JPS6035287B2 - Denitration equipment for uranyl nitrate and/or plutonium nitrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention makes it possible to denitrate uranyl nitrate and/or plutonium nitrate by thermal decomposition using a flat plate fluidized bed and convert it continuously and stably into uranium trioxide and/or plutonium dioxide. The present invention relates to a denitrification device for uranyl nitrate and/or plutonium nitrate.

Although the present invention is directed to uranyl nitrate and/or plutonium nitrate, in order to simplify the description, the case where only uranyl nitrate is targeted will be described first.

In spent nuclear thermal reprocessing plants, uranium is separated from fission products and plutonium and is obtained as a uranyl nitrate solution, which is concentrated, denitrated by thermal decomposition, and converted into uranium trioxide. is the usual law. In this case, the pyrolysis denitrification methods include the pot method, rope azusa bed method,
The fluidized bed method is used, but today the fluidized bed method is the most efficient method and has come into widespread use. On the other hand, all the fluidized bed reactors that have been put into practical use as denitrification equipment are cylindrical, and when using this type of cylindrical fluidized bed reactor as a denitrification equipment for slightly enriched uranium such as uranyl nitrate, criticality control is required. From the above point of view, the maximum diameter of the fluidized bed reactor is limited. Denitrification using a fluidized bed reaction of uranyl nitrate is usually performed by maintaining the reaction equipment at an appropriate temperature, introducing fluidizing gas from the bottom of the equipment to maintain the fluidized bed, and spraying at appropriate locations such as the side walls of the equipment. This is done by spraying an aqueous solution or melt of uranyl nitrate together with a misting gas into the device through a nozzle. 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 has started, the uranium trioxide particles produced by the reaction form a fluidized bed, which slows down the progress of the reaction. The operation is carried out continuously by removing the uranium trioxide particles produced during the process from the refill by a suitable method. In general, it is practical to use a fluidized bed reactor so that the linear velocity of gas is constant inside the reactor, and even in the case of a fluidized bed denitration equipment for uranyl nitrate, the gas is supplied from the bottom of the equipment to form a fluidized bed. The total amount of the fluidizing gas, the atomizing gas accompanying the introduction of the uranyl nitrate aqueous solution, and the reaction product gas (ratio 0, NOx, etc.) generated by denitration by thermal decomposition of uranyl nitrate will be an amount commensurate with the equipment cross-section type. If not controlled in this way, it will be difficult to maintain a normal fluidized bed.

When using a conventional cylindrical fluidized bed reactor for denitrification by thermal decomposition of uranyl nitrate, as mentioned above, the maximum diameter is limited due to criticality control, so the processing capacity per unit number is limited. will receive.

As a countermeasure, the use of a flat plate type fluidized bed reactor was proposed. In other words, if a flat plate type fluidized bed reactor is used, although the thickness of the fluidized bed is limited by criticality control, it is possible to increase the width of the fluidized bed in the lateral direction. By enlarging it, the cross-sectional area and heat transfer area of the fluidized bed reactor can be increased, and therefore the processing capacity per unit number of the equipment can be increased, and it is possible to easily respond to fluctuations in the load vehicle. It is also possible to do so. However, this type of flat plate type fluidized bed reactor has a problem in that the width of the fluidized bed in the lateral direction is large due to its structure, and in some cases, internal particles cannot be mixed and dispersed sufficiently. There is. In the conventional general cylindrical fluidized bed reactor and the flat plate fluidized bed reactor proposed above,
In both cases, the fluidizing gas supply section (hereinafter referred to as the wind box) from the bottom of the device consists of a single section.
The fluidizing gas supplied from outside the wind box has a uniform pressure inside the wind box, and is introduced into the fluidized bed at a substantially uniform linear velocity through a rectifier, which is usually constructed of a metal wire mesh or the like.

On the other hand, in JP-A-55-7527, the present applicant has disclosed a fluidized bed denitrification reaction in which a uranyl nitrate solution is evaporated into a fluidized bed using a spray nozzle, and the uranyl nitrate is denitrified by thermal decomposition and converted into uranium trioxide. discloses that unless the average particle size of the uranium trioxide powder produced is kept below 400 mm, the stability of the fluidized bed will drop rapidly and it will be impossible to continue stable operation for a long time. ing. The fluidized bed in this case has a cylindrical shape, a conical shape, or a combination of both, and the average particle size of the produced uranium trioxide particles is 400 mm.
The denitrification reaction conditions for maintaining the temperature below m are as follows. Reaction temperature 240 to 350 ○ Linear velocity of fluidizing gas 20 to 60 cm/sec (sky column standard) Forging (air/solution) ratio 250 to 500 (volume ratio) Fluidized bed height/bed ratio 4 to 6 So, the average particle pot of produced uranium trioxide particles is 400
In order to maintain the denitrification fluidized bed at or below 100 yen, it is necessary to appropriately select the reaction temperature, the linear velocity of the fluidizing gas, the conditions for spraying the nitrate solution into the fluidized bed reactor, etc. In order to maintain stability over a long period of time, it is essential to maintain uniformity, especially thermal uniformity, within the fluidized bed.

