JPS5924736B2 - Microwave heating continuous denitrification equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a denitrification device in the process of obtaining powder of uranium dioxide or plutonium dioxide, respectively, or a mixture thereof for nuclear fuel production from a solution of uranyl nitrate or plutonium nitrate, or a mixture thereof.

More specifically, the present invention relates to a microwave heating denitrification device that precipitates and separates the crystals from the above-mentioned solution, and further applies microwaves to raise the temperature to cause a denitrification reaction.

As shown in Figure 1, the microwave heating denitrification equipment raises the temperature of the raw material solution to 100-120℃ (
At point A), the solution boils, the solution is concentrated, the liquid depth decreases, and nitrates begin to precipitate.Then, as the nitrate cake dries (point B), the temperature of the heated object rises rapidly.

When the temperature reaches 350 to 400°C (point C), the pre-denitrification process proceeds and a dried cake of the denitrification product is obtained.

FIG. 2 is a longitudinal sectional view showing the denitrification device.

As can be seen from the figure, the microwave irradiation space of the heating device of the denitrification device is formed by the container 38 of the heating device, the upper and lower driving parts, and the rotating turntable 33.

A stock solution 35, which is an object to be heated, is filled in a saucer 34 in advance within or outside the heating device and set on a turntable.

On the other hand, the output of the microwave is controlled by a microwave oscillator, and the heated object 35 is irradiated through a waveguide 37 through an opening provided in the ceiling of the container 38 .

Steam and gas generated during heating are traded by an off-gas processing system connected to the container 38 by a pipe 39 attached to the upper part.

A dry cake of the denitrification product is obtained using the apparatus as described above.

However, in the case of the above-mentioned microwave heating device, since microwaves are directly applied to the raw material solution, nearly 80 parts of the energy is consumed in the process of evaporating nitric acid other than uranyl nitrate and plutonium nitrate, moisture, etc. necessary for the denitrification reaction.

Furthermore, since the denitrification reaction completion time differs depending on the concentration of the raw material solution, it is very difficult to control the apparatus.

Furthermore, these processes are performed in batches, making large-scale processing difficult.

The present invention was made in view of the above circumstances, and involves precipitating and separating the crystals from a uranyl nitrate and plutonium nitrate solution in a raw material solution, and then applying microwaves to obtain a dry cake of the denitrification product. Our goal is to provide a device for this purpose.

An embodiment of the apparatus according to the present invention will be described below with reference to FIG.

In FIG. 3, the raw material solution 1 is supplied to a pump 2, a flow rate adjustment valve 3
and enters the crystallizer 4.

The crystallizer is maintained at a predetermined pressure and temperature by a vacuum evacuation device 5 and a heat exchanger 6.

Of the introduced solution, water and nitric acid are evaporated and exhausted by the vacuum evacuation device 5.

As the water and nitric acid evaporate, the uranyl nitrate, plutonium nitrate, or a mixture thereof in the solution is concentrated, and its crystals are precipitated and collected in the form of a slurry at the bottom of the crystallizer.

The crystal slurry passes through the liquid feed pump 7 and the flow rate adjustment valve 8.
It is sent to a centrifuge 9.

The crystal slurry is separated into crystals and solution using a centrifuge.

The separated solution is stored for a certain amount in the receiver 30 and is returned to the crystallizer through the liquid sending pump 10 and the flow rate adjustment valve 11, or
or discharged.

The crystals of uranyl nitrate, plutonium nitrate, or a mixture thereof separated by the centrifuge are transferred through the outlet pipe 12 to the belt conveyor 13 and sent to the microwave heating furnace 14 having a microwave oscillator 26 and a waveguide 27. .

While the crystals are being moved through a microwave heating furnace on a belt conveyor, the temperature is raised, the denitrification reaction proceeds, and a dry cake of the denitrification product is obtained.

The dry cake 22 is scraped off from the belt conveyor by a scraping device 15 and collected.

Gas and steam generated during the denitrification reaction are exhausted through the exhaust pipe 16.

FIG. 4 shows a specific example of the crystallizer 4 described above.

The solution introduced from the raw material solution supply pipe 17 is transferred to the heat exchanger 1
8, it is heated or cooled to reach a predetermined temperature.

Water and nitric acid in the solution pass through the mist separator 19 and are exhausted under reduced pressure by the aforementioned vacuum exhaust device 5 connected to the steam exhaust pipe 20.

As water and nitric acid evaporate, uranyl nitrate or plutonium nitrate or a mixture thereof is concentrated, crystallized, precipitated, and becomes a slurry.

