JP2913513B2 - Method for producing pellets for nuclear fuel - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for efficiently producing nuclear fuel pellets having different densities in the radial direction.

[Prior Art] When manufacturing pellets for nuclear fuel having different densities in the radial direction, conventionally, as shown in FIG. 2, a central molded body 1 shown in FIG. 2A and an outer peripheral molded body shown in FIG. After separately molding the body 2, the two are combined and molded again to form the same figure (c).
Thereafter, the molded body 3 was fired.

However, the above-described method requires a complicated process of forming parts having different densities in the radial direction or parts at the center part and the outer peripheral part, and then combining and molding these parts, and sintering them. Had its own limits.

[Problems to be Solved by the Invention] To explain in more detail what has been described in the preceding section, in order to produce nuclear fuel pellets having different densities in the radial direction by a conventional method, the central molded body 1 and the central molded body 1 It is necessary to form an outer peripheral molded body 2 in which holes having the same size as the outer molded body 1 are aligned.

The center part molded body 1 uses a die through hole for the center part molded body 1 and upper and lower punches of a size that can be inserted into the die through hole, and inserts the lower punch from the lower side of the die through hole into the die through hole. After the insertion, the die is filled with fuel powder, and an upper punch disposed above the through hole is inserted to compress the fuel powder, thereby forming the die.

The outer peripheral part 2 has a die through hole for the outer peripheral part 2, an upper and lower punch of a size that can be inserted into the die through hole, and a center hole of the same size as the central part 1. After inserting the lower punch into the die through-hole from below the die through-hole using a core rod for, filling the fuel powder into the die through-hole with the core rod arranged in the center of the die through-hole, Next, an upper punch disposed above the through-hole is inserted to compress the fuel powder, thereby forming a compact.

That is, in the conventional method, the outer peripheral molded body is individually formed for each density, and it becomes a complicated process of combining these into pellets. It is difficult to manufacture an outer peripheral molded body having a small thickness.

The present invention has been made to solve the above problems, and has as its object to provide a method for producing nuclear fuel pellets that can easily produce nuclear fuel pellets having different densities in the radial direction.

[Means for Solving the Problems] The method of the present invention is a method for producing one type of nuclear fuel pellets by compressing one kind of fuel powder. A lower punch capable of adjusting the insertion amount into the die through hole is arranged below the through hole, and each of the divided portions of the lower punch is inserted into the die through hole by a predetermined insertion amount, and then the die through hole is inserted. Is filled with the fuel powder, and then a lower punch is inserted from above the through-hole, and the fuel powder is compressed by aligning the surfaces of the divided portions of the lower punch that are in contact with the fuel powder so that the density is different in the radial direction. It is said to manufacture pellets for nuclear fuel.

Preferably, in the above method, the upper punch is radially divided similarly to the lower punch, and each of the divided portions of the upper punch is inserted into the die through hole by a predetermined insertion amount. In this method, the fuel powder is compressed by aligning the surfaces of the divided portions of the upper punch in contact with the fuel powder.

[Operation] In the method of the present invention, a lower punch to be inserted into the die through-hole is used, which is divided in the radial direction and can adjust the amount of insertion into the die through-hole for each divided portion. Thus, for example, as shown in FIG. 1 (a), when the density of the central portion of the pellet is desired to be lower than the density of the outer peripheral portion, the insertion amount of the split punch in the central portion is made larger than that in the outer peripheral portion. If this is the case, the amount of the fuel powder to be filled in that region is reduced. Therefore, by compressing the fuel powder into a column in this state, pellets having a lower density at the center than at the outer periphery can be obtained. As described above, according to the present invention, pellets having different densities in the radial direction can be produced in a single molding step.

Furthermore, pellets having three or more types of densities in the radial direction can be easily manufactured by using lower punches having a configuration in which three or more types are divided in the radial direction and making the insertion amounts different from each other. At this time, by adjusting the width of the divided punches, it is possible to adjust the thickness of each density to a desired width, such as reducing or increasing the thickness of each density.

More preferably, as in the case of the lower punch, the upper punch having a radially divided portion can be used to adjust the compression amount with respect to the fuel powder more finely. It is possible to produce pellets having a very large density difference with the part.

Embodiment FIG. 1 shows an embodiment of the present invention, in which the density at the center of the pellet is lower than the density at the outer periphery.

