JPS6050730B2 - Denitration equipment for uranyl nitrate and/or plutonium nitrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a flat plate type fluidized bed having an injection nozzle to thermally decompose uranyl nitrate and/or plutonium nitrate, and continuously stabilizes the fluidized bed regardless of its width. Then Ξ
The present invention relates to a uranyl nitrate and/or plutonium nitrate denitrification device for producing uranium oxide or/and plutonium dioxide.

The present invention relates to the denitrification of uranyl nitrate and/or plutonium nitrate, but to simplify the description, the case where only uranyl nitrate is targeted will be described below.

At many natural uranium hexafluoride conversion plants, a purified uranyl nitrate solution is obtained using a solvent extraction method, which is concentrated and then denitrified by thermal decomposition to obtain Ξ uranium oxide.

Furthermore, in spent fuel reprocessing plants at nuclear power plants, uranium is separated from fission products and plutonium and is obtained as a uranyl nitrate solution, which is denitrified by thermal decomposition to obtain uranium trioxide. Methods for thermally decomposing uranyl nitrate include the pot method, stirred bed method, microwave heating method, fluidized bed method, etc., but the fluidized bed method is being widely put into practical use as the most efficient method. The fluidized bed used for denitrification of uranyl nitrate is mainly a cylindrical fluidized bed, but from the viewpoint of criticality control, there is a limit to the maximum allowable diameter of the cylindrical fluidized bed, so the diameter per unit base is limited. Processing power will be limited.

For this reason, the thickness of the fluidized bed is also subject to criticality control restrictions, but a flat fluidized bed that allows the length of the fluidized bed in the width direction to be expanded can increase the throughput per unit base. Because of its ability to denitrify uranyl nitrate, it is attracting attention as a fluidized bed for denitrifying uranyl nitrate.

Generally, when installing an injection nozzle to a flat plate type fluidized bed reactor, the injection nozzle is installed in a cross-sectional view in the width direction of the flat plate type fluidized bed, that is, in Fig. 1, which schematically shows a cross section of the flat plate type fluidized bed reactor. In this case, it is common to install the device horizontally with respect to the direction of the arrow X or x'' or both.

In addition, even if a flat plate fluidized bed is used to perform the denitrification reaction, the thickness of the fluidized bed must be determined from the viewpoint of criticality control, especially when handling slightly enriched uranium, etc., such as in the reprocessing and denitration of spent nuclear fuel. is limited.

In that case, the maximum allowable thickness is determined by the uranium enrichment of the raw material; for example, in the case of 4% enriched uranium, the maximum allowable thickness is 10 cm, which is inversely proportional to the enrichment. On the other hand, under the normally employed spraying conditions for the reactant (raw material), the velocity of the atomized body (reactant and atomizing gas) sprayed from the injection nozzle reaching the fluidized bed is several cm to 10 cm. cm, so if the spray nozzle is installed horizontally in the thickness direction of the flat plate fluidized bed, that is, in the direction of the arrow Y or Y'' in FIG. It reaches the wall on the opposite side of the machine or bounces off the opposite wall and deposits on the wall on the opposite side of the device or on the spray nozzle (including its surrounding walls), where it causes caking and the operation is stopped. In addition, in a fluidized bed, the fluidized gas from the rectifier initially becomes fine bubbles and rises in the fluidized bed, but on the way up, it coalesces with other bubbles and gradually grows. The target becomes large bubbles and rises in the fluidized bed.

Furthermore, it is a well-known phenomenon that slugging occurs when the linear velocity of the fluidizing gas in the fluidized bed is too high or when the height of the fluidized bed is too high. In this way, bubbles may grow in the fluidized bed or sludge may occur. When this occurs, a powder-free space (void) is created in a part of the fluidized bed. Therefore, in a flat plate type fluidized bed reactor, the injection nozzle is placed perpendicular to the projection line of the injection direction of the injection nozzle on the longitudinal direction of the apparatus wall in the horizontal cross section. When provided, when the air is emitted from the void and passes through the spray locus of the spray body, the reach to the wall surface on the opposite side of the spray body becomes particularly significant. However, a flat plate type fluidized bed reactor for thermally distributing uranyl nitrate usually has the following characteristics:
The spray nozzle is installed in the width direction of the device, but if the length of the width of the fluidized bed becomes large, this method will result in poor mixing of particles in the width direction of the fluidized bed, resulting in a stable product of uranium trioxide. A problem arises in that it is no longer possible to obtain .

