JP4451267B2 - Neutron absorbing material and method of manufacturing the same - Google Patents

Description

  The present invention relates to a boron carbide-containing metal matrix composite material having a recriticality preventing action and a neutron absorption action and useful as a material for transporting or storing a spent nuclear fuel that emits neutrons, and a method for producing the same. .

  As a means to safely transport and store spent nuclear fuel without recriticality and without excessive leakage of radiation, the container itself (eg, a basket for containing fuel assemblies) Various studies have been conducted on the design and materials used. The materials used for these applications are required to have properties such as the ability of the materials themselves to absorb neutrons and the like, and the ability to cool spent nuclear fuel efficiently. As materials for neutron absorption, Al-based alloys and composite materials containing boron, and materials called borals in which boron-containing substances are sandwiched between Al plates have been used in many cases. It is used as a constituent material for storage containers.

The method disclosed in Patent Document 1 increases the concentration of isotope boron ¹⁰ B having a high neutron absorption capability, thereby suppressing the total amount of boron in Al, and the neutron absorption effect and mechanical properties of the alloy material. To achieve both. However, the problem is that the isotope boron ¹⁰ B is expensive in price. Further, a material called “boral” that has been used for a long time is uneasy to be used for transporting or storing spent nuclear fuel due to insufficient strength of the boron-containing layer. The method disclosed in Patent Document 2 uses inexpensive B ₄ C as a boron source, and creates a target composite material by pressure sintering with Al powder.
JP 2003-268471 A JP 2001-042089 A

In general, as an inexpensive method for producing a metal matrix composite material, there is a non-pressure permeation method introduced in Patent Document 3. This is a composite of a reinforcing material in a metal matrix. This method is suitable for those with a volume ratio of reinforcement of 50% or more, and the volume ratio of the reinforcement is too high to satisfy the mechanical properties required here, such as elongation, and strengthens B ₄ C. When used as a material, the neutron absorption capacity is excessive. The method of creating a low reinforcing material concentration by the non-pressure permeation method is disclosed in Patent Document 4, and a composite material of about 40 to 50% is produced by the non-pressure permeation method and dissolved again. Then, it is diluted with a matrix alloy to a predetermined amount. While this approach is practical if reinforcement of SiC, when applied to a B ₄ C, seemed to react between the aluminum is B ₄ C and the matrix metal, and B ₄ C by the pressureless permeation Although there was a composite material of Al, there was a problem that even if it was heated to dissolve again to dilute it, it did not dissolve. As a method for making the filling rate of the reinforcing material variable in the non-pressure permeation method, there is Patent Document 5. Although it is possible to create a composite material containing B ₄ C by this method, it is difficult to say that it is an inexpensive manufacturing method because it is necessary to process a composite material that is difficult to process in order to obtain the required plate shape.
Japanese Patent No. 2641901 Patent No. 2905520 Japanese Patent No. 2905521

As mentioned above, boron-containing Al alloys have many preconditions that significantly increase production costs, such as the use of extremely expensive concentrated boron in order to increase neutron absorption capacity, making it difficult to put it to practical use at the industrial level. Met. Also, Bola, which has a high B ₄ C content of 30 to 40% by weight, has a problem in workability and cannot be used as a structural material. Against this background, it has high neutron absorption capacity by increasing the B content, as well as excellent mechanical properties such as tensile strength and elongation, and can be easily processed and used as a structural material. There has been a demand for an Al-based composite material having neutron absorption capability and an inexpensive manufacturing method thereof.
The present invention has been made in view of the situation as described above, using normal B ₄ C, which are cheaply distributed in community as an abrasive or refractory material, to satisfy well-balanced neutron shielding ability and strength characteristics necessary A method for producing an Al-based composite material at low cost by using a non-pressure permeation method.

