JPS623095B2 - - Google Patents

Description

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

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 thermal denitrification method for uranyl nitrate includes the bot method, stirred bed method, microwave heating method, fluidized bed method, etc., but the fluidized bed method has been put into practical use as the most efficient method.

All conventionally used fluidized bed reactors are cylindrical. The fluidized bed reactors used for thermal denitrification of uranyl nitrate are all cylindrical, and the maximum diameter of the equipment is limited due to criticality control, so the processing capacity per unit number is limited. . Therefore, recently, as an alternative to the cylindrical fluidized bed, in the thermal denitrification reaction of uranyl nitrate, the thickness is also subject to criticality control restrictions, but the width is also subject to criticality control restrictions. Flat-plate fluidized beds, which do not have the same structure, are attracting attention.

In other words, the width of a flat plate fluidized bed can theoretically be increased to infinity, so by increasing this width, the cross-sectional area and heat transfer area of the fluidized bed device can be increased. , which has the advantage of increasing the processing capacity per unit radix.

However, due to the structure of flat plate type fluidized bed denitrification equipment, there is a problem with the strength of the equipment materials, and depending on the width of the fluidized bed, internal particles may not be mixed and dispersed sufficiently. In practice, it is not possible to increase the lateral length of the device to infinity because it would be difficult to maintain uniformity, especially thermal uniformity.

In the conventional cylindrical fluidized bed reactor used for pyrolytic denitrification of uranyl nitrate and the flat plate fluidized bed reactor described above, both have a fluidizing gas supply section (hereinafter referred to as a wind box) that supplies fluidizing gas from the bottom of the device. ) consists of a single category. The fluidizing gas supplied from the fluidizing gas supply pipe has a uniform pressure within this wind box, and is introduced into the fluidized bed at a substantially uniform linear velocity through a rectifier usually constructed of a metal wire mesh or the like. In addition, since the thermal denitrification reaction of uranyl nitrate is a rapid endothermic reaction, the equipment itself is usually maintained at an appropriate temperature by an external wire such as an electric heating device, and the uranyl nitrate is The solution is atomized into the fluidized bed along with an atomizing gas. At the start of operation, a predetermined amount of uranium trioxide is usually introduced into the equipment as seed particles, but once the denitrification reaction starts, the uranium trioxide particles generated by the denitrification reaction form a fluidized bed. The operation is carried out continuously by removing the uranium trioxide particles produced as the reaction progresses from the apparatus in a suitable manner. At that time, it has been confirmed that it is necessary to maintain the average particle size of the uranium trioxide particles produced at 400 μm or less in order to ensure the stability of the fluidized bed and to ensure continuous operation. for,
It is necessary to select the reaction temperature, the linear velocity of the fluidizing gas, and the conditions for spraying uranyl nitrate, and at the same time, it is essential to maintain uniformity, especially thermal uniformity, within the fluidized bed.

In particular, in the currently proposed flat plate type fluidized bed denitrification equipment, as mentioned above, the thermal denitrification reaction of uranyl nitrate is a rapid endothermic reaction, and due to thermal decomposition of uranyl nitrate, evaporation of water, etc. A large amount of gas is generated near the uranyl nitrate introduction part in the layer, and the heat transfer rate near the introduction part decreases significantly.
Furthermore, under normally applicable spray conditions, the depth of the spray from the spray nozzle (uranyl nitrate solution and spray gas) reaching into the fluidized bed is several centimeters at most.
The denitrification reaction of the sprayed uranyl nitrate proceeds as the mixed region of the spray and the fluid diffuses into the fluidized bed.
Therefore, if this diffusion is insufficient, the ratio of uranyl nitrate in the spray to the fluid becomes locally excessive near the spray nozzle, and
As the effective supply of heat required for the denitrification reaction becomes insufficient, the uniformity within the fluidized bed, especially thermal uniformity, is lost and a caking phenomenon occurs, making it difficult to form a normal fluidized bed. It becomes impossible to operate the fluidized bed reactor stably and continuously over a long period of time.

In addition, in the currently proposed flat plate type fluidized bed denitrification equipment, the wind box has a single section structure. Mixing and dispersion of the produced uranium trioxide particles at the sides (in a fluidized bed with two spray nozzles in symmetrical positions, the uranyl nitrate introduction part, that is, the part near the wall side and the center part) may be insufficient. ,In that case,
The inventors believe that the amount of heat transferred to the reaction part in the fluidized bed is insufficient, causing the above-mentioned caking phenomenon, or that the physical properties (particle size, amount of residual uranyl nitrate, etc.) of the produced uranium trioxide become non-uniform. It was confirmed by et al.

