JPH02216090A - Nuclear fuel material and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to hold soundness without damage of a coated layer of coated particles by providing a marking forming layer composed of a graphite matrix material at the end part of a columnar compact containing the coated fuel particles in the matrix material. CONSTITUTION:A binding agent composed of graphite powder and thermosetting resin is hot-press-molded into a plate by a die 10 to obtain a graphite matrix member 5. Next, the member 5 is charged on the side of the upper punch 21 to charge overcoated particles 6 allowed to adhere to the matrix material on the surface of coated fuel particles in a space formed by the member 5 and a lower punch 22 to perform hot press so as to obtain a solid cylindrical nuclear fuel compact provided with a marking forming layer composed of the member 5. Thereby, if marking is performed in the range of thickness of the member 5, the touch of the edge of marking and the particles 6 can be prevented and the soundness of the nuclear fuel material can be held surely without damage of a coated layer.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a nuclear fuel assembly and a method for manufacturing the same, and more specifically, the present invention relates to a nuclear fuel assembly and a method for manufacturing the same, and more specifically, the present invention relates to a nuclear fuel assembly and a method for manufacturing the same. To efficiently obtain a nuclear fuel body in which the tip of the stamp does not come into contact with the coated fuel particles even when a stamp is formed, and the integrity is reliably maintained without causing damage to the coating layer of the coated fuel particles, and this nuclear fuel body is efficiently obtained. Regarding the possible manufacturing method.

[Prior Art and Problems to be Solved by the Invention] Nuclear fuel bodies used in high-temperature gas reactors are generally formed from a mixture of coated fuel particles dispersed in graphite powder.

Here, the coated fuel particles include, for example, uranium, thorium,
A fuel core made of nuclear fuel material such as plutonium and having a diameter of several hundred liters is coated with a layer of silicon carbide, zirconium carbide, pyrolytic carbon, etc. 1.2 g/cm3) pyrolytic carbon layer (buffer layer) and a high density (1.8 g/am3) isotropic pyrolytic carbon layer. A TRl5O type is known, in which a silicon carbide layer and a high-density isotropic pyrolytic carbon layer are added around the heavy coating to form a quadruple coating.

Each of these coating layers can, for example, 1) absorb fission fragment damage, 2) absorb gaseous fission products (hereinafter abbreviated as FP), 2) absorb nuclear fuel swelling, and 2) contain gaseous FP in a pressure vessel. , ■ Preventing reactions between fuel nuclei and FP and silicon carbide layers, ■ Mechanical protection of particles, ■ Maintaining structural strength and dimensional stability of particles, ■ Confining solid FP, ■ Protecting inner layers, etc. It is an extremely important component for maintaining the integrity of the fuel.

A conventional nuclear fuel assembly using coated fuel particles provided with a coating layer having such an action or function is, for example, as shown in FIG. 6, in which coated fuel particles a are dispersed in a graphite matrix material. The molded body A is shaped like a column.

On the other hand, in order to prevent incorrect loading in nuclear fuel assemblies,
It is essential to know the enrichment level, manufacturing history, etc. of each nuclear fuel assembly individually, but since each nuclear fuel assembly has the same shape and dimensions, it is necessary to know the enrichment level, manufacturing history, etc. through non-destructive testing. Since it is difficult to do so, usually a stamp is formed on each nuclear fuel assembly to individually display the enrichment level, manufacturing history, etc.

However, when the above-mentioned markings are formed in the conventional nuclear fuel assembly shown in FIG. 6, for example, as shown in FIG. 7, the tip of the marking portion C contacts the coated particle a,
There is a problem in that the coating layer, which has the various actions and functions described above, may be damaged.

This problem leads to an even more serious problem of impairing the integrity of the nuclear fuel assembly.

The present invention has been made based on the above circumstances.

The purpose of the present invention is to display information such as concentration and manufacturing history, which is extremely important in order to prevent incorrect loading into a high-temperature gas furnace, by stamping, without damaging the coating layer of the coated particles. The object of the present invention is to provide a nuclear fuel assembly that can maintain its integrity, and a manufacturing method that can efficiently produce a nuclear fuel assembly that has such advantages.

