Method for producing monophase salts of actinides and device for producing same

Abstract

Method and device for the preparation of monophasic powders of actinide salts which are precursors in the production of fuel pellets. In one aspect, a compact and simple device is provided to obtain dry monophasic powders of actinide salts in one stage, while increasing the productivity, chemical and nuclear safety of the process. In a second aspect, the method comprises feeding of nitric actinides-containing solution and formic acid to a cylindrical heated reactor, grinding the resulting powder, and discharging the powder. The nitric actinides-containing solution and formic acid are continuously metered to the upper zone of the reactor so that the reactive chemicals are mixed in a thin film on the heat-exchange surface, where the reaction mixture is continuously stirred by rotor blades. Also occurring are the processes of denitration, formation of the relevant compounds, their drying and grinding and collecting dry salts of actinides in a hopper by gravity.

Claims

1. A method for producing monophase powders of actinide salts, comprising feeding a solution of one or more nitric actinides and formic acid in a cylindrical heated reactor, thereby forming a powder, grinding the resulting powder, and discharging the grinded powder, characterized in that the solution of one or more nitric actinides and formic acid are continuously metered to the upper zone of the reactor, wherein the solution and formic acid are mixed in a thin film on a heat-exchange surface and continuously stirred by rotor blades, wherein the grinded powder is collected in a hopper by gravity.

2. The method according to claim 1 characterized in that the solution of one or more nitric actinides and formic acid are batched separately and continuously in a (1:4.3)-(1:4.5) molar ratio of nitrate ion and formate ion.

3. The method according to claim 1 characterized in that the heat exchange surface temperature is maintained at 140?5? C.

4. A device for producing monophasic powders of actinide salts, including a vertical rotary-film reactor equipped with a heater, one or more chokers for entering reactive chemicals and for removing a vapor-gas phase, inside which is a rotor, with blades fixed along its entire length, characterized in that the one or more chokers for the reactive chemicals entering is made in the form of a tee, and a receiving hopper is made with the possibility of joining to a reactor and is equipped with a heater.

5. The device according to claim 4 characterized in that the rotor is made welded with four blades, and the gap between the blade edge and the wall is 0.5-1.5 mm.

6. The device according to claim 4 characterized in that the one or more chokers for the supply of solutions and a choke for the discharge of an outgoing vapor-gas phase are located in the upper part of the reactor above the edge of the blades.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is the nuclear and explosion-proof device (for implementing a method for producing monophase salts of actinides and device for producing same);

(2) FIG. 2 is the X-ray diffraction pattern of the powder obtained by Example 1, where ? is a compound with the CH.sub.2O.sub.5U; structure; ? is a compound with the C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O structure;

(3) FIG. 3 is the X-ray diffraction pattern of the powder obtained by Example 2, where ? is a compound with the CH.sub.2O.sub.5U; structure; ? is a compound with the C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O structure;

(4) FIG. 4 is the X-ray diffraction pattern of the powder obtained by Example 3, where ? is a compound with the structure of C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O; and

(5) FIG. 5 is the X-ray diffraction pattern of the powder obtained by Example 4, where ? is a compound with the structure of C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O.

(6) To achieve the specified technical result we propose the following: the method of preparation of monophasic powders of actinide salts, which involves feeding of nitric actinides-containing solution and formic acid in the cylindrical heated reactor, grinding the resulting powder, its discharge, characterized in that nitric actinides-containing solution and formic acid are continuously metered to the upper zone of the reactor, thus the reactive chemicals are mixed in a thin film on the heat-exchange surface, where the reaction mixture is continuously stirred by the rotor blades, while sequentially the processes of denitration, formation of the relevant compounds, their drying and grinding and collecting dry salts of actinides in a hopper by gravity.

(7) According to the method, the nitric acid solution containing actinides and formic acid are continuously batched in the molar ratio of the nitrate ion to the formate ion (1:4.3)-(1:4.5), and the temperature of the heat exchange surface is maintained equal to 140?5? C.

(8) The device for preparation of monophasic powders of actinide salts is also proposed in order to achieve this technical result. The proposed device comprises a vertical rotary-film reactor equipped with a heater and chokes for entering the reactive chemicals and removing waste gases, inside which there is a rotor made with the possibility of rotation, with blades fixed along its entire length. The choke for the reactive chemicals input is made in the form of a tee and the intake hopper configured to connect to the reactor vessel to reduce suction of cold air inside it and provided with a heater.

(9) Moreover: the rotor is welded with four blades, and the gap between the blade edge and the wall is 0.5-1.5 mm; a tee flow choke for the supply of solutions and a choke for the discharge of the outgoing vapor-gas mixture are located in the upper part of the reactor above the edge of the blades.

