JPS6239959B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an apparatus for producing nuclear fuel oxide by microwave irradiation of a nitrate solution of nuclear fuel material.

Conventionally, there has been a method of producing nuclear fuel oxides, such as uranium oxide, plutonium oxide, etc., by irradiating a heated object made of a nitrate solution of nuclear fuel material, such as a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution of both, with microwaves. Are known.

In this method, the nitrate solution is concentrated by microwave heating and evaporated to dryness, and the nitric acid content is denitrified.
Eventually, it undergoes a process of changing into oxides, but the following method is used to detect the end point of this denitrification process.

In other words, near the end point of denitrification, microwaves are locally concentrated on the object to be heated, causing an excessive local temperature rise in that area and causing a luminescence phenomenon, so the amount of light emitted is measured. The purpose is to detect the end point of denitrification.

(Problem to be solved by the invention) However, in this case, the denitrification reaction ends at 350°C to 400°C, but the excessive temperature rise reaches 800°C or more, so the surface activity of this part decreases. The drawback is that the quality of the oxide for producing nuclear fuel deteriorates.

The present invention was made to eliminate the above-mentioned drawbacks, and uses an infrared detection device that can detect only wavelengths outside the absorption range of water, nitric acid vapor, and nitrogen oxides to detect the sudden rise in temperature that occurs upon completion of the denitrification reaction. It is an object of the present invention to provide an apparatus that can reliably control the denitrification process through detection and produce a nuclear fuel oxide that is uniform and has better physical properties without causing an excessive temperature rise.

[Structure of the Invention] (Means for Solving the Problems) That is, the nuclear fuel oxide manufacturing apparatus of the present invention has the following features:
An oven that absorbs a heated object made of nitrates of nuclear fuel material, a microwave oscillator that irradiates microwaves into the oven, and an absorber of water, nitric acid vapor, and nitrogen oxides from the infrared rays generated from the heated object. The present invention is characterized in that it includes an infrared detection device that can detect only wavelengths outside the range, and a control device that controls the microwave output of the microwave oscillation device based on a signal from the infrared detection device.

(Example) Hereinafter, an example of the nuclear fuel oxide manufacturing apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 is a partially block sectional view showing an embodiment of the nuclear fuel oxide production apparatus of the present invention.

Reference numeral 1 denotes an oven, and this oven 1 is a metal container for shielding the atmosphere from the outside and forming a microwave irradiation field.

An opening 2 is formed in the lower end plate 1a of the oven 1, and a turntable-shaped saucer stand 3 is inserted so as to be movable up and down so as to close the opening 2, and is arranged so as to form a part of the bottom surface of the oven 1. has been done.

This saucer stand 3 is used to place a saucer 5 for sucking and storing the object to be heated 4 and to take it out into the oven 1.The saucer stand 3 is provided with a tray 5 on which the object to be heated 4 is placed and placed in the oven 1.The saucer table 3 is mounted on the bottom surface of the saucer table 3 so that it can be rotated and rotated in the axial direction. An elevating and rotating device 6 that can move up and down along is connected.

On the other hand, the microwave generated by the microwave oscillator 7 is placed on the upper end plate 1b of the oven 1.
A waveguide 8 is connected thereto for guiding the inside of the oven 1, and an exhaust pipe 9 is connected thereto for exhausting gas generated during the denitrification process from inside the oven 1.

Furthermore, in the center of the upper end plate 1b of the oven 1, there is a
1.8μm~2.5μm or 3.5μm~5μm or
An infrared detection device 10 that detects infrared rays outside the range of 8.0 μm to 13.0 μm is installed.

Further, a metallic protection tube 11 is provided at the connection portion between the infrared detection device 10 and the oven 1 to prevent microwave leakage to the infrared detection device 10.

Note that the diameter and length of the protective tube 11 are determined based on the wavelength of the microwave so that the microwave does not pass through the protective tube.

Further, a control device 12 is connected between the infrared detection device 10 and the microwave oscillation device 7 via signal lines 13 and 14.

This control device 12 stops or controls the microwave output oscillated from the microwave oscillation device 7 based on the signal from the infrared detection device 10.

Next, a method for producing nuclear fuel oxide using this apparatus will be explained.

A predetermined amount of the object to be heated 4 of a uranyl nitrate solution, a plutonium nitrate solution, or a mixed solution of both is poured into a saucer 5, and the saucer 5 is placed on the saucer stand 3 in a lowered state.

Then, the saucer stand 3 is raised by the lifting/lowering rotation device 6, and the saucer 5 is housed in the oven 1.

Thereafter, the microwave oscillator 7 is operated and the generated microwaves are irradiated into the oven 1 through the waveguide 8.

The irradiated microwaves are absorbed by the object to be heated 4 in the saucer 5.

As a result, the temperature of the heated object 4 increases, and the second
As shown in the figure, evaporation of water and nitric acid and denitrification reaction of nitrate occur.

That is, in FIG. 2, when the heated object 4 is irradiated with microwaves, the solution (heated object 4) between points A and B boils, water and nitric acid evaporate, and then the solution (heated object 4) reaches point C. The denitrification process progresses between and D points to form oxides.

While this denitration process is progressing, infrared rays emitted from the object to be heated 4 are detected by an infrared detection device 10.

Note that at this time, water, nitric acid vapor, and NOx generated in the denitrification process are present in the oven 1.

