Patent Application
20150151360
The present invention relates to a method for manufacturing a boron-containing aluminum plate material. Hereinafter, boron may be referred to as “B”.
Recently, there is an increased demand for interim storage of spent fuel (hereinafter, referred to as “SF”) in a nuclear power plant. Furthermore, in a recent trend, the interim storage of SF is shifted from wet storage (storage in water) to dry storage (storage with air cooling). Consequently, SF shows a higher calorific value and higher neutron formation density than in the past. Hence, a boron-containing aluminum plate material for forming a cask or a canister as a SF storage container is also required to have higher boron content than in the past.
A melting-and-casting process has been used for manufacturing boron-containing aluminum alloy. The melting-and-casting process includes a process in which powdery boron is mixed in aluminum alloy metal that is then melted and casted (hereinafter, referred to “former melting-and-casting process”), and a process in which a boron fluoride such as KBF4 and a catalyst are mixed into molten aluminum to produce an aluminum-boron intermediate alloy that is then casted while boron concentration is adjusted (hereinafter, referred to “latter melting-and-casting process”). The ingot casted in this way is formed into a plate material through rolling or extruding.
In the former melting-and-casting process, various boron compounds are formed in the aluminum-boron alloy through crystallization and precipitation, leading to degradation in workability. Furthermore, the formed various boron compounds each settle out or surface depending on their specific gravities different from one another, resulting in nonuniform boron distribution (i.e., segregation). As a result, there occurs a portion having a low boron concentration with respect to the amount of added boron, so that actually achievable boron concentration has an upper limit of about 1 mass %.
The latter melting-and-casting process inevitably requires boron (enriched boron) having an increased concentration of boron isotope with a mass number of 10 (hereinafter, referred to “B-10”) which has thermal neutron absorbing power. Such enriched boron, however, is extremely expensive, leading to a cost problem.
Furthermore, the following techniques have been proposed.
There is disclosed a technique for manufacturing an aluminum alloy material, in which aluminum alloy powder containing 0.5 mass % to 5 mass % of boron is produced, a compact is formed of the aluminum alloy powder, and the compact is melted and casted into the aluminum alloy material (see PTL 1). Use of this technique definitely leads to uniform distribution of boron since the powder includes small particles.
In addition, there is disclosed an aluminum-based composite material including a ceramic frame containing a matrix of aluminum or aluminum alloy and a neutron absorbing material such as a boron compound, and a technique for manufacturing the aluminum-based composite material (see PTL 2). The ceramic frame disclosed in PTL 2 is configured as a porous preform produced in such a manner that a slurry is prepared by mixing whisker or short fiber of aluminum borate as ceramics, boron compound particles, and the like, the slurry is dehydrated and pressurized, and the pressurized slurry is sintered into the porous preform. The aluminum-based composite material is manufactured by highly impregnating the ceramic frame formed as the porous preform with molten aluminum or molten aluminum alloy, and casting and solidifying such molten metal into a matrix form.
PTL 1: Japanese Patent No. 3207840.
PTL 2: Japanese Unexamined Patent Application Publication No. 2003-121590.
However, the techniques disclosed in PTL 1 and PTL 2 also have the following problems.
Specifically, in the technique described in PTL 1, boron is definitely uniformly distributed in the powder due to the small powder particles. However, since the compact formed of the powder is produced through melting and casting of the powder, boron is also non-uniformly distributed in the compact due to aggregation/coarsening or sedimentation/surfacing of boron compound particles, and therefore boron segregation occurs in the material, leading to a possibility of insufficient neutron absorbing power.
