JPS5924735B2 - Nuclear fuel nitrate denitration 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 or mixtures thereof for nuclear fuel production from solutions of uranyl nitrate or plutonium nitrate or mixtures thereof, respectively.

More specifically, the present invention relates to a nuclear fuel nitrate denitrification device that internally heats the solution by applying microwaves to the solution to raise the temperature of the solution to cause a denitrification reaction.

Conventional microwave heating denitrification equipment applies microwaves to the above-mentioned solution and heats it internally to evaporate, concentrate and dry the solution, and further raises the temperature to cause a denitrification reaction, thereby obtaining the above-mentioned powder for fuel production. Figure 1 shows the reaction curve of the heated material obtained in an example of the denitrification process, which shows that at the same time as the microwave is applied, the temperature of the raw material solution rises to 100 to 120°C.
At (point A), the solution boils, becomes concentrated, and the depth of the solution decreases, and soon nitrate begins to precipitate, and then, as the nitrate cake dries (point B), the temperature of the object to be heated rises rapidly.

When the temperature reaches 350 to 400°C (point C), the denitrification reaction proceeds and a dry cake of the denitrification product is obtained.

In this process, the amount of heat required for the evaporation step is four or five times greater than the amount of heat required for the denitrification step.

Therefore, when evaporation and denitrification are performed in the same microwave heating denitrification device, the denitrification process is very short, making it difficult to determine when denitrification has been completed, resulting in problems with the quality of the fuel manufacturing powder.

Furthermore, the composition of the raw material solution differs depending on the operation, and the microwave heating time, especially the evaporation time, changes, making quality control difficult.

Furthermore, the solubility of uranyl nitrate increases as the evaporation temperature increases, so the energy efficiency of microwave heating is also poor.

The present invention has been made in view of the above circumstances, and provides an evaporative crystallizer for evaporating and concentrating the above-mentioned solution under reduced pressure to recover a crystal slurry of uranyl nitrate, plutonium nitrate, or a mixture thereof, and the above-mentioned crystal slurry. It is an object of the present invention to provide a nuclear fuel nitrate denitrification device equipped with a microwave heater that raises the temperature and denitrates it.

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

FIG. 2 shows a specific embodiment equipped with the above-mentioned vacuum evaporation crystallizer and microwave heater.

A solution of uranyl nitrate, plutonium nitrate, or a mixture thereof passes through a flow control valve 1 and enters a vacuum evaporation crystallizer 2 maintained at a predetermined degree of vacuum and a predetermined temperature.

Of the introduced solution, water and nitric acid are evaporated and exhausted by the exhaust pressure reducer 3.

As water and nitric acid evaporate, crystals of uranyl nitrate, plutonium nitrate, or a mixture thereof in the solution precipitate and accumulate at the bottom in the form of a slurry.

The above crystal slurry passes through a flow rate regulating valve 4 and is transferred to a crystal slurry storage tank 6 by a pump 5.

A predetermined amount of the introduced crystal slurry is sent to the microwave heater 8 through the flow rate regulating valve T at predetermined time intervals, and is heated by microwaves applied by the microwave oscillator 9.

Denitrification results in a dry cake of uranium dioxide or plutonium dioxide or a mixture thereof.

Steam generated during heating 1. Gas is discharged via pipe 10.

FIG. 3 shows a specific example of the vacuum evaporation crystallizer 2 mentioned above.

The solution introduced from the raw material solution supply pipe 11 is transferred to the heat exchanger 1
2, it is heated or cooled to reach a predetermined temperature.

Water and nitric acid in the solution pass through the mist separator 13 and are exhausted under reduced pressure by the aforementioned vacuum exhaust machine 3 connected to the steam exhaust pipe 14.

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 15 at the bottom of the vacuum evaporation crystallizer.

FIG. 4 shows a specific example of the microwave heater mentioned above.

As can be seen from the figure, the microwave irradiation space of the heating device of the denitrification device is formed by the container 21 of the heating device, the upper and lower drive parts, and the rotating turntable 23.

A stock solution 25, which is an object to be heated, is filled in a saucer 21 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 25 is irradiated through the waveguide 24 through an opening provided in the ceiling of the container 21 .

Steam and gas generated during heating are sucked by an off-gas treatment system connected to the pipe 10 attached to the upper part of the container 21.

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

When 2 kg of metallic uranium and 710 kg of nitric acid aqueous solution are supplied to a vacuum evaporation crystallizer with an operating pressure of several torr and an operating temperature of room temperature, approximately 3.0 kg of walanyl nitrate dihydrate is discharged from the crystal slurry discharge pipe.
6 kg of crystals and a nitric acid aqueous solution (HNO3.1,5 H2
A crystal slurry containing a small amount of O) was obtained.

This crystal slurry is denitrified using a microwave heater, and
4 kg of uranium dioxide dry cake was obtained.

Compared to the case where the solution is directly heated with microwaves for evaporative denitration, the microwave output was able to be reduced by about 70 times.

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 vacuum evaporation crystallizer and a microwave heater, microwave output and required energy can be saved, and the quality of the powder can be reduced due to fluctuations in the composition of the raw material solution. It is possible to provide a device that can reduce the influence of

[Brief explanation of the drawing]

The drawings are for explaining the device according to the present invention.
Figure 2 is a graph showing the reaction curve of the denitrification process, Figure 2 is a flow sheet showing one embodiment of the present invention, Figure 3 is a cross-sectional view showing an example of the vacuum evaporation crystallizer of the present invention, and Figure 4 is the present invention. It is a sectional view showing an example of the microwave heater in the invention. 2...Reduced pressure evaporation crystallizer, 3...Reduced pressure exhaust machine, 1°4.7...Flow rate adjustment valve, 5...
...Pump, 6...Crystal slurry storage tank,
9...Microwave oscillator, 10...Exhaust gas pipe, 8...Microwave heater, 12...
... Heat exchanger, 13 ... Mist separator, 21 ... Container, 23 ... Turntable, 24 ... Waveguide, 27 ... ...Saucer.

Claims (1)

[Claims] 1 A vacuum evaporative crystallizer in which a solution of uranyl nitrate, plutonium nitrate, or a mixture thereof is introduced through a flow control valve, and a crystal slurry of uranyl nitrate, plutonium nitrate, or a mixture thereof recovered by this vacuum evaporator crystallizer flows. Denitration of nuclear fuel nitrate, characterized by comprising a storage tank to which the crystal slurry is transferred via a control valve and a pump, and a microwave heater to which a predetermined amount of the crystal slurry is introduced from the storage tank via a flow control valve. Device.