JP5729995B2 - Neutron absorber - Google Patents

Description

  The present invention is a cement-based neutron absorber suitable for neutron shielding in facilities that generate neutrons such as nuclear power generation facilities, nuclear fuel reprocessing facilities, RI research facilities, accelerator facilities, medical facilities, etc. The present invention relates to a neutron absorber that exhibits performance and good initial strength.

  Accelerator facilities such as cyclotrons are widely used in engineering and science, as well as in the medical field such as the manufacture of PET tracers. However, radiation is generated with nuclear reactions, preventing adverse effects on the human body and the environment. It is necessary to construct a shield to do this. Radiation is also generated in nuclear facilities such as reactor buildings and reprocessing plants, and in the storage and transportation of nuclear fuel and spent nuclear fuel, and a shield is also necessary here.

  There are various types of radiation such as charged particles, alpha rays, beta rays, X-rays, gamma rays, neutron rays, etc., but charged particles are easy to shield because of their large interaction with matter. It is known that beta rays can be shielded with a thin aluminum plate, and gamma rays and X-rays are well absorbed by heavy atoms, so they can be shielded with iron, lead, or concrete. Yes.

  However, neutron rays cannot be shielded by heavy elements that are effective against gamma rays and x-rays. It is known that light elements such as hydrogen effectively slow down fast neutrons having high energy, and that specific elements having a large neutron absorption cross section such as boron are effective in absorbing low energy thermal neutrons.

  Against this background, neutron shielding materials containing boron and hydrogen have been developed. Above all, the material is relatively inexpensive and easy to manufacture, excellent in mechanical properties such as strength and heat resistance, and cement-based neutron shields such as concrete and mortar containing free water and crystal water related to hydrogen. Many have been studied.

  In the case of cement-based materials, the water used for kneading reacts with the cement and is fixed as crystal water, so the presence of hydrogen derived from the crystal water can be expected to some extent. Since boron does not contain boron, it was necessary to use a boron-containing material as an aggregate or admixture to construct a cement-based neutron shield containing boron.

It is most economical to use a naturally occurring boron-containing mineral as the boron-containing material. Known natural boron-containing minerals include colemanite (2CaO · 3B ₂ O ₃ · 5H ₂ O) and kurnacobite (2MgO · 3B ₂ O ₃ · 15H ₂ O), among which colemanite is an industrial product such as glass. Since it is a mineral product that is also used as a raw material and is easily available, it has long been shown as a neutron absorber. These natural boron-containing minerals are all characterized in that boron exists in the form of boric acid (B ₂ O ₃ or H ₃ BO ₃ ), which is an oxide.

  The problem here is that boric acid adversely affects cement hydration. In other words, when an aggregate containing boron in the form of boric acid is kneaded with normal cement, the hardening of the cement is significantly delayed, and even if it is hardened, the strength development is poor. This is due to the alkaline environment caused by the cement. It is considered that a part of the boron-containing mineral is dissolved below and boric acid that inhibits cement hydration is eluted.

  Several methods have been proposed for solving this problem, such as using a calcium aluminate-based cement with good initial strength and using a borate aggregate containing no fine particles having a particle size of less than 1 mm.

  For example, Patent Document 1 discloses a neutron shielding material comprising a borate aggregate containing crystal water such as colemanite and an inorganic adhesive such as hemihydrate gypsum or calcium aluminate cement. The desirable particle size is 1 mm or more.

Patent Document 2 discloses a calcined product using one or more of municipal waste incineration ash and sewage sludge incineration ash as a raw material, and one or more of C ₁₁ A ₇ CaCl ₂ , C ₁₁ A ₇ CaF ₂ , and C ₃ A. Is disclosed as a neutron shield containing an aggregate containing boron using a hydraulic material composed of a calcined product containing 10 to 40% by weight of C ₂ S and C ₃ S and at least one of C ₃ S and gypsum as a binder. In the examples, examples using colemanite having a particle diameter of 1 to 3 mm are described.

Japanese Patent Publication No.58-6704 JP-A-11-202090

C. Cau Dit Coumes, S. Courtois, Cementation of a low-level radioactive waste of complex chemistry: Investigation of the combined action of borate, chloride, sulfate and phosphate on cement hydration using response surface methodology, Cement and Concrete Research, Vol. 33, pp305-316 (2003)

The calcium aluminate cement described in Patent Document 1 is not necessarily low alkalinity. For cements that are not low alkalinity such as cements mainly composed of 11CaO · 7Al ₂ O ₃ · CaF ₂ and 3CaO · Al ₂ O ₃ , However, there is a problem in that it is necessary to use a borate aggregate whose particle size is adjusted and does not contain fine particles.

That is, boric acid has an adverse effect on the hydration reaction, not only for calcium silicate but also for calcium aluminate. According to Non-Patent Document 1, amorphous 2CaO · 3B ₂ O ₃ · 8H ₂ O is formed in the form of a film on the cement particle surface, which inhibits the progress of the hydration reaction. This film-like product can occur in all cement minerals containing calcium, as can be judged from its composition.

