JPS6028768B2 - Process and equipment for producing uranium tetrafluoride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to significant improvements in the process of producing uranium fluoride from oxides of uranium metal currently used on an industrial scale.

The method is described in French Patent No. 1,107,592 filed June 18, 195 France and Patent of Addition No. 72,
No. 44 and Supplementary Patent No. 74,259. The object to be achieved according to the method is to obtain U03 or U308 which are obtained in turn by chemical treatment of concentrates derived from uranium iron ore deposits.
The goal is to convert high uranium oxides such as uranium to uranium tetrafluoride.

Uranium tetrafluoride is a component of intermediate products subsequently used in the production of such fuels based on natural or enriched uranium in the form of metals, oxides or other compounds. The method consists of two consecutive steps.

First, high uranium oxides such as U03 or U308 are
02 and then simultaneous fluorination of U02 to yield UF4 as the final product. The first process is up to 60
This is accomplished by action on the high oxides produced by decomposed ammonia at temperatures between 0° and 70°.

The resulting uranium dioxide is then decomposed with hydrochloric acid and a reaction process occurs which can be described in a general manner by the equation below. U02 14m→Plate 40 is 20 FIG. FIG. 2 is a schematic diagram of an apparatus for performing the two steps sequentially according to the technology of the present invention.

In this figure, particles consisting essentially of one or more high oxides of uranium, such as U03 or U308, are 0.
It is continuously introduced through a hopper 1 into a tube 2 of a refractory metal, such as steel, containing 15% carbon, 25% chromium and 20% nickel, the balance being iron and small amounts of additives and impurities. Ru.

This tube 2 can hold the filling at a maximum temperature of 6000~700oo
External heating is performed by an electric furnace 3 which plays a role of heating during the heating process. Ammonia gas is injected into the base of the tube 2 at position 4 and passes upwardly therein countercurrently with the filling. The ammonia initially serves to contribute to the cooling of the uranium dioxide already formed and then gradually decomposes as its temperature increases in contact with the charge.
The nascent hydrogen that forms reduces the high uranium oxides to U02. The total heat balance of this first reaction step is negative, which means that heat has to be supplied by the furnace 3. The particles which pass through the throat 8 and are then discharged at the bottom of the tube 2 therefore essentially consist of uranium dioxide U02.

The particles pass through passage 10 into Monel (Monel, 63
Int on a Ni-Cu alloy consisting of up to 68% Ni and small amounts of Fe, Mn, Si and C with the remainder being
erMtio Misaki 1, a registered trademark of Nickel Co.)
, where it is brought into contact at high temperature with hydrohydric acid introduced from tube 7 and circulated countercurrently in gaseous form.

The tube 9
The separation device into which injection of a neutral gas, such as nitrogen gas, is made through is necessary to mix the gaseous reagent introduced or formed in tube 2 with the gaseous reagent introduced or formed in tube 5. , the gaseous reagent introduced or formed in the tube 5 is discharged through the orifice 11.

Under these conditions, the combined reaction of reduction of U02 and formation of UF4, as represented by the above equation, is significantly exothermic. However, since it may be introduced into tube 5 when the temperature of the charge at the outlet of tube 2 is very low, it may be necessary to heat the charge to start the reaction. This heating operation is performed in the furnace 6.
It is carried out by Once the reaction starts, heat is generated equivalent to 52 calories per gram of gaseous HF injected. This results in rapid heating of the U02 charge and tends to result in deviations from reaction conditions in short sections of the lower part of the charging zone. If the temperature exceeds about 600 pm, this results in a rapid density increase of the U02 particles and a surface layer of UF4 with low permeability is formed around each particle, which prevents the fluorination in the center of the particle. It was observed that substantially no interference was observed.

In order to reduce these disadvantages, the diameter of the tube 5 is limited to a value such that the generated heat can be removed through the tube stub of the tube 5 in such a way that it is established that temperature changes do not occur with appreciable values. Saw what needed to be done and served.

