Method and system cleanup gaseous uranium hexafluoride

 

(57) Abstract:

The method of cleaning a gas stream UF6provides exposure to the gas flow UF6laser radiation. The cleaning system includes a reaction vessel. The vessel serves untreated UF6. The reaction vessel is irradiated with laser radiation with an energy of less than 24,000 cm-1using a generator. UF6not dissociate. Impurities pass into the non-volatile state. Gases produced from the reaction vessel. Non-volatile impurities remaining in the vessel, foryouth gaseous fluorinating agents and release the formed gases. Impurity - neptunium and plutonium. Fluorinating agents IF7, BrF3, ClF3. The result is the absence of waste in the process. 2 C. and 22 C.p. f-crystals, 4 Il.

The present invention relates to the purification of gaseous uranium hexafluoride (UF6), and more specifically, the present invention relates to the removal of fluoride impurities from the gas stream UF6.

During reprocessing of irradiated nuclear reactor fuel with the aim of obtaining recycled uranium raw material, which is perereca to obtain UF6usually there is a number of impurities that are in the process of ferroviaires, obtained from irradiated fuel commercial nuclear reactor, containing transuranium elements Np, Pu and Am, and transition elements Tc, Rh and Ru. Transuranium elements usually form approximately 0.95 wt.% the metallic base, and the above-mentioned transition elements form approximately 0.38 weight. %. Uranium is usually present at the level of approximately 96 wt.%.

While the fluorides mentioned above transition elements usually have a volatility that is significantly different from volatility UF6that allows them to be separated by means of fractional distillation, fluorides such as hexafluoride Neptune (NpF6) and plutonium (PuF6) do not differ in volatility from UF6so that they remain in the gas stream UF6after it is processed by means of fractional distillation.

Previously known methods of removing fluoride impurities from uranium materials from irradiated fuel of a nuclear reactor, involve the use of a range of technologies. In some cases the raw material is in contact with an aqueous solution of an earlier education UF6. The disadvantage of this solution is the increase of the volume of radioactive waste. In other cases the use of fluorides of alkali the volume of radioactive waste products.

Among other known processes can be specified on the process described in U.S. patent N 4364906, according to which use calcium carbonate as a catching substance for cleaning a gas stream UF6. However, in this process there is a tendency to the formation of large amounts of waste products. In U.S. patent N 3806579 described distillation pollution MoF6and WF6from UF6. In U.S. patent N 4311678 described the use of agent synthesized to remove deposits of the hydrolysis products UF6from the walls of the equipment, which was treatment UF6. This process will lead to the loss of a certain amount UF6and to the formation of impurities. More successful in some ways, the technology described in U.S. patent N 4555318, which provides for the contacting of the gas stream UF6with a layer of solid UF5. This technology is based on the recovery of gaseous NpF6using UF5to remove impurities, resulting in the process creates a solid NpF5. Indicates that this process cannot be attributed to the highly effective and that, perhaps, the desired recovery and removal of impurities is not only flowing esults similar to that described for UF5. The use of solid fluoride layer to remove impurities necessarily lead to the formation of large amounts of solid waste, which will later be subjected to additional processing. In addition, it is known that the use of CoF2is not a very effective method of removing NpF6. Both of these methods have disadvantages, namely, have a low efficiency and a high degree of waste.

The present invention is to provide a method of cleaning a gas stream UF6without accompanying this way increase the amount of waste products.

In accordance with the first aspect of the present invention proposes a method of cleaning a gas stream UF6that involves the irradiation of a gas stream UF6laser radiation in the reaction vessel, in order to selectively convert the fluoride contamination in the gas stream in the non-volatile products with the subsequent withdrawal of the purified gas flow UF6from the reaction vessel and separate impurities from the vessel.

Fluoride contamination in the gas stream UF6may contain NpF6and PuF6.

Mainly the gas flow UF6is irradiated with laser light in three different bands of wavelengths, for example, three laser sources, in order to selectively excite impurities NpF6and PuF6.