[Means for Solving the Problems] In order to solve the above problems, as a result of intensive studies, we have found that a nuclear fuel assembly consisting of a specific layer of graphite matrix material provided at the end of a molded body has a Even if information such as history is displayed by stamping, the tip of the stamp does not come into contact with the coated particles, so the coating layer of the coated particles is not damaged and the integrity can be maintained reliably; The present invention was achieved by discovering that a nuclear fuel assembly having such advantages can be efficiently obtained by a specific manufacturing method.

The structure of the invention according to claim 1 is a nuclear fuel assembly characterized in that a stamp forming layer made of graphite matrix material is provided at the end of a columnar molded body containing coated fuel particles in the matrix material, The structure of the invention is to load a graphite matrix member, which is formed by press-molding a graphite matrix material containing a binder into an uncured plate shape, into an end in a die, and then apply the matrix material to the surface of the coated fuel particles. 2. The method of manufacturing a nuclear fuel assembly according to claim 1, wherein the overcoat particles are filled into the die and warm press-molded.

As shown in FIG. 1, for example, the nuclear fuel assembly according to claim 1 is provided with a stamp forming layer 4 made of a graphite matrix material 2' at the end of a columnar molded body 3 in which coated fuel particles 1 are dispersed in a matrix material 2. Equipped with

There is no particular restriction on the coated fuel particles, for example, BIS
Any conventionally known coated fuel particles such as O-type and TRl5O type may be cited as suitable examples, and cured overcoat coated fuel particles previously proposed by the present applicant may also be cited as suitable examples.

Here, the cured overcoat coated fuel particles are obtained by curing the surface of coated fuel particles such as BISO type and TRl5O type with a matrix material containing graphite powder and a thermosetting resin such as a phenol resin. These coated fuel particles are coated with an overcoat layer, and the failure rate of the coating layer is further reduced.

The above-mentioned materials 71 to 6 contain at least graphite powder and a binder.

The average particle size of the graphite powder is usually 20 to 3 Jtm.

Examples of the binder include thermosetting resins such as phenol resin, urea resin, melamine resin, xylene resin, polyester resin, epoxy resin, and urethane resin.

Among these, phenolic resin is preferred,
Particularly preferred are novolac type phenolic resins.

It is preferable that the thermosetting resin has a residual rate of gel residue of 70% by weight or more when heated by boiling in acetone. Ace1
The residual rate of gel residue after boiling and heating is 70% by weight or more.
If it is 2, there will be less deformation during pressing.

The blending ratio of the graphite powder and the binder in the matrix (graphite powder):(binder) is usually in the range of 9:1 to 6:4, preferably 8
．． 5:1.5 to 7:3.

In addition to the graphite powder and the binder, the matrix material may contain additives commonly used in powder molding, such as lubricants such as stearic acid and zinc stearate.

The nuclear fuel body according to the first aspect is formed by dispersing the coated fuel particles in the matrix material and forming a columnar molded body.

The shape of the columnar molded body may be, for example, a solid prismatic shape,
Examples include a hollow prismatic shape, a solid cylindrical shape, and a hollow cylindrical shape.

Among these, preferred shapes are solid cylinders and hollow cylinders as shown in FIGS. 3(a) and 3(b).

In the nuclear fuel assembly according to claim 1, an stamp forming layer made of a graphite matrix material is provided at an end of the columnar molded body.

The stamp forming layer is a layer that displays information such as enrichment level and manufacturing history by stamping, and since it does not contain the coated fuel particles, it prevents the tip of the stamp from contacting the coated particles. It has an action or function of preventing the coating layer of the coated fuel particles from being damaged by the stamping.

The graphite forming layer having such an action or function can be formed from the graphite matrix material.

The graphite matrix material may contain at least graphite powder and a binder, and usually a mixture having the same composition as the matrix material constituting the columnar molded body can be suitably used. Further, the graphite matrix material may be a mixture having a composition different from that of the matrix material.

Although it is important that the thickness of the stamp forming layer be equal to or greater than the depth of the groove in which the stamp is formed, it cannot be determined unconditionally because it varies depending on the depth of the groove in which the stamp is formed. Usually, about 1 to 2 mm is sufficient. If the thickness of the stamp forming layer is less than the depth of the groove forming the stamp, the tip of the stamp will come into contact with the coated fuel particles constituting the molded body. I can't achieve it.