This limited diameter rarely allows more than about 25 mm. Furthermore, in order to remove a large amount of heat of formation, it was found necessary to equip the furnace 6, which serves to start the reaction, with a cooling device such as a coil 12 through which running water is passed for cooling after the start of the reaction. Ta. This technique does not allow for very significant differences in the cross-section of the tube, since the central part of the tube is heated to a temperature around 600°C, whereas the peripheral part can be at a temperature too low for complete reaction. cannot be prevented. In order to provide a partial remedy for these shortcomings, it has been proposed to provide a reaction band with a substantial height and as described in the first patent specification of French Patent No. 1,107,592. As such, it is necessary to provide a take-off worm 13 which is considerably longer than the take-off worm that would be required in the case of a simple take-out. This worm 13 is combined with the mixing of the particles emitted by tube 5 and the countercurrent-like injection of gaseous HF through tube 14 and furnace 15.
This makes it possible to complete the fluorination of each particle by heating. Despite the various improvements made in this way, it is not possible to exceed the production rate of approximately 50k9/hour for the UF4, which requires the production of very large quantities of the same equipment to meet the rapidly increasing demand. You will not need to install it.

The possibility of establishing a significantly larger diameter reaction tube fitted with an internal cooling system was contemplated by us, however,
Circulating cooling fluid through conduits which are exposed to the mechanical action of the fill at relatively high temperatures and, in particular, to the severe corrosive action of hydrofluoric acid, has been both cumbersome and dangerous.

Because of the potential risk of leakage, a device with sufficient composite stability was therefore planned. In order to solve all these problems in a significantly simpler way, we conceived the unexpected concept of relying on the use of hydrofluoric acid itself for reaction control.

In the chemical industry, this acid is mostly used in the form of an aqueous solution. It has been found and provided that when the acid is used in anhydrous form as in the present invention, it is preferable to dispense it in gaseous form from a reservoir in which the acid is present in liquid form.

The reservoir is heated to obtain the desired pressure of gaseous HF above the liquid and passes the gas to a distribution system. This does not pose any particular difficulties since hydrofluoric acid boils at about 20 qo at atmospheric pressure. To achieve the desired objective, we decided to use hydrofluoric acid in the liquid and non-gaseous state in a direct reaction zone.

At last it has been achieved to advantageously use the very characteristic properties of hydrofluoric acid, namely in its polymerized state at low temperatures. In fact, when hydrofluoric acid is boiled, the vapor formed has the structure of (HF)6, which gradually depolymerizes as a function of temperature and at about 100 °C
Completely depolymerized in .

HF vapor at around 20:00 o'clock absorbs about 97 calories per gram of heat.

It is therefore clear that approximately 43 calories per gram of heat needs to be supplied to the hydrofluoric acid in order to move it from the liquid state to the depolymerized gas state. This figure is comparable to 525 fewer calories per gram of HF released by the perfluorination reaction of UQ with gaseous HF. It is therefore clear that if gaseous HF is replaced by liquid HF, the balance of the reaction will be only slightly exothermic. It is thus possible to very easily control the temperature of the liquid HF and to establish the desired temperature regime in the reaction tube to ensure that the reaction takes place at optimal reaction rates and efficiencies. It will be possible. Provided that it proves practical to carry out the evaporation and depolymerization of HF in the actual center of the reaction zone, a high rate of heat transfer effect will be obtained and the temperature variation will be reduced. Thus, the flow cross-sectional area of the reaction tube is increased to a very substantial extent and thus an apparatus is provided which has significantly increased productivity compared to apparatus installed according to the prior art. Is possible. An example of the implementation of the invention is described in the example below.