It is desirable to select a combination of laser energy so that each of the impurities NpF6and PuF6in the gas flow UF6absorbed photons of radiation fields, so that molecules NpF6and PuF6were excited above threshold dissociation, with the result that they dissociatively would nonvolatile lower fluorides and fluorine atoms. Molecules UF66and PuF6excited field of laser radiation having energy in the range from 10 000 cm-1up to 7000 cm-1and 13000 cm-1up to 9000 cm-1respectively, and more preferably laser radiation having energy in the range from 9528 cm-1before 9583 cm-1respectively; in the second phase molecules NpF6and PuF6excited by laser radiation having energy in the range from 17500 cm-1up to 24000 cm-1and more preferably laser radiation having energy 19570 cm-1in fact , in the two-stage irradiation molecules NpF6and PuF6excited over their dissociation thresholds so that they dissociate in non-volatile products containing lower fluorides, which are deposited on the walls of the vessel in the form of solid deposits.

The energy of laser radiation at the second stage can be mainly such energy that the radiation is not absorbed by the molecules UF6and therefore the gas UF6remains unchanged.

Usually at the first stage of laser irradiation molecules NpF6and PuF6can be irradiated by means of two separate solid-state lasers, predominantly as lasers choosing and using porcelanato laser with an impurity (alloying additive) Nd3+, while molecules PuF6can be irradiated using verbarrator glass laser with an admixture of Nd3+.

In the second stage of laser irradiation molecules NpF6and PuF6usually irradiated with radiation of a copper vapor laser, or using argonovogo a high power laser.

Mainly the removal of non-volatile products from the vessel can be carried out by contacting the above products with one or more fluorinating agents to form gaseous products. Can be used chemical fluorinating substances, and appropriate chemical fluorinating agents are IF7, BrF3and ClF3. Alternatively can be used photochemical fluorinating agents in combination with radiation from a source of ultraviolet energy to form gaseous products. Suitable photochemical fluorinating agents are F2and ClF.

In accordance with another aspect of the present invention suggests a system of purification of the gas stream UF6using the method, corresponding to the first aspect of the present invention, and this system VKV, for example fluorine, inlet means specified not cleared UF6and the fluorinating substances in the reaction vessel, means for separating gases from the reaction vessel, and means for collecting the separated gases.

Mostly the contents of the reaction vessel may be irradiated by a combination of laser and ultraviolet sources.

Typically, the reaction vessel may be optically transparent window that is optically transparent to laser energies and ultraviolet radiation from sources.

Mainly a number of these systems may be connected in series to obtain UF6high purity.

A further advantage is that section of the cascaded system can be disconnected for maintenance and removal of accumulated dirt.

The method in accordance with the present invention is particularly well suited for the purification of a gas stream UF6as it is possible to avoid the use of wet chemical processing, and also because they do not produce large amounts of waste products that require further processing and/or storage.

In n the th radiation. However, this photodissociate was not used for the separation of gas PuF6from the other compounds, but simply used as a method of preparation of PuF5.

Next will be described embodiments of the present invention, is shown only as an example with reference to the accompanying drawings.

In Fig.1 shows a graph of energy depending on the absorption cross-section, showing the sectors absorption of molecules UF6, NpF6and PuF6.

In Fig.2 schematically shows the absorption of molecules UF6, NpF6and PuF6.

In Fig.3 schematically shows a system for cleaning a gas stream UF6.

In Fig.4 with the increase shown in the cross-section of part of the system of Fig.3.

We now turn to a consideration of Fig. 1, which shows absorption spectra of molecules UF6, NpF6and PuF6in the range of from 50000 cm-1up to 5000 cm-1. In Fig.2 shows the absorption for each of the above-mentioned molecules, which is represented schematically together with their measured energies of dissociation. You can see that each of the molecules has a broad intense absorption in the region above approximately 20000 cm-1and that is Fig.2, molecules NpF6and PuF6absorbed in discrete transitions at energies below 20000 cm-1(in particular, in the range from 10 000 cm-1up to 7000 cm-1for NpF6and 13000 cm-1up to 9000 cm-1for PuF6).

