexafluoride is supplied, as in the previous analogue example, and VKOF is converted to molten salts, then Pu can be purified from PD by the pyrochemical method and extracted in the form of PuO ₂ [V.F. Gorbunov et al. Journal of Radiochemistry, t.18, issue 1, p.109-114, 1976] or other known methods.

The disadvantage of this method is the low productivity of Pu extraction and purification, the impossibility of directly using the extracted PuO ₂ in vibration compaction technology, as well as the limited options for its transfer to other fuel compositions, except for oxide: metal (alloy), nitride (rigidity of the technology).

A known method of processing spent nuclear fuel using molten alkali metal chlorides [A.V. Bychkov, S.K.Vavilov, O.V. Skiba, P.T. Porodnov et al. Pyroelectrochemical Reprocessing of Irradiated FBR MOX Fuel. III. Experiment on High Burn-Up Fuel of the BOR-60 Reaktor. Proc. Int. Confer, on Fut. Nucl. Syst. GLOBAL'97. Oct.5-10, 1997, Yokohama, Japan], comprising dissolving the ground oxide SNF by bubbling chlorine gas. Then carry out:

- separation electrolysis with the allocation at the cathode of a fraction of U in the form of UO ₂ with a partial (or full) inclusion of electropositive PD: Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag;

- melt oxidation followed by bulk crystallization of PuO ₂ ;

- electrolysis of the extra recovery of U (in the form of UO ₂ ) with PD (part of REE) and components of structural materials (CCM);

- melt regeneration for its reuse (using sodium phosphate), PD remains in the melt: Sr, Ва, Cs.

The disadvantages of the discussed method are:

- transfer of U to a substandard state (which is unacceptable for spent nuclear fuel of thermal neutron reactors (RTN) and RB RB);

- low productivity due to the periodicity of the process, the operations of which (in several stages) are carried out in one apparatus, the bath of which has a short service life;

- the absence of other options for the allocation of Pu, except for bulk crystallization of PuO ₂ (inflexibility of the technology).

From available sources it is known that during chlorination (high temperature, the presence of a reducing agent), any oxides and mixtures of oxides can be converted to chlorides [Brief Chemical Encyclopedia / Ed. I.L. Knunyantsa, G.Ya. Bakharovsky, A.I. Busev, etc. M .: Soviet Encyclopedia, 1963]. It is known that the resulting chlorides have a significantly different boiling point (condensation) in the range of more than 1500 degrees [Goronovsky I.T., Nazarenko Yu.P., Nekryach E.F. A quick reference to chemistry. Kiev: AN USSR, 1967. P.40]. One can imagine the process by which oxides (SNF) are chlorinated, chloride pairs are sent to an extended condenser, in which increasingly low-boiling chlorides precipitate as the temperature decreases. However, a technical solution that allows high-performance chlorination of oxides and continuously removed from the condenser separated (in whole or in part) chlorides was not found.

The technical result of the invention (goal) is the development of a high-performance method for processing spent nuclear fuel of almost any composition (oxides, nitrides, metal alloys) from RTN, RBN, the reproduction zone of RBN and some other types of reactors with the possibility of producing several types of fuel compositions (oxides, nitrides, including U-Pu fuel based on a mechanical mixture, metals and alloys).

The essence of the invention lies in the fact that at the initial stage of the processing process, the crushed fuel is fluorinated, while U is partially left in VKOF, in this case Pu remains in a “non-volatile” state due to the thermodynamic properties. The bulk of U in the form of hexafluoride and all NKF PD are sent to the “uranium” redistribution, where the hexafluoride is purified by known methods, if necessary, the isotopic composition is corrected and, depending on the task, fuel compositions (oxide, nitride, metal, alloys) are produced by known methods ( preferably in continuous mode).

VKOF, including fluorides Pu, MA, and PD are transferred (by pneumatic transport or by gravity) to pyrohydrolysis (in a flame apparatus) for the purpose of conversion again to oxides by a generalized reaction

where n is the coefficient for determining stoichiometry;

Q ₁ is the thermal effect of the reaction, kJ / mol.

Since the heat Q ₁ for the reaction may not be enough, it is envisaged to obtain additional heat from the reaction

where Q ₂ is the thermal effect of the reaction, kJ / mol.

