JP4743532B2 - Neutron absorber and manufacturing method thereof - Google Patents

Description

  The present invention relates to a neutron absorbing material in which boron is added to a stainless alloy in a homogeneous state and formed into a predetermined shape, and a method for manufacturing the neutron absorber, and is devised so that more boron can be added more uniformly.

Conventionally, a neutron absorber made of stainless steel to which boron B10 having a mass number of ¹⁰ is added is known. Preferably added as much boron B ¹⁰ from the boron B ¹⁰ absorbs neutrons in such materials, limit homogeneously adding boron in stainless steel is about 2.2% by weight. Therefore, conventionally, after concentration of boron ^{B 10} boron ^{B 11} having a mass number of 11 from natural boron containing about 80% of boron ^{B 10} 2.2% by weight of the neutron absorbing material is added to a stainless Is used, and this is the limit.

Here, when the neutron absorber is used, for example, in a rack of a pool of spent nuclear fuel, it has strength characteristics such as earthquake resistance, and of course, the higher the neutron absorption performance, the higher the safety and the same safety. Assuming that the neutron absorption performance is ensured, a material having high neutron absorption performance can be used to reduce the size and wall thickness. Therefore, a neutron absorber with improved neutron absorption performance is desired. Even with the addition of boron in the prior art above the limit, so resulting in segregation, processing such as brittle becomes rolling difficult, uniform neutron absorbing performance can not be obtained and in members for boron B ¹⁰ is unevenly distributed Therefore, safety is reduced.

  In view of the above-described circumstances, it is an object to provide a neutron absorber having improved neutron absorption performance and a method for manufacturing the same.

  As a result of repeated studies to solve the above problems, if the method for producing fine particles previously filed by the present applicant is used under predetermined conditions, a functional additive is contained in the base material in a desired addition amount. As a result, the present invention has been completed.

A first aspect of such invention, a neutron absorber obtained by adding boron containing boron B ¹⁰ having a mass number of 10 in a stainless steel alloy, the molten material obtained by melting a raw material containing the boron and the stainless steel alloy It is obtained by solidifying, using raw fine particles obtained by supplying into liquid refrigerant and atomizing by vapor explosion and solidifying by cooling, and contains boron in an amorphous state. The neutron absorber is characterized by

In such a first aspect, boron is contained in the stainless alloy in an amorphous state by supplying the molten material of the raw material containing boron and the stainless alloy into the liquid refrigerant and atomizing by vapor explosion . Therefore, it exists homogeneously and the homogeneity of neutron absorption ability is ensured.

According to a second aspect of the present invention, in the neutron absorbing material according to the first aspect, together with the homogeneous fine particles, the stainless alloy fine particles are used as a raw material to solidify by compression molding or sintering. It exists in the neutron absorber characterized by being.

In the second aspect, a neutron absorber containing boron in an amorphous state can be obtained by solidifying the fine particles containing boron in an amorphous state uniformly by compression molding or sintering. it can.

A third aspect of the present invention, the neutron absorbing material according to the first or second aspect, in the neutron absorbing material, characterized in that the boron B ¹⁰ is content exceeds 2.2 wt% .

In the third aspect, in the conventional melting method is difficult to process, such as rolling and exceeds 2.2% by weight of stainless steel, exceed 2.2 wt% because boron B ¹⁰ amorphous Can be contained.

A fourth aspect of the present invention, the neutron absorbing material according to any one of the aspects of the first through 3 enriched boron with increased concentration of boron B ¹⁰ was concentrated natural boron or boron B ¹⁰ as the boron It exists in the neutron absorber characterized by containing.

In such a fourth aspect, for example, when the boron naturally occurring raw material, since boron ^{B 10} is contained 18 to 19 wt%, the inclusion of this 10-11% by weight, boron ^{B 10} is 2 More than 2% by weight can be contained.

According to a fifth aspect of the present invention, there is provided the neutron absorber according to any one of the first to fourth aspects, wherein the boron is contained in an amount of 4% by weight or more.

In the fifth aspect, the neutron absorbing material contains 4% by weight or more of boron that could not be contained homogeneously in the prior art.