In the technique disclosed in PTL 2, although it is described that boron or a boron compound such as boron nitride and boron oxide may be used as the neutron absorbing material, boron carbide (B4C) is industrially recommended in consideration that the boron carbide has a high content of boron having excellent neutron absorbing power, and is stable even at high temperature. However, B4C is expensively used. Although it is further described that nonpressurized casting may be used as a method of impregnating the ceramic frame configured as the porous preform with aluminum, the molten aluminum insufficiently penetrates into each space between the boron compound particles contained by the ceramic frame, leading to formation of defects such as voids in the compound after casting. Hence, a high-pressure casting process must be actually used in order to produce a useful compound after casting. In order to manufacture a large aluminum-based composite material such as a cask or a basket used in the cask by the high-pressure casting process, however, a large-scale machine such as a large high-pressure press is disadvantageously required for uniform penetration of molten aluminum into each space between boron compound particles.
An object of the invention is to provide a method for manufacturing a boron-containing aluminum plate material, which secures high content of boron having the neutron absorbing power, and allows uniform boron distribution in a plate plane to be achieved at low cost while inexpensive natural-boron-containing alloy particles (hereinafter, simply referred to as “boron-containing alloy particles”) are used.
To achieve the object, according to claim 1 of the invention, there is provided a method for manufacturing a boron-containing aluminum plate material, the method being characterized by having:
a spreading step of spreading boron-containing alloy particles containing borate particles having a boron content of 5 mass % or more in a layer shape over a bottom plate of aluminum or aluminum alloy placed in a container;
a preheating step of mounting a tundish for control of pouring amount on a top of the container after the spreading step, and preheating the container and the tundish together at 300° C. to 500° C.;
a casting step of enveloped-casting the layer of the boron-containing alloy particles in the container preheated in the preheating step with molten aluminum or molten aluminum alloy (hereinafter, referred to as “molten Al”) by pouring the molten Al at 580° C. to 900° C. into the tundish preheated in the preheating step to fabricate an enveloped-cast plate with a predetermined thickness; and a cutting step of cutting off shrinkage cavities formed in a feeder section in an upper part of the enveloped-cast plate fabricated in the casting step.
According to claim 2 of the invention, the method according to claim 1 is characterized in that
the borate particles include at least one selected from the group consisting of Al—B alloy, Ca—B alloy, Si—B alloy, Fe—B alloy, MnB alloy, and Mo—B alloy.
According to claim 3 of the invention, the method according to claim 2 is characterized in that
the Al—B alloy is at least one of AlB12 and AlB2.
According to claim 4 of the invention, the method according to claim 1 is characterized in that
the borate particles include first borate particles having a boron content of 60 mass % or more and second borate particles having a boron content of 5 mass % to less than 60 mass %.
According to claim 5 of the invention, the method according to claim 4 is characterized in that
the borate particles include first borate particles including at least one selected from the group consisting of AlB12, CaB6, and SiB6, second borate particles including at least one selected from the group consisting of FeB, MnB2, Fe2B, and AlB2, and inevitable impurity particles.
According to claim 6 of the invention, the method according to claim 4 or 5 is characterized in that
proportion of the first borate particles in the borate particles is 50 mass % or more.
According to claim 7 of the invention, the method according to any one of claims 1 to 5 is characterized in that
particle diameter of the boron-containing alloy particles is 15 mm or less (not including zero).
According to claim 8 of the invention, the method according to any one of claims 1 to 5 is characterized in that
the molten aluminum alloy is casting aluminum alloy including at least one selected from the group consisting of Al—Si alloy, Al—Cu alloy, and Al—Mg alloy.
According to claim 9 of the invention, the method according to any one of claims 1 to 5 is characterized in that
total thickness of the enveloped-cast plate after the cutting step (hereinafter, referred to as “total enveloped-cast plate thickness”) is 5 mm to 50 mm, thickness of the bottom plate is ⅕ to ⅓ of the total enveloped-cast plate thickness, and thickness of the layer of the boron-containing alloy particle is ⅓ to ⅗ of the total enveloped-cast plate thickness.
According to claim 10 of the invention, the method according to any one of claims 1 to 5 is characterized by further having
a plate thickness adjusting step for adjusting plate thickness by facing or forging after the cutting step.
According to claim 11 of the invention, the method according to any one of claims 1 to 5 is characterized by further having
a rolling step for producing an enveloped-cast plate having a further small thickness after the cutting step.
