JPS631248B2 - - Google Patents

Description

Detailed Description of the Invention The present invention produces uranium oxide, plutonium oxide, or a mixed oxide of these for nuclear fuel production by heating, vaporizing, and denitrating a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution of both by microwave irradiation. This invention relates to a microwave heating denitrification device for obtaining.

Conventionally, in order to obtain oxides from uranyl nitrate solution, plutonium nitrate solution, or a mixed solution of both by microwave irradiation, the undiluted solution was placed in a metal saucer, placed in a box-shaped microwave oven, and microwave irradiated. Microwave heating denitrification equipment is used. In this case, the temperature of the stock solution is raised by microwave irradiation as shown in Figure 1, boiling begins at point A (approximately 120°C), the solution is concentrated and nitrates precipitate, and then as the nitrates dry ( Point B) The temperature of the heated object rises and reaches Point C (350℃).
When it reaches a certain temperature (nearly 30%), the denitrification reaction progresses and it becomes an oxide.

However, in the case of the above-mentioned microwave heating denitrification equipment, since the saucer is made of metal, the microwaves are only incident from the top of the solution, which causes residual denitrification parts to remain in the denitrification product, and also the absorption of microwaves. This is not desirable from the standpoint of improving efficiency. To solve this problem, a saucer made of microwave transparent material such as glass or ceramics may be used. However, with conventional microwave heating denitrification equipment, if heating is continued until the denitrification reaction is completely completed,
Local heating occurs and there are areas where the temperature rises locally, so the temperature difference may cause cracks or breaks in saucers such as glass.
It was not possible to use a saucer made of microwave transparent material.

The present invention has been made to eliminate the above-mentioned drawbacks, and provides a microwave heating denitrification device capable of improving processing capacity by obtaining a homogeneous denitrification product and improving microwave absorption efficiency. There is a particular thing.

An embodiment of the apparatus according to the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view partially showing a system diagram of the structure of the microwave heating denitrification apparatus according to the present invention.

Reference numeral 1 denotes a metal container-shaped microwave oven for isolating the atmosphere from the outside and forming a microwave field. A saucer stand 4 for taking in and out of the microwave oven 1 is placed in an elevated state so as to form part of the bottom surface thereof. Note that a packing 3 is installed between the microwave oven 1 and the saucer stand 4 in order to seal the atmosphere inside the microwave oven 1. Further, a saucer table lifting device 5 is connected to the saucer table 4 to move the tray up and down.

On the other hand, a waveguide 7 is connected to the microwave oven 1 to guide the microwaves generated by the microwave oscillator 6 into the microwave oven. , a sealing plate 8 made of a microwave transparent material is installed. The microwave oven 1 also includes a vacuum pump 11 for reducing pressure inside the microwave oven.
and are connected by an exhaust pipe 10. Further, the microwave oven 1 is equipped with a thermometer 9 for measuring the temperature of the object to be heated.

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

A predetermined amount of a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution of both is injected into the saucer 2, and the saucer 2 is placed on the saucer stand 4 in a lowered state. The saucer stand 4 is raised by the saucer table lifting device 5, and the saucer 2 is placed into the microwave oven 1. At this time, the saucer stand 4 and the microwave oven 1 are brought into close contact with each other via the packing 3.

Next, the vacuum pump 11 is activated to exhaust the air inside the microwave oven through the exhaust pipe 10, thereby bringing the inside of the microwave oven 1 into a reduced pressure state.

When the inside of the microwave oven 1 reaches a predetermined reduced pressure state, the microwave oscillator 6 is activated to generate microwaves. This microwave is irradiated into the microwave oven 1 through the waveguide 7, and the microwave is absorbed by the solution in the saucer 2, increasing the temperature of the solution. Note that since the saucer 2 is made of a microwave-transparent material, microwaves are absorbed not only from the surface of the solution but also from the sides. If microwave irradiation is continued, water and nitric acid evaporate, nitrate denitrification reactions occur, and oxides are generated. Gas generated during this evaporation and denitrification reaction is exhausted through the exhaust pipe 10.

Furthermore, since the inside of the microwave oven is under reduced pressure, the temperature of the evaporation and denitration reaction of the heated object during microwave irradiation is lower than when the atmosphere is at normal pressure.For example, the temperature change when the atmosphere is set to 150 mmHg As shown by the broken line in Figure 1, evaporation begins at about 60°C (point A'), and then the denitrification reaction occurs at about 130°C (point C'). During this time, check the temperature of the heated object using the thermometer 9.
When the temperature reaches the specified temperature, the microwave oscillation is stopped. Thereafter, the saucer stand 4 is lowered by the saucer lifting device 5, and the saucer 2 containing the denitrified product is taken out.

As explained above, when the microwave heating denitrification device of the present invention is used, the denitrification reaction is completed at a relatively low temperature under reduced pressure. Microwave-transparent saucers can be used, as this prevents localized heating to high temperatures that would cause them to penetrate or crack. Since it is also absorbed from the sides and the efficiency of microwave absorption into the heated object is improved, the reaction time is significantly shortened, processing capacity is improved, and a more homogeneous denitrified product can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a curve diagram showing a heating denitrification reaction for explaining the present invention, and FIG. 2 is a sectional view partially showing a system diagram of an embodiment of the microwave heating denitrification apparatus according to the invention. DESCRIPTION OF SYMBOLS 1... Microwave oven, 2... Saucer, 3... Packing, 4... Saucer stand, 5... Saucer stand lifting device, 6...
Microwave oscillator, 7... Waveguide, 8... Seal plate,
9...Thermometer, 10...Exhaust pipe, 11...Vacuum pump.

Claims (1)

[Claims] 1. In a microwave heating denitration apparatus for obtaining uranium oxide, plutonium oxide, or a mixed oxide of both by irradiating a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution of the two with microwaves, the microwave irradiation is performed. a microwave oven forming a space in which the microwave oven is placed, a microwave oscillator connected to the microwave oven via a waveguide, a vacuum pump connected to the microwave oven, and a vacuum pump housed within the microwave oven. A thermometer for measuring the temperature of an object to be heated, a saucer made of a microwave transparent material into which the object to be heated is placed, and an ejector for taking the saucer into and out of the microwave oven. Microwave heating denitrification equipment.