JP2874291B2 - Method for treating massive particles generated by fluidized bed denitration - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a case where a uranyl nitrate and / or plutonium nitrate solution is denitrated using a reactor such as a fluidized bed in a process such as reprocessing in the field of nuclear power. And a method of treating the aggregated particles generated in the above.

(Prior art and its problems) The present invention can be applied to a case where a uranyl nitrate solution or a plutonium nitrate solution or a mixed solution thereof is denitrified by thermal decomposition to be converted to an oxide. The denitration of the uranyl solution will be described as an example.

In the prior art, in a process such as reprocessing in the field of nuclear power, a separated and purified uranyl nitrate solution is thermally decomposed by heating using a reactor such as a fluidized bed to form oxides (UO ₃ ).
Convert to powder. Specifically, while urging the oxide (UO ₃ ) particles having a particle size distribution of about several microns to several hundred microns, a uranyl nitrate solution is sprayed and supplied thereto using a spray nozzle or the like, and heated from the outside. To produce oxide (UO ₃ ) particles.

At this time, in the process of forming the oxide (UO ₃ ) particles, agglomeration of wet particles or drying (pyrolysis) of droplets adhering to the tip of a nozzle or the like causes a massive oxide (UO ₃₎ ) Particles are usually formed. The production amount of the agglomerated particles is less than a few percent of the whole, and not very much, but at present, there is no technique for reducing this production amount to zero. The composition of the agglomerated particles themselves is chemically the same as the powdery oxide (UO ₃ ) particles, which is the target product, but is usually a few millimeters to a maximum of about 40 to 50 millimeters. Yes, handling and reaction when considered as a raw material for subsequent processes (for example, UO ₃ generated in this way is converted to uranium hexafluoride etc. for reuse as reactor fuel) This is problematic in terms of gender. That is, in the case of agglomerated particles, compared to the finely divided particles, clogging occurs in the apparatus during handling, or the reaction yield decreases due to a small specific surface area involved in the reaction during the chemical reaction. There is a problem, and it cannot be said that it is appropriate as a raw material for the subsequent process. Therefore,
Powdered oxides to produce for normal among (UO ₃₎ particles, sorting Yotsute the massive particles sieve or the like to fine powder of oxide only (UO ₃₎ particles and products. At present, the massive UO ₃ particles selected are dissolved in a nitric acid solution to form a uranyl nitrate solution, mixed with a uranyl nitrate solution as a raw material solution, supplied again to the fluidized bed reactor, denitrated, and powdered. In general, oxide (UO ₃ ) particles are used.

As described above, in the prior art, a receiving container for agglomerated particles, a transfer device for the receiving container, a supply device to the dissolving tank, a dissolving tank, a dissolving solution receiving tank, an apparatus for supplying a dissolving solution (nitric acid and water),・ Steam and cooling water supply equipment ・ Tank off-gas treatment equipment generated during dissolution ・ Equipment for preventing leakage liquid from spreading (Drip tray etc.) ・ Equipment and equipment such as pumps and instrumentation equipment attached to the above equipment and equipment In addition to these, these devices and equipment require that the oxide (UO ₃ ) particles generated dislike water (UO ₃ is a hydrating substance, which reacts with water to form a strong solid Changes to a substance, making it difficult to handle as a powder)
It is necessary to treat in a space separate from the space where the fine powdery oxide particles are handled, and the following operation is required to treat the massive particles.

・ Separation of the bulk container from the main unit → transport (transport) → connection / disconnection to the supply device and the reverse operation ・ Dissolution operation ・ Processing operation of the generated liquid (uranyl nitrate solution): transfer, concentration, Denitration, etc.In order to install these operations and devices, equipment, etc., a large space separate from the space that handles fine powder oxide particles is necessary, and it is necessary to secure space and to use equipment, equipment, etc. Equipment cost increases. In the conventional method, heating (electric heating or the like) is necessary to convert UO ₃ once converted into oxide into nitric acid solution and concentrate and denitrate the solution, and a dissolving operation is required to dissolve the aggregated particles. First, the nitric acid solution for dissolution is heated (the temperature is low, the dissolution rate is slow, so it is usually heated to about 50 to 70 ° C.), and the dissolution of UO ₃ has progressed to some extent. (For suppressing the rise in temperature due to the generation of heat of dissolution), the heating and cooling also require the use of steam and cooling water, and both consume energy. In addition, the maintenance of the confinement function is required as a problem peculiar to the handling of radioactive materials. Therefore, it is necessary to maintain a negative pressure in the space (space) for handling these materials by providing ventilation. According to the conventional method which requires a large space as described above, equipment for this ventilation is required, and at the same time, energy (electric power) consumption is considerable.

 Next, an example of the related art will be described with reference to the drawings.

FIG. 1- (a) shows an example of a process flow of a denitration facility according to the prior art, and FIG. 1- (b) shows a process flow of a process (dissolution) of a lump particle of the prior art. An example is shown.

In FIG. 1- (a), a uranyl nitrate solution a, which is a raw material, is received in a uranyl nitrate storage tank 1, heated by a vapor b in an evaporator 2, and concentrated by evaporation. The concentrated uranyl nitrate solution is supplied to the denitration tower 4 via the concentrated liquid receiving tank 3. The concentrated liquid receiving tank is also heated with steam b for keeping the temperature. The denitration tower 4 is heated by an electric heater c or the like to thermally decompose the uranyl nitrate solution. The UO ₃ powder generated by the thermal decomposition reaction in the denitration tower is extracted through the sealing tank 5, which contains the above-mentioned agglomerated particles. Under the screen)
UO ₃ is received in the UO ₃ receiving tank 7. On the other hand, the massive UO ₃ (on the screen) is received in the massive particle receiving tank 8, filled in the massive particle receiving container 9, and transported by the transport device 10 to the melting step.