However, this is not intended to limit the invention. With reference to the accompanying drawings, FIG. 2 represents a modified furnace for the practical application of the method according to the invention, in which the first step of the reaction, namely the production of U02 by reduction of high uranium oxides, is shown. The relevant parts have not been appreciably modified and have therefore been omitted from the drawings. 3 and 4 are elevational and plan views, respectively, showing details of an apparatus in which the method of the invention can be utilized. At the top of the figure is shown the lower end of the tube 16 in which the reduction of high oxides of uranium such as U03 and U308 takes place, and then the resulting material from the reduction step is converted into substantially uranium dioxide. A connecting part 17 is shown through which particles with a corresponding composition can pass. The connecting part is provided with conventional devices for separating the gas injected from the pipe 18 into the lower region of the outlet pipe 16. Such a device was awarded the first French patent,
No. 107,592 in two additional patent specifications. A reduction-fluorination tube 18 is connected to the flange of the connection in a conventional manner. In the tube 18, the tube 16
The particles fed through first pass through the connection and then form an annular structure between the inner wall of tube 18, which has an outer diameter of about 40 mm, and the outer wall of concentric tube 19, which has an inner diameter of about 150 mm. distributed. The tube 19 is open at the lower end and closed at the top by a preferably conical leak-proof cap 20'. The tube is made of a material such as Monel, a metal that can withstand temperatures up to 600 oo and withstand corrosive atmospheres formed by liquid or gaseous HF mixed with water vapor. It is possible.

The tubes 18 and 19 are connected to each other by three substantially radially located connections 21 of Monel plate-like elements, which are arranged at an angle of about 12 degrees. The plate-shaped connecting element vertically welds the two tubes over a distance of about 50 ribs. A cylindrical HF reservoir 22 with a length of approximately 80 ribs and a diameter of 10 ribs.
are fixed circularly inside the tube 19 by three radially positioned combinations of Monel plate elements 23 placed at an angle of 12,000°, and the plate elements are used for storage. The vessel 22 and the tube 19 are welded together. Finally tube 2
4 serves to supply the reservoir 22 with liquid HF obtained from an external storage device. When the furnace is in operation, the reaction between the annularly distributed downwardly moving charge and the gaseous hydrofluoric acid flowing countercurrently and upwardly passes at 52 milk per gram.・Emits a powerful amount of heat equivalent to a calorie.
This results in heating the filling to a temperature in the range of 5000 to 600 qo. Most of the heat thus generated is transferred to the inner tube 19 and the liquid HF in the reservoir 22 by radiation and conduction. This heat successively causes the evaporation of the HF and then the depolymerization of the vapor produced, which moves downward in tube 19 to its lower end and then forms between tube 18 and tube 19. The particles pass upward through the space where they are formed and react with the particle packing moving downward. At the bottom of the tube 18, the extraction system consists of a worm 25 with a heating furnace 26 and a countercurrent injection of gaseous HF via the tube 27.
It serves to mix the particles and complete the reaction, as described in the first patent specification of French Patent No. 1,107,592. As mentioned above, the heat balance of the reaction is only slightly positive when liquid HF is used. If too much of the HF is introduced in liquid state as a result, tube 1 is
In addition to insulating the tube 8, it is also necessary to heat the tube externally by conventional means such as a relatively low capacity electric furnace 28. It is possible to maintain the temperature of the reaction zone by other methods. The method therefore consists of varying the proportion of the amount of HF in liquid state introduced through tube 24 and the amount introduced in gaseous form through tube 27. This adjustment is carried out by means known to those skilled in the art, for example, by continuously measuring the temperature in the annular space between tubes 18 and 19, and by continuously measuring the temperature in the annular space between tubes 24 and 27. This can be done by applying this to a system for controlling the distribution of , correcting deviations from the reference value. It should be noted that if the distribution device supplies HF in liquid state, a heating system for vaporizing and depolymerizing the HF must be provided on the conduit connecting the distribution device to pipe 27. It is. If the temperature in the reaction zone becomes too low, the supply of liquid HF in tube 24 can be reduced in this way, with the result that the total heat balance of the reaction in tube 18 is sufficiently positive. It is possible to increase the supply of gaseous HF in tube 27. This ultimately increases the temperature measured within the annular space. Conversely, if the temperature in the counter zone becomes too high, the regulating device will act in the opposite direction and reduce the temperature of the tube 2.
The flow of liquid HF in tube 27 is increased and the flow of gaseous HF in tube 27 is decreased. With this adjustment method,
It is possible to obtain excellent stability of operation and a high degree of uniformity in terms of product quality.