That is, the denitrification reaction of uranyl nitrate according to the present invention is a rapid endothermic reaction, and a large amount of gas is generated in the vicinity of the uranyl nitrate introduction part in the fluidized bed due to thermal decomposition of uranyl nitrate, evaporation of water, etc. , the heat transfer rate of the introduced portion is significantly reduced. Furthermore, under normally applicable fog conditions, the depth of the fog from the fog nozzle to the fluidized bed is about a few skins to one skin, and the denitrification reaction takes place between the fog and the fluid. This occurs as the animal mixing region diffuses into the fluidized bed. If this diffusion is insufficient, the amount of heat required for the denitrification reaction will not be effectively supplied, and in that case, fog The ratio of liquid substances in the body to the fluid becomes locally excessive, causing a caking phenomenon and making it difficult to form a normal fluidized bed, making it difficult to operate the fluidized bed reactor stably and continuously over a long period of time. It becomes possible. The present inventors discovered that in the denitrification reaction of uranyl nitrate using a flat plate fluidized bed reactor in which the wind box has a single compartment structure, when the horizontal width of the flat plate fluidized bed becomes larger than a certain size. , inside the fluidized bed, the uranyl nitrate introduction part and the opposite side (in a fluidized bed with two mist nozzles in symmetrical positions, the uranyl nitrate introduction part, that is, the part near the wall side and the center part)
If the mixing and dispersion of the produced uranium trioxide particles becomes insufficient, the amount of heat transferred to the reaction part will be insufficient, causing the above-mentioned caking, or the physical properties of the produced uranium trioxide (particle size, residual uranyl nitrate) After observing the occurrence of a phenomenon in which the fluidizing gas (amount, etc.) becomes non-uniform, and considering countermeasures against this phenomenon, we focused on changing the supply mechanism of the fluidizing gas and arrived at the present invention.

Although the above is a case where only uranyl nitrate is targeted, the same applies to the case where plutonium dioxide or a mixture of uranyl nitrate and plutonium nitrate is targeted. That is,
The present invention denitrates uranyl nitrate and/or plutonium nitrate by thermal decomposition through a flat plate fluidized bed reaction, and continuously and stably directly converts uranyl nitrate and/or plutonium nitrate into uranyl trioxide or/and The present invention provides a denitrification device for uranyl nitrate and/or uranyl nitrate, which enables conversion of uranyl nitrate and/or plutonium dioxide into plutonium dioxide. In a denitrification device for uranyl nitrate and/or plutonium nitrate, which denitrates plutonium nitrate by thermal decomposition and converts it into uranium trioxide or/and plutonium dioxide, the fluidizing gas supply section at the bottom of the device is divided into a plurality of sections, The method is characterized in that the amount of fluidizing gas supplied to each divided section is changed to forcefully generate a flow of uranium trioxide and/or plutonium dioxide particles within the flat plate fluidized bed. uranyl nitrate and/or plutonium nitrate denitrification equipment.

As described above, the present invention divides the wind box into a plurality of sections, changes the amount of fluidizing gas supplied to each divided section, and distributes the fluidizing gas horizontally as in the case of conventional devices. By controlling the linear velocity of the fluidizing gas in the lateral direction of the fluidized bed by blowing it into the fluidized bed through a rectifier held in the The flow is generated to promote the mixing and dispersion of the uranium trioxide and/or plutonium dioxide particles, thereby resolving the insufficient amount of heat transfer to the reaction section in the fluidized bed, and removing the heat of the uranyl nitrate and/or plutonium nitrate. Denitrification by decomposition is carried out continuously and stably, and the physical properties of the produced uranium trioxide and/or plutonium dioxide can be made uniform.

The present invention can further adopt a configuration in which the rectifier is tilted in combination with the above-described division of the wind box.

The angle of inclination of the rectifier in this case varies depending on the type of rectifier used and the physical properties of the uranium trioxide and plutonium dioxide particles produced, but is preferably equal to or greater than the angle of repose of these particles. However, in this case, since these particles are made to flow, it is thought that the angle of repose or lower is sufficiently effective. This combination structure more strongly promotes the forced flow of the uranium trioxide and/or plutonium dioxide particles in the fluidized bed, and allows the particles to be mixed and dispersed more effectively, thereby allowing the uranyl nitrate or It is possible to more reliably denitrify plutonium dioxide by thermal decomposition and continuously and stably convert it into uranium trioxide and/or plutonium dioxide having uniform physical properties. Next, the present invention will be explained with reference to the drawings.

