RU2090510C1 - Method of processing uranium hexafluoride - Google Patents

Abstract

FIELD: production of inorganic substances. SUBSTANCE: uranium hexafluoride is loaded into reactor to interact with steam plasma. Steam is used in stoichiometric excess as high as 5%. Plasma treatment is conducted beyond discharge zone with consuming at least 0.5 kW-h per 1 kg uranium hexafluoride. Treatment time is at least 4,1 × 10^-3 s. Anhydrous hydrogen fluoride and its azeotrope with water are obtained via rectification. Azeotrope is used to supply 5% steam. Uranium hexafluoride is fed into heat carrier to heat it to high temperatures, while steam and uranium hexafluoride pressure difference is higher than 2 kPa. Mixture is then compressed to steam pressure and subjected to pyrohydrolysis. EFFECT: optimized process parameters. 2 cl, 1 tbl

Description

 The invention relates to methods for processing uranium hexafluoride to produce uranium oxides and can be used in the conversion of uranium hexafluoride.

A method of processing of uranium hexafluoride to uranium dioxide yield [1] A process comprises: a) reacting UF ₆ with the vapor steam at a temperature of 200 ^o C700 ^o C to form UO ₂ F ₂ and with a ratio of oxides: ^O: U = 2,7 ^o C3; b) the dissolution of UO ₂ F ₂ and oxides in water or a solution of nitric acid; C) the interaction of the resulting solution with ammonia to obtain ammonium diuranate; d) filtering ammonium diuranate; d) drying and calcining ammonium diuranate with the formation of uranium dioxide during reduction. The process is multi-stage, requires the cost of a large number of reagents, energy-intensive.

The closest method of processing oxides in the uranium hexafluoride is the method described in [2] The process consists in carrying out the pyrohydrolysis (hydrolysis at 600 ^o C700 ^o C) UF ₆ in a fluidized bed. For this, UF ₆ vapors are mixed at high temperature with water vapor and hydrogen at a reagent ratio of UF ₆ H ₂ OH ₂ 1 (2 ^° C12): (5 ^° C20). Intermediates are UF ₄ , U ₃ O ₈ and UO ₂ F ₂ . Under the conditions of a "fluidized bed" when interacting with water vapor and hydrogen, they rapidly transform into uranium dioxide according to the general equation: UF ₆ + 2H ₂ 0 + H ₂ = UO ₂ + 6HF.

The process is carried out in two stages: for the first stage of the reaction, a temperature of 600 ^o C650 ^o C is sufficient, for the second 700 ^o C750 ^o C. The process is implemented respectively in the hydrolysis chamber and in the defluorination chamber. In addition, the method low productivity optimal performance 300 ^o C400 g / h

The difference of this method lies in the fact that the pyrohydrolysis process is carried out by the interaction of uranium hexafluoride vapors with water vapor plasma. To do this, the water vapor in the plasmatron is converted into oxygen-hydrogen plasma with an initial temperature of 2500 ^° C 5000 K and the uranium hexafluoride is mixed with this plasma in a plasma chemical reactor. The gross reaction-reaction is described by the equation:
(UF ₆ ) _gas +3 (H ₂ O) _gas = 1/3 (U ₃ O ₈ ) _tv +6 (HF) _gas +1/3 (O ₂ ) _gas .

To stabilize the output of hydrogen fluoride, water vapor is supplied with a five percent excess relative to the stoichiometrically necessary. To prevent the interaction of hydrogen fluoride with uranium oxides at the outlet of the reactor where the solid and gas phases are separated, a temperature of at least 850 ^° C is maintained. The gas phase leaving the reactor containing 92 ^° C95% hydrogen fluoride is directed to the separation of hydrogen fluoride by a distillation method . Anhydrous hydrogen fluoride is used to feed the fluorine electrolyzers of sublimation production or for other purposes.

The azeotrope HF-H ₂ O, remaining after distillation separation of anhydrous hydrogen fluoride, containing 1 ^o C3% of the total amount, is sent to the process head and mixed in a plasma chemical reactor with oxygen-hydrogen plasma. The return of water vapor in the form of an azeotrope to the plasma-chemical reactor creates a 5% excess in the reaction zone necessary to stabilize the yield of hydrogen fluoride and reduce the fluorine content in the obtained uranium oxides.

 Uranium hexafluoride is supplied to the coolant at a pressure of 2 kPa lower than water vapor pressure, after which the mixture is compressed to water vapor pressure, and then subjected to pyrohydrolysis in water vapor plasma.

 When mixing, the process of transferring thermal energy from the coolant to uranium hexafluoride occurs, while the temperature of the coolant drops and the hexafluoride increases. The heating of hexafluoride is accompanied by its thermal dissociation into lower fluorides and fluorine with an increase in the volume of the mixture. A chemical reaction that causes a change in volume intensifies the mixing process. A decrease in the pressure of hexafluoride reduces the temperature of the onset of thermal dissociation, therefore, it intensifies the transfer of thermal energy from the coolant to hexafluoride and the mixing process at the level of globules. Subsequent compression of the mixture causes a partial recombination of the products of dissociation, which is accompanied by a decrease in volume and heat. Thus, the recombination process contributes to the redistribution of energy at the molecular level. Compression of the mixture to a pressure equal to the pressure of water vapor eliminates the influence of recombination processes on the subsequent hydrolysis of the mixture.

The main differences of the present method from the existing prototype method:
1. The processed raw materials of uranium hexafluoride are converted by chemically active plasma of water vapor with its excess not exceeding 5% of the stoichiometric ratio. The conversion time is not less than 4.1 • 10 ^-3 s depending on the ratio of the completeness of mixing of the reagents and the temperature of the water vapor plasma.