Said furnace has a production capacity of 400 k9 of UF4 per hour, ie substantially eight times the capacity of a conventional furnace with a diameter of 250 mm. The example described above is only one particular embodiment of the use of the present invention.

Concerning the introduction of liquid hydrofluoric acid for the purpose of cooling the reaction zone, it is thereby possible, without departing from the scope of the invention, to introduce said liquid acid directly into one or more geothermal tubes. It is possible to bring the material into contact with the filling material.

In this case, the circular inner tube can be omitted and a sprinkler device or means suitably distributed establishing a jet of fluid hydrofluoric acid preferably directed towards the shank area, i.e. the area producing the highest temperature. The hydrofluoric acid can be flowed over the packing. It is also possible to use the same circular inner tube filled with a packing such as a Raschig ring, over whose surface liquid hydrofluoric acid moves.

Many alternative arrangements may be devised without departing from the general scope of the invention.

[Brief explanation of the drawing]

FIG. 1 shows a conceptual diagram of the apparatus used to carry out the method of the subordinate technique, and FIGS. Represents a side view and a plan view. In the figure, 1 is a hopper, 2 is a tube, 3 is an electric furnace, 4 is a position, 5 is a tube, 6 is a furnace, 7 is a tube, 8 is a throat, 9 is a tube, 10 is a passage, 11 is an orifice, 12 is a coil, 13 is a worm, 14 is a tube, 15 is a furnace, 16 is a tube, 17 is a connecting part,
18 is a pipe, 19 is a pipe, 2 rivers and a cap, 21 is a combined body,
22 is a storage device, 23 is a plate element, 24 is a tube, 25 is a worm, 26 is a furnace, and 27 is a tube. FIG.
．． lFIG. 3 FIG. 2 FIG. 4

Claims (1)

[Claims] 1. The temperature increase resulting from the heat generated by the reaction between gaseous hydrofluoric acid and uranium oxide is used to evaporate the required hydrofluoric acid and at least Hydrofluoric acid, characterized in that at least a portion of the heat is used to depolymerize some of the evaporated components, and the evaporated components are introduced in a liquid state into a reaction zone or an area adjacent to the zone. and a process for producing uranium tetrafluoride by reaction of uranium oxide present essentially in the form of dioxide during the reaction. 2. Adjusting the reaction temperature by varying the amount of hydrofluoric acid introduced in liquid state into the reaction zone or an area adjacent to said zone, and introducing the necessary replenishment in the form of gaseous hydrofluoric acid. A method according to claim 1. 3. Introducing liquid hydrofluoric acid into a reservoir heated by radiation and/or conduction by the heat generated by the reaction zone, and at least a portion of the heat so transferred being evaporated and then heated by the acid. 3. A method according to claim 1 or claim 2, wherein the hydrofluoric acid is absorbed by at least partial depolymerization of the hydrofluoric acid before reacting with uranium oxide. 4. Process according to claim 1 or 2, in which the hydrofluoric acid is introduced in liquid state directly into the uranium oxide charge at one or more points. 5 Containing a plurality of vertical concentric tubes of material resistant to heat and corrosion by HF and/or H_2O, the tubes being open-topped and equipped with an annular zone containing uranium dioxide and a supply of liquid hydrofluoric acid. The central region is arranged to define a central region in which a reservoir is located, the central region being such that hydrofluoric acid vapor emanating from the reservoir penetrates into the annular region and flows countercurrently with the uranium dioxide charge. hydrofluoric acid, which is arranged to connect with said annular region by its lower part so as to pass upward therethrough; Equipment for producing uranium tetrafluoride through the reaction of uranium oxide.