JPS6144811B2 - - Google Patents

Description

Detailed Description of the Invention The present invention denitrates uranyl nitrate or/and plutonium nitrate using a fluidized bed having a spray nozzle, and continuously and stably denitrates uranyl trioxide or/and plutonium dioxide while saving labor. This invention relates to a uranyl nitrate and/or plutonium nitrate denitrification device for producing uranyl nitrate and/or plutonium nitrate.

At the uranium hexafluoride conversion plant, a purified uranyl nitrate solution is obtained using solvent extraction methods, and after concentrating it,
Denitration is performed by thermal decomposition to obtain uranium trioxide.

In addition, in spent fuel reprocessing plants at nuclear power plants, uranium separated from fission products and plutonium is obtained as a uranyl nitrate solution.
This is denitrified by thermal decomposition to obtain uranium trioxide.

Furthermore, in the reprocessing of spent fuel, for reasons of nuclear non-proliferation, a method is being planned in which a mixed solution of uranyl nitrate and plutonium nitrate is simultaneously thermally denitrified to obtain a mixed oxide. Although the present invention relates to the denitrification of uranyl nitrate and/or plutonium nitrate, only uranyl nitrate will be described below to simplify the description.

The pyrolytic denitrification method for uranyl nitrate includes a pot method, a stirred bed method, a microwave heating method, a fluidized bed method, etc., but the fluidized bed method is being widely put into practical use as the most efficient method.

In the fluidized bed method, the raw material uranyl nitrate solution is concentrated in advance to a predetermined concentration, and this is transferred to the inlet of the spray nozzle using a pump, etc., and the fluidized bed (uranyl trioxide) is (consisting of particles, fluidizing gas, reaction product gas, etc.) and thermally decomposed to obtain uranium trioxide (hereinafter referred to as UO ₃ ). Since this uranyl nitrate thermal decomposition is an endothermic reaction, it is heated externally using an electric heater or the like.

As shown in FIG. 1, a conventional fluidized bed denitrification device usually includes a device main body 101, a fluidizing gas supply section (hereinafter referred to as a wind box) 102, and a rectifier 1.
03, solid-gas separation filter 104, _UO3 seed filter 105, spray nozzle 106, overflow pipe 107, extraction pipe 108, etc. Rectifier 103 is typically flat. Some rectifiers have a tilted structure, but in that case the tilted rectifier remains inside when the operation is stopped.
The purpose is to make it easier to extract UO ₃ particles. Further, the extraction pipe 108 is usually equipped with a mesh at the pipe inlet to prevent coarse particles from entering the pipe and causing blockage. Furthermore, the valve 108a attached to the extraction pipe 108 is closed during operation.

In FIG. 1, a fluidizing gas 111a from a fluidizing gas supply pipe 111 is supplied from a wind box 102 at the bottom of the main body 101 through a rectifier 103, and UO ₃ particles generated by thermal decomposition of uranyl nitrate and reaction product gas (NO _x , H ₂ O, etc.) in a fluidized bed 1
09 is formed, and a new uranyl nitrate solution is blown into this fluidized bed 109 from the spray nozzle 106 to cause a reaction. The generated UO ₃ particles are allowed to have an appropriate residence time and then are continuously taken out from the overflow pipe 107. The UO ₃ seed hopper 105 is utilized to form a fluidized bed 109 at the start of operation. Also,
The solid-gas separation filter 104 is for separating fine UO ₃ particles accompanying the gas from the gas. The gas from which the UO ₃ particles were separated is transferred to the off-gas treatment system 1.
Sent to 10. In this type of overflow type fluidized bed denitrification apparatus, the extraction pipe 108 is used to extract UO ₃ particles remaining inside when the operation is stopped to the outside as necessary.

The above is a case of an overflow type fluidized bed denitrification equipment, but the _UO3 particles generated in the reaction zone are continuously removed from the extraction pipe (underflow pipe) installed at the bottom of the equipment body, without using the overflow pipe. Alternatively, an underflow type fluidized bed denitrification device that extracts water intermittently has also been put into practical use. Generally, in the denitrification reaction of uranyl nitrate, UO ₃ is produced in the reaction zone as described below.
Since it is inevitable that coarse particles (including lumps, the same shall apply hereinafter) are produced, underflow type fluidized bed denitrification equipment has the following drawbacks.

(1) The UO ₃ particles generated in the reaction zone and the above UO ₃ coarse particles are discharged together.

(2) Therefore, these particles tend to form a bridge in the middle of the extraction tube, causing blockage of the extraction tube.

(3) In order to perform a stable fluidized bed denitrification reaction, it is necessary to keep the fluidized bed height approximately constant in relation to heat transfer or residence time (if the fluidized bed height is not stable, operational control However, in underflow type fluidized bed denitrification equipment, it is difficult to balance the extraction amount with the production amount and keep it constant, and the height of the fluidized bed constantly fluctuates. do.