  Calcium aluminate-based cements are fast-curing and are quick to cure and develop strength, and hydration inhibition by boric acid is unlikely to be a problem, but when fine-grained borate aggregates are used, poor curing and insufficient expression of strength occur, An adverse effect occurs. Calcium aluminate-based cement is generally expensive, and adjusting the particle size of borate aggregate also leads to an increase in cost. Therefore, it is difficult to supply a relatively inexpensive neutron shielding material with the technology of the present invention.

  Moreover, the waste of the borate aggregate which is not used will generate | occur | produce by adjusting a particle size. Further, if the fine particle portion is excluded, boron in the neutron absorber is unevenly distributed and it is desirable not to adjust the particle size from the viewpoint of neutron absorption performance.

In addition, the alumina cement mainly composed of CaO.Al ₂ O ₃ has a relatively low pH, and the influence of hydration inhibition by boric acid is small. However, when the temperature is increased, the hydrated product becomes spherical CaO.Al ₂ O _3. · 6H 2 metastasized to _O, strength there is a problem of a decrease.

Especially in places where radiation is a problem, the temperature is often higher than the normal room temperature, and this reduction in intensity is expected to be a serious problem. In addition, as described above, the presence of crystal water is effective for neutron shielding, but cement mainly composed of CaO and Al ₂ O ₃ as chemical components has little crystal water to be fixed as a hydrated product, and fast neutrons. There was also room for improvement from the viewpoint of slowing down.

In order to suppress the above-described decrease in strength, a method of mixing a pozzolanic material mainly composed of SiO ₂ has been reported, but the main hydrate produced in this case is 2CaO.Al ₂ O ₃ .SiO _2. 8H ₂ O, which is a hydrate with a smaller proportion of crystal water. Similarly, when hemihydrate gypsum is selected as the binder, dihydrate gypsum (CaSO ₄ .2H ₂ O) is produced as a result of the hydration reaction, which is also a hydrate with a small ratio of crystal water.

Further, 3CaO.3Al ₂ O ₃ .CaSO ₄ (auin) has a low pH when coexisting with gypsum, and the adverse effect of boric acid is small, but there are problems in dimensional stability and durability after curing. This is the same when gypsum is added to cement mainly composed of CaO and Al ₂ O ₃ as chemical components.

  In the one described in Patent Document 2, since the cement used is ecocement and is not low alkalinity, the same problem as described above occurs with respect to the aggregate containing boron. That is, since the curing time is relatively short, hydration inhibition by boric acid is unlikely to be a problem, but when a fine-grained borate aggregate is used, the adverse effect increases. Moreover, since municipal waste incineration ash or sewage sludge incineration ash is used as a cement raw material, there is a risk that it may become difficult to supply a large amount of cement of a certain quality in the future.

  The present invention is intended to solve the above-mentioned problems, and has excellent neutron absorption performance and neutrons exhibiting good initial strength expression even when using aggregates made of colemanite containing particles having a particle size of less than 1 mm. It aims to provide an absorber.

  The neutron absorber according to claim 1 of the present application includes: “the main hydration product is ettringite and C—S—H, a low alkaline cement that does not generate calcium hydroxide, and an aggregate containing colemanite. It is a characteristic neutron absorber.

  The neutron absorber of the present invention is a cement-based hardened body having neutron absorption performance, and specifically, mortar products such as panels and concrete products, hardened mortar and hardened concrete cast on site. The cement used for the cement-based hardened body is a low alkaline cement whose main hydration products are ettringite and C—S—H, and does not produce calcium hydroxide.

  The “low alkalinity cement” as used herein refers to a cement exhibiting alkalinity having a pH value of pore water of 12.5 or less after 1 hour or more after kneading. Examples of the cement in which the hydrated product becomes such a combination include, for example, a cement mainly composed of Auink linker containing Auin and Belite, and a high sulfate slag cement in which gypsum and a small amount of stimulant are added to blast furnace slag. Here, the composition of the cement before hydration is not questioned.

Ettringite is a hydrate represented by the chemical formula of 3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O, hydration reaction between Auin and other calcium aluminate minerals and gypsum, blast furnace slag and gypsum It is produced by hydration reaction of In addition to contributing to the initial strength of the hardened body, it also contributes to the attenuation of fast neutrons because it has a lot of crystal water. Ettringite is known to be a low-alkaline hydrate whose pH value of equilibrium water is less than 12.

C—S—H is an abbreviation for CaO—SiO ₂ —H ₂ O, and is generally referred to as calcium silicate hydrate in the cement industry and is a non-stoichiometric compound. There are various types of C—S—H depending on the production conditions, but “C—S—H” mentioned here is a low crystalline C—S—H gel formed by cement hydration.

CSH contributes to the strength expression and stability of the cured body. The pH value of C—S—H varies depending on the CaO / SiO ₂ ratio, and when this ratio is large, the pH value of equilibrium water increases. C—S—H coexisting with calcium hydroxide is known to have a large CaO / SiO ₂ ratio, but C—S—H not coexisting with calcium hydroxide in the present invention has a CaO / SiO ₂ ratio. Small and low pH value.