The contribution of reaction (2) (up to 100%) is determined depending on the productivity and is regulated by the supply of reagents. The reaction of burning hydrogen in oxygen by itself is easily controllable and can serve as a “standby”, supporting the apparatus in “standby mode” when there is no supply of input product and reagents.

Excess reagents and gaseous reaction products are not waste, since they can be separated by known methods and used again. Hydrogen fluoride, oxygen and hydrogen can be easily separated by step cooling and returned to the cycle [for example, see Pat. 1716574 of the Russian Federation. The method of purification of chlorine-containing gases from radioactive aerosol particles of actinides / R.K.Gazizov, L.G. Babikov, A.F. Sirotkin and others // BI, 1992. No. 8; Pat. 2071805 of the Russian Federation. A method of condensation of chlorine from exhaust gases and a device for its implementation / R.K.Gazizov, L.G. Babikov, A.F. Sirotkin and others // BI, 1997. No. 2].

Oxides are sent (by pneumatic transport or "gravity") to the stage of chlorination (reduction in a flame apparatus) according to a generalized reaction

where n and m are the coefficients for determining stoichiometry;

Q ₃ is the thermal effect of the reaction, kJ / mol.

The heat generated by the reaction Q ₃ may not be enough; to increase the heat generation, use the reaction

where Q ₄ is the thermal effect of the reaction, kJ / mol.

Since UO ₂ will be present in the input oxide product, when chlorinated in the presence of Cl ₂ , in addition to UCl ₄ , UCl ₅ and UCl ₆ can form.

To regulate the redox environment in the reaction zone, you can use the options:

- an increase in the proportion of H ₂ in reaction (4);

- the addition of UCl ₃ , U _(meth) or UH ₃ (all in a finely divided state);

- Additive Na in a vapor state.

Additives (except for UCl ₃ ) also contribute to the heat effect Q _add .

On the contrary, to increase the oxidizing abilities of the medium, it is possible to increase the addition of Cl ₂ (to reduce the proportion of H ₂ in reaction (4)).

Like the combustion of hydrogen in oxygen, reaction (4) is easily controllable and can also serve as a “standby”, maintaining the apparatus in “standby mode” when there is no supply of input product and reagents.

For some tasks, the stage of “chlorination-condensation” can play a leading role, i.e. The initial oxide SNF can come to the chlorination stage (after grinding: chemical for SNF RTN, as well as uranium SNF and RB RB material; mechanical - for mixed SNF RBN), then the “role” of the uranium component and low boiling chlorides (NLC) of PD will dominate.

High boiling chlorides (WCC) of PD and components of structural materials (CCM) (even taking into account their joint fusion) at the working temperature of reaction (3) can remain in the solid state. To transfer them to a liquid state (for withdrawal from the reaction zone), either the already mentioned addition of Na, which is converted to NaCl, or directly the addition of NaCl to the reaction zone, is provided. The options are:

- feed in a finely divided state with oxides or with gaseous reagents, which may be useful for controlling the reaction rate;

- feed in granular or molten state into the condensation zone of the water supply complex of PD and KKM.

Gaseous reaction products and excess reagents (HCl, H ₂ O, Cl ₂ , H ₂ ) pass through the condensation zones, then they are sent for cleaning from radioactive aerosols and other impurities by known methods and used again after separation, or discarded if it is cheaper.

Chlorides U (UCl ₄ ), Pu (PuCl ₃ ), minor actinides (MA), PD, CMC (as well as NaCl additive) will condense in and around the reaction zone at a temperature corresponding to their properties at the selected working pressure. Depending on the set technological task, the condensation of chlorides can be carried out in two (separation of only U and Pu) or several (from three to any reasonable n: separation of U, Pu, MA; group and individual separation of valuable PD) sections.

Two condensation options are possible:

- in a liquid state (including due to fusion of a mixture of chlorides close in boiling or sublimation temperature); in this case, the withdrawal of products from the condensation zone (including from each section) can be organized in a continuous mode. In addition, with a partial flow of liquid condensate from overlying areas to lower ones, a regime approaching distillation can be implemented, that is, with a more “strict” separation of chlorides into sections;

- in the solid (or, basically, in the solid state), then for each section periodical heating should be provided until the chlorides completely melt on the condensation surface or introduction of low-melting salt to the corresponding sections and their joint removal from the condensation zone.