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 embodiment shown in FIG. 1, the rectifier 8 is held horizontally;
The wind box 7 is divided into three sections, and the object of denitration is uranyl nitrate.

The three divisions of the wind box 7 will be referred to as section A, section B, and section C from the side closest to the mist nozzle 9. In the figure, the fluidizing gas (air, water vapor) sent from the fluidizing gas supply system 15 is set to a predetermined flow rate by the flow rate indicators 4 to 6 and the flow rate adjustment valves 1 to 3, and then the wind box 7 It is supplied to parts A, B, and C, respectively.

The fluidizing gas in the wind box 7 is blown into the fluidized bed 10 from a rectifier 8 held horizontally. The fluidized bed 10 is composed of uranium trioxide particles, a fluidizing gas, a fin fogging gas, and a reaction product gas. On the other hand, the uranyl nitrate solution, which is a raw material supplied in a preheated state from the uranyl nitrate (UNH) supply system 16, flows together with the spraying gas, which is also preheated, from the dawn misting gas supply system 17. The fluidized bed 10 is sprayed from a spray nozzle 9 attached to one end of the bed 10 .

The device is externally heated to a predetermined temperature by electric resistance heating means. In addition, the uranium trioxide particles needed to form the fluidized bed at the start of the movement are U03 seed hopper 1.
Supplied from 3. Thus, A of wind box 7
Different amounts of fluidizing gas are blown into the fluidized bed 10 maintained at a required temperature at different linear velocities from the parts B, B, and C. At the same time, the uranyl nitrate solution and the misting gas are blown from the fog nozzle 9. Similarly, it is atomized into the fluidized bed 10.

In this configuration, by setting the linear velocity of the fluidizing gas from the C part of the wind box 7 to the highest and the linear velocity of the fluidizing gas from the A part to the slowest, the trioxide in the fluidized bed 10 above the C part is Some of the uranium particles are lifted toward the upper surface of the fluidized bed 10 together with the fluidizing gas, and move toward the left on the upper surface of the fluidized bed 10, while at the same time, the uranium trioxide particles near the bottom of the fluidized bed 10 move toward the right. and move.

In this way, by appropriately changing the linear velocity of the fluidizing gas from parts A, B, and C of the wind box 7, a flow of uranium trioxide particles is forced into the fluidized bed 10, By promoting their mixing and dispersion, thermal uniformity within the fluidized bed 10 is ensured, thereby denitrifying uranyl nitrate through thermal decomposition and converting it continuously into uranium trioxide with stable and uniform physical properties. There are many things that make it seem possible. Thus, uranium trioxide particles generated by denitrification of uranyl nitrate are continuously taken out of the fluidized bed 10 through the overflow pipe 12.

Further, when the fluidizing gas, the atomizing gas, and the reaction product gas pass through the nursery filter 11, the accompanying uranium trioxide particles are collected by the solid fraction filter 11, and then sent to the off-gas treatment system 14. Another embodiment shown in FIG. 2 has rectifier 8a tilted and windbox 7 also
This is a case where the structure is divided into three parts: part, B part, and C part,
The target of denitrification is uranyl nitrate.

All symbols other than rectifier 8a are the same as in FIG. 1. In this case, the combination of the inclined rectifier 8a and the divided wind box 7 more strongly promotes the forced flow of the uranium trioxide particles in the fluidized bed 10, making the mixing and dispersion of the particles more effective. 1, thereby making the effect of the embodiment of FIG. 1 more reliable. In the above, regarding the linear velocity of the fluidizing gas from the A section, B section, and C section of the wind box 7, the linear velocity of the fluidizing gas from the B section can be made the slowest. In addition, the wind box 7 is divided into the three above.
It is not limited to division. It is also possible to provide one spray nozzle at each end of the fluidized bed. Furthermore, although the case where only uranyl nitrate is targeted for denitration has been described above, it is also possible to target only plutonium nitrate or a mixture of uranyl nitrate and plutonium nitrate. As described above, by adopting the above structure, the present invention denitrates uranyl nitrate and/or plutonium nitrate through thermal decomposition and stabilizes it continuously, regardless of the width of the flat plate fluidized bed in the lateral direction. The present invention is a denitrification device for uranyl nitrate and/or plutonium nitrate that can be directly converted into uranium trioxide and/or plutonium dioxide having uniform predetermined physical properties, and is extremely useful in nuclear thermal fuel processing.

