JPS5849626A - Denitration apparatus of uranyl nitrate and/or plutonium nitrate - Google Patents

Abstract

PURPOSE:To carry out the thermal decomposition and denitration of uranyl nitrate and/or plutonium nitrate, continuously, stably, uniformly throughout the width of the fluidized layer, by attaching a spray nozzle to the wall of the denitration apparatus at the width side of the flat-type fluidized layer making a specific angle between the nozzle and direction of the thickness of the fluidized layer. CONSTITUTION:A spray nozzle 4 is attached slantly facing upward to the wall of a denitration apparatus at the width size of the flat-type fluidized layer making an angle theta between the nozzle and the perpendicular axis along the direction of the thickness of the fluidized layer to satisfy the formula (lw is thickness of the fluidized layer; ls is the depth of the fluidized layer impregnated with the sprayed material). UO3 and/or PuO2 are introduced into the apparatus through the seed hopper 7, and a flat-type fluidized layer 3 is formed by the fluidizing gas blasted through the wind box 1 and the straightening vanes 2. A solution of uranyl nitrate and/or plutonium nitrate 12 is sprayed together with spraying gas 11 into the fluidized layer 3 through the nozzle 4 to effect the thermal decomposition and denitration of the nitrate, and the produced UO3 and PuO2 particles are exhausted through the overflow pipe 6. The generated gas is sent to the off-gas treating system 13 via the solid-gas separation filter 5.

Description

Detailed description of the invention - The present invention denitrates uranyl nitrate and/or plutonium nitrate by thermal denitrification using a flat plate fluidized bed having a J-type mist nozzle, and continuously denitrates uranyl nitrate and/or plutonium nitrate regardless of the width of the fluidized bed. The present invention relates to a denitrification device for uranyl nitrate and/or plutonium nitrate, which is stably converted into uranium trioxide or/and plutonium dioxide.

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

At many natural uranium fluoride conversion plants, purified uranyl nitrate solutions are obtained using solvent extraction methods, which are concentrated and then denitrified by thermal decomposition to obtain uranium trioxide. 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.

Thermal decomposition methods for uranyl nitrate include the pot method, stirred bed method,
There are microwave heating methods, fluidized bed methods, etc., but the fluidized bed method is being 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. Capabilities will be limited.

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

Generally, when a spray nozzle is attached to a flat plate type fluidized bed reactor, the spray nozzle is installed in a cross-sectional view in the width direction of the flat plate type fluidized bed, that is, in FIG. , is normally mounted horizontally to the direction of arrows X, Y', 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 about 10 Crn, and is inversely proportional to the enrichment. on the other hand,
Under the normally adopted spraying conditions for the reactant (raw material), the depth of the spray (Af) that the spray body (reactant and spray gas) sprayed from the spray nozzle reaches into the moving bed is in the range of several cm to several tens of meters. Therefore, if the spray nozzle is installed horizontally in the thickness direction of the flat plate fluidized bed, that is, in the direction of arrow Y or Y' in Fig. 1, the spray body sprayed from this spray nozzle will be directed to the opposite side of the device. Reaching the wall or bouncing off the opposite wall and depositing on the opposite wall of the equipment or on the spray nozzle (including its surrounding walls), causing caking and resulting in the suspension of operations. .

In addition, in a fluidized bed, the fluidized gas from the rectifier initially becomes fine bubbles and rises all the way up in the fluidized bed, but on the way up, it coalesces with other bubbles and gradually grows, becoming relatively large bubbles. , the total rise in the fluidized bed. Furthermore, it is a well-known phenomenon that slackening occurs if the linear velocity of the fluidizing gas in the fluidized bed is too high or the height of the fluidized bed is too high. In this way, if air bubbles grow or slugging occurs in the fluidized bed, a powder-free space (empty area) will be created in a part of the fluidized bed.
occurs. Therefore, in a flat plate type fluidized bed reactor, when a spray nozzle is provided on the wall surface in the width direction perpendicular to the thickness direction of the fluidized bed, the above-mentioned voids are generated and the spray 1! When the spray passes through the entire trajectory of the spray body, the reach of the wall surface on the opposite side of the spray body becomes particularly significant.

However, in a flat plate fluidized bed reactor for thermally denitrifying uranyl nitrate, the spray nozzle is usually installed in the width direction of the device a, as shown by the arrows X or Y' shown in FIG. When the length becomes large, this method poses a problem in that the mixing properties of the particles in the width direction of the fluidized bed deteriorate, making it impossible to obtain a stable product of uranium trioxide.

The present invention solves the problems of the above-mentioned conventional flat plate fluidized bed reactor g in which the spray nozzle is attached in the width direction of the flat plate fluidized bed, and the uranium nitrate The present invention provides a denitrification device for uranyl nitrate and/or plutonium nitrate that can continuously and stably perform pyrolytic denitrification of plutonium nitrate. In a uranyl nitrate or/and plutonium nitrate denitrification device that denitrates a uranyl nitrate or/and plutonium nitrate solution using a layer using a thermal component to continuously produce uranium trioxide or/and plutonium dioxide, the spray nozzle The device wall surface VC in the width direction of the flat plate type fluidized bed is set at an angle θ that satisfies the following condition with respect to the thickness direction of the fluidized bed.
r) Here, there is a uranyl nitrate or/and plutonium nitrate denitrification device, which is characterized by: shadow: #, thickness of the moving layer: depth reached by the spray.

