JPS5930653B2 - Microwave heating denitrification equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microwave heating denitrification method for producing uranium oxide, plutonium oxide, or a mixed oxide thereof for nuclear fuel production by heating a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution thereof, for example. The present invention relates to an apparatus, and particularly to a microwave heating denitrification apparatus in which a heated object storage container is formed of silicon nitride ceramics or mica ceramics.

When uranyl nitrate solution, plutonium nitrate solution, or a mixed solution of these is heated by irradiation with microwaves,
As shown by the solid line in FIG. 1, A was first heated to about 120°C.

At this point boiling begins and the solution concentrates to precipitate the nitrates. B. The nitrate is then dried. The temperature rises again from around this point, and the denitrification reaction progresses from around the Co point when it reaches approximately 300°C, forming uranium oxide, plutonium oxide, or a mixed oxide of these.Such oxides are used in the production of nuclear fuel. . Conventionally, in a microwave heating denitrification apparatus used for the above-mentioned applications, a solution to be heated is placed in a container made of stainless steel, and the solution is irradiated with microwaves.

However, in such a configuration, the microwave is reflected by the container, so the solution in the container is irradiated with microwaves only through the upper opening of the container, resulting in poor heating efficiency and a high output of more than 2 OKW. and took a long time.

There was also the problem that the entire solution was not heated uniformly, leaving undenitrated portions. Therefore, it may be possible to use a material for the container that allows microwaves to pass through.
Glass and alumina ceramics, which are generally known as materials that transmit microwaves, have low strength, so
There is a risk of damage during transportation.

In addition, denitrification requires a micro-output that is incomparably larger than that of a general microwave oven, and especially when the object to be heated changes from a liquid phase to a solid phase, a large output is required. A very large thermal shock will be applied near the end point of the process, but glass, alumina ceramics, etc. are susceptible to thermal shock and are unsuitable for use as containers for heated objects in microwave heating denitrification equipment. The present invention has been made based on the above-mentioned circumstances, and an object thereof is to make the heated object storage container less likely to be damaged by forming the heated object storage container from silicon nitride ceramics or mica ceramics. It is an object of the present invention to provide a microwave heating denitrification device that can quickly and uniformly heat a heated object with a relatively low output.

The configuration of the present invention will be explained below based on the embodiment shown in FIG.

In the figure, 1 is a microwave oven made of a metal plate such as stainless steel, and this oven 1 has an opening 1A at the center of the bottom, and this opening 1A is closed by an elevator platform 2 to an extent that microwaves cannot pass through. ing.

The lifting platform 2 is driven up and down by a 5-driving unit 2A, and the opening 1A is closed at the position shown by the solid line in the figure to isolate the atmosphere inside the microwave oven 1 from the outside, and the internal space of the oven 1 is irradiated with microwaves. Make it a place. A container 3 for storing objects to be heated is placed on the lifting platform 2, and inside this container 3 there is a heated object 4 to be heated and denitrified, such as a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution thereof. is accommodated. The heated object storage container 3 is made of silicon nitride ceramics or mica ceramics.

The components and thermal shock resistance of silicon nitride ceramics and mica ceramics are as follows. By the way, the thermal shock resistance of soda glass (the maximum temperature at which it will not break even if dropped into water) is around 94℃, and that of alumina ceramics is 40℃.
It is clear that both silicon nitride ceramics and mica ceramics have extremely excellent thermal shock resistance.

Further, a microwave oscillator 5 is connected to the soil portion of the microwave oven 1 via a waveguide 6, and a photodetector 7 and an exhaust pipe 8 are further connected.

Next, the operation of the microwave heating device configured as above will be explained.

First, a heated object 4 such as a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution thereof is put into the heated object storage container 3, and the lifting platform 2 is lowered by the drive unit 2A to the position shown by the imaginary line in FIG. Then, the storage container 3 containing the object to be heated 4 is placed on the lifting table 2.

Next, when the lifting table 2 is raised by the driving unit 2A to the position shown by the solid line in FIG. The internal space becomes the microwave irradiation field.