(10) For the purpose of the embodiment of the method, the nuclear and explosion-safe device is used, which is shown in FIG. 1, and which comprises the vertical cylindrical reactor (1), heated by a heater (2), the tee flow choke (3) for separate supply of solutions and the choke (4) for removing the vapor-gas mixture. The reactor (1) comprises a rotor (5) with a distribution disk and blades, the receiving hopper (6) equipped with a heater (7).

(11) The use of the proposed method for obtaining monophasic actinide salts and the proposed device for their preparation provides: short residence time of reactive chemicals continuously batched under thermal conditions with simultaneous deep evaporation to dry, resulting in increased productivity and safety of the process; the compactness of the device and the simplicity of its design allows it to be disassembled if necessary for inspection and washing of the internal surfaces; nuclear safety is ensured by minimizing the amount of nuclear materials in a thin film inside the device when scaling the process and using solutions with a high content of actinides.

(12) The method is as follows: an actinide-containing nitric acid solution and formic acid are fed separately to the reactor (1) via the choke (3), which is located above the heater (2), to the rotor disk (5) using metering pumps. The reaction mixture is discharged from the rotor disk onto the heated surface of the reactor (1) under the action of centrifugal force when the rotor (5) spins. The rotor blades (5) continuously stir the reaction mixture as it moves from top to bottom along the heat exchange surface, ensuring that dry actinide salts are obtained and collected by gravity in the hopper (6) equipped with a heater (7), and a vapor-gas mixture is removed from the reactor (1) through the choke (4).

Example 1

(13) Solutions of uranyl nitrate in 1 molar HNO.sub.3 with the uranium concentration of 100 g/l and concentrated formic acid at room temperature are fed separately to the reactor using metering pumps through a tee flow choke, while the molar ratio of nitrate-ion/formic acid is 1:3.6. The temperature on the reactor wall is 142? C., and the temperature on the receiving hopper wall is 145? C. The powder was poured into the receiving hopper homogeneously. According to XRF data, the powder consists of two crystalline phases: 50 wt. % of hydrate formate (CH.sub.2O.sub.5U) and 50 wt. % of aqueous formate (C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O). The X-ray diffraction pattern of the powder obtained by Example 1 is shown in FIG. 2, where: ? is a compound with the CH.sub.2O.sub.5U; structure; ? is a compound with the C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O structure.

Example 2

(14) Solutions of uranyl nitrate in 1 molar HNO.sub.3 with the uranium concentration of 100 g/l and concentrated formic acid at room temperature are fed separately to the reactor using metering pumps through a tee flow choke, while the molar ratio of nitrate-ion/formic acid is 1:4.0. The temperature on the reactor wall is 140? C., and the temperature on the receiving hopper wall is 130? C. The powder was poured into the receiving hopper homogeneously. According to XRF data, the powder consists of two crystalline phases: 20 wt. % of hydrate formate (CH.sub.2O.sub.5U) and 80 wt. % of aqueous formate (C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O). The X-ray diffraction pattern of the powder obtained by Example 2 is shown in FIG. 3, where: ? is a compound with the CH.sub.2O.sub.5U; structure; ? is a compound with the C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O structure.

Example 3

(15) Solutions of uranyl nitrate in 1 molar HNO.sub.3 with the uranium concentration of 100 g/l and concentrated formic acid at room temperature are fed separately to the reactor using metering pumps through a tee flow choke, while the molar ratio of nitrate-ion/formic acid is 1:4.3. The temperature on the reactor wall is 142? C., and the temperature on the receiving hopper wall is 160? C. The powder was poured into the receiving hopper homogeneously. According to the XRF data, the monophasic powder consists of 100 mass. % of aqueous formate (C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O). The X-ray diffraction pattern of the powder obtained by Example 3 is shown in FIG. 4, where: ? is a compound with the structure of C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O.

Example 4

(16) Nitric acid solution in 0.845 molar HNO.sub.3 with a concentration of 91.1 g/l for uranium, 9.0 g/l for thorium, and concentrated formic acid at room temperature is fed separately to the reactor using metering pumps through a tee flow choke, while the molar ratio of nitrate-ion/formic acid is 1:4.5. The temperature on the reactor wall is 142? C., and the temperature on the receiving hopper wall is 160? C. The powder was poured into the receiving hopper homogeneously, and according to the XRF data comprised a compound with the structure of aqueous formate and the formula of (C.sub.2H.sub.2O.sub.6(U, Th).Math.H.sub.2O). The X-ray diffraction pattern of the powder obtained by Example 4 is shown in FIG. 5, where: ? is a compound with the structure of C.sub.2H.sub.2O.sub.6U.Math.H.sub.2O.