The device of the present invention has critical dimensions in terms of device dimensions, and appropriate shielding considerations are also required, but these issues can be easily determined and designed by a person skilled in the art in light of knowledge of radiochemistry and nuclear engineering. Since this is a possible problem, I will not go into details here.

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.

In the example, the linear velocity of the fluidizing gas introduced into the fluidized bed from the rectifier is simply the fluidizing gas linear velocity, the introduction rate of the uranyl nitrate solution is the treatment speed, and the volume ratio of (air/uranyl nitrate solution) is referred to as the atomization condition (A/L). Example In this example, uranyl nitrate was denitrated using the apparatus shown in FIG. 1 under the following conditions.

Reaction temperature: 28,500 Uranyl nitrate solution concentration: 1,200 taU/so Processing speed
50k9U/hr atomization conditions (A/L)
500 Fluidized bed height 1.5 Linear velocity of fluidized gas from skin A section 20 m/secB
〃 〃 40C/SecC ″
``'' The U03 particles produced at 60 skins/Sec were allowed to freely flow out from the overflow pipe and could be continuously taken out.

Under these conditions, the device was operated continuously for 4 hours in the fields, but no particular disadvantages were observed, and further continuous operation was possible.

In particular, under the reaction temperature conditions, the temperature at the same horizontal position as the temperature indicated by the thermometer (hereinafter referred to as T) attached to the wall surface where the spray nozzle is installed, and near the wall surface on the opposite side of the spray nozzle. The temperature indicated by the attached thermometer (
There was almost no difference in temperature (hereinafter referred to as T2). Comparative Example In this comparative example, uranyl nitrate was denitrated using the same equipment as in Example 1 under the following conditions.

Reaction temperature: 28,500 Uranyl nitrate solution concentration: 1,200 taU/treatment speed
50k9U/hr atomization conditions (A/L)
500 Fluidized bed height 1.5 Linear velocity of fluidized gas from skin A part 40 skin/secB
〃 〃 40 arcs/SecC 〃
〃 〃 40 k/Sec As a result of driving under this condition,
Immediately after the introduction of the uranyl nitrate solution, the temperature indication values T and T
A temperature difference begins to appear between 2 and 2, and this temperature difference increases as the reaction time progresses, and after 6 hours T2 = 28500.
, T, = 265oo.

From around that time, the flow condition deteriorated rapidly, and the spray pressure increased.
It was observed that part of the fluidized bed was not fluidized, so
I stopped driving.

[Brief explanation of drawings]

FIG. 1 is a front view including a partial sectional view of an embodiment of the present invention;
FIG. 2 is a partially sectional front view of another embodiment of the present invention. In the figure, 1, 2, 3...flow rate adjustment valve,
4, 5, 6...Flow rate indicator, 7...Wind box, 8...Horizontal rectifier, 8a.
... Slanted rectifier, 9 ... Fake nozzle, 10 ... Fluidized bed, 11 ... Solid-gas separation filter, 12 ... Overflow pipe, 13・・・・・・U03
Seed hopper, 14...Off gas treatment system, 1
5...Fluidization gas supply system, 16...U
NH supply system, 17... Gas supply system for spraying. ticket? Figure 2

Claims (1)

[Claims] 1. Uranyl nitrate or/and nitric acid, which is converted into uranium trioxide or/and plutonium dioxide by denitrifying the uranyl nitrate or/and plutonium nitrate by thermal decomposition using a flat plate fluidized bed having a spray nozzle. In a plutonium denitrification equipment, the fluidizing gas supply section at the bottom of the equipment is divided into multiple sections, and the amount of fluidizing gas supplied to each divided section is changed, and the fluidized gas is forced into the flat plate fluidized bed. 1. A denitrification device for uranyl nitrate and/or plutonium nitrate, characterized in that it is configured to generate a flow of uranyl trioxide or/and plutonium dioxide particles. 2. In a uranyl nitrate and/or plutonium nitrate denitrification device that uses a flat plate fluidized bed having a spray nozzle to denitrify uranyl nitrate or/and plutonium nitrate by thermal decomposition and convert it into uranium trioxide or/and plutonium dioxide, A rectifier that supplies fluidizing gas from a fluidizing gas supply section at the bottom of the device to the flat fluidized bed is tilted, and the fluidizing gas supply section is divided into a plurality of sections, and each of the divided sections Uranyl nitrate or/and nitric acid, characterized in that the amount of fluidizing gas to be supplied is changed to forcefully generate a flow of uranium trioxide and/or plutonium dioxide particles within the flat plate type fluidized bed. Plutonium denitrification equipment.