JP2012215429A - Granulation method of nuclear fuel powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a granulation method for efficiently manufacturing fine granulated bodies of a uniform grain size when granulating nuclear fuel powder using a rotary blade type granulating machine.SOLUTION: In a method of granulating nuclear fuel powder by using a rotary blade type granulating machine, the granulation method includes a step of adding and mixing a binder under low-speed rotation of a rotary blade and a step of stopping the rotary blade, measuring an addition amount of the binder and accurately managing the addition amount of the binder, and preferably includes a step of performing agitation at the low-speed rotation without adding the binder before and after the steps. By performing granulation under high-speed rotation thereafter, segregation of the binder is prevented and uniform and fine nuclear fuel granulated bodies are manufactured with excellent reproducibility and at a high yield.

Description

The present invention relates to a method for granulating nuclear fuel powder. More specifically, the present invention relates to a granulation method for MOX fuel powder which is a uranium oxide powder or a mixed oxide powder of uranium and plutonium for producing particles for nuclear fuel pellets used for fuels such as nuclear power generation.

As fuel for nuclear power generation, uranium dioxide fuel or MOX fuel which is a mixed oxide of uranium and plutonium is used. These nuclear fuels are used as a fuel assembly in which raw powders such as uranium dioxide powder are formed into pellets and sintered in a reducing atmosphere, and the sintered pellets are sealed in fuel rods and bundled with many fuel rods. .

In general, in order to produce sintered pellets of nuclear fuel efficiently industrially, particles for pellets are produced so that they can be easily placed in a pellet mold. For example, a binder such as water is added to a raw material powder such as uranium oxide powder and granulated into particles having a particle size of several hundreds of μm.

For example, in JP2010-190718A (Patent Document 1), a mixed nitric acid solution of plutonium and uranium is microwave-heated to obtain a denitration powder, the denitration powder is roasted and reduced, and then a binder is added and granulated. In addition, it is described that this granulated body is formed into pellets. In JP 2010-190720 (Patent Document 2), a mixed nitric acid solution of plutonium and uranium is microwave-heated to form a denitration powder, and then a binder is added to granulate, and the granulated body is roasted and reduced. To make particles for pellets.

JP 2010-190718 A JP 2010-190720 A

Patent Document 1 and Patent Document 2 describe that a binder is added to denitration powder (for example, water is sprayed), and granulation is performed by rotating blades. The amount of water added is preferably 18 wt%, It is sufficient that the powder is sprayed uniformly over the entire powder, and it may be before or during granulation.

However, in the conventional granulation method using a rotary blade granulator, when the binder is added in a state where the rotary blade is stopped before granulation, the contents are not mixed and the binder is easily segregated. There is a problem that the grain state tends to be non-uniform.

In addition, when the binder is added while the rotary blades are rotated at a high speed during granulation, since the enlargement of the granulated body further proceeds in a portion where the amount of the binder temporarily increases, the particle diameter of the granulated body is increased. It tends to be over-targeted or non-uniform. In addition, since the binder or powder together with the binder is bounced and adhered to the inner wall of the granulator, there is a problem that the net amount of binder added to the powder tends to be inaccurate.

The present invention provides a granulation method that solves the above problems when granulating powders of uranium oxide or the like using a rotary blade granulator.

According to this invention, the granulation method which consists of the following structures is provided.
[1] In a method of granulating nuclear fuel powder using a rotary blade granulator, a step of adding and mixing a binder under the low speed rotation of the rotary blade, and measuring the amount of binder added by stopping the rotary blade And a granulating method characterized by comprising a step of granulating by rotating a rotating blade at a high speed after adding a binder.
[2] After rotating the rotating blades at low speed to make the nuclear fuel powder uniform, add a small amount of binder under low speed rotation, stir and mix, and then stop the rotating blades to measure the amount of binder added. The granulation method as described in [1] above, in which the rotating blades are rotated at a low speed to agitate and homogenize the nuclear fuel powder, and the rotating blades are rotated at a high speed to granulate the nuclear fuel powder.
[3] The granulation method according to [1] or [2] above, wherein the binder addition amount is adjusted by adding the binder to the nuclear fuel powder in the step of measuring the addition amount of the binder by stopping the rotating blades.
[4] The granulation method according to any one of the above [1] to [3], wherein the rotating blade is rotated at a low speed of 20 to 50 rpm and the high speed rotation is performed at 300 to 600 rpm.
[5] The granulation method according to any one of [1] to [4] above, wherein a nuclear fuel granule having a particle size of 500 μm or less is produced.
[6] The granulation method according to any one of [1] to [5] above, wherein the nuclear fuel powder is a uranium oxide powder or a MOX fuel powder that is a mixed oxide powder of uranium and plutonium.