“Does not produce calcium hydroxide” means that no Ca (OH) ₂ peak is observed by X-ray diffraction. Calcium hydroxide is a highly alkaline hydrated product having a balanced water pH value of 12.6 or higher.

The neutron absorber of the present invention is mortar or concrete, and the aggregate is an aggregate containing colemanite. Colemanite is also called a halite or colemanite, and is a natural hydrous calcium borate mineral represented by the chemical formula 2CaO · 3B ₂ O ₃ · 5H ₂ O, having a normal grade of 40% by weight or more of B _2. Contains O ₃ component.

  And it is known conventionally that this boron component has neutron absorption performance. Aggregates are composed of fine aggregates or fine aggregates and coarse aggregates, but in addition to the aggregates from the above-mentioned colemanite, as necessary, fine aggregates include silica sand, crushed sand, river sand, land sand, etc. The coarse aggregate may include crushed stone, natural gravel and the like.

  The present invention is characterized in that a low alkaline cement that produces a large amount of ettringite and colemanite are combined. As described above, colemanite has been conventionally known as a natural mineral with neutron absorption performance, but by combining it with a cement that produces a large amount of ettringite, a lot of crystal water possessed by ettringite contributes to neutron absorption. A synergistic effect is born.

  Furthermore, we have found that the amount of boric acid eluted from colemanite can be suppressed by reducing the pH of the reaction system, and we use only fast-hardening cements (for example, calcium aluminate cements) that can reduce the negative effects of boric acid. Rather, the present invention uses a low-alkaline cement capable of suppressing boric acid elution itself.

  The neutron absorber according to claim 2 of the present application is “the low alkaline cement is a cement containing at least an Auink linker containing beinite as a main component, dihydrate gypsum or anhydrous gypsum, and blast furnace slag. The neutron absorber according to claim 1 characterized by the above.

Auin is also known as calcium sulfoaluminate or erymite, and is a mineral represented by the chemical formula of 3CaO · 3Al ₂ O ₃ · CaSO ₄ , which consumes gypsum and calcium hydroxide due to the presence of gypsum and calcium hydroxide. Is generated.

3CaO · 3Al ₂ O ₃ · CaSO ₄ (auin) + 8CaSO ₄ (gypsum) + 6Ca (OH) ₂ (calcium hydroxide) + 90H ₂ O → 3 (3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O) (etringite) ... [Formula 1]
Thus, since Auin consumes calcium hydroxide when producing ettringite, a low alkaline cement that does not produce calcium hydroxide can be easily obtained by using an Auink linker. In addition, the calcium hydroxide in the above formula 1 does not indicate a free calcium hydroxide crystal but means a calcium component in the system.

Since calcium is consumed as much as possible by this reaction, calcium hydroxide exhibiting high alkalinity is not liberated at any time. The calcium content is supplied from belite and blast furnace slag in the Auink linker, and the calcium content that is not fixed as ettringite becomes C—S—H with a low CaO / SiO ₂ ratio, contributing to medium- to long-term strength development and stability. .

  The gypsum made of dihydrate gypsum or anhydrous gypsum is necessary for the reaction that produces a large amount of ettringite, as shown in the above formula 1. Gypsum can be either natural or by-product from other industries. Also, gypsum is contained in the outink linker, and gypsum in the clinker also contributes to the reaction.

Blast furnace slag is granulated blast furnace slag, mainly composed of CaO, SiO ₂ , and Al ₂ O ₃ , and close to the chemical composition of melilite, but most of it is glass. It has latent hydraulic properties and becomes hydrated in an alkaline environment. Since C—S—H and ettringite are produced by consuming calcium hydroxide and gypsum in the system, it plays the same role as the above-mentioned ink-ink linker in that calcium hydroxide is consumed to make the system low alkaline.

  Auin is not a general-purpose material and is expensive and contributes to the development of short-term strength, but does not contribute to long-term strength. When used in large quantities, it becomes difficult to ensure fluidity during kneading, or it expands into the cured body. Since there are drawbacks such as the risk of cracking, it is preferable to use blast furnace slag, which is an industrial byproduct, with gypsum in order to suppress these disadvantages. The blast furnace slag is not particularly limited as long as it is used for blast furnace cement, cement admixture and the like.

The neutron absorber of the present invention, fineness of the upper Symbol low alkali cement is preferably a 4000~5000cm ² / g in Blaine value. If the brain value is less than 4000 cm ² / g, it may be difficult to ensure sufficient initial strength. If it exceeds 5000 cm ² / g, the hydration activity becomes too strong, and it may be difficult to ensure workability or an expansion phenomenon may occur. Further, it is not preferable from the viewpoint of cost to make it more fine than necessary.