According to a sixth aspect of the present invention, a molten material obtained by melting a raw material containing boron and a stainless alloy is supplied into a liquid refrigerant, and atomized by vapor explosion and cooled and solidified to form uniform fine particles, which are used as a raw material. It is used as a neutron absorber by solidifying by compression molding or sintering, and is in a method for producing a neutron absorber.

In such a sixth aspect, by supplying a raw material molten material containing boron and a stainless alloy into a liquid refrigerant and atomizing by vapor explosion, boron exists in the stainless alloy in an amorphous state, Can be a neutron absorber that is present uniformly in each particle.

According to a seventh aspect of the present invention, there is provided the method for producing a neutron absorber according to the sixth aspect, wherein the homogeneous fine particles contain boron in an amorphous state. It is in the manufacturing method.

In the seventh aspect, the fine particles are those in which boron is present in an amorphous state in the stainless alloy.

According to an eighth aspect of the present invention, in the method for manufacturing a neutron absorber according to the sixth or seventh aspect, the homogeneous fine particles are mixed with stainless steel alloy fine particles as a raw material, and used for compression molding or sintering. It is in the manufacturing method of the neutron absorber characterized by solidifying into a neutron absorber.

In the eighth aspect, since the fine particles containing boron uniformly in the stainless alloy are mixed with the fine particles of the stainless alloy, the neutron absorber that is uniformly mixed and solidified by compression molding or sintering is homogeneous in boron. Will exist.

A ninth aspect of the present invention is a method of manufacturing a neutron absorbent material according to the 6-8 one embodiment of the control means controls the cooling rate in a predetermined range in obtaining the homogeneous microparticles There is a method for manufacturing a neutron absorber.

In the ninth aspect, when fine particles are obtained by vapor explosion, the cooling rate is appropriately controlled to obtain homogeneous fine particles in which boron is uniformly present in the stainless alloy.

  The neutron absorber of the present invention is made of a stainless alloy and contains boron in an amorphous state.

  Here, the stainless steel alloy as the base material may be a stainless steel alloy used as a conventional neutron absorber, and examples thereof include SUS304 (L) and SUS316 (L).

On the other hand, the boron may be a naturally occurring boron including a boron B ¹⁰ having a mass number of ¹⁰ and a boron B ¹¹ having a mass number of 11, or the concentration of the boron B ¹⁰ may be increased by concentrating the boron B ¹⁰ from the naturally existing boron. it may be those raised mostly be a boron B ^10.

  The neutron absorbing material of the present invention uses homogeneous fine particles obtained by supplying a molten material obtained by melting a raw material containing boron and a stainless alloy into a liquid refrigerant and atomizing by vapor explosion and cooling and solidifying, and Since it is solidified by compression molding or sintering, it has a higher concentration than the conventional one, for example, it exceeds the upper limit of 2.2% by weight, preferably 4% by weight or more, more preferably 5% by weight. % Or more of boron can be contained, and boron can be contained up to 11% by weight.

Even if natural-derived boron is used as it is, if 5% by weight is contained, if boron ¹⁰ is contained in an amount of about 1% by weight and 10% by weight, boron B ¹⁰ is contained in an amount of about 2% by weight. It can have the same neutron absorption performance. In this case, there is an advantage that the cost can be reduced because it is not necessary to concentrate the boron B ¹⁰ as compared with the conventional case.

On the other hand, the use of conventional ones concentrated boron B ¹⁰ Similarly, a high concentration of boron B ¹⁰ in the absence of segregation, for example, can be contained about 2.2 wt% to 11 wt%, the prior art There can be no neutron absorber with neutron absorption performance. In this case, for example, when used for a rack of a spent nuclear fuel pool, the safety can be remarkably improved, and if the same safety is ensured, the rack can be made smaller and thinner. Therefore, there is an advantage that significant space saving can be achieved.

  In order to produce the neutron absorbing material of the present invention, first, a molten material obtained by melting a raw material containing boron and a stainless alloy is supplied into a liquid refrigerant, atomized by vapor explosion, and cooled and solidified to obtain a homogeneous material. Fine particles are obtained.