Although the superiority of these overflow type and underflow type fluidized beds is still debated, the present invention relates to overflow type fluidized beds.

In the fluidized bed denitrification reaction of uranyl nitrate, as described above, the raw material uranyl nitrate solution is blown into the spray nozzle and UO ₃ particles are produced by thermal denitration. As a result, the temperature drops considerably, so the tip of the spray nozzle contains undecomposed uranyl nitrate, condensed H ₂ O,
UO ₃ powder etc. adheres and gradually grows into a lump. Once these lumps have grown to a certain extent, they fall from the tip of the spray nozzle and remain on the rectifier because of the intense agitation in the fluidized bed. This phenomenon is repeated one after another, and the amount of lumps on the rectifier increases. These lumps may also grow on the walls of the equipment and on the tips of temperature detectors, etc. Furthermore, if operating conditions, especially temperature control, etc. are disturbed for some reason, coarse particles may be generated due to agglomeration of UO ₃ particles.

Therefore, it is possible to reduce the generation of the above-mentioned UO ₃ coarse particles or agglomerates to some extent by appropriately selecting operating conditions or by implementing various measures, but at present technology does not allow for the generation of UO 3 particles, especially at the tip of the spray nozzle. In the fluidized bed denitrification reaction of uranyl nitrate, it is impossible to prevent the formation of coarse UO ₃ particles and lumps in the fluidized bed. In the fluidized bed denitrification reaction of uranyl nitrate, maintaining the average particle size of UO ₃ particles in the fluidized bed at _400μ or less is an essential condition for continuous stable operation. The formation of agglomerates and lumps are unfavorable for operation. i.e. UO ₃ like this
If coarse particles, especially lumps, accumulate on the rectifier, the flow state will be disturbed, making it impossible to carry out the normal denitrification reaction, and stopping the equipment.
Those coarse particles and lumps must be discharged. Therefore, work efficiency and processing capacity are reduced.

The present invention solves the above-mentioned drawbacks of the conventional equipment, denitrates uranyl nitrate and/or plutonium nitrate using an overflow fluidized bed with a spray nozzle, and denitrates uranyl nitrate and/or plutonium nitrate continuously and stably while saving labor. The present invention provides a denitrification device for uranyl nitrate or/and plutonium nitrate that makes it possible to obtain uranyl nitrate or/and plutonium dioxide. In a uranyl nitrate and/or plutonium nitrate denitrification device that denitrates a plutonium solution by thermal decomposition to continuously produce uranium trioxide or/and plutonium dioxide, the lower part of the device body is a conical cone part, and the cone part A denitrification device for uranyl nitrate and/or plutonium nitrate, characterized in that an extraction pipe for uranium trioxide or/and plutonium dioxide coarse particles is opened at the lowest point of the uranium trioxide or/and plutonium dioxide coarse particles, and a fluidizing gas supply pipe is connected to the extraction pipe. ,It is in.

Next, the present invention will be explained with reference to the drawings.

FIG. 2 is a partially cross-sectional front view of an embodiment of the present invention, FIG. 3 a is an enlarged perspective view of a cone portion of a modification of the embodiment of FIG. It is an enlarged perspective view of a cone part of another modification.

Fig. 2 shows an embodiment of the present invention, in which the lower part of the device main body 1 in which a cylindrical fluidized bed is formed is a conical cone part 1a, and a wind box and a rectifier are omitted, and an extractor is connected to the cone part 1a. Fluidizing gas 7a is directly introduced into fluidized bed 4 through pipe 8. That is, an extraction pipe 8 for extracting coarse particles of UO ₃ was opened at the lowest point of the conical cone portion 1a at the bottom of the device main body 1, and the fluidizing gas supply pipe 7 was directly connected to this extraction pipe 8. It is the composition.

With this configuration, the fluidizing gas 7a passes directly to the fluidized bed 4 through the fluidizing gas supply pipe 7 and the extraction pipe 8.
be introduced within. The mechanism for extracting coarse particles from UO ₃ is as follows. That is, generally, an object falling through a gas has a terminal velocity determined by its shape (equivalent diameter), density, and the density and viscosity of the gas. Now, if we let the gas flow upward from below the falling object, the object whose terminal velocity is smaller than the velocity of the gas will be lifted upward,
An object with a terminal velocity greater than the velocity of the gas will fall downward. For example, the terminal velocity of UO ₃ particles having an equivalent diameter of 5 mmφ in air at 100° C. is calculated to be about 25 m/sec. Therefore, if you want to extract _UO3 particles larger than a certain particle size, the second
In the figure, the gas may be caused to flow through the gas introduction pipe 7 so that the flow velocity in the extraction pipe 8 corresponds to the terminal velocity of the particles. Thus, the extraction mechanism is based on exploiting the difference in terminal velocity of _UO3 particles in the gas.