The infrared transmittance of water and nitric acid vapor has wavelengths as shown in Figure 3, ranging from 1 μm to 1.8 μm and 2.5 μm.
There are absorption bands between μm and 3.5 μm and between 5 μm and 8 μm.

Further, the infrared transmittance of NOx gas has wavelength dependence as shown in FIG. 4, and has an absorption band between 5 μm and 6 μm.

On the other hand, the temperature of the object to be heated 4 changes as shown in FIG. 2, and a denitrification reaction occurs at 300 to 350 degrees Celsius.

However, as shown in Figure 5, at this temperature,
Infrared rays with a wavelength of 1 μm or less emitted from the heated object have low intensity, so stable measurements cannot be made.

However, in the device according to the present invention, 1.8μ
m~2.5μm or 3.5μm~5μm or 8.0μm
Since an infrared detection device that detects infrared rays having a wavelength outside the range of m to 13.0 μm is used, it is possible to stably detect the end point of denitrification.

On the other hand, the gas generated during the denitrification process is
It is discharged to the outside of the oven 1 through the exhaust pipe 9.

The oven 1 and the infrared detection device 10 are connected to a protective tube 11
The presence of the protective tube 11 prevents microwaves from entering the infrared detection device 10, and the infrared detection device 10 is not affected by noise caused by the microwaves.

In this way, the infrared detection device 10 detects infrared rays from the object to be heated 4, and when the object to be heated 4 reaches a predetermined temperature that is above the denitrification temperature and below the temperature at which light emission occurs, the microwave oscillation device 7 starts oscillating. Temperature control is performed to stop or vary the output.

When the denitrification process is completed in this manner, the saucer stand 3 is lowered by the lifting/lowering rotation device 6, and the saucer 5 containing the denitrified oxide is taken out.

However, with the device of the present invention, stable temperature measurement can be performed without contact and without interference from gases generated during the denitrification process or microwaves themselves, so that the heated object can emit light after the denitrification process is completed. The microwave oscillator can be controlled before an excessive local temperature rise occurs.

Note that the control device 12 sends, for example, an absorption band current obtained by absorbing infrared rays of a predetermined wavelength by the infrared detection device 10 to the power source of the microwave oscillation device 7, and turns the power on and off, or controls the voltage to generate a microwave. It is equipped with an electric circuit that can stop or adjust the output of microwaves by controlling the voltage.

In addition, in order to rotate the saucer base 3 at a desired rotation speed or to move it up and down in the axial direction, the lifting/lowering rotation device 6 is configured such that the shaft 3a of the saucer base 3 is attached to a variable speed motor (not shown) and a gear is mechanically connected to the shaft 3a of the saucer base 3. It is configured so that it can be converted into and moved up and down.

Furthermore, the exhaust pipe 9 is connected to an exhaust pump (not shown) to keep the inside of the oven 1 at a reduced pressure and to exhaust vapors such as moisture and NOx from the object to be heated 4.

[Effects of the Invention] As explained above, according to the present invention, the end point of denitrification in the heating denitrification process using microwaves can be reliably detected by stabilizing the temperature of the heated object, thereby preventing excessive temperature rise in the heated object. The denitrification process can be completed without adding

Therefore, it is possible to produce nuclear fuel oxides of excellent quality that have uniform and better physical properties without producing undesirable undenitrified portions and excessive temperature portions during compaction or sintering during the production of nuclear fuel pellets. can be manufactured.

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and FIG. 1 is a cross-sectional view partially showing an embodiment of the nuclear fuel oxide manufacturing apparatus according to the present invention, and FIG. Characteristic curve diagram showing the reaction curve when irradiated, Figure 3 is a characteristic diagram showing the infrared transmittance of water and nitric acid vapor, Figure 4 is a characteristic diagram showing the infrared transmittance of NOx gas, and Figure 5 is a characteristic diagram showing the infrared transmittance of NOx gas. body temperature
It is a curve diagram showing the relationship between the wavelength of the infrared rays emitted and the radiant energy at 300°C. 1...Oven, 2...Opening, 3...Saucer stand,
4...Object to be heated, 5...Saucer, 6...Elevating and rotating device, 7...Microwave oscillator, 8...Waveguide,
9...Exhaust pipe, 10...Infrared detection device, 11...
...Protection tube, 12...Control device, 13, 14...Signal line.

Claims (1)

[Scope of Claims] 1. An oven that absorbs a heated object made of nitrate of nuclear fuel material, a microwave oscillator that irradiates microwaves into the oven, and a microwave oscillator that absorbs water and nitric acid out of the infrared rays generated from the heated object. It is characterized by having an infrared detection device capable of detecting only wavelengths outside the absorption range of steam and nitrogen oxides, and a control device that controls the microwave output of the microwave oscillation device based on a signal from the infrared detection device. Nuclear fuel oxide production equipment. 2. The nuclear fuel oxide manufacturing apparatus according to claim 1, wherein the infrared detecting device is provided with a protective tube for preventing oven leakage on the infrared incident side. 3 The infrared detection device has a wavelength of 1.8 μm to 2.5 μm.
The apparatus for producing nuclear fuel oxide according to claim 1, which is capable of detecting infrared rays outside the wavelength range of 3.5 μm to 5.0 μm and 8.0 μm to 13.0 μm.