JPS6031765B2 - Denitration equipment for uranyl nitrate and/or plutonium nitrate - Google Patents

Description

Detailed Description of the Invention The present invention uses a flat plate fluidized bed having a spray nozzle to denitrify uranyl nitrate and/or plutonium nitrate through thermal decomposition and continuously convert it into uranium trioxide or/and plutonium dioxide. The present invention relates to an improvement in a desulfurization device for uranyl nitrate and/or plutonium nitrate in which uranium trioxide or/and plutonium dioxide is discharged out of the fluidized bed through an overflow pipe.

Currently, in the reprocessing of spent nuclear fuel, uranium is first separated as a uranyl nitrate solution, and then recovered as uranium trioxide through denitrification through thermal decomposition.

Furthermore, in the reprocessing of spent nuclear 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 above-mentioned denitrification methods include a pot method, a sealed bed method, a microwave heating method, a fluidized bed method, etc., but the fluidized bed method is attracting attention as the most efficient method.

Generally, cylindrical types are mainly used as fluidized bed reactors, but there are restrictions due to coastal management in equipment that handles slightly enriched uranium, such as in the reprocessing of spent nuclear fuel. The maximum diameter of the device is limited depending on the nature of the material being handled, such as the degree of enrichment of uranium and the presence or absence of plutonium. In the fluidized bed denitrification reaction, in order to maintain a stable fluid state and carry out the reaction smoothly and continuously over a long period of time, the linear velocity of the fluidizing gas in the fluidizer and the height of the fluidized bed must be adjusted appropriately. It is necessary to control it.

In denitrification equipment for uranyl nitrate that uses a normal cylindrical fluidized bed, as mentioned above, the maximum diameter of the cylinder is limited by coastal management, so the cross-sectional area of the equipment, heat transfer area, etc. are also limited. , there is naturally a limit to the processing capacity per unit radix. Therefore, recently, in the fluidized bed reaction in which uranyl nitrate is nitrated by thermal decomposition to produce uranium trioxide, the thickness is subject to coastal management restrictions, but the width is not subject to such restrictions. is gaining attention. If this flat plate fluidized bed is used, the horizontal length of the fluidized bed can theoretically be increased to infinity, so by increasing the horizontal length, the cross-sectional area and heat transfer surface of the fluidized bed reactor can be increased. Since it is possible to increase , there is an advantage that the processing capacity per unit radix can be increased.

However, as mentioned above, although theoretically it is possible to make the width of the device infinite in the flat plate type fluidized bed, it is practically impossible to increase the width from the viewpoint of the strength of the device material. It cannot be made infinitely large.

In other words, the length of this width is determined by the material, thickness, usage conditions (temperature, pressure, etc.) of the device material, presence or absence of reinforcement, and its method, but usually the thickness of the device material is made as thin as possible (by coastal management). First, since the external dimensions are limited, it is advisable to reduce the thickness of the device material in order to increase the internal dimensions as much as possible, or to solve the problem of strength through reinforcement, etc. Furthermore, in the denitrification reaction in which uranyl nitrate is thermally decomposed to produce uranium trioxide using a fluidized bed, water vapor is present as part of the reaction product, and this water vapor passes through an overflow pipe to the uranium trioxide product receiving tank. The condensed water and uranium trioxide react with each other to form a solid solid, which could potentially clog the pipes, so it is necessary to prevent this from happening. In the conventional method, as shown in FIG. 1, in order to heat the part of the overflow pipe 6 outside the apparatus to a temperature higher than the water condensation temperature, a heating heater 7 is attached to the part and a predetermined amount of heated air is supplied as a purge gas 15. A complex mechanism is employed to prevent the condensed water from entering the overflow pipe 6. In Fig. 1, 1 is a fluidized bed gas supply unit (wind box), 2 is a rectifier, 4 is an Akebono nozzle, 5 is a solid-gas separation filter, 8 is a uranium trioxide product receiving tank, and 9 is an extraction pipe. ,1
0 is a uranium trioxide seed hopper, 11 is an off-gas treatment system, 12 is a fluidizing gas, 13 is a uranyl nitrate solution, 14
is a false gas. In this way, the currently proposed flat plate fluidized bed denitrification equipment with an overflow tube for uranyl nitrate has improved strength based on the shape of the fluidized bed itself and the thinner thickness of the equipment material, as well as the heating mechanism of the overflow tube. Each of them has its own problems.