The present invention solves the problems of the above-mentioned conventional flat plate fluidized bed reactor in which injection nozzles are installed in the width direction of the flat plate fluidized bed. / and thermal decomposition of plutonium nitrate Uranyl nitrate or /
and plutonium nitrate denitrification equipment.
The gist of this is that uranyl nitrate or/and plutonium nitrate solution is denitrified by thermal decomposition using a flat-plate fluidized bed with an injection nozzle to continuously produce uranium trioxide or/and plutonium dioxide. In a uranyl or/and plutonium nitrate denitrification device, the injection nozzle is placed on the device wall in the longitudinal direction in the horizontal cross section of the flat plate fluidized bed, and the following conditions are satisfied with respect to the projection line in the device horizontal cross section in the jetting direction of the jet nozzle. Take the angle θ〉COs-1 (Fw/Fs) where, Ew: Equipment water in the injection direction of the injection nozzle
Length of projected line in plane cross section Es: A denitrification device for uranyl nitrate and/or plutonium nitrate, which is characterized by a depth of reach of the spray body.

In the present invention, the angle θ with respect to the vertical axis with respect to the projection line in the horizontal cross section of the device in the jet direction of the jet nozzle attached to the wall surface of the device, which corresponds to the longitudinal direction in the horizontal cross section of the flat plate type fluidized bed, is determined by the following condition 0〉COs-1(Ew /Es)
Here, Ew: equipment water in the injection direction of the injection nozzle
Length of projected line in the plane section Es: satisfies the reach depth of the injection body, and this mounting angle θ is such that the spray body consisting of uranyl nitrate and atomizing gas sprayed from the injection nozzle hits the opposite wall surface of the device. This indicates the angle range to avoid reaching the target.

The thickness of the flat plate fluidized bed is determined from the viewpoint of criticality control, and for example, in the case of 4% enriched uranium used as fuel for light water reactors, it is actually about 8 cm when safety factors are taken into consideration. (The thickness of the fluidized bed can be calculated, but a control curve has been prepared for the relationship between concentration and thickness, and the above-mentioned thickness is usually determined from this curve.) Also, the depth reached by the above-mentioned spray body is usually Under the spraying conditions of the reactant employed, for example, when a currently commercially available spray nozzle is used and optimum operating conditions are taken into account, the spraying distance is usually about 10 cm. Therefore, under normal operating conditions, 'W: 8Cm. ．． eS: d 10cm, so θ≧COS-1(8110)=36.8m Of course, when reducing the thickness of the fluidized bed, the installation angle θ
The minimum value of becomes larger.

On the other hand, the upper limit of the mounting angle θ does not need to be particularly restricted due to the reaction mechanism in the fluidized bed, but from an empirical viewpoint such as maintainability, a value of 70 to 75 is optimal.

Next, the present invention will be explained with reference to the drawings. FIG. 2 is a longitudinal sectional view in the thickness direction of a fluidized bed including a spray nozzle according to an embodiment of the present invention, FIG. 3 is a front view including a partial cross section of the embodiment of FIG. 2, and FIG. 5 is an Es , lw is a perspective view showing an example.

In this example, uranyl nitrate is the object of denitrification.

In the figure, the spray nozzle 4 is attached to the device wall in the width direction of the flat fluidized bed at an angle of 0 with respect to the vertical axis in the thickness direction of the fluidized bed 3, and is inclined upward. As described above, this mounting angle θ is an angle that prevents the spray body consisting of uranyl nitrate and spray gas sprayed from the spray nozzle 4 from reaching the opposite wall surface of the device. Fluidization gas 1
0 passes from the wind box 1 to the fluidized bed 3 through the rectifier 2.
Meanwhile, the uranyl nitrate solution 12 is atomized together with the atomizing gas 11 from the atomizing nozzle 4 into the fluidizer 3.

The fluidized bed 3 is composed of uranium trioxide particles, fluidizing gas, atomizing gas, and reaction product gas. At the start of operation, uranium trioxide particles for forming the fluidized bed are supplied from the uranium trioxide seed hopper 7. The generated uranium trioxide particles 9 are continuously discharged from the overflow pipe 6 and sent to a product receiving tank (not shown). The gas is sent to an off-gas treatment system 13 after separating fine uranium trioxide particles entrained therein by a solid-gas separation filter 5 . 8 is an extraction tube.

A commercially available nozzle can be used as the spray nozzle of the device of the present invention without requiring a special nozzle.