During operation, valves 8a, 8b, and 7b are normally opened, and when the apparatus is stopped, valve 8a is closed. Also,
When replacing the UO ₃ coarse particle receiving hopper 2, close the valve 8b. The diameter of the extraction pipe 8 is designed taking into account the cross-sectional area of the fluidized bed, the linear velocity of the gas in the fluidized bed, the maximum and minimum diameters of the UO ₃ coarse particles to be extracted, etc. By providing the auxiliary gas introduction pipe 13 in 1a, the extraction pipe diameter and UO ₃
It is also possible to widen the selection range of coarse particle diameters. The inclination angle of the cone portion 1a may be at least the angle at which UO ₃ coarse particles roll to the opening of the extraction pipe 8, that is, the gas inlet portion 1b, but
Considering the stability of

FIGS. 3a and 3b are both enlarged perspective views of the cone portion in a modification of the embodiment shown in FIG. 2 in which the fluidized bed is of a flat plate type. The cone portions are both pyramid-shaped.

The features of the embodiment shown in FIGS. 2 and 3a and 3b are as follows.

(1) Since rectifiers, wind boxes, etc. are omitted, the design, manufacture, and maintenance of the device are simple.

(2) When it becomes difficult to maintain a normal fluidized state in the fluidized bed, the _UO3 particles inside may be extracted and the inside cleaned with nitric acid, etc. If so, it is necessary to first disassemble the device and then clean it, and since disassembly work is a dry process, residual _UO3 particles may scatter, which is not good for the working environment.However, with the device of the present invention, You can clean the inside directly without disassembling it.
This is extremely advantageous in terms of equipment maintenance.

(3) The structure is simple even when a heat source (heater), etc. is inserted inside.

The present invention has been described above in the case of denitrating uranyl nitrate alone, but it goes without saying that the present invention can also be applied to the case of denitrating plutonium nitrate alone or a mixture of uranyl handate and plutonium nitrate.

As described above, the apparatus of the present invention can be applied to both a cylindrical fluidized bed and a flat plate fluidized bed, and by having the above configuration, it can be used for uranyl nitrate or
and denitration of plutonium nitrate by thermal decomposition,
And only the coarse particles of uranium trioxide and/or plutonium dioxide are extracted, and uranium trioxide or/and plutonium dioxide can be produced continuously and stably with labor saving without stopping the operation of the equipment. The present invention provides a denitrification device for uranyl nitrate and/or plutonium nitrate that enables improved processing capacity, and is extremely useful in nuclear fuel processing.

[Brief explanation of the drawing]

FIG. 1 is a front view including a partial cross section of an example of a conventional fluidized bed denitrification apparatus for uranyl nitrate, FIG. 2 is a front view including a partial cross section of an embodiment of the present invention, and FIG. b is an enlarged perspective view of a cone portion of a modification of the embodiment shown in FIG. 2; b is an enlarged perspective view of a cone portion of another modification of the embodiment shown in FIG. 2; In the figure, 1... device main body, 1a... cone section, 1b... gas inlet section, 2... _UO3 coarse particle receiving hopper, 3... rectifier, 4... cylindrical fluidized bed,
5...Spray nozzle, 5a...Uranyl nitrate, 6...
...Overflow pipe, 6a...UO ₃ particles, 7...Fluidizing gas supply pipe, 7a...Fluidizing gas, 7b, 8a, 8b
... Valve, 8 ... Extraction pipe, 9 ... Solid-gas separation filter, 10 ... UO ₃ seed hopper, 11 ...
UO ₃ Off-gas treatment system, 101...Equipment main body, 10
2... Fluidization gas supply section (wind box),
103... Rectifier, 104... Solid-gas separation filter, 105... UO ₃ seed hopper, 106...
Spray nozzle, 106a...Uranyl nitrate, 107
...Overflow pipe, 107a...UO ₃ particles, 108...
Extraction pipe, 108a...Valve, 109...Fluidized bed, 110...Off gas treatment system, 111...Fluidization gas supply pipe, 111a...Fluidization gas.

Claims (1)

[Claims] 1 Denitration of uranyl nitrate or/and plutonium nitrate solution by thermal decomposition using a fluidized bed with a spray nozzle, and continuous denitrification of uranyl trioxide or/and plutonium nitrate solution.
In a uranyl nitrate and/or plutonium nitrate denitrification device for producing plutonium dioxide, the lower part of the device body is a cone-shaped cone,
Uranyl nitrate or/and plutonium nitrate, characterized in that an extraction pipe for uranium trioxide or/and rutonium dioxide coarse particles is opened at the lowest point of the cone part, and a fluidizing gas supply pipe is connected to the extraction pipe. denitrification equipment.