  In this process, the fine particle production methods disclosed in WO01 / 81033, WO01 / 81032, and WO / 2004/0776050 may be applied. However, the point in the present invention is that stainless steel and boron are used. It is to obtain uniform fine particles by using a molten material obtained by melting the mixed raw materials and atomizing by setting an optimum cooling rate for these combinations. Here, the term “homogeneous” refers to a state in which boron is not segregated and is uniformly contained in the base material. In the fine particles produced in this way, boron not only exists uniformly, but also dissolves homogeneously and the entire particle exists in an amorphous state.

  Further, in order to obtain uniform fine particles free from such segregation in the present invention, both are mixed with a composition in the vicinity of the eutectic point of stainless alloy and boron, and are atomized at a predetermined cooling rate. Uniform fine particles can be easily obtained.

  In addition, such fine particles preferably have a predetermined particle diameter in order to obtain a homogeneous neutron absorber, and for example, the average particle diameter is preferably 1 to 100 μm. If it is larger than this, there is a possibility that it will not be uniformly mixed thereafter with the stainless alloy fine particles, while if it is smaller than this, handling becomes difficult. Moreover, when it mixes with a stainless alloy and solidifies by compression molding etc., it is preferable that the particle size of both is near. This is because both powders are mixed uniformly.

  The homogeneous fine particles made of stainless steel and boron and the fine particles of stainless alloy thus obtained are used as raw materials, and both are uniformly mixed and solidified by compression molding or sintering to obtain a neutron absorber. Here, since the fine particles in which the boron is uniformly present in the stainless alloy are mixed with the fine particles of the stainless alloy, as a result, the boron is present in a uniform manner and does not become a segregated state. More than 2 wt%, preferably 4 wt% or more, more preferably 5 wt% or more boron can be contained, and boron can be contained up to 11 wt%. Moreover, since it is only solidified by compression molding, sintering or the like in a powder state, boron is present in the neutron absorber in an amorphous state.

  In the present invention, solidification refers to forming a bulk material while maintaining a powdered body, that is, without directly dissolving powders, or by closely contacting with a binder, for example, compression molding. , Sintering, or compression molding and sintering, and further includes mechanical alloying and fixing using a binder.

Thus, according to the present invention, as the boron naturally occurring, or even used in low concentration, the inclusion of 10 wt%, will be boron B ¹⁰ causes the content exceeds 2.2 wt%, prior It is possible to have a neutron absorption performance comparable to In this case, there is an advantage that the cost can be reduced because it is not necessary to concentrate the boron B ¹⁰ as compared with the conventional case.

On the other hand, the use of conventional ones concentrated boron B ¹⁰ Similarly, a high concentration of boron B ¹⁰ in the absence of segregation, for example, can be contained about 2.2 wt% to 11 wt%, the prior art There can be no neutron absorber with neutron absorption performance. In this case, for example, when used for a rack of a spent nuclear fuel pool, the safety can be remarkably improved, and if the same safety is ensured, the rack can be made smaller and thinner. Therefore, there is an advantage that significant space saving can be achieved.

Of course, only the homogeneous microparticles consisting of a stainless steel alloy and the boron and solidified, and more at the compression molding and sintering may be a neutron absorber, in this case, it contains a high concentration more boron B ¹⁰ in the absence of segregation Can be made.

(Example)
SUS304 (Fe ₇₄ Cr ₁₈ Ni ₈ ) as a base material and Fe—B are melt-mixed so that boron is 4 wt% (Fe ₇₇ Cr ₁₃ Ni ₆ B ₄ ), and the molten raw material is flowed from the nozzle. The solution was dropped into a water stream (water temperature 4 ° C., flow rate 110 L / min) at 0.8 kg / min, and rapidly cooled and atomized.

The obtained functional fine particles were irregular, but the particle size D ₅₀ measured by Nikkiso Microtrack was about 30 μm. In addition, since the crucible after the hot water was confirmed and all the hot water was discharged, the composition of the functional fine particles is Fe ₇₇ Cr ₁₃ Ni ₆ B ₄ .