In the present invention, the spray nozzle attached to the device wall in the width direction of the flat fluidized bed is perpendicular to the thickness direction of the fluidized bed on the device wall. I! 11] The angle θ with respect to K satisfies the following condition θ≧cOS−' Ce w /136 >Here, −e
3w: thickness of the fluidized bed βB: satisfies the depth reached by the spray body, and this mounting angle θ is such that the spray body consisting of uranyl nitrate and spray gas sprayed from the spray nozzle reaches the opposite wall surface of the device. It shows the full range of angles to avoid reaching.

The thickness of the flat plate fluidized bed is determined based on criticality control considerations, 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 account. (The thickness of the fluidized bed can be calculated, but there is a control curve for the relationship between concentration and thickness, and the thickness is usually determined from this curve.) Also, the depth reached by the spray is: Generally, 1017 mL of spraying conditions are used for the reactant, for example, when a currently commercially available spray nozzle is used and optimum operating conditions are taken into consideration.
It will be around 71.

Therefore, under normal operating conditions! , 8 cm in -13B, 10 cm in -13B, so θ≧cos-' (8/10) = 36.8° Of course,
Naturally, when the thickness of the fluidized bed is made thinner, the minimum value of the mounting angle θ becomes larger.

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

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, and FIG. 3 is a front view including a partial cross section of the embodiment of FIG.

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

In the figure, the spray nozzle 4 is attached to the wall surface of the apparatus in the width direction of the flat fluidized bed at an angle θ with respect to the vertical axis in the thickness direction of the fluidized bed 3, diagonally 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.

Fluidizing gas 10 is blown from wind box 1 through rectifier 2 into fluidized bed 3, while triranyl nitrate liquid 12 is sprayed together with atomizing gas 11 from spray nozzle 4 into fluidized bed 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 a fluidized bed are supplied from the uranium trioxide seed hopper 7. The generated uranium trioxide particles 9 are continuously discharged from the overflow u6 and sent to a product receiving tank (not shown). The gas is sent to an off-gas treatment system 13 after all fine uranium trioxide particles entrained therein are separated by a solid-gas separation filter 5 . 8 is an extraction tube.

As the spray nozzle of the apparatus of the present invention, a commercially available nozzle can be used 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 obvious that it will cause discontinuation, such a commercially available spray nozzle 4, as shown in FIG.
from the spray nozzle 4 by attaching it to the wall surface in the width direction of the device at an angle to the vertical IK axis in the thickness direction of the fluidized bed, for example, at an angle of about 50° or more to the inner metal of the device with a thickness of 8 m. Since the distance ffl' of the sprayed atomized body toward the wall on the opposite side of the device can be extended by about twice or more, the atomized body can be prevented from reaching the wall on the opposite side of the device, and This makes 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 direction of arrow 2°Z' (preferably on both sides); One of the shortcomings of the layer, flow in the width direction @ poor mixing of particles within the layer, can be covered to some extent.

Although the above is a case in which ranyl nitrate alone is denitrated, it goes without saying that the apparatus of the present invention can also be applied to denitrification of plutonium nitrate alone or a mixture of uranyl nitrate 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 sprays the fluidized bed 3 on the device wall in the width direction of the fluidized bed 30.
The upward direction of 50° with respect to the vertical axis in the thickness direction is attached to the Fth position.

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°C Uranyl nitrate solution concentration: 1200/'U/l゛
Processing speed: 20 kIPU/hr Atomization conditions (A/L): 400 Fluidized bed height: 1.5 m Linear velocity of fluidizing gas: 30 cm/sec It was operated under these conditions for 12 hours, 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 opposite wall of the device corresponding to the spray nozzle 4 and on the tip of the spray nozzle 4.
Comparative Example This comparative example is the same device as the example (however, the spraying position of the spray nozzle in this case is the same as in the example, but the installation direction is the same as in the example). This is a case where uranyl nitrate was denitrated under the same conditions using the thickness direction of a flat plate type fluidized bed, that is, the direction perpendicular to the mounting wall surface.

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 the inside of the reactor 1 was observed, and a huge caking had occurred between the spray nozzle and the wall on the opposite side.

[Brief explanation of drawings]

＠1 Figure shows 1 perpendicular to the wall of flat plate fluidized bed reactor a.
u direction [FIG. 2 is a cross-sectional view including the attached spray nozzle, FIG.
The figure is a front view including a partial cross section of the embodiment shown in Fig. 2, and Fig. 4 is a plane parallel to the wall surface in the 1st direction of the flat plate type fluidized bed reactor and at an angle of θ with respect to the thickness direction VC of the fluidized bed. FIG. 2 is a cross-sectional view including one spray nozzle arranged in the sludge direction. In the figure, 411111+11 fume, O,, 10e...
・Fluidization gas 5...Solid gas separation filter 11--
--Atomizing gas 6 am60 overflow pipe 1
2Φ...I1 Shoranil liquid (131 13...Off gas treatment system patent applicant Mitsubishi Metals Corporation Representative Yoshi Shirakawa Nao0滲$40 2nd □ □22■ 151- d\0

Claims (1)

[Scope of Claims] ill Uranyl nitrate in which uranyl nitrate or/and plutonium nitrate d solution is denitrified by thermal decomposition using a flat plate fluidized bed having a spray nozzle to continuously produce uranium trioxide or/and plutonium dioxide. Furthermore, in a plutonium nitrate denitrification device, the spray nozzle is attached to the wall surface of the device g in the width direction of the flat plate type fluidized bed at an angle θ that satisfies the following condition with respect to the thickness direction VC of the fluidized bed. Characteristic θ≧嘱−′ (Jl?W/, 8B) where IW: thickness of the fluidized bed, e8: denitrification device for uranyl nitrate or/and plutonium nitrate, where the depth of reach of the spray body is a characteristic.