When the denitration tower 4 is stopped, UO ₃ particles remaining inside are extracted from the bottom of the denitration tower 4, and powdered UO ₃ and agglomerate particles are also mixed therein. And sieved.

Next, the operation of the dissolving step will be described with reference to FIG. 1- (b). The massive particles d conveyed from the denitration process are supplied to the dissolution tank 12 by a supply device 11 for the dissolution tank (usually composed of a hopper, a valve, an instrumentation device, etc.) and dissolved therein. In this example, a double-type dissolving tank is shown.
For this, nitric acid e for dissolution and pure water f for concentration adjustment are used. It is common to use steam g and cooling water h for heating and cooling at the same time.

The dissolved liquid (in this state, a uranyl nitrate solution i) is received in a dissolved liquid storage tank 13 and then transferred to a uranyl nitrate storage tank shown in FIG. 1- (a) by a pump or the like.

In this step, a drip tray 14 is installed to prevent leakage and expansion of the liquid, and gas generated from each tank is sent to an off-gas processing facility for processing. A space (room, etc.) where the entire process for performing these operations is installed
The whole is maintained at a negative pressure by ventilation equipment.

(Objects of the Invention) The present inventors have studied to solve the above-mentioned problems of the prior art and to provide a method capable of easily and effectively treating the agglomerated particles generated by fluidized bed denitration. As a result, it has been found that the above object can be achieved by pulverizing only the massive particles, and the present invention has been achieved.

(Constitution of the Invention) That is, according to the present invention, when the uranyl nitrate and / or plutonium nitrate solution is subjected to thermal decomposition denitration in a fluidized bed reactor to produce corresponding oxide particles, the produced oxide particles A method of treating mixed massive particles, wherein the oxide particles extracted from the fluidized bed reactor are separated into fine powder particles and massive particles, and the separated massive particles are pulverized by dry grinding. And a method for treating massive particles generated by fluidized bed denitration, characterized by mixing the obtained finely divided particles with the finely divided particles.

Next, the present invention will be described specifically with reference to examples, but the examples do not limit the scope of the present invention.

This embodiment will be described with reference to FIG. In FIG. 2, UO ₃ extracted from the denitration tower 101 via the sealing tank 102
Is sieved once by a sieve 103 and is divided into fine powder particles and agglomerated particles.The massive particles are received by a dry mill 105, pulverized, and then received as finely divided particle particles in a UO ₃ receiving tank 104. Is mixed with the above-mentioned fine powdery particles to obtain a product. Many pulverizers 105 also serve as receiving hoppers.
(A) The massive particle receiving tank 8 in the figure can also be omitted. In this embodiment, a one-stage dry crusher is exemplified.
Depending on the properties of the agglomerated particles, the use of a combination of a coarse pulverizer and a fine pulverizer may be considered.

(Effects of the Invention) By adopting the above configuration, the present invention can expect the following effects. That is, according to the present invention, the operation of dissolving the agglomerated particles is eliminated.

(2) Equipment / apparatus for dissolution (shown in FIG. 1- (a)
(8), (9), (10) and devices (11, 12, 13, 14, etc.) shown in FIG.

(3) Energy for processing the dissolved liquid (No. 1-
(A) b, c shown in FIG. 1 and e, f, g, h shown in FIG. 1- (b)
Etc.) can be saved, and a device for supplying such energy can be omitted.

(4) The elimination of equipment and devices and the elimination of the wet process reduce the room and space (space volume) required for the installation of equipment and devices, thereby reducing the size of equipment required for ventilation. Can also reduce energy consumption.

[Brief description of the drawings]

FIG. 1- (a) shows an example of a process flow of a denitration facility according to the prior art, and FIG. 1- (b) shows a process flow of a process (dissolution) of a lump particle of the prior art. FIG. 2 shows an example of the present invention. In the figure, a ... uranyl nitrate solution, 1 ... uranyl nitrate storage tank b ... steam (for heating), 2 ... evaporator c ... electricity (for heating), 3 ... concentrated liquid receiving tank d ... massive particles , 4 ...... denitrating tower e ...... nitrate, 5 ...... seal tank f ...... pure water, 6 ...... sieve g ...... steam (for heating), 7 ...... UO ₃ receiving tank h ...... cooling water, 8 ...... Lumped particle receiving tank i: uranyl nitrate solution, 9: Lumped particle receiving vessel p: pump, 10: transport device 11: supply device to the dissolving tank 12 ... dissolving tank 13 ... dissolving liquid receiving tank 14 ... Drip tray 101: denitration tower 102: seal tank 103: screen 104: UO ₃ receiving tank 105: dry mill

Claims (1)

(57) [Claims] 1. A method for producing a corresponding oxide particle by subjecting a uranyl nitrate and / or plutonium nitrate solution to thermal decomposition denitration in a fluidized bed reactor to treat massive particles mixed in the produced oxide particle. A method, wherein the oxide particles extracted from the fluidized bed reactor are separated into fine powder particles and bulk particles, and the separated bulk particles are pulverized by dry pulverization, and the obtained micronized particles are obtained. Is mixed with the finely divided particles described above, a method for treating massive particles generated by fluidized bed denitration.