FIG. 1 (a) shows the inside of a through hole provided in the die 4;
The lower punch, which is divided into two parts in the radial direction, is inserted.
The state where the fuel powder 9 is filled in the space where the lower punch is not inserted is shown.

The lower punch is divided into a lower first punch 5 occupying the outer peripheral portion and a lower second punch 6 occupying the central portion. The lower second punch 6 has a larger insertion amount than the lower first punch 5. I have. Therefore, the amount of the fuel powder 9 filled in the upper region of the lower second punch 6 is smaller than the amount of the fuel powder 9 filled in the upper region of the lower first punch 5.

FIG. 1 (b) shows a state during the molding of the pellet. An upper punch is inserted from above the through hole. The upper punch is divided into an upper first punch 7 occupying an outer peripheral portion and an upper second punch 8 occupying a central portion in order to obtain a good density distribution. ing. In the upper punch, as in the lower punch, the upper second punch 8 has a larger insertion amount than the upper first punch 7.

After the space formed between the upper punch and the lower punch is uniformly filled with the fuel powder 9, FIG. 1 (c)
As shown in (1), the upper and lower punches are inserted into the through holes to a predetermined position. At this time, the lower first punch 5 and the lower second punch 5
A surface formed between the upper punch and the lower punch by aligning a surface of the punch 6 in contact with the fuel powder 9 and a surface of the upper first punch 7 and the upper second punch 8 in contact with the fuel powder 9. Is formed into a columnar shape, thereby compressing the fuel powder 9 filled therein into a columnar shape. Thereby, pellets having two types of densities in the radial direction are obtained.

In this embodiment, the upper punch is also divided into the upper first punch 7 and the upper second punch 8, but the compression of the fuel powder is performed by using the upper punch which is not divided in the radial direction. It goes without saying that pellets having different densities in the radial direction can be produced even if the above method is performed.

When the density distribution is opposite to that of this embodiment (that is, when the density in the central part is higher than that in the outer peripheral part), the fuel powder 9
Before the filling, the insertion amount of the lower second punch is adjusted to the first amount.
What is necessary is just to supply less powder than a punch and to supply more powder to a center part.

Further, in the case of producing pellets whose density is three or four kinds in the radial direction, the upper punch and the lower punch are divided in the radial direction by the number thereof and the insertion amount into each through hole is changed, and the same as above. If compression is performed in a procedure, it can be easily manufactured.

[Effects of the Invention] As described above, according to the method for producing pellets for nuclear fuel of the present invention, it is not necessary to form a molded body for each density and mold them in combination. Fuel pellets having different densities in the radial direction can be manufactured. At this time, it is possible to easily produce pellets having three or more densities in the radial direction by using a plurality of radially-divided punches, and to further divide the pellet into a desired width in the radial direction. It is also possible to adjust the thickness for each density by using a punch.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment of the pellet production method of the present invention, in which (a) shows a state in which powder is supplied, (b) shows a state during powder molding, and (c) shows a state in which molding is completed. ing. FIG. 2 is an explanatory view of a conventional pellet production method,
(A) is the center molded body, (B) is the outer peripheral molded body, (C)
Is a molded article combining both. 4: die, 5: lower first punch, 6: lower second
Punch, 7 Upper first punch, 8 Upper second punch, 9
Fuel powder.

Claims (2)

(57) [Claims] 1. A method for producing a columnar nuclear fuel pellet by compressing one kind of fuel powder, wherein the nuclear fuel pellet is divided in a radial direction, and an insertion amount of each divided portion into a die through hole can be adjusted. Place the lower punch below the through hole,
Each of the divided portions of the lower punch is inserted into the die through hole by a predetermined insertion amount, and then the fuel powder is filled into the die through hole, and then the upper punch is inserted from above the through hole into the fuel. A method for producing pellets for nuclear fuel, characterized in that powders having different densities in the radial direction are produced by aligning and compressing the powder in such a manner that the surfaces of the divided portions of the lower punch which come into contact with the fuel powder are compressed. 2. The upper punch is radially divided in the same manner as the lower punch, and each of the divided portions of the upper punch is inserted into a die through-hole by a predetermined insertion amount so that the fuel powder is removed. The method for producing pellets for nuclear fuel according to claim 1, wherein the surfaces of the divided portions of the upper punch that are in contact with the fuel powder are aligned and compressed.