The neutron absorber according to claim 3 of the present application is as follows: "The aggregate is a fine aggregate having a particle size of 5 mm or less partially or wholly made of colemanite , or a coarse particle having a particle size of more than 5 mm and less than 25 mm. are those consisting of aggregates, the colemanite contained in the fine aggregate in the neutron-absorbing body according to claim 1 or 2 characterized in that including a fine powder of particle size less than 1 mm 20 wt% or more It is.
Further, the neutron absorber according to claim 4 of the present application is as follows: “The coarse aggregate includes an aggregate made of colemanite in an aggregate having a particle diameter of more than 5 mm and not more than 10 mm. Is a neutron absorber.
Moreover, the neutron absorber according to claim 5 of the present application is “the coarse aggregate does not include an aggregate made of colemanite, but is made of crushed stone or gravel. It is a neutron absorber.

  When the neutral absorber is made of mortar, the aggregate contained in the neutron absorber is a fine aggregate having a particle size of 5 mm or less, and if the neutral absorber is made of concrete, the fine aggregate and the particle size exceed 5 mm and 25 mm or less. The coarse aggregate. The fine aggregate is partly or entirely made of colemanite, and the colemanite preferably contains fine powder having a particle size of less than 1 mm.

  By including the fine powder, the boron distribution becomes uniform and a sufficient neutron absorption effect is obtained, and the work of adjusting the particle size of colemanite can be saved. Coarse aggregate may contain aggregate made of colemanite in a part (for example, more than 5 mm and less than 10 mm) due to the balance between strength development and neutron absorption. In the present invention in which a small amount of cement is used, there is not much merit that the coarse aggregate is made of colemanite. Therefore, in applications where a large amount of boron is not required, the coarse aggregate is preferably made of conventional crushed stone or gravel.

The neutron absorber according to claim 6 of the present application states that “the aggregate is 50 to 800 parts by weight with respect to 100 parts by weight of the low alkaline cement, and the amount of colemanite in the aggregate is determined by shielding calculation or irradiation experiment. a neutron absorber "according to any one of claim 1 to 5, characterized in that the amount to be.

  The aggregate amount varies depending on whether the neutron absorber is made of mortar or concrete, the required strength, and the amount of colemanite required in the neutron absorber (boron amount), but generally 50 to 800 parts per 100 parts by weight of the low alkaline cement. Part by weight is preferred. If the amount is less than 50 parts by weight, sufficient strength may not be obtained due to insufficient aggregate, or neutron absorption may not be achieved due to insufficient boron. If it exceeds 800 parts by weight, sufficient strength may not be obtained due to insufficient cement.

  Aggregates made of colemanite are mostly contained in fine aggregates, and the amount of colemanite in the aggregates is determined by shielding calculations and irradiation experiments (details will be described later). In the present invention, the amount of colemanite required in the neutron absorber is determined in this way, and the necessary amount is systematically contained, so that the strength can be ensured and neutron absorption can be performed efficiently. The amount of aggregate is based on the above-mentioned amount of colemanite, and when the amount of aggregate is insufficient from the viewpoint of securing strength, it is appropriately supplemented with conventionally used silica sand, crushed sand, crushed stone, gravel and the like.

The neutron absorber according to claim 7 of the present application is as follows: “The low alkaline cement is CaSO as a total amount of Auin linker containing 10 to 70% by weight of Auink linker containing belite and gypsum in combination with gypsum in clinker. ₄ to 10% by weight, 10 to 60% by weight of blast furnace slag, 10 to 35% by weight of Portland cement as the total amount of belite in the outink linker, and the Auin content in the outink linker It is 20 to 80 weight%, It is a neutron absorber as described in any one of Claims 1-6 characterized by the above-mentioned.

As described above, in the low alkaline cement of the present invention, the main hydration products are ettringite and C—S—H, and calcium hydroxide is not generated. At the same time as realizing this, one of the preferred specific blends that can ensure good workability and physical properties of the absorber after curing is according to claim 7 of the present application. Auinklinker and gypsum are used to produce ettringite, blast furnace slag is used to produce ettringite and C—S—H, and belite in Portland cement and clinker is used to supply calcium hydroxide and C—S—H necessary to produce ettringite. Contributes to the generation of

  In the low alkaline cement, the amount of the outink linker is 10 to 70% by weight. If it is less than 10% by weight, the amount of ettringite produced is reduced, and it becomes difficult to ensure low alkalinity and initial strength. When it exceeds 70% by weight, it becomes difficult to ensure workability or an expansion phenomenon occurs.

The gypsum is dihydrate gypsum or anhydrous gypsum, and the total amount with gypsum in the clinker is 10 to 30% by weight in terms of CaSO ₄ . If it is less than 10% by weight, the amount of ettringite produced is reduced, and it becomes difficult to ensure low alkalinity and initial strength. If it exceeds 30% by weight, unreacted gypsum remains and adversely affects dimensional stability and durability. The amount of blast furnace slag is 20 to 60% by weight.

  If it is less than 20% by weight, the production amount of C—S—H is reduced, and the elongation of the long-term strength is deteriorated. If it exceeds 60% by weight, the amount of the outink linker is relatively reduced, the amount of ettringite produced is reduced, and the initial strength development is deteriorated. The total amount of Portland cement and the amount of belite in the Auink linker is 10 to 35% by weight.