The present inventors studied to solve the above-mentioned problems of the currently proposed flat plate type fluidized bed denitrification device, and as a result, they focused on changing the mechanism for supplying fluidizing gas to the fluidized bed, and arrived at the present invention. did. That is, the present invention denitrates uranyl nitrate and/or plutonium nitrate by thermal decomposition using a flat fluidized bed having a spray nozzle, and denitrates uranyl nitrate and/or plutonium nitrate continuously and stably, regardless of the horizontal length of the flat fluidized bed. Uranyl nitrate/ which can be directly converted to uranium trioxide or/and plutonium dioxide and allows for simplified equipment.
The present invention provides a denitrification device for plutonium nitrate, the gist of which is to denitrify uranyl nitrate and/or plutonium nitrate by thermal decomposition using a flat plate fluidized bed having a spray nozzle. In a uranyl nitrate and/or plutonium nitrate denitrification device for producing uranium oxide or/and plutonium dioxide, the lower part of the device main body has a plurality of parallel cone-shaped cone parts, and the lowest part of each of the plurality of cone parts. A denitration apparatus for uranyl nitrate and/or plutonium nitrate, characterized in that a fluidizing gas supply pipe is opened at the uranyl nitrate and/or plutonium nitrate.

As described above, the device of the present invention basically has a plurality of cone-shaped cone portions arranged in parallel at the bottom of the device main body,
The configuration is such that fluidizing gas supply pipes are opened in each of these multiple cone sections and fluidizing gas is directly supplied to the cone sections.This configuration eliminates the need for the wind box and rectifier of conventional equipment. This makes it possible to simplify the device itself, thereby facilitating the design, manufacture, and maintenance management of the device.

In the apparatus of the present invention, when the horizontal length of the fluidized bed becomes large and it becomes difficult to maintain the fluidized bed,
The structure is such that a flow rate adjusting means is attached to each of the fluidizing gas supply pipes. With this configuration, different flow rates of fluidizing gas are supplied from the fluidizing gas supply pipe to each cone section, and the particles in the fluidized bed are forced to flow, making it possible to maintain the fluidized bed. . That is, as illustrated in FIG.
c, and flow rate adjustment valves 12a, 12b, 12c and a flow rate indicator 13 are installed in the fluidizing gas supply pipe 3 opened to these cone portions 2a, 2b, 2c, respectively.
a, 13b, and 13c to change the flow rate of the fluidizing gas for each cone part, for example, the flow rate of the fluidizing gas to the cone part 2c which is farthest from the spray nozzle 5 is the highest, and the flow rate to the cone part 2c which is the closest to the spray nozzle 5 is the highest. By minimizing the flow rate to the cone portion 2a,
A forced flow is generated in the uranium trioxide particles in the fluidized bed 4 to promote their mixing and dispersion, thereby ensuring thermal uniformity in the fluidized bed 4 regardless of the width of the fluidized bed 4. This makes it possible to continuously and stably carry out pyrolytic denitrification of uranyl nitrate while maintaining the same temperature, thereby converting it into uranium trioxide with uniform physical properties.

In the denitrification reaction using a flat plate fluidized bed having a uranyl nitrate spray nozzle, as shown in FIG. Uranium trioxide particles are produced by denitrification, and coarse particles of uranium trioxide are also produced at the same time in the reaction zone. In addition, as mentioned above, the denitrification reaction of uranyl nitrate is an endothermic reaction, so the temperature near the tip of the spray nozzle 5 drops considerably, so the tip of the spray nozzle 5 contains undecomposed uranyl nitrate, condensed H ₂ O, and Uranium oxide powder often adheres and gradually grows into lumps. Once the lumps have grown to a certain extent, they fall from the tip of the spray nozzle 5 because the inside of the fluidized bed 4 is in a vigorously agitated state. These lumps may also grow on the walls of the equipment and on the tips of temperature and other detectors.
Furthermore, if operating conditions, particularly temperature control, etc. are disturbed, coarse particles may be generated due to agglomeration of uranium trioxide particles.

In this way, as the coarse particles (including lumps) of uranium trioxide increase in the fluidized bed 4, the average particle size of the uranium trioxide particles in the fluidized bed 4 is reduced to 400 μm.
It becomes difficult to maintain the denitration reaction below, and it becomes impossible to stably and continuously perform the fluidized bed denitrification reaction of uranyl nitrate, so the apparatus must be stopped and the coarse particles must be discharged. Therefore, work efficiency and processing capacity are reduced.

In order to solve the problems caused by coarse particles in the flat fluidized bed, the present invention includes a plurality of cone-shaped cone sections arranged in parallel at the lower part of the device main body, and each of the plurality of cone sections A uranium trioxide or/and plutonium dioxide coarse particle extraction pipe is opened at the lowest part, a fluidizing gas supply pipe is connected to each of the extraction pipes, and a flow rate adjusting means is attached to each of the fluidizing gas supply pipes. It takes a composition.