2. In the zone of separation of the gas and solid phases formed as a result of the plasma-chemical reaction, a temperature of at least 850 ^° C. is maintained in order to prevent the recombination of fluorine and uranium.

 3. The gas phase, consisting of hydrogen fluoride with an admixture (up to 5%) of water vapor, is subjected to distillation distillation, in which anhydrous hydrogen fluoride and an azeotrope are isolated.

 4. Through the use of a combination of the above operations, the technical problem of isolating anhydrous hydrogen fluoride from “dump” uranium hexafluoride and converting uranium from volatile fluoride to non-volatile oxides is provided.

 Example 1. On a pilot plant having a plasma chemical reactor, a system for evaporating and dosing uranium hexafluoride, heating it by mixing with a coolant, a water vapor metering system, a hydrogen fluoride condensation system, a vacuum system and a high-frequency generator LGD-32 to power the plasma torch, hexafluoride is processed uranium to uranium oxides and hydrogen fluoride.

Water vapor is passed through a high-frequency plasmatron with a flow rate of not more than 5% with respect to the stoichiometric amount of the uranium hexafluoride to be hydrolyzed, supplied to the lower part of the reactor behind the discharge zone. At the moment of mixing uranium hexafluoride with a high-temperature coolant, the pressure difference between water vapor and uranium hexafluoride is 2.2 kPa. Then the mixture is compressed to water vapor pressure and subjected to pyrohydrolysis in water vapor plasma. The energy consumption for the process is not less than 0.5 kWh / kg of uranium hexafluoride. Processing time 4.2 • 10 ^-3 s. The temperature of the outer surface of the uranium oxide layer is maintained at 600 ^o C650 ^o C. The temperature of the inner surface of the uranium oxide layer deposited on the walls of the reactor is higher than the wall temperature and is 850 ^o C900 ^o C. The gas stream after separation in the reactor from the bulk of the oxides is filtered through nickel-metal filters, operating at a temperature of 200 ^o C250 ^o C. the hydrogen fluoride vapors from the gas stream is condensed in a condensation system consisting of a condenser and condensate collection container. The condensation temperature is maintained at 4 ^o C6 ^o C regulation of refrigerant flow. The resulting oxides contain 0.2% fluorine, the composition is close to uranium oxide. Hydrofluoric acid with a content of 98 ^° C.99 wt. hydrogen fluoride. After processing 30 ^o C35 kg of uranium hexafluoride, the obtained hydrofluoric acid in a distillation column is separated into anhydrous hydrogen fluoride (99.9% HF) and an azeotrope with a content of 38 ^o C40% HF. From 10 kg of hydrofluoric acid obtained by the interaction of uranium hexafluoride with oxygen-hydrogen plasma, after rectification, about 9.6 kg of anhydrous hydrogen fluoride and 0.4 kg of an azeotrope are obtained, which are evaporated and fed to a high-frequency plasmatron.

 Example 2. In the pilot plant of example 1, the process of processing uranium hexafluoride into uranium oxides is carried out. The energy consumption for the process is 0.3 kWh / kg of uranium hexafluoride. Other things being equal with example 1, the fluorine content in the obtained oxide increases to 1.5 wt.

Example 3. The method was tested on a pilot industrial plasma installation with a plasma torch EDP-109 in a production environment. As a compressor, a gas ejector is used, where the ejected gas is nitrogen plasma. Uranium hexafluoride is an ejected gas, its inlet temperature is 343 ^o C400 K and a flow rate of 5 ^o C10 g / s. A mixture of uranium hexafluoride with a coolant nitrogen enters the reaction chamber, where it reacts with plasma of water vapor, with its excess relative to the stoichiometric amount of processed uranium hexafluoride 5 wt. The specific energy consumption is 0.6 kWh / kg of uranium hexafluoride. Processing time 5 • 10 ^-3 s. The pressure in the reaction chamber is 70 kPa. Uranium oxides obtained in this mode contain, on average, 0.2% fluorine. Without changing the thermal and flow parameters of the process by varying the length of the ejector, the difference in the pressure of water vapor in the reaction chamber and the hexafluoride at the inlet of the ejector changes from zero to 10 kPa, after which the mixture is compressed to water vapor pressure. In this case, the content of fluorine and uranyl fluoride in the obtained uranium oxides changes as shown in the table.

 It follows from the table that the effect of the pressure difference on the fluorine content in the oxides begins to appear at values of 2 kPa or more.

The present method allows to obtain anhydrous hydrogen fluoride. The fluorine content in uranium oxide does not exceed 0.2%
Literature
1. Europatent N 322.481, cl. C 01 G 43/026, dated 05/07/1989.

 2. Galkin I.A. Veryatin U.D. Yakhonin I.F. et al. Investigation of the process of conversion of uranium hexafluoride to dioxide. Atomic Energy, 1982, v. 52, no. 1, p. 36-39.

Claims (2)

1. A method of processing uranium hexafluoride, including its interaction with water vapor at high temperature and the subsequent separation of solid and gas phases, characterized in that the interaction of uranium hexafluoride with water vapor is carried out in a plasma of water vapor behind the discharge zone, water vapor is taken in excess, not greater than 5% relative to the stoichiometric amount, the specific energy consumption of less than 0.5 kW • h / kg of uranium hexafluoride with the processing time of at least 4.1 • 10 ^-3 s and after phase separation, the gas phase is condensed and rivers ifikatsiey isolated anhydrous hydrogen fluoride azeotrope of hydrogen fluoride and water, wherein to create a 5% excess of steam used azeotrope of hydrogen fluoride water.  2. The method according to p. 1, characterized in that the pressure difference of the water vapor and uranium hexafluoride before mixing exceeds 2 kPa, after which the mixture is compressed to a water vapor pressure.

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