  If it is less than 10% by weight, the supply of calcium hydroxide necessary for the production of ettringite becomes insufficient, and the amount of C—S—H produced decreases, so that the strength development becomes worse. If it exceeds 35% by weight, the amount of calcium hydroxide produced becomes too large and calcium hydroxide remains in the system, so that it is not low alkaline.

  As the mineral composition of the Auinklinker, the Auin content is 20 to 80% by weight. If it is less than 20% by weight, the amount of ettringite produced will be small, and it will be difficult to ensure low alkalinity and initial strength.

  If it exceeds 80% by weight, it is difficult not only to ensure workability but also to cause an expansion phenomenon, but also to make stable firing of the clinker difficult. In addition, the amount of belite and the amount of Auin in the Auink linker are amounts obtained by calculation from the chemical composition of the raw material before firing. In the Auink linker, there are belite, ferrite, plaster and the like in addition to Auin.

  Since the neutron absorber of the present invention exhibits excellent neutron absorption performance and good initial strength, a thin mortar plate can also be manufactured, and the application range can be expanded. In addition, the colemanite aggregate used contains fine particles with a particle size of less than 1 mm, and even if such a colemanite aggregate is used, good initial strength developability is exhibited. Therefore, it can be manufactured efficiently and inexpensively. Further, the distribution of boron in the absorber can be made uniform.

It is a figure which shows the relationship between the boron content in mortar, and neutron transmittance.

  Hereinafter, the present invention will be described in more detail. Note that the present invention is not limited to the embodiments described below.

(A) Neutron absorber As described above, the neutron absorber of the present invention is a cement-based cured body having neutron absorption performance. Specifically, mortar products such as panels, concrete products, and hardened mortars placed on site. Or hardened concrete. Since good initial strength is obtained and the boron distribution is uniform, a mortar panel having a thin object (for example, a thickness of about 30 mm) can be obtained.

Compressive strength when the mortar products, 15~20N / mm ² approximately in wood age 1 day, 50~80N / mm ² approximately in wood age 28 days. For a concrete, 10~20N / mm ² approximately in wood age 1 day, 30~60N / mm ² approximately in wood age 28 days. The neutron absorption performance is determined by the amount of unit colemanite, the amount of unit cement, the cement composition, and the member thickness, and can be designed according to the required performance.

  The neutron absorber may be manufactured by a conventional method for manufacturing a cement-based hardened body, and the dimensions thereof are not particularly limited because they vary depending on applications. The neutron absorber of the present invention can be suitably used for buildings, shielding concrete, and the like, but in the case of a thin mortar panel, it can also be used as a cover member for reducing the reflection of neutron beams from walls and ceilings.

(B) Constituent material
(1) Low Alkaline Cement As described above, the low alkaline cement of the present invention is a cement in which the main hydration products are ettringite and C—S—H and does not generate calcium hydroxide. This cement basically consumes calcium hydroxide in the hydration reaction system (actually, calcium hydroxide and hydroxide ions are consumed, not calcium hydroxide), so strongly alkaline calcium hydroxide It becomes low alkalinity without producing.

In addition, it is more preferable to reduce Na ₂ O and K ₂ O in the cement clinker, which are other alkaline factors. By using a low alkaline cement, elution of boric acid from colemanite can be suppressed, and inhibition of cement hydration by boric acid can be reduced. The ratio of the amount of ettringite and C—S—H produced varies depending on the composition of the cement.

  As the amount of ettringite increases, the amount of hydrogen fixed as crystal water increases and is free to attenuate fast neutrons, but C—S—H required for medium- to long-term strength development and stability decreases. The proportion can be determined by the required neutron absorption performance and the physical properties of the absorber.

  In addition to ettringite and C—S—H, some hydrated products such as alumina gel and iron hydroxide are also produced depending on the type of cement and hydration conditions. In the present invention, a cement that generates a large amount of ettringite containing a large amount of crystal water is used, so that neutron absorption can also be expected by hydrogen from the crystal water.

One specific configuration of the low alkali cement is an aink linker containing Auin (3CaO.3Al ₂ O ₃ .CaSO ₄ ) as a main component and containing belite, dihydrate gypsum or anhydrous gypsum, and cement containing blast furnace slag. There is. Auink linkers containing Auin as a main component and including belite are conventionally used as main materials for Auin-based cement, CSA-based expansion material, and the like.

The manufacture of the Auink linker is obtained, for example, by calcining a calcined raw material of a predetermined composition at about 1350 ° C. with a rotary kiln or the like using limestone as the CaO source, alumina powder or bauxite as the alumina source, and anhydrous gypsum as the CaSO ₄ source. Depending on the conditions, C ₂ S, C ₄ AF, CaSO _{4 and the} like are also generated in the clinker. Gypsum and blast furnace slag are as described above.

  The mixing ratio of Auink linker, dihydrate gypsum or anhydrous gypsum and blast furnace slag is determined by the required performance, but the amount of gypsum that generates ettringite sufficiently from Auin but does not remain much after the reaction is necessary. A sufficient amount of blast furnace slag is required to generate C—S—H.