With this configuration, the fluidizing gas from the fluidizing gas supply pipe 3 is supplied to the flow rate adjusting valves 12a and 1, respectively.
2b, 12c and flow rate indicators 13a, 13b, 13
The flow rate is adjusted by c, and the cone portions 2a, 2b, and 2c are supplied at different flow rates through the extraction pipe 14, and the uranium trioxide particles in the fluidized bed 4 are forced to flow, mixing and dispersing them. By promoting this, it is possible to maintain thermal uniformity within the fluidized bed 4 and to proceed in a continuous and stable manner with thermal denitrification of uranyl nitrate blown from the spray nozzle 5. On the other hand, the coarse particles of uranium trioxide generated in the reaction zone in the fluidized bed 4 are
c and moves along the inside of the extraction pipe 14.
collected at the opening of the As described above, the fluidizing gas from the fluidizing gas supply pipe 3 is introduced into the extraction pipe 14, and the flow rate of the fluidizing gas in the extraction pipe 14 is adjusted to the terminal velocity of the uranium trioxide particles. When this is done, only the large particles of uranium trioxide phase can fall through the extraction pipe 14 and be extracted due to the difference in terminal velocity. A uranium trioxide coarse particle receiving tank 15 is connected to the lower end of the extraction pipe 14. During operation, the valves 14a, 15a, and 13d are normally opened, and when the apparatus is stopped, the valve 14a is closed. Receiving tank 15
When replacing the valve 15a, close the valve 15a.

The diameter of the extraction pipe 14 for selectively extracting coarse uranium trioxide particles is determined by taking into account the cross-sectional area of the fluidized bed, the linear velocity of the gas in the fluidized bed, the maximum diameter and minimum diameter of the coarse particles of uranium trioxide to be extracted, etc. Designed with

In FIG. 2, uranium trioxide particles generated by denitrification of uranyl nitrate are continuously taken out of the system through an overflow pipe 6, and the accompanying uranium trioxide particles are separated from the gas by a solid-gas separation filter 11. Thereafter, it is sent to an off-gas treatment system 8. 7 is a uranium trioxide seed hopper.

As described above, by adopting the configuration shown in FIG. 2, the present invention simplifies the equipment and does not stop the operation of the equipment even though coarse particles of uranium trioxide are generated. , it is possible to continuously and stably denitrify uranyl nitrate to uranium trioxide and to increase processing capacity.

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

[Brief explanation of the drawing]

FIG. 1 is a partially sectional front view of one embodiment of the present invention, and FIG. 2 is a partially sectional front view of another embodiment of the present invention. In the figure, 1... device main body, 2a, 2b, 2
c...Cone part, 3...Fluidization gas supply pipe, 4...
... Fluidized bed, 5 ... Spray nozzle, 6 ... Overflow pipe, 7
... Uranium trioxide seed hopper, 8 ... Off gas treatment system, 9 ... Uranyl nitrate solution supply system, 10
...Gas supply system for spraying, 11...Solid gas separation filter, 12a, 12b, 12c...Flow rate adjustment valve, 13a, 13b, 13c...Flow rate indicator, 1
4...Extraction pipe, 15...Uranium trioxide coarse particle receiving tank, 13d, 14a, 15a...Valve.

Claims (1)

[Claims] 1. Uranyl nitrate or/and plutonium nitrate that is denitrified by thermal decomposition using a flat plate fluidized bed having a spray nozzle to continuously produce uranyl trioxide or/and plutonium dioxide. and a denitrification device for plutonium nitrate, characterized in that the lower part of the main body of the device has a plurality of parallel cone-shaped cone portions, and a fluidizing gas supply pipe is opened at the lowest part of each of the plurality of cone portions. Denitrification equipment for uranyl nitrate and/or plutonium nitrate. 2. A uranyl nitrate and/or plutonium nitrate denitrification device that continuously produces uranium trioxide and/or plutonium dioxide by denitrating uranyl nitrate and/or plutonium nitrate by thermal decomposition using a flat plate fluidized bed having a spray nozzle. In this, the lower part of the main body of the device is made up of a plurality of parallel cone-shaped cone parts, and a fluidizing gas supply pipe is opened at the lowest part of each of the plurality of cone parts, and a flow rate is adjusted in each of the fluidizing gas supply pipes. A denitration device for uranyl nitrate or/and plutonium nitrate, characterized in that a means is attached thereto. 3. A uranyl nitrate and/or plutonium nitrate denitrification device that continuously produces uranium trioxide and/or plutonium dioxide by denitrating uranyl nitrate and/or plutonium nitrate by thermal decomposition using a flat plate fluidized bed having a spray nozzle. In this method, the lower part of the main body of the apparatus has a plurality of parallel cone-shaped cone parts, and a uranium trioxide or/and plutonium dioxide coarse particle extraction pipe is opened at the lowest part of each of the plurality of cone parts, and 1. A denitrification device for uranyl nitrate and/or plutonium nitrate, characterized in that a fluidizing gas supply pipe is connected to each outlet pipe, and a flow rate adjusting means is attached to each of the fluidizing gas supply pipes.