After the products are removed from the condensation zone (in liquid form), it is desirable to transfer them to a state that is more convenient both for transportation (when loading into devices) and for temporary storage. For this, liquid salt melts are transferred into drops and this state is fixed by solidification (granulation) in a low-boiling non-combustible liquid (for example, CC1 ₄ ) or other known methods.

VKH PD and KKM with the addition of NaCl (or without it, if at the operating temperature liquid-phase systems of several components are formed and will not require additional solvent) will be further removed from the reaction zone, also passing through granulation.

Since U plays a “service role” (reduces the transition of Pu to NKF at the head stage), it must be looped, i.e. transfer by known methods into a finely divided oxide and transfer to the head of the process (for fluorination).

Further, each of the remaining products (possibly through the temporary storage stage) is sent for processing in accordance with the technological task, mainly for the production of fuel compositions of AR fuel rods. Moreover, many well-known options for producing alloys, individual metals, oxides, nitrides are possible; when combining fuel components with MA (in particular, U with Np), PD (for the purpose of their transmutation) both directly in the process of their production and for subsequent mixing in the manufacture of fuel elements, it is possible. and individual production of MA for their irradiation in the form of "targets". The chemical and physico-mechanical state of the intermediate products (oxygen-free granular soluble in the melt salts without chlorination) allows you to organize high-performance continuous processes for the production of fuel compositions.

The well-known advantages of pyrochemical processes (a small number of operations, the minimum amount of waste in a convenient chemical and aggregate form, intrinsic safety) are supplemented with the possibility of organizing continuous high-performance processes in apparatuses made of resistant materials. The proposed method allows you to process several types of fuel in chemical composition and get almost any type of it (the versatility of the technology for input products and its flexibility for the production of any type of fuel and fuel compositions). Constant maintenance of the most attractive fissile material (Pu) with highly active PDs and incomplete purification from them at the final stages of production (oxide, nitride, metal) complement its protection against unauthorized use.

Installation for implementing the proposed method differs from the known ones in that it includes 3 apparatuses designed for continuous operation. The transfer of solid-phase products (powders) between them is provided for by known methods (storage hopper and metering feeder or pneumatic transport, if it is not possible to place the devices under each other).

The sequence of their placement in the processing chain, the functions performed, the input products and reagents, the movement of products and the recycling of reagents are shown schematically in figure 1.

The apparatus 3 performs the functions of a chlorinator (3a), a condenser (3b) and a granulator (3c), it can also (for certain tasks) play the role of the head unit.

The chlorinator is a unit of the flame apparatus, including a feeder for feeding oxide powder, a device for supplying gaseous and finely divided solid reagents and additives (not shown). These solutions are known, and the present invention does not introduce significant features into them.

The capacitor is the inner surface of the walls of the chlorinator, divided into zones and subzones (sections). Plots or zones are equipped with individual devices to maintain the desired temperature (cooling or heating). Each section (or zone) is equipped with conical "shoulders" and exits of melted chlorides in the form of holes and pipelines with elements for heating. The zone of the torch and gas expansion is made in the form of a body of revolution, resembling a pear incomplete in the upper part, which has a funnel-shaped depression in the lower hemisphere. The “pear” is docked with the cylindrical part of the chlorinator, for the exit of gases there is an annular gap sufficient to ensure their “moderate” speed (of the order of 0.1-1.0 cm / s).

An element of the apparatus placed along the central axis, ending with nozzles, is equipped with a heater (not shown in the diagram) to create a temperature on its outer surface that is higher than at the same level of the opposite wall, while none of the chlorides on it harden.

The division of condensation zones II and III into sections equipped with “beads” allows one to derive condensation products both from separate (optional) sections, and to combine them from several sections, including from the whole zone.

For granulation, devices are provided for crushing liquid chlorides into droplets and containers with low-boiling liquid (not shown in the diagram), into which droplets fall and solidify in the form of granules. Other known devices for granulation (cooled rolls for solidification and crushing, devices for organizing relative movements of droplets and cooling gas, etc.) can be used.