In the granulation method of the present invention, the nuclear fuel powder is made uniform by the low-speed rotation of the rotary blades in the step of adding and mixing the binder under the low-speed rotation of the rotary blades. Further, since the binder is added little by little under low speed rotation, the binder is uniformly added to the nuclear fuel powder. For example, the rotation speed of the low-speed rotation is a speed at which granulation does not proceed, for example, 20 to 50 rpm, and is uniformly added to the powder when the binder is dropped little by little.

In the granulation method of the present invention, the amount of the binder added is measured by stopping the rotating blades, so that the amount added can be managed accurately. If the added amount of the binder is inaccurate, the granulated state becomes non-uniform and it is impossible to efficiently produce a fine granulated body, but the granulating method of the present invention controls the added amount of the binder with high accuracy. Therefore, for example, a fine nuclear fuel granule having a particle size of 500 μm or less can be efficiently produced.

The granulation method of the present invention is a method in which an accurate amount of binder is uniformly added and then granulated by rotating the rotating blades at a high speed, and since no binder is added during high speed rotation, the binder is in a non-uniform state. Granulation can be avoided and a uniform granulated body can be obtained.

In the granulation method of the present invention, since the binder is added little by little under low speed rotation, it is possible to suppress a phenomenon in which the binder is blown to the upper part of the casing or the shaft of the rotary blade and adheres. A powder layer grows with the operation on the adhered part of the binder, and when it becomes so large that it cannot support its own weight, it peels off from the casing and falls. For example, when the powder layer falls in a state where no saucer is set, the radioactive material is scattered, but if the present invention is used, the growth of the powder layer can be suppressed.

In the granulation method of the present invention, since the binder is added little by little under low speed rotation, it is possible to suppress a phenomenon in which the binder is blown to the upper part of the casing or the shaft of the rotary blade and adheres. Since the powder layer grows with the operation on the part where the binder is attached, there arises a problem that the traceability is deteriorated and the hold-up amount is increased. However, if the present invention is used, the growth of the powder layer can be suppressed.

In the granulation method of the present invention, since the binder is added little by little under low speed rotation, it is possible to suppress a phenomenon in which the binder is blown to the upper part of the casing or the shaft of the rotary blade and adheres. In order to ensure the criticality safety, it is necessary to control the shape and weight of the nuclear fuel material, and if the powder layer grown on the adhered part of the binder becomes too large to ignore, the criticality safety cannot be maintained. Can be used to suppress the growth of the powder layer.

Process chart showing outline of granulation method of the present invention Schematic cross section of rotary blade granulator Process drawing which shows the granulation process of the Example of this invention

Hereinafter, the present invention will be specifically described based on embodiments.
The present invention relates to a method of granulating nuclear fuel powder using a rotary blade type granulator, a step of adding and mixing a binder under a low speed rotation of the rotary blade, and the amount of binder added by stopping the rotary blade. It is a granulation method characterized by having a step of measuring and a step of granulating by rotating a rotating blade at high speed after adding a binder.

An outline of the granulation method of the present invention is shown in FIG. Although the following description relates to uranium oxide powder, the granulation method of the present invention is not limited to uranium oxide powder. In addition to uranium oxide powder, the nuclear fuel powder in the present invention includes MOX fuel powder which is a mixed oxide powder of uranium and plutonium.

In the granulation method of the present invention, the rotating blade is rotated at a low speed to agitate and homogenize the uranium oxide powder. The rotation speed of the low-speed rotation is preferably 20 to 50 rpm. Next, under this low speed rotation, a binder is added little by little and stirred and mixed. Under this low-speed rotation, granulation is not started when the binder is dripped little by little, and since it is not scattered by the rotating blades, it is added uniformly. For example, water is used as the binder.