Next, when the microwave oscillator 5 is activated, this oscillator 5
The more oscillated microwaves pass through the waveguide 6 to the oven 1.
The light is irradiated inward and absorbed by the object to be heated 4 inside the container 3.

Thereupon, the object to be heated 4 is heated by microwave irradiation,
As shown by the broken line in FIG. 1, boiling begins at point A, where the temperature rises to about 120° C., and the solution is concentrated to precipitate nitrate. Next, when the drying of the nitrate is completed around point B, the temperature is raised again, and from around point C, when the temperature reaches about 300° C., the denitrification reaction proceeds to form uranium oxide, plutonium oxide, or a mixed oxide thereof. At this time, the microwave irradiated into the oven 1 is of course directly absorbed by the object to be heated 4 through the upper opening of the storage container 3.
Since the microwave is made of silicon nitride ceramics or mica ceramics that transmit microwaves, the microwaves are transmitted through the container 3 and absorbed by the object to be heated 4 . Therefore, as is clear from the comparison between the solid line and the broken line in FIG. 1, heating, evaporation, and denitrification of the heated object 4 over the entire area reach a maximum of 10.
The process is carried out quickly with a small output of about 4KW, and a uniform oxide is formed in a short time. Note that near the end point of the denitrification reaction, microwaves may be locally concentrated, and the temperature of the object to be heated 4 and the container dish 3 may locally rise sharply. Since all ceramics have an extremely high thermal shock resistance temperature, the container 3 can sufficiently withstand the thermal shock that occurs near the end point of the denitrification reaction. Further, gas generated during the denitration process is exhausted to the outside of the oven 1 through the exhaust pipe 8. When the denitrification reaction is completed, the object to be heated 4 emits light due to the local temperature rise.

Therefore, the light is detected by the light amount detector 7, and the detector 7
The operation of the microwave oscillator 5 is stopped by the detected output. After the microwave oscillator 5 stops operating, the drive section 2A
By lowering the lifting platform 2 again to the position shown by the imaginary line in the figure, the container 3 containing the denitrified oxide (material to be heated 4) can be taken out to the outside.

In the above embodiment, the opening 1A is provided at the center of the bottom of the microwave oven 1, and the object to be heated container 3 is taken in and taken out through the opening 1A, but the present invention is not necessarily limited to such a configuration. It's not something you can do. For example, a belt conveyor that passes through a microwave oven is provided, a large number of containers for storing objects to be heated are placed on this conveyor, the conveyor is operated, and the objects to be heated in each container are continuously heated. ″:7*畔咄).1*≦j,; You may put in and take out two vessels.

As described above based on the embodiments, the microwave heating denitrification apparatus according to the present invention includes a heated object storage container made of silicon nitride ceramics or mica ceramics,
It is configured to include a microwave oscillator that heats the object to be heated by irradiating the object to be heated housed in the container with microwaves.

Therefore, since the container for storing objects to be heated has excellent strength, there is no risk of the container being damaged during transportation, and since microwaves pass through the container, objects to be heated can be heated using a low-power microwave. It is heated quickly and uniformly by the waves, making it easy to denitrify uranyl nitrate solutions, plutonium nitrate solutions, and the like.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between microwave irradiation time and heating temperature when a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution thereof is heated by microwave irradiation, and Figure 2 is an example of the present invention. FIG. 1...Microwave oven, 2...Elevating platform, 3...Container for heated object, 4...
・Object to be heated, 5...Microwave oscillator.

Claims (1)

[Claims] 1. A container for storing objects to be heated made of silicon nitride ceramics or mica ceramics, and a microwave oscillator that heats the objects by irradiating microwaves onto the objects stored in the container. A microwave heating denitrification device characterized by comprising: 2. The microwave heating denitrification apparatus according to claim 1, wherein the object-to-be-heated container is placed in an oven. 3. The microwave heating denitrification apparatus according to claim 2, wherein the object-to-be-heated container is arranged in an oven such that it can be moved up and down.