The area on the path of the melt droplets from the nozzle to the surface of CCl ₄ must be sealed and filled with an inert gas (N ₂ , Ar) or CCl ₄ vapor.

The following are devices for extracting granules, drying and transporting them for use or temporary storage (not shown in the diagram).

During the operation of a chlorinator-condenser-granulator, conditions are possible under which part of the NCC can leave the condensation zone. On the way of the exhaust gases before their separation, a control trap with an intensely cooled container, which includes a pipe supplying gases, is provided. The container can be removed from the cooling slot for emptying. In order to prevent the slip of gases and NCC at this time, two control traps are provided with the possibility of switching the gas flow from one to the other.

Devices and devices for further operations for the production of fuel (or other purposes) are considered known, that is, the proposed solution does not introduce distinctive signs for them.

Figure 1, where operations (essential features) that do not contain new solutions (“uranium redistribution”) are summarized on the right and operations that have distinctive features on the left, a schematic diagram of the technological process according to the proposed method, which includes three located consistently continuous apparatus, the second and third of them are fiery. For ease of perception, “large-block” operations are given such as “Cleaning UF ₆ ”, “Recycling F ₂ ”, “Obtaining target products: PuO ₂ , PuN,

Pu _meth , Pu alloys and others, because the proposed solution does not introduce distinctive signs into them.

Figure 2 shows the basic structure of the third apparatus - a chlorinator-condenser-granulator (HCH) with the arrangement of condensation zones: I - high-boiling chlorides (WCC); II — chlorides with an intermediate boiling point; and III — low-boiling chlorides (LCC). The pairing between the element located along the apparatus axis and the top of the condensation zone is made as long as possible to reduce the mutual temperature effect. With cooling, as well as condensation of gases and vapors, their volume decreases, and the "living" cross section of the gas flow can be reduced. This explains the overall configuration of the device. The central element of the apparatus through which tubes and devices for supplying input products, reagents and additives (not shown) are passed has an additional heater to eliminate the possibility of condensation of any chlorides on its surface.

The ratio of the diameters (over the parts of the apparatus) and the height should be selected taking into account both the gas flow rate (reducing the temperature “erosion” of the condensation zones of individual components or their groups) and the thermal conductivity of the material of the apparatus to provide sufficiently “sharp” heating, . local heating mode similar to zone melting process mode.

Figure 3 schematically shows the device of the "control" NKH trap, which can exit the condensation zone of the chlorinator when unloading its upper, least heated section.

A refrigerated slot is provided for the container to be pulled down. Since condensation will occur from humid gases, and some NLCs are hygroscopic, liquid fractions of hydrates may be present simultaneously with solid condensate. For ease of unloading, the container can be made of a corrosion-resistant elastic material (plastic, rubber, etc.), including for single use. A variant of a container with a liquid shutter is provided for circumstances when liquid fractions will prevail, and unloading can be carried out without stopping the process.

The implementation of the method

1) ~ 2000 kg of RTN SNF was taken for reprocessing. After felling of the fuel rods, voloxidation, separation from the clippings and recovery (combining opening and grinding), finely dispersed oxides U, Pu, and PD are fed for fluorination to a reactor operating in a continuous mode with a capacity of ~ 100 kg / h.

Comparison of thermochemical reactions

and

shows that the change in free energy ΔZ ⁰ ₁₀₀₀ (at 1000K) for reaction (5) exceeds that for reaction (6) by ~ 3 times. [K.E. Wicks, F.E. Blok. Thermodynamic properties of 65 elements, their oxides, halides, carbides and nitrides. - M., Metallurgy, 1965] If, according to reaction (6), the productivity of an industrial apparatus is 450 kg / h [Proceedings of the Second International Conference on the Peaceful Use of Atomic Energy (Geneva, 1958). Selected Papers of Foreign Scientists, vol. 7. Technology of atomic raw materials. M., Atomizdat, 1959, p.641. Powell Modern processes used in the USA for mass production of UF ₆ ], the productivity adopted in our example (100 kg UO ₂ / h) is quite achievable.