According to claim 12 of the invention, the method according to any one of claims 1 to 5 is characterized by further having
a rolling step for producing a die material having a predetermined shape after the cutting step.
According to claim 13 of the invention, the method according to any one of claims 1 to 5 is characterized by further having
a pressing step for producing a forging material having a predetermined shape after the cutting step.
As described above, the method for manufacturing a boron-containing aluminum plate material according to the invention is characterized by having a spreading step of spreading boron-containing alloy particles containing borate particles having a boron content of 5 mass % or more in a layer shape over a bottom plate of aluminum or aluminum alloy placed in a container, a preheating step of mounting a tundish for control of pouring amount on a top of the container after the spreading step, and preheating both of the container and the tundish at 300° C. to 500° C., a casting step of enveloped-casting the layer of the boron-containing alloy particles in the container preheated in the preheating step with molten Al by pouring the molten Al at 580 to 900° C. into the tundish preheated in the preheating step to fabricate an enveloped-cast plate with a predetermined thickness, and a cutting step of cutting off shrinkage cavities formed in a feeder section in an upper part of the enveloped-cast plate fabricated in the casting step.
Consequently, the method secures high content of boron having the neutron absorbing power, and allows uniform boron distribution in a plate plane to be achieved at low cost while inexpensive boron-containing alloy particles are used.
Hereinafter, the invention is described in detail with example embodiments.
The method of manufacturing a boron-containing aluminum plate material according to the invention is characterized by having
a spreading step of spreading boron-containing alloy particles containing borate particles having a boron content of 5 mass % or more in a layer shape over a bottom plate of aluminum or aluminum alloy placed in a container,
a preheating step of mounting a tundish for control of pouring amount on a top of the container after the spreading step, and preheating the container and the tundish together at 300° C. to 500° C.,
a casting step of enveloped-casting the layer of the boron-containing alloy particles in the container preheated in the preheating step with molten Al by pouring the molten Al at 580° C. to 900° C. into the tundish preheated in the preheating step to fabricate an enveloped-cast plate with a predetermined thickness, and
a cutting step of cutting off shrinkage cavities formed in a feeder section in an upper part of the enveloped-cast plate fabricated in the casting step.
According to such a configuration, the invention secures high content of boron having the neutron absorbing power, and allows uniform boron distribution to be achieved at low cost while inexpensive boron-containing alloy particles are used.
The details leading to such a configuration are now described.
The inventers have made earnest study on how to secure high content of boron having the neutron absorbing power, and achieve uniform boron distribution in a plate plane at low cost while inexpensive boron-containing alloy particles are used.
As a result, the inventors have found that the object can be accomplished through a method having the spreading step, the preheating step, the casting step, and the cutting step (in detail, see
The method for manufacturing a boron-containing aluminum plate material according to the invention is now described with reference to the drawing.
In
Specifically, the borate particles preferably include at least one selected from the group consisting of Al—B alloy, Ca—B alloy, Si—B alloy, Fe—B alloy, Mn—B alloy, and Mo—B alloy. The Al—B alloy is at least one of AlB12 and AlB2.
In a possible configuration, the borate particles include first borate particles having a high B-10 content (i.e., having a boron content of 60 mass % or more), and second borate particles having a lower B-10 content than that of the first borate particles (i.e., having a boron content of 5 mass % to less than 60 mass %).
Specifically, particles including at least one selected from the group consisting of AlB12, CaB6, and SiB6 may be used as the first borate particles. In addition, particles including at least one selected from the group consisting of FeB, MnB2, Fe2B, and AlB2 may be used as the second borate particles. While various inevitable impurity particles are formed depending on selection of each of the first and second borate particles, the amount of the inevitable impurity particles is preferably controlled to be 10 mass % or less. Examples of the inevitable impurity particles include particles of composite borate such as Mn2AlB2, particles of oxide such as Al2O3, MnO2, FeO, B2O3, CaO, and SiO2, and the like.