The present invention employs the following means in order to solve the above problems.
a) using boron or boron compound (eg B ₄ C) as filler,
b) forming a breathable material by mixing matrix metal (eg aluminum powder) with said filler and / or coating said filler with matrix metal;
c) Arrange an excess of matrix metal source sufficient to remain after infiltration so as to be adjacent to the upper and lower and / or right and left sides of the breathable material,
d) heating the matrix metal to a temperature range above its melting point to form a molten matrix metal; and
e) infiltrating the molten matrix metal spontaneously into the breathable material by providing an infiltration atmosphere at least at some point during the process and supplying at least one of an infiltration enhancer or an infiltration enhancer precursor. ,
f) Furthermore, a boron-metal composite material (for example, B ₄ C-Al composite material) and a matrix metal (for example, Al) that have a predetermined thickness by processing the matrix metal layer that is easy to process after the penetration. A method of forming a material having a sandwich structure is provided.

According to the above-described method for producing a metal matrix composite having neutron absorption capability of the present invention, the following effects can be obtained. After adding B ₄ C powder with neutron absorption ability to aluminum or aluminum alloy powder and mixing, the metal matrix composite manufactured using non-pressure infiltration method is the conventional melting method and pressure sintering method Compared to, manufacturing at a low cost becomes possible. Also, by preparing excess Al on both sides of the composite material in excess of the amount required for infiltration, an easy-to-process Al layer is formed integrally with the composite material after infiltration, making it easy to process after infiltration . That is, by using the present invention, it is possible to obtain a metal matrix composite material that not only has a high neutron absorption capability but is suitable as a structural member at a low price.

Definitions As used herein, “aluminum” refers to substantially pure metal (eg, relatively pure and commercially available unalloyed aluminum) or impurities and / or iron, silicon, copper, magnesium, manganese, It means and includes other grades of metals and metal alloys such as commercially available metals having alloy components such as chromium and zinc. The aluminum alloy used in this definition is an alloy or intermetallic compound containing aluminum as a main component.
As used herein, “Infiltrating atmosphere” refers to interaction with matrix metal and / or filler and / or penetration enhancer precursor and / or penetration enhancer to reduce spontaneous penetration of matrix metal. It means the presence atmosphere that is created or promoted.
As used herein, “Infiltration Enhancer” means a substance that promotes or assists the matrix metal to spontaneously penetrate the filler. The penetration enhancer may be, for example, by reacting a penetration enhancer precursor with the penetration atmosphere to (1) a gaseous product and / or (2) a reaction product of the penetration enhancer precursor and the penetration atmosphere and / or (3 ) By producing a reaction product of a penetration enhancer precursor and a filler. Furthermore, the penetration enhancer is fed directly to at least one of the filler and / or the matrix metal and / or the penetration atmosphere to generate a penetration enhancer produced by a reaction between the penetration enhancer precursor and another species. You may make it act in the substantially similar method. Basically, at least during spontaneous penetration, the penetration enhancer must be located in at least a portion of the filler to achieve spontaneous penetration.
As used herein, “Infiltration Enhancer Precurcor” is a substance that, when used in combination with a matrix metal and / or osmotic atmosphere, induces or assists spontaneous penetration of the matrix metal into the filler. Means. Without being limited to a particular principle or description, it is necessary that the penetration enhancer precursor be able to be placed or moved to a location where the penetration enhancer precursor can interact with the penetration atmosphere and / or filler and / or metal. For example, in certain matrix metal / penetration enhancer precursor / penetration atmosphere systems, it is desirable for the penetration enhancer precursor to volatilize at the melting temperature of the matrix metal, near it, or in some cases somewhat higher. . Such volatilization may result in (1) the generation of gaseous matter that enhances the wetting of the filler by the matrix metal by reaction of the penetration enhancer precursor with the penetration atmosphere; and / or (2) the penetration enhancer precursor; Generation of a solid, liquid or gaseous penetration enhancer that promotes wetting to at least a portion of the filler by reaction with an osmotic atmosphere; and / or (3) a solid that enhances wetting within at least a portion of the filler. The reaction of the filler penetration enhancer precursor to produce a liquid or gaseous penetration enhancer occurs.

In the present invention, boron or a boron compound is used as a filler. In particular, B ₄ C is preferable in terms of price and availability. Boron or a boron compound is preferably used as a powder, but may be granular.

