JPS6031767B2 - Denitration equipment for uranyl nitrate and/or plutonium nitrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses uranyl trioxide or plutonium nitrate to remove uranium trioxide or plutonium dioxide when producing uranium trioxide or/and plutonium dioxide by thermal denitrification using a fluidized bed. The present invention relates to an apparatus for denitrifying uranium trioxide and/or plutonium dioxide from uranyl nitrate and/or plutonium nitrate, which makes it possible to reduce the wear of lumps made of plutonium dioxide.

As described above, the present invention relates to the denitrification of uranyl nitrate or/and plutonium nitrate, but to simplify the description, below, uranyl nitrate or/and plutonium nitrate will be referred to as UNH, uranium trioxide or/
and plutonium dioxide are respectively abbreviated as U03.

When originating from spent nuclear fuel reprocessing plants, uranium is usually refined in the form of UNH and then converted to U03.

This UQ can be further converted to U02 (uranium dioxide) as necessary.
Alternatively, it is converted to UF6 (uranium hexafluoride). The process in which uranium is converted from the UNH form to U03 is generally referred to as denitrification, and several methods have been proposed for this purpose, including the pot method, the denitrification method, the microwave heating method, and the fluidized bed method. ing. Among these, the fluidized bed method has attracted attention as the most efficient method due to its possibility of continuous operation, and has partially been put into practical use. UN by fluidized bed method
The conventional method for denitration of H is to blow the raw material UNH together with gas into a fluidized bed through a spray nozzle, and heat it from the outside to thermally decompose it to produce UQ powder.

This pyrolysis denitrification reaction of UNH is a rapid endothermic reaction, so
Since the temperature near the tip of the mist nozzle drops considerably, undecomposed UNH, condensed Q○, U03 powder, etc. adhere to the tip of the mist nozzle, and it is often the case that they gradually grow and become lumps. . When these lumps grow to a certain extent, they fall from the tip of the spray nozzle because the inside of the fluidized bed is in a sludgy state. These lumps may also grow on the walls of the equipment and on the tips of temperature and other detectors. Furthermore, if operating conditions, particularly temperature control, etc. are disturbed, coarse particles may be generated due to agglomeration of U03 particles. A method to completely prevent the occurrence of these lumps has not yet been perfected.
The thus generated lumps gradually accumulate in the fluidized bed, and when operating for a long time, they may adversely affect the flow characteristics and may even lead to the shutdown of the operation.

Furthermore, in order to remove the lumps from the fluidized bed after the operation has been stopped, it is necessary to disassemble the apparatus, so equipment must be provided to prevent U03 powder and the like from scattering during disassembly. If the diameter of the fluidized bed is sufficiently large, it is possible to solve the problem of extracting the lumps by making the diameter of the extraction pipe installed at the bottom of the fluidized bed large enough for the lumps to pass through. When handling enriched uranium or plutonium such as reprocessing nuclear fuel (in this case, the diameter of the fluidized bed is restricted due to criticality control), if this is not possible with a diameter of 4. Measures are being taken such as installing a plastic screen to prevent lumps from entering the extraction pipe (Tokuto Sho 53-
No. 78521), but in that case, the lumps remain on the baffle plate in the fluidized bed, and this is not a fundamental solution. The inventors of the present invention previously proposed a method to deal with this problem in 1982.
Although disclosed in the specification of No. 04, the method requires a rather complicated structure and operation.

In principle, it is desirable to completely remove these lumps, but the inventors have found through operational tests of UNH's denitrification fluidized bed equipment that these lumps can be removed due to the size of the equipment.
Although it depends on the operating conditions and the physical properties of the lumps, it is possible to operate UNH's denitrification fluidization equipment without adversely affecting the flow characteristics as long as the amount of produced lumps is below a certain amount. It has been found that a certain amount of lumps are actually present in the fluidized bed apparatus currently in practical use during operation.

The present inventors have arrived at the present invention by paying attention to such findings and the fact that the above-mentioned lumps mainly composed of U03 are relatively soft and easily abraded.