We now turn to a consideration of Fig.3, which shows a system 10 for treatment of gas flow UF6using the characteristics of the absorption NpF6and PuF6. In the reaction vessel 12 of the system 10 is served raw gas UF6from the source 14 and the fluorine gas from the source 16. The source 14 UF6connected via line 18 to the valve 20, which line 22 is connected to the input line 24, which is connected with the reaction vessel 12. The fluorine source 16 is connected via line 26 to the valve 28, line 30 is connected to the input line 24.

The output line 32 connects the reaction vessel 12 with the valve 34. Line 36 goes from the valve 34, passing through a cooled trap 38, and is connected with the valve 40 in four ways. The valve 40 is connected with the other three lines 42, 44 and 46, which respectively connect it with three tanks 48, 50 and 52.

In the immediate vicinity of one end of the reaction vessel 12 are three laser source 54, 56 and 58 and a source of ultraviolet light is one of their ends and connected to the output line 32 near the other of its ends. The reaction vessel 12 is made of such material as Nickel or Monel metal, which is resistant to UF6. At one end of the reaction vessel 12 has a window 62, made of a material that is optically transparent to laser energies and ultraviolet radiation from sources 54, 56 and 58 and 60. A suitable material for the manufacture of window 62 is magnesium fluoride. The reaction vessel 12 is used as the photolysis cell, in which the radiation from the sources 54, 56, 58 and 60 pass through the screen 62 and comes into contact with the material contained in the reaction vessel 12. In connection with the input and output lines 24 and 32 of the reaction vessel 12 has filters 64, which protect the outer gas path from the ingress of particles, which are formed in the reaction vessel 12.

When the system 10 (Fig. 3) initially, the valves 20 and 28 are closed and valve 34 is in the open state and the valve 40 operates so that were connected to line 36 (must be 46 and 42. Admission untreated UF6in the reaction vessel 12 is carried out by opening the valve 20, while the gas flow UF6from source 14 flows through lines 18, 22 and 24 into the reaction vessel 12. In the reaction vessel 12 which opens into the vessel 12 through the window 62 (see Fig. 4). The combination of laser energy is selected so that each of the impurities NpF6and PuF6in the gas flow UF6absorbs two photons from the field of irradiation. In this way molecules NpF6and PuF6excited above threshold dissociation, with the result that they dissociate in non-volatile lower fluorides and fluorine atoms. Molecules UF6no exposure field exposure.

Laser irradiation is carried out in two stages. In the first phase molecules NpF6excited field of laser radiation having energy 9528 cm-1from porcelanato laser 54 with an admixture of Nd3+(or from glass laser on the aluminum fluoride with an admixture of Nd3+), and molecules PuF6excited field of laser radiation having energy 9583 cm-1from verbarrator glass laser 56 with an admixture of Nd3+. In the second stage of laser irradiation molecules NpF6and PuF6irradiated with laser radiation 58 copper vapor having energy 19570 cm-1. The laser radiation causes the decomposition of the NpF6and PuF6in fluorides low valence, which are deposited on the walls of the vessel 12 in the form of non-volatile residue, and the fluorine gas.

The gas flow UF6udaetsya on lines 32 and 34 through a cooled trap 38, in which UF6condensed. Fluorine, which is not condensed in the cold trap 38, passes through lines 36 and 42 into the reservoir 48, which is its accumulation. To remove purified UF6from a cold trap 38 of the valve 34 is closed and valve 40 is switched so as to connect the line 36 to the line 44. Cooled trap 38 is heated to a temperature at which UF6becomes a volatile compound (approximately 57oC), and purified UF6is collected in the tank 50.