  Next, a breathable material is formed by mixing the filler with a matrix metal and / or coating the filler with the matrix metal. For example, after the filler and powdered matrix metal are mixed, they can be simply put into a mold to make a breathable material with a low level of filling rate, or press-molded into a plate shape. In order to improve the mixing state, a powder in which a filler is coated with a matrix metal may be used. For coating, plating, thermal spraying or mechanochemical reaction can be used. It is easy to mix the powdered filler and the powdered matrix metal, but in this case, in order to mix both uniformly, it is preferable to use a powder having an average particle size of about 10 to several tens of μm. Good.

  Here, in forming the breathable material, the content of the matrix metal in the breathable material is preferably 1 to 98% by volume. When the content is less than 1% by volume, the mechanical strength of the obtained plate material is insufficient. On the other hand, if it exceeds 98% by volume, the content of boron or boron compound becomes relatively small, and the ability of neutron absorption may be insufficient.

  Next, an excess of the matrix metal source is provided so as to remain sufficiently after infiltration so as to be adjacent to the upper and lower sides and / or the left and right sides of the breathable material. That is, the matrix metal source is disposed on both sides of the opposite side surfaces of the breathable material so as to sandwich the breathable material. For example, as shown in FIG. 1, the upper and lower surfaces of a breathable material molded or deposited in a plate shape are preferably brought into contact with a material (such as a plate) made of a matrix metal. At this time, the amount of the matrix metal contained in the matrix metal source is made sufficiently larger than the amount penetrating the breathable material. For example, it is preferable that the amount is about twice the theoretical amount permeating into the breathable material (obtained from the difference between the bulk density of the breathable material and the theoretical density of the metal composite to be produced).

  Next, the breathable material in a state where the matrix metal source is arranged is heated to form a molten matrix metal. The heating temperature may be a temperature that exceeds the melting point of the matrix metal. Although the heating method is not limited, for example, a method in which a matrix metal source and a breathable material are placed in an electric furnace and the both are kept in contact with each other is preferable.

  Further, the molten matrix metal is supplied to the breathable material by supplying an infiltration atmosphere at least at a certain point in the processes from a) to d) and supplying at least one of an infiltration enhancer or an infiltration enhancer precursor. To penetrate spontaneously. The permeation atmosphere may be supplied continuously from the beginning to the end of the step of heating the breathable material, or the supply may be stopped during the process. It is preferable to supply at least until the formation of the molten matrix metal and continue to supply until the end of heating. Further, it is preferable that the permeable atmosphere is in communication with at least one of the breathable material and the molten matrix metal for at least a part of the osmosis period.

  Here, in order to supply a penetration enhancer or a penetration enhancer precursor, they should be mixed with the breathable material in advance or added beforehand to the matrix metal source disposed adjacent to the breathable material. Alternatively, it is possible to supply the mixture in an osmotic atmosphere.

  The matrix metal used in the present invention is typically metallic aluminum, but may be an alloy containing aluminum as a main component. Specific examples include 1050 alloy and 5052 alloy that are easily available. In addition to metallic magnesium, AlMg can also be used as the penetration enhancer precursor. Nitrogen is preferred as the infiltration atmosphere.

Furthermore, the boron compound used for the filler is most preferably B ₄ C because of its price and availability. However, BN, boron oxide or the like may be used.

  Through the above process, for example, as shown in FIG. 3, it is possible to obtain a plate-like material made of a metal-based composite material made of a boron compound and a matrix metal on the inside and made of a matrix metal on the outside. The outer matrix metal portion of the plate-like material is easier to process than the inner metal matrix composite material, and the thickness can be adjusted by machining such as cutting as required. At this time, the thickness of the external matrix metal layer is grasped experimentally in advance and processed in the range of the thickness. By such a method, it can process without impairing an internal metal matrix composite material part.