That is, the present invention has a simpler structure and operation than the method described in the specification of Tokuho Sho 56-82042, and
The purpose of the present invention is to provide a uranyl nitrate and/or plutonium nitrate denitrification device that abrades and reduces the above-mentioned lumps and thereby enables continuous operation. In a denitrification equipment for uranyl nitrate and/or plutonium nitrate that produces uranium trioxide and/or plutonium dioxide by denitrating uranyl nitrate and/or plutonium nitrate by decomposition, the diameter of the equipment is changed from the installation part of the mist nozzle to the bottom of the fluidized bed. A denitrification device for uranyl nitrate and/or plutonium nitrate, characterized by having a structure in which a plurality of stages are successively narrowed toward the direction of the current plate. Next, the present invention will be explained with reference to the drawings.

The drawing is a sectional view of a main part of an embodiment of the present invention.

In this example, a cylindrical fluidized bed is used, and the diameter of the device is sequentially reduced in multiple stages (three stages in the figure) from the installation part of the fog nozzle tip 4 toward the direction of the rectifying plate 2 at the bottom of the fluidized bed 3. It is the composition.

That is, the device from the installation part of the mist nozzle 4 to the rectifying plate 2 consists of cylindrical parts b, c, and d whose diameters are successively narrowed, and connecting parts e, f, and g that connect these cylindrical parts b, c, and d. In this structure, the inclination angles of the connecting parts e, f, and g are generated by U0
It is larger than the angle of repose of 3 particles and is 70 degrees with respect to the horizontal direction. The diameters of the cylindrical part a above the attachment part of the spray nozzle 4 and these cylindrical parts b, c, and d are respectively 155.2 side, 106.3 side, 81.1 rib, and 53.5 side,
Further, the lengths of these cylindrical portions b, c, and d are all 125 ribs. In the figure, the fluidizing gas 6 is introduced into the fluidized bed 3 via the wind box 1 and the baffle plate 2, while the UNH solution 7 and the counterfeiting gas 8 are introduced into the fluidized bed 3 from the counterfeit nozzle 4.
The pyrolytic denitrification of UNH generates U03 particles.

In this embodiment, the gas velocity becomes progressively farther downward from the attachment part of the mist nozzle 4.

For example, the gas linear velocity based on the sky tower in the cylindrical part a is 4
In the case of 0 k/sec, the cylindrical part b is 85 k/sec, the cylindrical part c is 146 k/sec, and the cylindrical part d is 337 k/sec. Coarse particles generated in the fluidized bed 3 or lumps formed at the tip of the spray nozzle 4 (after these lumps grow to a certain extent, most of them fall from the tip of the spray nozzle 4) are once deposited in the lower part of the fluidized bed 3. They fall, but they fall into the cylindrical part b
, c, and d due to the U03 particles blown upward by the high gas flow rate, or the lumps roll in the cylindrical portions b, c, and d, causing the lumps to be separated from each other and the fluidized bed apparatus. Due to the collision with the inner wall,
It wears out and decreases, making continuous operation possible.

Although the above description is based on one embodiment, the ratio of the diameters of the cylindrical portion a and the cylindrical portion d is preferably 2 to 4.

Further, as described above, it is desirable that the inclination angle of the connecting portion of the cylindrical portion be equal to or greater than the angle of repose, but the effect can be obtained even if the angle is equal to or less than the angle of repose. There is no particular restriction on the number of stages of the aperture, and it is determined engineeringly based on the size and operating conditions of the device.

[Brief explanation of the drawing]

The drawing is a sectional view of a main part of an embodiment of the present invention. In the figure, 1... Wind box, 2... Rectifier plate,
3...Fluidized bed, 4...Spray nozzle, 5
...Extraction pipe, 6...Fluidization gas, 7.
...UNH solution, 8...Lamp gas, a
, b, c, d... Cylindrical part, e, f, g...
...Connection part.

Claims (1)

[Claims] 1. In a uranyl nitrate or/and plutonium nitrate denitrification equipment that produces uranium trioxide and/or plutonium dioxide by nitrifying uranyl nitrate or/and plutonium nitrate by thermal decomposition using a fluidized bed having a spray nozzle, 1. A denitrification device for uranyl nitrate and/or plutonium nitrate, characterized in that the diameter is successively narrowed in multiple stages from the spray nozzle attachment part toward the rectifier plate at the bottom of the fluidized bed.