The columnar molded body and the stamp forming layer are integrally formed, and are fixed to each other by the action of a binder in the matrix material in the molded body and a binder in the graphite matrix material constituting the stamp forming layer. .

Note that the stamp forming layer may be provided only on one end surface of the columnar molded object, or may be provided on both end surfaces of the columnar molded object.

In the nuclear fuel assembly according to claim 1 having such a configuration, even if the enrichment level, manufacturing history, etc., which are essential information to prevent erroneous loading, are displayed by stamping, there is no direct contact between the tip of the stamp and the coated fuel particles. It is a nuclear fuel assembly that can reliably maintain its integrity without contact, and can be suitably used in high-temperature gas reactors.

Is it possible to mold the nuclear fuel assembly according to claim 1 having such advantages by a molding method such as a warm press molding method, an extrusion molding method, or an injection molding method? By suitably employing the method described in claim 2, it is possible to efficiently manufacture.

In the method according to claim 2, the graphite matrix material to be used can be obtained by press-molding the graphite matrix material in the nuclear fuel assembly according to claim 1 into a plate shape.

When press-molding the graphite matrix member, an important point is not to harden the graphite matrix material.

When the graphite matrix material is hardened, it becomes difficult to fix the graphite matrix member to the end of the nuclear fuel assembly by warm press forming, which will be described in detail later.

The press molding of forming the graphite matrix material into a plate shape in an uncured state can be achieved by suitably employing a warm press molding method at a temperature that does not harden the binder in the graphite matrix material. Ru.

Here, the term "uncured state" refers to a state where curing has not yet been completed, and includes a state where curing has already begun.

For example, if the graphite matrix material is made of the graphite powder and phenol resin, warm press molding may be performed at a temperature of about 100°C.

Note that if a cold press molding method is adopted for forming the graphite matrix member, the bond between the graphite matrix materials may not be sufficient, and a graphite 71-lix member having a desired shape may not be obtained.

The graphite matrix member is formed in a shape that is congruent with the shape of the intended end face of the nuclear fuel assembly. That is, if the intended shape of the nuclear fuel assembly is a solid cylindrical shape, the shape of the end face will be circular, so it is necessary to form the graphite matrix member into a disc shape. If the shape is a hollow cylinder, the shape of the end face will be tornut-shaped, so it is necessary to form the graphite 71 to the lix member into a tornut-shape.

The thickness of the graphite matrix member is 1.5 to 2.5, considering the shrinkage margin due to warm pressing with respect to the thickness of the stamp forming layer in the nuclear fuel assembly according to claim 1.
About mm is sufficient.

Further, the density of the graphite matrix member can be determined as appropriate by selecting the press pressure, the filling amount of the graphite matrix material, etc., depending on the predetermined filling rate of the coated fuel particles in the nuclear fuel body and the predetermined density of the matrix material. Just adjust it.

In the method of the present invention, for example, as shown in FIG. Then, the graphite matrix member 5 and the lower punch 22 in this die 10
Graphite matrix members 5 loaded on the upper punch 21 side and the lower bunch 22 side respectively.
In between, overcoat particles 6 formed by adhering matrix material 2 to the surfaces of coated fuel particles 1 are filled.

The overcoat particles can be obtained, for example, by uniformly depositing a matrix material on the surface of coated fuel particles in a rotating drum.

The coated fuel particles and the matrix material that can be used are the same as the coated fuel particles and the matrix material in the nuclear fuel assembly according to claim 1, respectively.

In the overcoat particles, the thickness of the matrix material layer formed on the surface of the coated fuel particles varies depending on the desired filling rate and cannot be determined unconditionally, but is usually between 200 and 400 lumens. , preferably 25
0 to 300 river m.

In the method of the present invention, the graphite matrix member and the overcoat particles are integrally warm press-molded to form the nuclear fuel assembly according to claim 1.

Here, if the graphite matrix material to form the graphite matrix member is filled in the die as a powder without forming the graphite matrix member in advance,
It is difficult to fill the graphite matrix layer to a uniform thickness, and the graphite matrix material powder and the overcoat particles are mixed by the movement of the upper and lower punches, so it is difficult to form a graphite matrix layer with a uniform thickness by press molding. I can't come.