When the rotating blade is rotated at a high speed and the binder is dropped, the binder or the powder is blown together with the binder and the ratio of adhering to the inner wall of the apparatus increases, and it is difficult to accurately control the amount of addition to the powder. Also, under high speed rotation, the speed of the rotating blades in the outer peripheral portion is very high, but the speed in the center is close to zero. For this reason, the stirring force in a container changes with places and becomes non-uniform | heterogenous. In granulation, uniform mixing of the binder and the powder is important, and when the binder is segregated, the part becomes a granulated body enlarged and a uniform granulated body cannot be obtained.

For this reason, when granulating using a rotary blade granulator, it is necessary to accurately control the amount of the binder in advance and maintain the uniformity of the raw material powder and the binder. However, in the field of nuclear fuels such as uranium oxide, it is preferable to handle a certain amount of powder enclosed in a container in order to reduce the scattering of radioactive powder. Therefore, since it is difficult to employ an adjustment method in which the raw material powder that has been arranged is added little by little after the binder is added, an operation is required so that the binder amount does not become excessive from the beginning.

In the granulation method of the present invention, the binder is rotated under high speed rotation by changing the rotational speed of the rotating blades in the binder addition step and the powder granulation step, and by providing a low-speed rotation stage for adding the binder before granulation. The inconvenience when adding was eliminated.

In the granulation method of the present invention, after adding a binder under low-speed rotation, the rotating blade is stopped and the amount of binder added is measured. At this time, if necessary, a binder is added to adjust the addition amount. The amount of binder added can be obtained, for example, by measuring the weight of the granulation dish containing powder with an electronic balance, but it is difficult to accurately measure with the rotating blades rotated. To do. Thus, the granulation method of the present invention is provided with a stage for stopping the rotating blades and determining the binder amount before granulation so that the added amount of the binder can be strictly controlled.

After the above measurement, the rotating blades are rotated at a low speed to prevent the binder from segregating and make it uniform. Next, the rotation of the rotary blade is switched to a high speed to granulate the uranium oxide powder. The number of high-speed rotations is preferably 300 to 600 rpm, for example.

As described above, the granulation method of the present invention has a step of adding a binder little by little under low-speed rotation of a rotary blade, and a step of managing the amount of addition after the addition of the binder, preferably before and after that. A step of stirring at low speed without adding a binder, and then granulating under high speed rotation to prevent segregation of the binder, uniform and fine granulated material, for example, particle size of 500 μm or less Uranium oxide granules can be produced with high reproducibility and high yield.

Examples of the present invention are shown below. A process diagram of this embodiment is shown in FIG. Moreover, the outline of the rotary blade type granulator used in the Example is shown in FIG.
In the granulation method of the present invention, raw material powder (uranium oxide powder) 10 is put in a dish-like container 11 and mixed by rotating the rotary blade 12 at a low speed. Next, while rotating the rotating blade 12 at a low speed, the binder (water etc.) 13 is mixed while gradually adding (dropping) from the nozzle 14 little by little, and the mixing is continued until the behavior is stabilized after the binder is added. Thereafter, the addition and mixing of the binder are repeated until a predetermined amount of the binder is supplied, and finally the rotating blade is rotated at a high speed for granulation.

[Example 1]
250 g of uranium oxide (UO ₂ ) powder is loaded into the dish-shaped container 11 and water is supplied while rotating the rotary blade 12 at a low speed (30 rpm). At this time, when 10.9 wt% was supplied without supplying the entire amount of water, the supply was stopped, and the rotation of the rotary blade 12 was continued so that the moisture was acclimated to the entire uranium oxide powder (low-speed rotation time 120 seconds). . Subsequently, the rotation was stopped and water was supplied until the water content reached 11.7 wt%. At this time, since it is difficult to accurately measure the weight on the dish with the electronic balance in a state where the rotary blade 12 is rotating, the dish-like container 11 was removed from the granulator and weighed. After the amount of water was determined, the rotary blade 12 was again rotated at a low speed (30 rpm) for 120 seconds to make the entire powder uniform. Thereafter, the rotary blade 12 was rotated at a high speed (500 rpm) for 120 seconds to granulate the powder. By this granulation, a granulated body was obtained with a high recovery rate of 97.7%. Further, the total amount was a target particle size of 500 μm or less.