In addition to the above materials, the low alkaline cement may contain, in addition to these materials, pozzolanic substances such as silica fume and fly ash, ordinary portland cement, and limestone fine powder. The fineness of the low alkaline cement is not particularly limited, but in terms of initial strength development, a brane value of 4000 to 5000 cm ² / g, which is slightly higher than the fineness of ordinary Portland cement, is preferable.

  As a specific example of the cement containing the above-mentioned Auink linker, dihydrate gypsum or anhydrous gypsum, and blast furnace slag, there is a GRC (glass fiber reinforced concrete) cement which has been conventionally known as a low alkali and low shrinkage cement.

This cement for GRC is composed of one or more of Auin, gypsum, blast furnace slag, ordinary Portland cement, fly ash, and silica fume. For example, SiO ₂ 22.7 wt%, Al ₂ O ₃ 12.5 wt%, Fe ₂ It consists of chemical components of O ₃ 1.1% by weight, CaO 48.1% by weight, and SO ₃ 9.0% by weight.

  The cement for GRC includes a cement containing glass fiber (a glass fiber is premixed) and a cement not containing (a glass fiber is separately supplied). In the present invention, either of these can be used.

  This GRC cement has features such as low shrinkage and excellent dimensional stability, low alkalinity and excellent adhesion of organic paint, and glass fiber containing high bending strength. It is used for flooring, curtain walls, permanent formwork, etc. Further, several patents relating to GRC cement have been filed, such as JP-A-60-127252, JP-B-5-66347, JP-B-3-29034, and JP-B-6-96473.

There are a plurality of types of cement for GRC, such as those described in the above patents and those described above, and any of these can be used in the present invention. As described above, the low alkaline cement of the present invention can be a conventional GRC cement or a GRC cement equivalent, and among them, the total amount of the outink linker and the gypsum in the clinker is 10 to 70% by weight. as CaSO ₄ in terms of 10 to 30 wt%, the blast furnace slag from 20 to 60 wt%, contains 10 to 35 wt% as the total amount of the belite amount of a wink in the linker of Portland cement, and, Auin contained in a wink linker A low alkaline cement having an amount of 20 to 80% by weight is preferable because it has not only low alkalinity but also good physical properties such as workability, strength development and dimensional stability.

  The proportion of each constituent material is determined in the above range with reference to the theoretical calculation amount of ettringite, C—S—H and calcium hydroxide based on the hydration reaction formula of Auin, blast furnace slag and ordinary Portland cement. In addition, this cement is manufactured according to the conventional manufacture of cement for GRC.

(2) Aggregate The main aggregate used in the present invention is colemanite aggregate. As described above, colemanite is a natural hydrous calcium borate mineral represented by the chemical formula 2CaO · 3B ₂ O ₃ · 5H ₂ O, and contains 40% by weight or more boric acid component in a normal grade.

  Boron has neutron absorption capability, so there are various boron-containing compounds such as natural minerals such as colemanite and kurnacobite, boron carbide, boron powder, boron oxide, ferroboron, boric acid, volcalcite, borax, titanium boron, zirconium boron, etc. However, the reason why the colemanite is used in the present invention is that it is easily available, inexpensive, and has a relatively high boron content.

  In the present invention, when the neutron absorber is made of mortar, the aggregate is a fine aggregate having a particle size of 5 mm or less, partially or entirely made of colemanite. When a part of the fine aggregate is a colemanite aggregate, the remaining fine aggregate may be conventionally used as an aggregate for mortar such as quartz sand, crushed sand, mountain sand, river sand and the like. In addition, the said colemanite aggregate has a preferable thing containing about 20 weight% or more of the granular material with a particle size of less than 1 mm. In the present invention, neutron absorption can be efficiently performed by using a fine aggregate containing a colemanite powder having a particle size of less than 1 mm.

  Further, when the neutron absorber is made of concrete, the aggregate includes a fine aggregate having a particle size of 5 mm or less, partly or entirely made of colemanite, and partly containing colemanite aggregate, or not containing any colemanite aggregate. Coarse aggregate having a particle size of more than 5 mm and not more than 25 mm. The fine aggregate is the same as in the case of the mortar.

  The reason why the maximum particle size of the coarse aggregate is 25 mm or less is to reduce the uneven distribution of boron and improve the neutron absorption performance. Coarse aggregate is the same as conventional coarse aggregate such as crushed stone, gravel, etc., but if neutron absorption is not enough just by adding colemanite aggregate to fine aggregate, a part of coarse aggregate Is the colemanite aggregate.

  The amount of colemanite aggregate in the aggregate is determined by the amount judged necessary by the shielding calculation or shielding experiment. In the shielding calculation, codes that can calculate the absorption effect of neutron beams with a certain energy from the elemental composition and density of the entire neutron absorber (for example, codes developed at the Los Alamos National Laboratory in the United States) have been developed. This can be used. In addition, nuclear data necessary for calculation is maintained for many nuclides by nuclear related organizations (for example, Japan Atomic Energy Agency).