The fluoro agent is introduced in such a ratio that ~ 0.1-0.5% of the initial amount of U remains in VKOF together with Pu. The bulk of the NKF, including U and many PD, was given in the gaseous state to the “UF ₆ Purification” redistribution and then to the adjustment of the ²³⁵ U mass fraction (if necessary), then to the redistribution of the target product production.

VKOF is transferred to a redistribution of conversion to oxides in a continuously operating flame pyrohydrolysis apparatus with a capacity of ~ 4 kg / h. The intrinsic heat of reaction Q _{1 is} insufficient, therefore, H ₂ and O ₂ are additionally introduced for the energy-adding reaction (2). As a result, at this stage finely dispersed oxides U, Pu, and PD are obtained, which are transferred to the “chlorination-condensation-granulation” redistribution with a continuously operating flame chlorination apparatus. Since at a productivity of ~ 3.5 kg / h the intrinsic heat of reaction Q _{3 is} not enough, reagents Cl ₂ and Н ₂ are additionally introduced for energy-adding reaction (4), and to keep U in the tetravalent state, finely dispersed powder is fed into the torch together with gaseous Н ₂ UH ₃ .

In order to facilitate the removal of the PDVC of PD (and PuCl ₃ ) from the condensation zone I in the dog, NaCl granules were fed. Forming complex, less refractory, salt systems with each other and with NaCl, PDC (and PuCl ₃ ) by gravity leave the condensation zone by gravity, after which they are subjected to granulation.

The lower-boiling reaction products in a gaseous state rise upward (a velocity of the order of 0.1-1.0 cm / s) and condense on them as the temperature of the apparatus decreases. Excess non-condensable gases, together with the residues of PD chlorides (in the form of aerosols) leave the apparatus, go through a control trap and are sent for cleaning, separation and recycling. To unload the condenser from the zones where U and PD condense in the solid state, the walls are periodically heated until the condensates completely melt and drain into dripping devices and then in a container with liquid for solidification (granulation).

Granular intermediate products (from 2 to 10 in number, depending on the processing tasks) are sent to the appropriate stages:

- the fraction containing the largest amount of uranium - to obtain uranium oxide (by known methods) to return to the head of the process (fluorination) or to obtain U-MA compositions (for the purpose of their transmutation);

- fraction containing the largest amount of plutonium - for the production of target products (dioxide, nitride, metal, alloys with other metals). Simultaneously with obtaining the target products, PD is purified by known methods. The oxygen-free state of intermediate products (uranium tetrachloride and plutonium trichloride) allows you to organize continuous processes for the production of any of these target products on an industrial scale.

Over 20 hours of continuous operation of the installation, 2000 kg of SNF of RTH were processed, while the following products were obtained:

- uranium hexafluoride of high purity, from which ~ 1900 kg of UO ₂ (by the method of pyrohydrolysis in a fluidized bed with an electrode), suitable for the manufacture of RTN fuel elements using the technology of vibration compaction, can be produced after another 20-50 hours (if enrichment is necessary);

- plutonium trichloride with impurities PD and MA, from which after 20-50 hours (depending on the necessary purification) ~ 20 kg of PuO ₂ (coarse-grained powder) can be produced, suitable for the manufacture of fuel elements of RBN and RTN reactors using vibro-compaction technology using the synchronous dosing method ;

- ~ 20 kg UO ₂ , designed to return to the head of the process;

- ~ 60 kg of PD in the circulating chloride salt and in the waste fluoride-gas redistribution.

2) ~ 500 kg of SNF RBN was taken for reprocessing. After releasing the fuel from structural materials (by known methods) and grinding it to a particle size of ≤0.1 mm, the fuel is supplied for fluorination to a reactor operating in a continuous mode with a capacity of ~ 20 kg / h. The fluo agent is introduced in such a ratio that ~ 1.5% of the initial amount of U remains in VKOF together with Pu. The bulk of the NKF, including U and PD, is taken off in a gaseous state to the “UF ₆ Purification” redistribution and then to the redistribution of the production of target products.