  Similarly, SUS304 and Fe-B were mixed so that boron was 1 wt%, 2.5 wt%, 5.5 wt%, and 7 wt%, respectively, and functional fine particles were obtained in the same manner. .

  The results of X-ray diffraction of these functional fine particles are shown in FIG. FIG. 1 also shows the X-ray diffraction results after annealing the functional fine particles containing 7% by weight of boron at 1000 ° C. for 2 hours.

  As a result, it was found that boron in each functional fine particle was in an amorphous state. In addition, the α-Fe peak is somewhat detected in the functional fine particles of 1% by weight and 7% by weight, but since it is not detected at all by 4% by weight, it tends to be most amorphous at 4% by weight. It can be judged that some crystallinity is observed at 1 wt% and 7 wt%. However, judging from the X-ray diffraction result that α-Fe increased after annealing 7% by weight of functional fine particles, boron was amorphous even at 1% by weight and 7% by weight of functional fine particles. It turns out that it is quality. In addition, these X-ray diffraction results revealed that the crystals were not observed to be amorphous due to the small particle size.

As a result of suggested thermal analysis and X-ray diffraction, it is known that α-phase Fe precipitates as an initial crystal and further anneals at a high temperature, and peaks such as Fe ₂ B appear. Since no Fe-B peak appears, it can be judged that boron exists in an amorphous state.

Since the functional fine particles obtained in each example have similar properties to SUS fine particles, they can be homogeneously mixed with SUS fine particles, so they are mixed in a powder state and solidified by compression molding or sintering. By doing so, it is possible to obtain a SUS alloy neutron absorber containing homogeneous boron in an amorphous state. Since this time, it is possible to homogeneously incorporated into conventional or high concentration of boron, the use of conventional boron B ¹⁰ was similarly concentrated, to obtain a neutron absorbing material homogeneously boron B ¹⁰ at a high concentration compared with the conventional In addition, even if natural-origin boron is used as it is, it can be dissolved at a high concentration without segregation by this method. For example, boron ^{B 10} is obtained as a natural abundance 18-19 wt%, but reduced by polarized析無rather dissolving 10 ^wt%, it is possible to produce materials that are present the ^{B 10} 2.2 wt%, the cost of enriched There are advantages you can do.

It is a figure which shows the X-ray-diffraction result of the Example of this invention.

Claims (9)

A neutron absorbing material made by adding a boron containing boron B ¹⁰ having a mass number of 10 in a stainless steel alloy,
A material obtained by melting a raw material containing the boron and the stainless steel alloy is supplied into a liquid refrigerant and atomized by vapor explosion and cooled and solidified, and the material is solidified. A neutron absorber , wherein the boron is contained in an amorphous state. 2. The neutron absorber according to claim 1 , wherein the neutron absorber is solidified by using the fine particles of the stainless alloy as a raw material together with the homogeneous fine particles. In the neutron absorbing material according to claim 1 or 2, the neutron absorbing material, characterized in that the boron B ¹⁰ is content exceeds 2.2 wt%. In neutron absorber according to any one of claims 1-3, characterized in that the enriched boron with increased concentration of boron B ¹⁰ Natural boron or boron B ¹⁰ concentrated is contained as the boron neutron Absorber. The neutron absorber according to any one of claims 1 to 4 , wherein the boron is contained in an amount of 4% by weight or more. A molten material obtained by melting a raw material containing boron and a stainless alloy is supplied into a liquid refrigerant, atomized by a vapor explosion and cooled and solidified to form uniform fine particles, which are solidified using the raw material, and then a neutron absorber A method for producing a neutron absorbing material. 7. The method for producing a neutron absorber according to claim 6 , wherein boron is contained in an amorphous state in the homogeneous fine particles. The method for producing a neutron absorber according to claim 6 or 7 , wherein the homogeneous fine particles are mixed with stainless steel alloy fine particles and solidified as a raw material to obtain a neutron absorber. Production method. The method for producing a neutron absorber according to any one of claims 6 to 8 , wherein a cooling rate is controlled within a predetermined range when obtaining the homogeneous fine particles.

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