The temperature in the warm press forming is usually 100 to 2
00°C, preferably 130-190°C.

If this temperature is lower than 100° C., the adhesion of the graphite matrix member may not be sufficient or a molded product having a desired shape may not be obtained. On the other hand, even if the temperature exceeds 200°C, no corresponding effect will be achieved, and the energy efficiency will be disadvantageous.

Further, the molding pressure in the warm press molding is usually 2
0-50kg/co+2, preferably 20-30kg/
It is Cl112.

If the molding pressure is lower than 20 kg/c+n2, it may not be possible to obtain a molded article of the desired shape. On the other hand, 50kg/
If it exceeds c1g2, the coating layer of the coated particles may be damaged.

This warm press molding allows the graphite matrix member and the matrix material constituting the overcoat particles to flow and harden to obtain a molded body having a layer made of the graphite matrix member at the end.

The molded body thus obtained is then sintered in a conventional manner to form a nuclear fuel body.

That is, the sintering process is usually performed at a temperature of 1700 to 18
This can be achieved by holding the temperature at 00°C for 1 to 2 hours.

Through the sintering process, the graphite matrix material and the organic matter in the matrix material are carbonized to become a graphite matrix, and a nuclear fuel body consisting of coated fuel particles and a graphite matrix can be obtained.

The nuclear fuel assembly manufactured by the method of the present invention is equipped with a stamp forming layer using the graphite matrix member made of a graphite matrix material, and the thickness of the stamp forming layer is within a range of, for example, enrichment, manufacturing By forming a stamp such as a history, it is possible to prevent the tip of the stamp from coming into contact with the coated fuel particles, thereby preventing damage to the coating layer of the coated fuel particles.

There are no particular restrictions on the means for forming the markings, for example, a punch with unevenness for markings may be used during the warm press molding, or a marking machine, a vibrating pen, etc. may be used after the warm press molding. Alternatively, the marking can be formed by using a laser method. Regardless of the method used, it is important that the depth of the marking does not exceed the marking formation layer. If the depth of the stamp exceeds the stamp forming layer, the tip of the stamp may come into contact with the coated fuel particles, causing damage to the coating layer of the coated fuel particles.

A nuclear fuel assembly produced by the method yet to be invented can be suitably used, for example, in a high-temperature gas reactor while reliably maintaining its integrity.

[Example] Next, an example of the present invention and a comparative example will be shown to further specifically explain the present invention.

(Example 1) A graphite matrix material 2' consisting of graphite powder and phenolic resin, the content of which is 80% by weight of graphite powder and 20% by weight of phenolic resin, was placed in a die 10 as shown in FIG. The space formed by the upper bunch 21 and the lower punch 22 is filled, and the molding pressure is 20 kg/cm2 and the temperature is 100 ml.
Warm press molding was carried out under the conditions of °C, and the thickness was 1.51 mm.
A graphite matrix member 5 having a diameter of 1 m and a density of 1.72 g/cm3 was manufactured.

Next, as shown in FIG. 2, this graphite matrix member 5 is loaded into the upper punch 21 side in the die 10, and the graphite matrix member 5 is loaded into the space formed by the graphite matrix member 5 and the lower bunch 22 in the die 10. The graphite matrix member 5 is filled with coated particles 6 and subjected to warm press molding at a molding pressure of 10 kg/cm2 and a temperature of 190°C.
A solid cylindrical molded body having a stamp forming layer 4 at the end thereof was obtained.

Note that the overcoat particles were prepared as follows.

That is, coated fuel particles with a diameter of 900 μm are obtained by coating a uranium dioxide core with ceramics containing carbon and silicon carbide by pyrolytic vapor deposition using a conventional method.
A matrix material having a composition of 80% by weight of graphite powder and 20% by weight of phenolic resin was uniformly adhered to a thickness of 30 OpLm while spraying ethanol to obtain overcoat particles.

Thereafter, the molded body was subjected to a sintering treatment in which the temperature was raised to 1.800°C in a vacuum and maintained for 1 hour.

Next, an engraving indicating the enrichment level and production history was formed on the engraving layer 4 by a laser method to a depth of 33 m1 to obtain a nuclear fuel assembly.