VKOF (including Pu fluoride and partially U) is transferred to the redistribution of conversion to oxides in a continuously working flame pyrohydrolysis apparatus with a capacity of ~ 4 kg / h. The intrinsic heat of the reaction Q ₁ for intensive burning of the flame is not enough; therefore, H ₂ and O ₂ are additionally introduced for the energy-adding reaction (2). As a result, at this stage finely dispersed oxides Pu, U and PD are obtained, which are fed to the redistribution of “chlorination-condensation-granulation” with a continuously operating flame chlorination apparatus. Since at a productivity of ~ 3.5 kg / h the intrinsic heat of the reaction Q ₃ is not enough for intensive burning of the flame, reagents Cl ₂ and Н ₂ are additionally introduced for the energy-adding reaction (4), and to keep U in the tetravalent state in the flame together with gaseous Н ₂ serves fine powder UH ₃ .

A significant amount of Zr in SNF RBN leads to the condensation of ZrCl ₄ in the solid state. For its dissolution and withdrawal from the condensation zone, the melt of low-melting salt 3LiCl-2KCl is introduced onto the shelves of the corresponding sections.

They also use the option of increasing the oxidizing ability of the medium by adding a fraction of Cl ₂ , while the uranium goes into valence states +5 and +6, the sum of these chlorides condenses in the same zone as ZrCl ₄ , they melt and leave the condensation zone in liquid form.

Since the predominant fraction of the resulting chlorides is PuCl ₃ , it is not necessary to introduce additional additives into zone I of the condenser to lower the melting point of a complex salt system, and the products of zone I of condensation “leave by gravity” to leave it for granulation. The lower boiling chlorides in the gaseous state rise up and condense on them as the temperature of the apparatus walls decreases. Excess non-condensable gases together with non-condensed residues (as well as aerosols) leave the apparatus, pass a control trap and are sent for cleaning, separation and recycling. To unload the condenser from zone II and III, where U and PD can condense in the solid state, the walls are periodically heated until the condensates completely melt and drain into dripping devices (granulation).

With granular intermediates do the same as in the considered example 1.1.

For 25 hours of continuous operation of the installation, 500 kg of RBN SNF were processed, while the following products were obtained:

- Uranium hexafluoride of high purity, from which ~ 370 kg of UO ₂ (by pyrohydrolysis in a fluidized bed with an electrode) can be produced after another 20 hours, suitable for the manufacture of RBN fuel elements using vibration sealing technology;

- plutonium trichloride with impurities PD and MA, from which after 20-50 hours (depending on the necessary purification), it is possible to produce ~ 75 kg of PuO ₂ (coarse-grained powder) suitable for the manufacture of fuel rods of RTN and RBN reactors using vibro-compaction technology using the method synchronous dosing;

- ~ 7.5 kg UO ₂ , designed to return to the head of the process;

- ~ 50 kg of PD in the circulating chloride salt and in the waste fluoride-gas redistribution.

3) ~ 2000 kg of UO ₂ (dump isotopic composition) was taken from the RBN reproduction zone for processing. Further, the description of the example coincides with Example 1.1, differing only in the number of PDs and Pu, which is why the volume of work of the apparatuses at the “Pyrohydrolysis” and “Chlorination-condensation-granulation” stages decreased by ~ 2 times.

As a result, for 20 hours of continuous operation of the installation, the following were obtained:

- high purity uranium hexafluoride for the production of circulating UO ₂ reproduction zones;

- ~ 30 kg of plutonium trichloride with PD impurities, which can be used to redistribute the production of target products, as in examples 1.1 and 1.2;

- ~ 20 kg UO ₂ , designed to return to the head of the process;

- ~ 10 kg of PD in the circulating chloride salt and in the waste fluoride-gas redistribution.

Installation Implementation

The installation includes: three continuous apparatuses for fluorination, pyrohydrolysis (flame), chlorination (flame, followed by condensation and granulation) with independent power systems, life support, reagent recycling, control and management of technological processes and transport streams; redistribution equipment “Cleaning UF ₆ ”, “Pyrohydrolysis UF ₆ ”, “Production of target products” also with a full range of systems to ensure their operability. There is a redistribution for pyrohydrolysis of uranium chlorides with the possibility of returning the resulting uranium dioxide to the head of the process.