This crystal slurry is recovered from a crystal slurry recovery pipe 21 at the bottom of the vacuum evaporation crystallizer.

FIG. 5 shows an example of a specific cross section of the above-mentioned belt conveyor.

Crystals 22 of uranyl nitrate or plutonium nitrate or a mixture thereof are placed on a belt 23, supported by a support rotary table 24, and sent to a microwave heating furnace 14.

Note that the belt may be of a flat belt type.

FIG. 6 shows a specific example of the microwave heating furnace 14.

The aforementioned crystal 22 is placed on a belt 23 and enters a microwave trap section 25 that prevents leakage of microwaves to the outside.
It is further heated and denitrated in a heating section 28 having one or more microwave oscillators 26 and waveguides 27, and led out through a microwave trap section 29.

Gas and steam generated in the denitrification reaction are exhausted from the exhaust pipe 16.

Figures 7 and 8 are the A-A cross section and B-B cross section in Figure 6, respectively.
A cross section is shown.

Next, the operation of the above configuration will be explained.

When 9/hr metallic uranium/10 ky/hr nitric acid aqueous solution is supplied to a vacuum evaporation crystallizer with an operating pressure number of LOrr and an operating temperature of room temperature, about 3.6 kg/hr of uranyl nitrate dihydrate is discharged from the crystal slurry discharge pipe. A crystal slurry containing hr crystals and a nitric acid aqueous solution (HNO3.1.5 H2O) was obtained.

This crystal slurry was separated using a centrifuge and then denitrified using a microwave heater to obtain a dry cake of uranium dioxide weighing about 2.4 kg/hr.

Compared to direct evaporation denitration by heating the solution with microwaves, continuous denitrification was possible and the microwave output was reduced by approximately 70%.

Additionally, the energy required for the entire process was significantly reduced.

Furthermore, the quality of uranium dioxide was stable, and the influence of fluctuations in the composition of the raw material solution was small.

As described above, according to the present invention, by using a crystallizer, a separate charge, a belt conveyor, and a microwave heating furnace, continuous denitrification is possible, microwave output and required energy can be saved, and the composition of the raw material solution It is possible to provide an apparatus that can reduce the influence of fluctuations on the quality of product powder.

[Brief explanation of drawings]

The drawings are for explaining the device according to the present invention.
The figure shows the reaction curve of the denitrification process, Figure 2 is a vertical cross-sectional view of the denitrification equipment, Figure 3 is a system diagram showing an embodiment of the equipment according to the present invention, and Figure 4 is the crystallographic diagram according to the present invention. FIG. 5 is a longitudinal sectional view showing an example of the analyzer, FIG. 5 is a longitudinal sectional view showing an example of the belt conveyor of the present invention, FIG. 6 is an outline drawing of an example of the microwave heating furnace of the present invention, and FIG. Figure 6 is A-
Figure 8 is a diagram cut along line A and viewed in the direction of the arrow.
It is a view taken along the line B and viewed in the direction of the arrow. 1... Raw material solution supply tank, 4... Crystallizer, 9... Centrifuge, 13... Belt conveyor, 14...・Microwave heating furnace, 1
5... Scraping device.

Claims (1)

[Claims] 1. In a microwave heating denitrification device that generates a dried product of uranyl trioxide, plutonium dioxide, or a mixture thereof from a solution of uranyl nitrate, plutonium nitrate, or a mixture thereof by microwave irradiation, uranyl nitrate or nitric acid A crystallizer for precipitating crystals of plutonium or a mixture thereof, a separation device for separating crystals of uranyl nitrate or plutonium nitrate or a mixture thereof from a solution, and a belt for moving crystals of uranyl nitrate or plutonium nitrate or a mixture thereof. A microwave heating continuous denitrification device comprising a conveyor, a microwave heating furnace for causing a denitrification reaction, and a scraping device for scraping off reaction products. 2. The crystallizer for precipitating crystals of uranyl nitrate, plutonium nitrate, or a mixture thereof, includes a raw material supply pump, a flow control valve, a crystallizer having a heat exchanger, a liquid sending pump for taking out the precipitated crystal slurry, and a flow control valve. 2. The microwave heating continuous denitrification device according to claim 1, further comprising a valve and a vacuum evacuation device for maintaining the inside of the crystallizer at a reduced pressure. 3. The separation device for separating crystals of uranyl nitrate, plutonium nitrate, or a mixture thereof includes a centrifuge, a receiving tank for the separated solution, a liquid sending pump and a flow control valve for returning the solution to the crystallization device, and a separation device for separating the separated crystals. 2. The microwave heating continuous denitrification device according to claim 1, further comprising an outlet pipe for taking out the nitrogen.