The obtained nuclear fuel body was roasted at a temperature of 800°C, and the obtained coated fuel particles were immersed in nitric acid to analyze the eluted uranium and examine the failure rate. Here, the breakage rate is the breakage rate of the silicon carbide layer (ceramic layer) in the coated fuel particles.

As a result, the failure rate of the coating layer of coated particles in a nuclear fuel body is 2. There was an IX 10-6.

(Comparative Example 1) The same overcoat particles 6 as in Example 1 were applied to the lower punch 21 in the rice 10 as shown in FIG.
Then, the space formed by the lower punch 22 was filled, and warm press molding was performed at a molding pressure of 30 kg/cm 2 and a temperature of 1908 C to obtain a solid cylindrical molded product.

Thereafter, the molded body was heated to 1.800°C in a vacuum.
A sintered body was obtained by heating and holding for 1 hour.

Next, a stamp indicating the enrichment level and production history was formed at a depth of 0.3 mm on the end of this sintered body by a laser method to obtain a nuclear fuel assembly having the stamp.

The damage rate of the obtained nuclear fuel assembly was examined in the same manner as in Example 1 above.

As a result, the failure rate of the coating layer of the coated particles in the nuclear fuel assembly was 7.7 Xl0-5.

(Comparative Example 2) A nuclear fuel assembly was manufactured in the same manner as in Comparative Example 1 except that no markings were formed, and the failure rate of the obtained nuclear fuel assembly was determined in the same manner as in Example 1. I looked into it.

As a result, the failure rate of the coating layer of coated particles in a nuclear fuel body is 2. I Xl0-6 was there.

(Evaluation) As is clear from the results of Example 1, Comparative Example 1, and Comparative Example 2, the nuclear fuel assembly according to claim 1 obtained by employing the manufacturing method according to claim 2 has no markings. It was confirmed that there was no damage to the coating layer on the coated particles, and that the integrity of the coated particles was maintained.

[Effects of the Invention (1) According to the invention of claim 1, by providing a stamp forming layer made of a graphite matrix material at the end, and forming a stamp within the thickness of this stamp forming layer, the tip of the stamp To provide a nuclear fuel assembly in which it is possible to prevent contact between the fuel particles and the coated fuel particles, and the integrity of the coated fuel particles can be reliably maintained without causing damage to the coating layer of the coated fuel particles due to stamping. I'll come.

(2) According to the invention of claim 2, the graphite matrix member formed in advance to have a uniform thickness and the specific overcoat particles are integrally molded by warm press molding, thereby achieving the above-mentioned advantages. It is possible to provide a method for manufacturing a nuclear fuel assembly that can efficiently obtain the industrially useful nuclear fuel assembly according to claim 1 with excellent reproducibility.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a nuclear fuel assembly according to claim 1, and FIG. 2 is an explanatory diagram showing a filling state of graphite matrix members and overcoat particles in a die in the manufacturing method according to claim 2. , FIG. 3(a) is a front view showing another example of the nuclear fuel assembly according to claim 1, FIG. 3(b) is a plan view thereof, and FIG. 4 is a graphite matrix in the manufacturing method according to claim 2. FIG. 5 is an explanatory diagram showing press forming of a conventional nuclear fuel assembly, FIG. 6 is an explanatory diagram showing an example of a conventional nuclear fuel assembly, and FIG. 7 is an explanatory diagram showing an example of a conventional nuclear fuel assembly. FIG. 3 is an explanatory diagram showing the relationship between markings and coated fuel particles. 1... Coated fuel particles, 2... Matrix material, 2'
... graphite matrix material, 3 ... columnar molded body, 4.
... Stamp forming layer, 5... Graphite matrix member, 1O... Dice overcoat particles, (N ○ O

Claims (2)

[Claims] (1) A nuclear fuel assembly comprising a stamp forming layer made of a graphite matrix material at the end of a columnar molded body containing coated fuel particles in the matrix material. (2) After loading a graphite matrix member made by press-molding a graphite matrix material containing a binder into a plate shape in an uncured state into the end of the die, the matrix material is attached to the surface of the coated fuel particles. 2. The method of manufacturing a nuclear fuel assembly according to claim 1, wherein the die is filled with overcoat particles consisting of the above-mentioned overcoat particles, and warm press molding is carried out.