A small amount of B4C particles may be contained as the first borate particles to the extent that wettability to the aluminum alloy to be poured as a boron-containing aluminum material is not adversely affected.
Use of the above-described configuration of the boron-containing alloy particles 3 increases the B-10 content of the boron-containing aluminum material mainly due to the first borate particles and subsidiarily due to the second borate particles. Use of the above-described configuration provides the neutron absorbing power of the boron-containing aluminum material mainly due to the first borate particles and subsidiarily due to the second borate particles. From the viewpoint of improving the neutron absorbing power of the boron-containing aluminum material, proportion of the first borate particles in the boron-containing alloy particles 3 is preferably 50 mass % or more.
Since an appropriate combination of the first borate particles and the second borate particles can be used as the boron-containing alloy particles 3, a degree of the neutron absorbing power can be widely adjusted.
Particles of each of FeB or Fe2B as the Fe—B alloy, MnB2 as the Mn—B alloy, the Mo—B alloy, AlB12 or AlB2 as the Al—B alloy, CaB6 as the Ca—B alloy, and SiBe as the Si—B alloy, the particles being corresponding to the borate particles contained by the boron-containing alloy particles 3, are desirable in having a higher melting point than the aluminum alloy to be poured (the molten Al 10 illustrated in
A usable particle diameter of the boron-containing alloy particles 3 is 15 mm or less (not including zero).
The particle diameter is measured by a laser diffraction scattering method. In the case of the boron-containing alloy particles 3 having a particle diameter of less than 5 mm (not including zero), the molten Al 10 is less likely to penetrate into each space between the boron-containing alloy particles 3, and the boron-containing alloy particles 3 are easily stirred by casting flow. It is therefore more preferred that the boron-containing alloy particles 3 are formed into a highly-filled plate-like preform with a binder or by sintering so as to be formed as a uniform layer of the boron-containing alloy particles 3. The boron-containing alloy particles 3 having a particle diameter of 5 mm to 15 mm are most preferred since even if such boron-containing alloy particles 3 are simply disposed in a layer shape, the molten Al 10 easily penetrate into a space between the boron-containing alloy particles 3, and 95% or more of spaces between the boron-containing alloy particles 3 can be filled with the molten Al 10. In the case of using the boron-containing alloy particles 3 having a particle diameter of more than 15 mm, the enveloped-cast plate 15 (illustrated in a lower view of
In
In
During solidification of the molten Al 10, the shrinkage cavities 13 (illustrated in the upper view of
In
The thickness of the layer of the boron-containing alloy particles 3 is desirably ⅓ to ⅗ of the total thickness of the enveloped-cast plate 15. This is because the thickness of less than ⅓ of the total thickness results in low total boron concentration of the enveloped-cast plate 15, and thus prevents the boron concentration of 5 mass % or more from being maintained. In addition, the thickness of more than ⅗ thereof results in a thin aluminum alloy portion (a portion 11 of the solidified molten Al 10) enveloping the layer of the boron-containing alloy particles 3, leading to insufficient material strength of the enveloped-cast plate 15.
The thickness of the bottom plate 2 is desirably ⅕ to ⅓ of the total thickness of enveloped-cast plate 15. This is because the thickness of less than ⅕ of the total thickness results in insufficient material strength of the enveloped-cast plate 15. In addition, the thickness of more than ⅓ thereof results in small thickness of the layer of the boron-containing alloy particles 3 relative to the total thickness of the enveloped-cast plate 15, leading to low total boron concentration of the enveloped-cast plate 15. Since the bottom plate 2 having a flat and smooth surface can be used, the total thickness of the enveloped-cast plate 14 after solidification of the molten Al 10 can be easily controlled.