Hereinafter, an embodiment of an aluminum composite material having a neutron absorption capability and a method for producing the same according to the present invention will be described. In the following embodiments, B ₄ C as a filler, aluminum powder as a powdered matrix metal, an aluminum alloy having a composition of 1050 alloy as a metal source of the molten matrix metal, nitrogen as an infiltration atmosphere, metal as an infiltration enhancer precursor Although magnesium powder was used, the present invention is not limited to this.
About 5 mm thick aluminum alloy plate (matrix metal source), a mixture (breathable material) 1 consisting of about 7% by weight of B ₄ C, 4% by weight of magnesium and a powdered aluminum alloy with the remaining composition About 8 mm was deposited on 2 and the same alloy plate 3 was placed thereon (FIG. 1).

The air-permeable material and aluminum alloy plate in the state shown in Fig. 1 were heated to 790 ° C in about 3 1/2 hours in a nitrogen atmosphere furnace, kept for 2 hours, and naturally cooled to achieve non-pressure permeation (Fig. 1). 2). What was created was a metal matrix composite 4 consisting of B ₄ C and Al in the middle, and further aluminum alloy was supplied from above and below into the voids of the mixture before penetration, and the concentration of B ₄ C in the metal matrix composite As it was about 5%. Moreover, since the upper and lower aluminum alloy plates 5 and 6 are much more than the required supply amount, they remained with a thickness of 2-3 mm even after penetration. By processing this to about 1 mmt on both sides, a plate with a neutron absorption capability of a sandwich structure with a total thickness of 10 mm and containing a composite ₄ of B ₄ C and Al at the center and Al layers 5 and 6 on both sides It was possible to create (Fig. 3).

It is a schematic sectional drawing of the lay-up before the permeability | transmittance material and matrix metal source infiltration in an Example. It is a schematic sectional view after the penetration of the air-permeable material and the matrix metal source in the examples. It is a schematic sectional drawing after the process of the plate-shaped material in an Example.

Explanation of symbols

1 Mixed layer of boron compound and powdered matrix metal (before penetration)
2 Matrix metal source (before penetration)
3 Matrix metal source (before penetration)
4 Composite layer of boron compound and matrix metal (after infiltration)
5 Matrix metal source remaining after infiltration 6 Matrix metal source remaining after infiltration

Claims (6)

A method for producing a neutron absorbing material comprising a metal matrix composite and having a sandwich structure of matrix metal layers, comprising the following steps:
a) using boron or boron compound as filler,
b) forming a breathable material by mixing matrix metal with said filler and / or coating said filler with matrix metal;
c) Arrange an excess of plate-like matrix metal source that remains sufficiently after infiltration so as to be sandwiched between the upper and lower and / or left and right sides of the breathable material formed or deposited in a plate shape,
d) heating the matrix metal to a temperature range above its melting point to form a molten matrix metal; and
e) providing a permeation atmosphere at least at some point during the process and supplying at least one of a permeation enhancer or a permeation enhancer precursor to spontaneously permeate the molten matrix metal into the breathable material;
Adjusting the thickness of the matrix metal layer remaining on both sides of the breathable material after permeation by machining;
A method for producing a neutron-absorbing material, comprising: The method for producing a neutron absorbing material according to claim 1 , wherein the air-permeable material contains 1 to 98% by volume of a matrix metal. The method for producing a neutron absorbing material according to claim 1 , wherein the matrix metal contains aluminum, the penetration enhancer precursor contains magnesium, and the penetration atmosphere contains nitrogen. The method for producing a neutron absorbing material according to claim 1 , wherein the boron compound of the filler is B ₄ C. A neutron absorbing material comprising a metal matrix composite,
Using boron or boron compound as filler,
Using a breathable material obtained by mixing a matrix metal with the filler, and / or a breathable material obtained by coating the filler with a matrix metal,
Arrange an excess plate-like matrix metal source enough to remain after infiltration so as to be sandwiched between the upper and lower and / or left and right sides of the breathable material formed or deposited in a plate shape,
Heating the matrix metal to a temperature range above its melting point to form a molten matrix metal and infiltrate the breathable material;
Obtained by adjusting the thickness of the matrix metal layer remaining on both sides of the breathable material after permeation by machining,
A neutron absorbing material characterized by having a sandwich structure having a matrix metal layer on both sides of a plate-like metal matrix composite. The matrix metal is an aluminum alloy, and the filler is B _Four The neutron-absorbing material according to claim 5, which is C.

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