The present invention solves the above two problems at the same time, and makes it possible to strengthen the strength of the device and simplify the heating mechanism of the overflow pipe. The purpose is to denitrify uranyl nitrate and/or plutonium nitrate by thermal decomposition using a flat plate fluidized bed with a mist nozzle to produce trioxidized In a denitrification device for uranyl nitrate and/or plutonium nitrate, which converts uranium or/and plutonium dioxide into uranium trioxide and/or plutonium dioxide and takes out the generated uranium trioxide and/or plutonium dioxide through an overflow tube, the overflow tubes are connected to the opposing inner walls of the device, respectively. Alternatively, there is provided a denitrification device for uranyl nitrate and/or plutonium nitrate, which is characterized in that they are provided in close contact with each other.

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

FIG. 2 is a front sectional view of one embodiment of the present invention, and FIG.
It is an AA dysopia view of a figure.

In FIG. 2 and FIG. 3, the present embodiment is a case in which the overflow pipe 6a is joined to the inner walls 16, 16 of the device which face each other in the width direction.

With this configuration, the inner walls 16, 16 of the device facing each other in the width direction
The overflow pipes 6a, which are connected to each other, serve as reinforcing ribs to reinforce the strength of the apparatus, thereby making it possible to increase the width of the fluidized bed apparatus and improve its throughput.

In addition, since most of the overflow pipe 6a is inside the device, it is heated to the same temperature as the fluidized bed 3 (approximately 300 oo), so the conventional heater can be omitted and the heating mechanism can be simplified. Become. In this case as well, the purge gas 15 is fed into the overflow pipe 6a in the same manner as in the prior art to prevent the moisture in the gas in the fluidized bed 3 from entering the overflow pipe 6a and the uranium trioxide product receiving tank 8. In FIG. 2, the overflow pipe 6a is constructed to pass through the bottom of the apparatus, but the overflow pipe 6a may also be provided so as to pass through the lower part of the side wall of the apparatus.

FIG. 2 shows a case where the fluidized bed 3 is divided into two sections by an overflow pipe 6a, and each divided section has a spray nozzle 4, a blowout pipe 9, a fluidizing gas supply section 1, and a solid gas supply section 1. Separation filter 5 etc. are installed.

A plurality of overflow pipes 6a can be installed, and their installation positions are not specified. Although the cross-sectional shape of the overflow pipe 6a is free, it is preferably rectangular. Note that 6b is a reinforcing member having the same structure as the overflow pipe 6a, but it may have a different structure or may be omitted. Although FIG. 2 shows a case in which the overflow pipe 6a is provided by joining the widthwise opposing inner walls 16, 16 of the device, it is also possible to provide the overflow pipe 6a in close contact with these inner walls of the device. be.

In this case, the overflow pipe 6a does not provide reinforcement against internal pressure, but it can provide the effect of reinforcing the device against external pressure, and the same effect can be obtained in place of a separately provided reinforcement means against internal pressure. In the above, the present invention was 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 case of denitrification of plutonium nitrate or a mixture of uranyl nitrate and plutonium nitrate.

As described above, the present invention enables reinforcement of the strength of the device and simplification of the heating mechanism of the overflow pipe at the same time, thereby improving processing capacity and workability. The present invention provides a denitrification device with an overflow pipe that uses a flat plate fluidized bed having a plutonium nitrate mist nozzle, and is extremely useful for treating the fuel.

[Brief Description of the Drawings] Fig. 1 is a front sectional view of an example of a conventional device, Fig. 2 is a front sectional view of an embodiment of the present invention, and Fig. 3 is a view taken along arrow A-A in Fig. 2. be. In the figure, 1... Fluidization gas supply unit (wind box), 2... Rectifier, 3... Fluidized bed, 4... Spray nozzle, 5... Solid brocade filter, 6, 6a...
・Overflow pipe, 6b... Reinforcement material, 7... Heater,
8... Uranium trioxide product receiving tank, 9... Extraction pipe, 10
... Uranium trioxide seed hopper, 11 ... Off gas treatment system, 12 ... Fluidization gas, 13 ... Uranyl nitrate solution, 14 ... Misting gas, 15 ... Purge gas, 1
6... Inner wall of the device in the width direction. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 Uranyl nitrate or/and plutonium nitrate are continuously converted into uranium trioxide or/and plutonium dioxide by denitrification by thermal decomposition using a flat plate fluidized bed having a spray nozzle, and the uranium trioxide and/or plutonium dioxide are produced. A desulfurization device for uranium nitrate and/or plutonium nitrate in which plutonium dioxide is taken out through an overflow pipe, characterized in that the overflow pipes are connected to or in close contact with the opposing inner walls of the device, respectively. denitrification equipment.