  An example of the shielding experiment will be described later. For example, in the case of a thermal neutron beam, the relationship between the boron content and the neutron transmittance is derived, and the amount of necessary colemanite that matches the required performance can be obtained.

(3) Others In the present invention, in addition to the above-mentioned materials, setting agents such as citric acid and salts thereof, lignin sulfonic acid and salts thereof, carbonates, and the like used for producing ordinary mortar and concrete, water reducing agents, etc. Chemical admixtures such as viscosity modifiers can be used as necessary.

(C) Mixing ratio of cement and aggregate In the neutron absorber of the present invention, the mixing ratio of the low alkaline cement and the aggregate is 50 to 800 parts by weight of the aggregate with respect to 100 parts by weight of the low alkaline cement. Is preferred. More specifically, when the neutron absorber is made of mortar, the fine aggregate is 50 to 300 parts by weight with respect to 100 parts by weight of the low alkaline cement. By setting the amount of fine aggregate within this range, a neutron absorber made of mortar having excellent neutron absorption performance and good strength development can be obtained.

  When the neutron absorber is made of concrete, the aggregate made of the fine aggregate and the coarse aggregate is 300 to 800 parts by weight with respect to 100 parts by weight of the low alkaline cement. By setting the aggregate amount within this range, a concrete neutron absorber having excellent neutron absorption performance and good strength development can be obtained.

  The ratio of fine aggregate to coarse aggregate is as described above. Moreover, the low alkaline cement said here contains the cement composition which consists of a some component material like the said cement for GRC, and also contains this, when reinforcing fibers, such as glass fiber, enter.

(D) Evaluation of neutron absorber performance
(1) Materials used • 2 types of Auink linker (trial product) • Anhydrite (by-product of hydrofluoric acid manufacturing industry)
・ Blast furnace slag fine powder (Brain 4000cm ² / g class, manufactured by Day Shi)
・ Normal Portland cement (manufactured by Taiheiyo Cement)
・ Commercially available cement for GRC (manufactured by Taiheiyo Cement Co., Ltd., brain value; about 4700 cm ² / g)
・ Commercially available alumina cement for comparison ・ Water reducing agent (Mighty 150 manufactured by Kao)
・ Retarding agent (citric acid)
・ Colemanite (particle size 5mm or less, including fine particles)
・ Silica sand (No. 5)
・ Glass fiber (Nippon Electric Glass ARG fiber 19mm)
·Tap water

(2) Low alkaline cement Three low alkaline cements used in the examples of the present invention were prepared using the above materials. Of these, the low alkaline cements A and B are trial products, and the low alkaline cement C is a commercial product. Two types of commercial cements D and E were also prepared for comparison. The details of these five types of cement are shown in Table 1.

  About these 5 types of cement, the mineral composition of the hydrate after hydration was evaluated by X-ray powder diffraction. The sample for evaluation is a hardened cement paste of W / C = 50% that has been sealed and cured at 20 ° C. for 28 days. After curing, it was coarsely pulverized to 5 mm or less, dried in a nitrogen stream for 7 days, and further finely pulverized for evaluation.

  Moreover, the ignition loss of 1000 degreeC was calculated | required with respect to the same sample, and it was set as the amount of crystallization water. These evaluation results are shown in Table 2. In addition, kneading | mixing was continued intermittently until bleeding was lost at the time of kneading any cement.

  In cements A to C (low alkaline cement), only ettringite and C—S—H were observed, and calcium hydroxide was not detected. These cements A to C are cements that can satisfy the claims 2, 3 and 6 of the present invention. In cement D, calcium hydroxide exhibiting high alkalinity was observed. As for cement E, calcium aluminate hydrate and aluminum hydroxide, which are characteristic of alumina cement, were detected.

  The amount of water of crystallization was higher in cements A to C than cements D and E, and was confirmed to be effective for fast neutron attenuation.

(3) Colemanite mortar test For the purpose of evaluating the performance of each cement when using colemanite as an aggregate, mortar with essentially the same composition containing colemanite as an aggregate was prepared, and the curing status, etc. was evaluated. It was.

  The mortar was blended with cement, colemanite (particle size of 5 mm or less, including fine particles) and silica sand at a mass ratio of 1: 1: 1, and kneaded with kneading water with W / C = 0.40. At the time of kneading, a water reducing agent of 0.5 to 1.6% was added to the cement so as to have the same fluidity. Further, for the cements other than D, a retarder of 0.3% was also added to the cement.

  First, a portion of fresh mortar was collected and evaluated for pore water. The mortar for evaluation of pore water was kneaded every 10 minutes after kneading, and after 60 minutes of kneading, the pore water was collected by a centrifuge and analyzed for pH and boron concentration of the pore water. The results are shown in Table 3. Cement D was found to have a high pH exceeding 12.8 and a higher boron concentration than other cements. The other cements had a lower pH than D and the boron concentration was an order of magnitude lower than D.