When a commercially available nozzle is attached to the wall in the width direction of a flat plate type fluidized bed reactor in the thickness direction of the fluidized bed, the spray easily reaches the wall on the opposite side of the device, immediately causing caking and disrupting operation. Although it is clear that it will cause cancellation,
As shown in FIG. 2, such a commercially available spray nozzle 4 is attached to the wall surface in the width direction of the device at a certain angle to the vertical axis in the thickness direction of the fluidized bed, for example, in the case of a device thickness of 8 cm. Approximately 5
By attaching it at an angle of 0 or more, the distance that the spray body sprayed from the spray nozzle 4 can reach toward the wall on the opposite side of the device can be increased by about twice or more.
This prevents the spray from reaching the opposite wall of the device, thereby making it possible to denitrate uranyl nitrate continuously and stably without causing caking. In the above, we have described the case where the spray nozzle is installed on the device wall in the width direction of a flat plate type fluidized bed, facing upward and obliquely with respect to the vertical axis in the thickness direction of the fluidized bed, but the same effect can be obtained even when the spray nozzle is installed downward and diagonally. is obtained.

Furthermore, as shown in FIG. 4, the object of the present invention can also be achieved by installing the spray nozzle horizontally in the directions of arrows Z and Z'' (preferably on both sides); This can compensate to some extent the poor mixing properties of particles in the fluidized bed in the width direction, which is one of the disadvantages of the bed.The above is a case where uranyl nitrate alone is used as the target for denitration, but the device of the present invention can denitrate plutonium nitrate alone or nitric acid. Of course, it can be applied to the case of denitrification of a mixture of uranyl and plutonium nitrate.

Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless the gist thereof is exceeded.

Example In this example, the apparatus shown in FIGS. 3 and 4 is used to denitrify uranyl nitrate.

The spray nozzle 4 is attached to the wall surface of the apparatus in the width direction of the fluidized bed 3 so as to be obliquely upward at an angle of 500 with respect to the vertical axis in the thickness direction of the fluidized bed 3. The denitrification conditions are as follows.

The atomization condition (A/L) indicates the volume ratio of the atomization gas 11 and the uranyl nitrate solution 12. reaction temperature
285℃ uranyl nitrate concentration 12
00yuIe processing speed 20k9
U1hr atomization conditions (A/L) 4
00 Fluidized bed height 1.5TrL
The fluidizing gas linear velocity was 30 cmIsec, and the system was operated for one full day under these conditions, but there were no particular operational difficulties. After the operation was completed, when the inside of the reactor was observed, only slight caking was observed on the wall on the opposite side of the device corresponding to the spray nozzle 4 and at the tip of the spray nozzle 4, and the spray nozzle during operation was blocked. No problems occurred. Comparative Example This comparative example uses the same equipment as the example (however, the installation position of the spray nozzle in this case is the same as in the example, but the installation direction is in the thickness direction of the flat fluidized bed, that is, perpendicular to the installation wall surface). This is the case when uranyl nitrate was denitrated under the same conditions using

As a result, the spray nozzle began to become clogged approximately 4 hours after the start of operation, and although the spray nozzle was restored several times by needle operation,
After a period of time, the flow decreased, so the operation was stopped, and when the inside of the reactor was observed, a huge caking had occurred between the spray nozzle and the opposite wall.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view including the spray nozzles vertically attached to the wall of a flat plate type fluidized bed reactor, FIG. 2 is a longitudinal cross-sectional view including the spray nozzles of an embodiment of the present invention, and FIG. FIG. 4 is a front view including a partial cross section of the embodiment shown in FIG. 2, and FIG. FIG. 5 is a perspective view showing an example of 'S,'w. In the figure, 1... Fluidized gas wind box supply section, 2... Rectifier, 3... Fluidized bed, 4... Spray nozzle, 5... Solid-gas separation filter, 6... Overflow. vessel,
7... Uranium trioxide seed hopper, 8... Extraction pipe, 9... Uranium trioxide particles of product, 10... Fluidization gas, 11... Gas for spraying, 12... Uranyl nitrate solution, 13...off gas treatment system.

Claims (1)

[Claims] Uranyl nitrate or/and brutonium nitrate solution is denitrified by thermal decomposition using a flat plate fluidized bed having an injection nozzle to continuously produce uranyl trioxide or/and brutonium dioxide. In a brutonium nitrate denitrification device, the injection nozzle is attached to the wall surface of the device in the longitudinal direction in the horizontal section of the flat plate fluidized bed at an angle θ that satisfies the following condition with respect to the projection line of the injection direction of the injection nozzle in the horizontal section of the device. A denitrification device for uranyl nitrate and/or plutonium nitrate, which is characterized in that it is attached thereto. θ≧cos＾−＾1 (lw/ls) where, lw: Projection line length in the horizontal cross section of the device in the injection direction of the injection nozzle ls: Depth reached by the injection body