A plate thickness adjusting step for adjusting plate thickness by facing is provided after the cutting step for cutting off the shrinkage cavities 13 illustrated in
A rolling step is provided after the cutting step for cutting off the shrinkage cavities 13 illustrated in
A pressing step is provided after the cutting step for cutting off the shrinkage cavities 13 illustrated in
Detailed description is now made on a first embodiment to which the method of manufacturing the boron-containing aluminum plate material according to the invention as illustrated in
Container 1: graphite container 100 mm in depth, 200 mm in width, and 70 mm in height (inside dimension each).
Tundish 6: 120 mm in depth, 220 mm in width, and 70 mm in height.
Bottom plate 2: pure aluminum plate 3 mm in thickness.
Boron-containing alloy particles 3: Fe-20 mass % B alloy 1 mm in particle diameter.
Layer of boron-containing alloy particles 3: boron-containing alloy particles 3 are preformed into a layer shape with an inorganic binder so as to be formed as a plate 4 mm in thickness, and the plate is placed on the bottom plate 2.
Particle filling rate of layer of boron-containing alloy particles 3: 65%.
Molten Al 10: molten Al-13 mass % Si alloy at 750° C.
Preheating temperature of container 1 and tundish 6: 500° C.
Cutting of shrinkage cavities 13: facing.
The enveloped-cast plate 15 prepared according to the above-described manufacturing conditions had a total thickness of 10 mm and a total boron concentration of 5.2 mass %.
As with the first embodiment, the method of manufacturing the boron-containing aluminum plate material according to the invention as illustrated in
Bottom plate 2: pure aluminum plate 4 mm in thickness.
Boron-containing alloy particles 3: Fe-20 mass % B alloy particles 4 mm in diameter.
Layer of boron-containing alloy particles 3: boron-containing alloy particles 3 are preformed into a layer shape with an inorganic binder so as to be formed as a plate 10 mm in thickness, and the plate is placed on the bottom plate 2.
Particle filling rate of layer of boron-containing alloy particles 3: 55%.
The enveloped-cast plate 15 prepared according to the above-described manufacturing conditions had a total thickness of 19 mm and a total boron concentration of 5.8 mass %.
As with the first embodiment, the method of manufacturing the boron-containing aluminum plate material according to the invention as illustrated in
Bottom plate 2: pure aluminum plate 4 mm in thickness.
Boron-containing alloy particles 3: Fe-20 mass % B alloy particles 9 mm in diameter.
Layer of boron-containing alloy particles 3: boron-containing alloy particles 3 corresponding to one layer are spread over the bottom plate 2.
Particle filling rate of layer of boron-containing alloy particles 3: 50%.
The enveloped-cast plate 15 prepared according to the above-described manufacturing conditions had a total thickness of 17 mm and a total boron concentration of 5.3 mass %.
As with the first embodiment, the method of manufacturing the boron-containing aluminum plate material according to the invention as illustrated in
Boron-containing alloy particles 3: boron-containing alloy particles 1 mm in diameter (see the following Table 1).
Layer of boron-containing alloy particles 3: boron-containing alloy particles 3 are preformed into a layer shape with an inorganic binder so as to be formed as a plate 4 mm in thickness, and the plate is placed on the bottom plate 2.
Particle filling rate of layer of boron-containing alloy particles 3: 65%.
The enveloped-cast plate 15 prepared according to the above-described manufacturing conditions had a total thickness of 10 mm, and a total boron concentration of 10 mass % since the boron-containing alloy particles 3 shown in Table 1 had a total boron concentration of 60 mass %.
Although the invention has been described in detail with reference to specific embodiments, it should be understood by those skilled in the art that various alterations and modifications thereof may be made without departing from the spirit and the scope of the invention.
The present application is based on Japanese patent application (JP-2012-118567) filed on May 24, 2012 and Japanese patent application (JP-2013-010054) filed on Jan. 23, 2013, the content of each of which is hereby incorporated by reference.
According to the invention, a boron-containing aluminum plate material having a high boron content, which is used for an interim storage vessel of spent fuel in a nuclear power plant, can be manufactured at low cost.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-118567 | May 2012 | JP | national |
| 2013-010054 | Jan 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP13/63306 | 5/13/2013 | WO | 00 |