The apparatus of the installation, which has no analogues, is the “Chlorinator-condenser-granulator”, in which oxygen-free chlorides are obtained from finely dispersed Pu, U, and PD oxides, due to the different saturated vapor pressure of which it is possible to organize the separation of U and Pu and their partial release from PD.

1) The apparatus for the organization of condensation in the solid state is a cylindrical body with a base at the bottom. In the center of the cylindrical body are pipelines for supplying the input product, reagents and additives to the nozzles. Pipelines (not shown in the diagram) are enclosed in a common conical-shaped casing, which is also a heater to prevent condensation of any possible chloride in the solid state. The transition between the aforementioned heated and cooled upper part of the housing is made as long as possible to reduce the mutual temperature effect. The base is designed as an extension in the form of a "pear" with a funnel-shaped depression in the lower hemisphere, directed inward. A device is provided for feeding the NaCl additive in solid or molten form (not shown), the salt enters the same zone where the combustion torch is directed. The cylindrical body inside is equipped with several beads forming ring funnels (grooves) with exits to the granulation system. The height of each shoulder is chosen so that the circumference of its inner edge fits into the circumference of the inner edge of the overlying shoulder. This is necessary so that when a solid product collapses between the shoulders (after melting the part adjacent to the heated wall), part of the product does not fall down. Each section of the wall between the shoulders or several such sections (zone) has the possibility of additional heating (cooling).

The ratio of the dimensions of the body, the ratio of the diameters of the central element and the height of the shoulders are selected so as to "correctly" organize the movement of gases.

The gases generated (and heated) in the flare initially have the ability to expand in the lower zone (base), reduce speed and change direction (in this case, part of the mass condenses, which also leads to a decrease in gas pressure and speed. To accelerate the condensation of water-vapor in the central a part of the base (in the funnel region, which inside is a conical elevation), an intensive cooling zone is provided due to an external heat exchanger To reduce the turbulence of gas flows, the nozzle head of the fence on a bell cap.

The annular gap between the central element of the apparatus and the inner edge of the lower flange has such a “live” section so that the gases entering it have a moderate speed (without trapping liquid droplets of the WSS). Further, as the temperature of the inner walls of the casing decreases and the mass and volume of gas are lost due to the condensation of chlorides, the gas velocity decreases, which makes it possible to reduce the living section of the overlying sections of the casing.

In each condensation zone (section), a product yield is provided. For this, holes were made in the housing with heated pipelines (their connection by a collector into groups is allowed). Further, drip forming devices (not shown) and separate containers with liquid for solidifying the droplets (granulation), devices for extracting, drying and packing (transporting) the granules (not shown) are provided. Outside the casing there is a system of additional heating (cooling) of the walls (not shown in the diagram) that creates a smooth change in temperature from ~ 800 ° C in the condensation zone I to ~ 40 ° C in the zone of gas exit from the casing.

The material of the apparatus was chosen so that the frequency of its replacement did not make a significant contribution to the costs of SNF regeneration. The ratio of the characteristics of the material (thickness and thermal conductivity) and the external heater (inductor) allows for “sharp” additional heating of the sections, approaching zone melting in mode.

2) The apparatus for organizing condensation in a liquid state differs from that shown in Example 1 in that devices for maintaining the liquid level (not shown) are provided on the discharge pipelines, allowing it to partially flow through the beads. In this example, when the apparatus is operated with a continuous output of products, a mode approaching rectification can be realized.

3) Depending on the type of SNF and on the condensation modes in the KHG apparatus, the composition of the exhaust gases (mass fraction of condensed impurities) is different, therefore, two versions of the control trap can be used:

3.1 To collect "sublimates" in solid form, the trap consists of a gas supply and exhaust unit, a cooled socket and a container. The nest and the container are hermetically connected along a conical surface made with exactly the same inclination to the axis, which creates a more snug fit for efficient heat transfer. The container, partially filled with condensate containing a solid fraction, is removed from the nest and replaced with a free one.

3.2 In the case when solid fractions are formed in an insignificant amount, the trap is equipped with a stationary container with a provided hydraulic seal, which allows condensate to be removed without depressurization of the trap.