Periodically, the valve 20 is blocked to interrupt the flow of the crude gas UF6from source 14 into the reaction vessel 12. Purified UF6and fluoride are removed from the reaction vessel 12 in the tanks 48 and 50 respectively in the manner described above. The valve 28 is opened and the fluorine gas is supplied into the reaction vessel 12 from a source of fluorine 16 lines 26, 30 and 24. The reaction vessel 12 and its contents are irradiated from a source of ultraviolet (UV) radiation 60, and UV radiation passes into the reaction vessel 12 through the window 62. As a result of this non-volatile solids in the vessel 12 photochemically ftorida in NpF6and PuF6. The valve 40 is switched so as to connect the line 36 to the cooled trap 38, in which NpF6and PuF6condense. All the fluoride that is not entered into the reaction, is not subjected to condensation in a cold trap 38 and passes through lines 36 and 42 into the reservoir 48, where it is absorbed. To remove NpF6and PuF6from a cold trap 38 of the valve 34 is closed and valve 40 is switched so that it connects lines 36 and 46. Cooled trap 38 is heated to a temperature at which the NpF6and PuF6become volatile compounds (approximately 60oC), and purified NpF6and PuF6going in the tank 52.

In order to realize the cost-effective removal of impurities from the gas stream UF6with the purpose of receiving cleared UF6acceptable quality for use in gaseous diffusion plants, it may be necessary to turn on sequentially in a cascade of several of the above systems. Cascade also provides the additional advantage associated with the ability to disconnect from the technological cycle of the sections of the complete system during maintenance, as well as for periodic discharge of accumulated impurities.

In an alternative method of cleaning UF6gas flows NpF6 is that PuF6can be photodissociated in two-photon process, in accordance with the previously described dissociation can occur more than simply using a single-photon process.

In accordance with an alternative way of molecules PuF6in the gas flow photodissociation in the reactor using laser radiation of relatively low energy, when the irradiation has no effect on molecules UF6and NpF6. After this non-volatile solid fluoride products can be collected and processed accordingly. The gas flow UF6containing pollution NpF6passed to the second reactor, in which the excitation and photodissociation using two-photon process described above. The second non-volatile solid photo product is collected and processed as necessary, and the cleaned gas stream UF6is sent to the appropriate tank for accumulation.

1. The method of purification of gaseous uranium hexafluoride by irradiation, characterized in that the gas flow UF6irradiated into the reaction vessel by laser radiation with the energy at which molecules UF6not dissociate, p is, then remove the gas flow UF6from the vessel and removed from pollution.

2. The method according to p. 1, characterized in that the fluoride contamination of the gas stream UF6include NpF6and PuF6separately or together.

3. The method according to p. 1 or 2, characterized in that the irradiation of the gas flow UF6laser radiation is produced in three different wavelength ranges from three separate laser sources for selective excitation of pollution NpF6and PuF6.

4. The method according to one of paragraphs.1 to 3, characterized in that use such a combination of laser energy that each of contamination NpF6and PuF6in the gas flow UF6absorbs two photons of the incident field, while molecules NpF6and PuF6excited above threshold dissociation and dissociate into non-volatile lower fluorides and fluorine atoms.

5. The method according to one of paragraphs.1 to 4, characterized in that the laser radiation has energy less than 24,000 cm-1.

6. The method according to one of paragraphs.1 to 5, characterized in that the irradiation of the gas flow UF6laser radiation is carried out in two stages with the excitation of the NpF6and PuF6the s, which are deposited on the walls of the reaction vessel in the form of solid deposits.

7. The method according to p. 6, characterized in that, in the first phase molecules NpF6and PuF6excited field of laser radiation having energy in the range of 10000 cm-1- 7000 cm-1and 13000 cm-1- 9000 cm-1respectively.

8. The method according to p. 7, characterized in that the molecules NpF6and PuF6excited field of laser radiation having energy 9528 cm-1and 9583 cm-1respectively.