  The mortar was placed in a 4 × 4 × 16 cm mold and the compressive strength was measured. One day after kneading, the mold was removed and sealed and cured in a thick plastic bag until a predetermined age. The temperature was 20 ° C. until the age of 28 days, and then the curing was continued at 50 ° C. for another 28 days assuming the high temperature of the nuclear facility. Table 4 shows the measurement results of the compressive strength.

  A to C, which are low alkaline cements, exhibited good strength expression at any age.

  Since cement D did not harden even at 7 days of age, the test was abandoned. This is judged to be the influence of boron as a delay component from the result of boron analysis in the pore water. Although cement E exhibited good strength when cured at 20 ° C., the strength was greatly reduced at 50 ° C., which revealed problems in high temperature environments and long-term durability.

  Three mortars using cements A to C are examples of the present invention, and two mortars using cements D and E are comparative examples.

(4) Neutron absorber performance test Cement C was used to produce mortars with different boron contents, and the shielding performance and strength characteristics of the neutron absorber were evaluated. These mortars are all examples of the present invention. Table 5 shows the blending of these mortars. The ratio of colemanite (particle size of 5 mm or less, including fine particles) and silica sand was changed so that the boron content in the mortar was 20 mg / cm ³ , 40 mg / cm ³ , and 80 mg / cm ³ . Each mortar was kept constant at W / C = 0.32, the water reducing agent was a cement ratio of 3.0%, and the retarder was a cement ratio of 0.3%. In addition, assuming the actual thin mortar panel, the bending strength was reinforced by adding glass fiber.

  The curing was assumed to be steam curing in the initial stage assuming the actual panel manufacturing process. The steam curing condition was 40 ° C. for 8 hours, and after cooling, the mold was removed and the wet curing at 20 ° C. and 60% humidity was continued. The wet-curing period of the specimens subjected to the shielding test was 14 days. The strength test was conducted on the 3rd and 14th days of wet air curing.

  The specimen for the shielding test was a panel shape of 100 × 100 mm square, and the thickness was set at three levels of 10, 20, and 30 mm. The shielding test was performed with a thermal neutron beam, and the following beam characteristics were obtained.

Thermal neutron flux: 1.6 × 10 ⁸ n / cm ²
Thermal neutron E: n _E = 42 meV, n _λ = 0.14 nm
Beam size: 20mm x 20mm
The measurement was performed by a method of measuring neutron transmittance with an prompt gamma ray analyzer.
The strength test was a 4 × 4 × 16 cm specimen, and the bending strength and the compressive strength were measured respectively.

  FIG. 1 shows the result of the shielding test. It can be seen that the neutron absorber of the present invention can effectively shield neutrons. Moreover, the boron content and the neutron transmittance showed a very good correlation, which means that the material can be designed by determining the amount of colemanite according to the required performance of shielding.

  That is, when the amount of colemanite in the aggregate is determined by a shielding experiment, the relationship between the boron content per unit volume and the neutron transmittance in the designed absorber member thickness as shown in FIG. It can be determined by calculating from the boron content required when the safety factor is multiplied by the neutron transmittance.

  As shown in Table 6, as a result of the measurement of the bending strength and the compressive strength, all the amounts of colemanite had sufficient practical strength.

Claims (7)

  A neutron absorber characterized in that the main hydration product is ettringite and C—S—H, and includes a low alkaline cement that does not produce calcium hydroxide and an aggregate containing colemanite.   2. The neutron absorber according to claim 1, wherein the low alkaline cement is a cement containing an Au-ink linker containing Auin as a main component and containing belite, dihydrate gypsum or anhydrous gypsum, and blast furnace slag. The aggregate, in which some or all may consist consisting particle diameter 5mm or less fine aggregate, or said fine aggregate and exceed a particle size 5mm 25 mm or less coarse aggregate from colemanite, said fine aggregate in The neutron absorber according to claim 1 or 2 , wherein the colemanite contained in the nuclei contains 20% by weight or more of fine particles having a particle diameter of less than 1 mm. 4. The neutron absorber according to claim 3, wherein the coarse aggregate includes an aggregate made of colemanite in an aggregate having a particle diameter of more than 5 mm and not more than 10 mm. The neutron absorber according to claim 3, wherein the coarse aggregate does not include an aggregate made of colemanite, but is made of crushed stone or gravel. The aggregate is 50 to 800 parts by weight with respect to 100 parts by weight of the low alkaline cement, and the amount of colemanite in the aggregate is an amount determined by shielding calculation or irradiation experiment. The neutron absorber according to any one of 5 . The low alkaline cement is 10 to 70% by weight of the Auink linker containing Auin as a main component and containing belite, 10 to 30% by weight in terms of CaSO ₄ as a total amount of gypsum and the amount of gypsum in the clinker, and 10% of blast furnace slag. -60 wt%, Portland cement is contained in a total amount of 10-35 wt% with the amount of belite in the outinklinker, and the Auin content in the outinklinker is 20-80 wt% Item 7. The neutron absorber according to any one of Items 1 to 6 .

Images