[Example 2]
When 250 g of uranium oxide powder is put into the dish-like container 11 and 12.2 wt% of water is supplied while rotating the rotary blade 12 at a low speed (30 rpm), the supply of water is stopped and the rotation of the rotary blade 12 is continued to keep moisture. Was acclimated to the whole uranium oxide powder (low-speed rotation time 120 seconds). Next, the rotation of the rotary blade 12 was stopped, water was supplied until the water content reached 12.6 wt%, the dish-like container 11 was removed from the granulator, and the water content was weighed. After the amount of water was determined, the rotary blade 12 was again rotated at a low speed (30 rpm) for 120 seconds to make the entire powder uniform. Thereafter, the rotary blade 12 was rotated at a high speed (500 rpm) for 60 seconds to granulate the powder. The recovery rate of the granulated product was 98.0%, and the total amount was a target particle size of 500 μm or less.

[Comparative Example 1]
250 g of uranium oxide powder was put into the dish-like container 11, 13 wt% of water was supplied while rotating the rotating blade 12 at a low speed (30 rpm), and the rotation of the rotating blade 12 was continued to allow moisture to become familiar with the entire uranium oxide powder. (Low speed rotation time 120 seconds). Subsequently, the rotary blade 12 was rotated at a low speed (30 rpm) for 120 seconds to make the entire powder uniform. Thereafter, the rotary blade 12 was rotated at a high speed (500 rpm) for 120 seconds to granulate the powder. All of the granules were defective.

[Comparative Example 2]
250 g of uranium oxide powder is put into the dish-like container 11, 15.6 wt% of water is supplied while rotating the rotating blade 12 at high speed (500 rpm), and the rotating blade 12 is rotated at high speed for 90 seconds to granulate the powder. did. The recovery rate of the granulated body was 38.9%, and the ratio of 500 μm or less was 21.1%.

[Comparative Example 3]
250 g of uranium oxide powder is put in the dish-shaped container 11, 14.8 wt% of water is supplied while rotating the rotating blade 12 at a high speed (500 rpm), and the rotating blade 12 is rotated at a high speed for 90 seconds to granulate the powder. did. The recovery rate of the granulated body was 86.4%, of which the ratio of 500 μm or less was 30.7%.

[Comparative Example 4]
250 g of uranium oxide powder is put into the dish-like container 11, 14.8 wt% of water is supplied while rotating the rotating blade 12 at a high speed (500 rpm), and the rotating blade 12 is rotated at a high speed for 210 seconds to granulate the powder. did. The recovery rate of the granulated body was 74.9%, and the ratio of 500 μm or less was 46.7%.

10-uranium oxide powder, 11-dish container, 12-rotary blade, 13-binder, 14-nozzle.

Claims (6)

In a method of granulating nuclear fuel powder using a rotary blade granulator, a step of adding and mixing a binder under a low speed rotation of the rotary blade, and a step of measuring the amount of binder added by stopping the rotary blade A granulation method comprising a step of granulating by rotating a rotary blade at a high speed after adding a binder.
After rotating the rotating blades at a low speed to homogenize the nuclear fuel powder, a binder is added little by little under low-speed rotation, followed by stirring and mixing. Then, the rotating blades are stopped and the amount of binder added is measured. The granulation method according to claim 1, wherein the nuclear fuel powder is agitated and homogenized by rotating at a low speed, and the nuclear fuel powder is granulated by rotating the rotating blade at a high speed.
The granulation method according to claim 1 or 2, wherein the binder addition amount is adjusted by adding the binder to the nuclear fuel powder in the step of measuring the addition amount of the binder by stopping the rotating blades.
The granulation method according to any one of claims 1 to 3, wherein the rotating blades are rotated at a low speed of 20 to 50 rpm and a high speed of rotation at 300 to 600 rpm.
The granulation method according to any one of claims 1 to 4, wherein a nuclear fuel granule having a particle size of 500 µm or less is produced.
The granulation method according to any one of claims 1 to 5, wherein the nuclear fuel powder is a uranium oxide powder or a MOX fuel powder which is a mixed oxide powder of uranium and plutonium.

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