9. The method according to p. 7 or 8, characterized in that the molecules NpF6and PuF6excited respectively by two separate solid-state lasers.

10. The method according to p. 9, characterized in that use solid-state lasers with an admixture of Nd+3.

11. The method according to p. 10, characterized in that the molecules NpF6excited using porcelanato laser with an admixture of Nd+3or laser on the glass from the aluminum fluoride with an admixture of Nd+3and molecules PuF6excited by laser on the glass of ferberite with an admixture of Nd+3.

12. The method according to p. 6, characterized in that the second phase molecules NpF6and PuF6excited by laser radiation, with e the6and PuF6excited by laser radiation having energy 19570 cm-1.

14. The method according to p. 12 or 13, characterized in that the laser radiation has such energy that the radiation not absorbed by the molecules UF6and therefore the gas UF6remains unchanged.

15. The method according to one of paragraphs.12 to 14, characterized in that the molecules NpF6and PuF6excited by radiation from a copper vapor laser or from argonovogo a high power laser.

16. The method according to p. 1, characterized in that the removal of non-volatile products from the reaction vessel is carried out by contact of these products with one or more fluorinating agents with the formation of gaseous products.

17. The method according to p. 16, wherein the fluorinating agents are chemical fluorinating agents.

18. The method according to p. 17. characterized in that the chemical fluorinating agents include IF7, BrF3and ClF3.

19. The method according to p. 16, characterized in that the photochemical fluorinating agents are used in combination with irradiation from a source of ultraviolet energy to form gaseous products.

20. The method according to p. 19, characterized in that the CSOs of uranium hexafluoride including the reaction vessel, the source of the crude gaseous UF6the source of gaseous fluorinating agents, such as fluorine, means intake of these UF6and substances in the reaction vessel, means for irradiating the contents of the reaction vessel, means to conduct gases from the reaction vessel, means separation of gases produced from the reaction vessel, and means for collecting the separated gases, characterized in that the means for irradiating the contents of the reaction vessel are a generator of laser radiation with an energy of less than 24,000 cm-1.

22. The system under item 21, wherein the means for irradiating the contents of the reaction vessel are a combination of laser sources and ultraviolet radiation.

23. The system under item 21 or 22, characterized in that the reaction vessel has a window that is optically transparent to energy of the laser radiation and ultraviolet sources.

24. System according to one of paragraphs.21 to 23, characterized in that the number of enabled cascade of these systems is chosen in such a way as to produce UF6the desired high purity.

 

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The reactor // 2093259
The invention relates to equipment for carrying out mass transfer processes in the system "gas-solid substance, namely to obtain uranium hexafluoride by fluorination of uranium oxides

FIELD: methods of unloading of uranium hexafluoride from steel containers and utilization of these containers.

SUBSTANCE: the invention is dealt with the methods of extraction of liquid and gaseous substances from steel containers and utilization of these containers. The invention allows extract uranium hexafluoride from steel containers of any volume filled in with uranium hexafluoride irrespective of the share of uranium isotope 235. The method provides for heating of the container in a closed space up to the temperature of uranium hexafluoride transition into a gaseous state. The process is conducted in a tight induction furnace with a metal segmented chilled crucible, a penetrable for an electromagnetic field metal transported chilled tray, a metal chilled inductor and a metal chilled body. The method is realized in two stages: heating of the container up to the temperature of 70-195°С and aging in the heated state under action of inductive currents at a frequency of 500-70000 Hz. The temperature of the crucible sections, the tray, the inductor and furnace body is kept in the limits of 70-195°С. Cooling of the crucible sections, the tray, the inductor and the furnace body is conducted with a high-boiling organic heat-transfer agent: diphenyl, orthoterphenyl and others.

EFFECT: the invention allows extract uranium hexafluoride from steel containers of any volume filled in with uranium hexafluoride irrespective of the share of uranium isotope 235.

4 cl, 2 ex

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EFFECT: reduced power and materials consumption.

5 cl, 2 tbl

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