Claims (19)

1. A method of processing spent nuclear fuel containing uranium and plutonium, including the stage of fuel fluorination with the conversion of uranium to hexafluoride, in addition to the amount sufficient to hold all plutonium in high boiling fluorination residues, separate processing of uranium hexafluoride to clean it of low boiling fission products with further conversion in fuel components and high-boiling fluorination residues for the extraction and use of plutonium and other valuable components, characterized in that high-boiling First, the fluorination residues are successively converted first to oxide and then chlorinated at high temperature, the resulting chlorides are condensed in zones with different temperatures to separate them and partially purify plutonium. 2. The method according to claim 1, characterized in that the conversion of high-boiling fluorination residues to oxides is carried out by pyrohydrolysis in a flame apparatus with an additional energy-adding reaction of burning hydrogen in oxygen. 3. The method according to claim 1, characterized in that the chlorination of the oxides after their conversion is carried out in a flame apparatus using hydrogen chloride with an additional energy-adding reaction of combustion of hydrogen in chlorine. 4. The method according to claim 3, characterized in that the redox ability of the medium control the change in the ratio of hydrogen to chlorine. 5. The method according to claim 3 or 4, characterized in that an additional reducing agent is introduced into the flare zone in the form of sodium vapor, or fine uranium powder (in a metallic state), or uranium trihydride, or uranium trichloride. 6. The method according to claim 3, characterized in that the condensation of the chlorides is carried out from the zone around the plume and further from the upward flow of gases (as their temperature decreases) through the zones (sections) from which the removal of products is organized. 7. The method according to claim 6, characterized in that the condensation is carried out in a solid state, chlorides are periodically melted to remove products and they are removed from the condensation zone. 8. The method according to claim 6, characterized in that the condensation is carried out in a solid state, and to transfer the product into a liquid state, a fusible chloride salt is supplied to the appropriate shelves. 9. The method according to claim 6, characterized in that the condensation is carried out in a liquid state with continuous removal of products. 10. The method according to claim 9, characterized in that they organize a partial flow of fluid through the flanges from the overlying areas to the underlying. 11. The method according to claim 6, characterized in that the products withdrawn from the condenser are granulated by droplet formation and solidification in a low-boiling non-combustible liquid. 12. The method according to claim 6, characterized in that from a previously isolated group of chlorides with plutonium trichloride produce fuel components with additional purification from fission products and the possibility of organizing continuous processes. 13. The method according to claim 1, characterized in that after the chlorination and separation operation, uranium chloride is converted into uranium oxide and returned to fluorination as a recycled product. 14. The facility for processing spent nuclear fuel containing uranium and plutonium includes three devices sequentially placed along the technological chain (for fluorination, pyrohydrolysis of high-boiling fluorination residues and for chlorination of oxides after pyrohydrolysis, hereinafter referred to as condensation and granulation) with the possibility of continuous operation mode, and the last two are fiery; redistribution equipment for cleaning and correcting the isotopic composition of uranium hexafluoride, the manufacture of fuel components from it; equipment for processing a mixture of plutonium trichloride with some fission products (after separation from uranium residues and other fission products) into fuel components with partial purification of fission products; equipment for the recycling of reagents and for the life support of each redistribution. 15. Installation according to 14, characterized in that in the third apparatus (chlorinator-condenser-granulator) the first condensation zone is made expanding in the form of a pear, with a funnel-shaped recess in its lower hemisphere, from the lower point there is an exit of liquid condensation products, cylindrical the surface of the condensation zones is provided with shoulders dividing it into sections, each of which has an outlet through openings in the housing. 16. The apparatus of claim 15, wherein the beads are tapered, the upper edge is horizontal, and the lower is inclined with one hole at a lower point to allow complete drainage of liquid when the apparatus stops. 17. Installation according to claim 15, characterized in that the exits from the plots are equipped with heaters for storing products in liquid form with the possibility of combining them in collectors. 18. The apparatus of Claim 15, wherein the chlorinator-condenser-granulator has devices for droplet formation and solidification of droplets in a low boiling non-combustible liquid, granules extraction, drying and transportation thereof. 19. The apparatus of Claim 15, characterized in that after the chlorinator-condenser-granulator, intensely cooled control traps are provided on the gas path with the possibility of removing condensation products from them.

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