JP6481816B2 - Low activation concrete - Google Patents

Description

  The present invention relates to low activation concrete that can reduce residual radioactivity due to activation of cobalt and europium.

  2. Description of the Related Art Conventionally, in a facility that handles radioactive substances such as a nuclear power plant, a structural frame is constructed of concrete because it has sufficient strength and excellent radiation shielding properties. Since concrete exposed to radiation for a long time is activated, it is necessary to store and manage it as radioactive waste when dismantling the facility. As a method to reduce the cost of storage management, radioactive nuclides are chemically extracted from activated concrete and treated as radioactive waste liquid that can be concentrated, and the remaining non-radioactive concrete is simplified. Disposal methods are disclosed (for example, Patent Documents 1 and 2).

  In addition, low radiation reduction formed by selecting materials with low cobalt and europium content in concrete materials for the purpose of preventing or suppressing concrete activation after prolonged exposure to neutron beams. Concrete is disclosed (for example, Patent Document 3).

Japanese Patent No. 5294116 JP 2013-57591 A Japanese Patent No. 5388411

  However, when the radionuclide is separated from the activated concrete as in Patent Documents 1 and 2, and the remaining non-radioactive concrete is disposed of, the non-radioactive concrete becomes a waste, resulting in disposal costs. Further, even when the low-activation cement of Patent Document 3 is adopted, it is considered that cobalt and europium are contained in the concrete, and the contents thereof are not known unless various measurements are performed, and are used for many measurements. The efficiency of the sample is low.

  This invention is made | formed in view of the said situation, manufactures the material which reduced content of cobalt or europium, and provides the low activation concrete which is hard to activate.

[1] with cobalt or primary material europium is included, a low-activation Concrete Using secondary material obtained by performing chemical treatment to remove these elements, as said secondary material Molten slag is included, and the molten slag is heated in the presence of chlorine in the activated concrete containing at least one radionuclide of cobalt 60, europium 152 and europium 154, and the radioactive slag is heated from the molten activated concrete. Low activation concrete characterized by being slag obtained by cooling after nuclide chloride is removed by evaporation .
[2] The low activation concrete according to [ 1 ], wherein the molten slag contains 1% by mass or more of calcium.
[3] The composition comprising aggregate, one or more types of cement and water is solidified, and the molten slag is contained in at least one of the aggregate and the cement. [ 1 ] or [ 1 ] [2 ] Low activation concrete.
[8] In the above [ 3 ], the molten slag may be contained in at least one of coarse aggregate and fine aggregate.
[9] In the above [ 3 ] or [8], a blast furnace cement containing clinker, gypsum and the molten slag may be mixed as the cement.
[10] In any one of the above [ 3 ] to [9], Portland cement may be mixed as the cement.

  In the secondary material used as the material of the low activation concrete of the present invention, cobalt and europium, which cause activation of the concrete in the process of obtaining the secondary material, are removed. For this reason, the manufactured concrete can be made difficult to be activated. Further, by reusing a primary material containing cobalt or europium as a material for low activation concrete without discarding, environmental conservation and effective use of resources can be achieved.

It is a flowchart which shows an example of the manufacturing process of the low activation concrete concerning this invention. It is a graph which shows the change of the drying shrinkage | contraction strain with the age progress of the concrete test body produced in the Example. It is a graph which shows the change of the compressive strength with the age progress of the concrete test body produced in the Example.

《Low activation concrete》
The low activation concrete according to the first embodiment of the present invention uses a secondary material obtained by subjecting a primary material containing cobalt or europium to chemical treatment to remove these elements. is there. For example, a secondary material can be used as the aggregate or cement material of the low activation concrete. A known concrete material can be applied to the concrete material other than the secondary material.

  Since concrete usually contains cobalt and europium, examples of the primary material include concrete lump such as concrete lump, concrete scrap, and concrete scrap. The concrete waste material may be derived from activated concrete or non-activated concrete (general concrete). Also suitable as primary materials are construction by-products such as asphalt, construction generated wood, construction sludge, construction mixed waste, etc., and wood, sludge, building materials, and incinerated ash produced by radioactive decontamination work. .

  As the chemical treatment for removing at least one of cobalt and europium from the primary material, a method in which the primary material is melted by a heat treatment described later to generate molten slag as a secondary material is preferable. According to this method for producing molten slag, radionuclides such as cobalt 60, europium 152 and europium 154 can be volatilized and removed from the primary material.

  In addition to the above-described method for producing molten slag, as the chemical treatment method, the primary material is washed with a decontamination solution containing a chelating agent, acid, alkali, etc., and the radionuclide containing cobalt or europium is removed from the primary material. And a method of generating waste material as a secondary material.

<Second embodiment>
The low activation concrete of the second embodiment according to the present invention is low activation concrete containing molten slag. Further, the molten slag is obtained by reacting activated concrete containing at least one radionuclide of cobalt 60 ( ⁶⁰ Co), europium 152 ( ¹⁵² Eu) and europium 154 ( ¹⁵⁴ Eu) at 1000 ° C. in the presence of chlorine in the furnace. The radionuclide chloride was vaporized and removed from the activated and melted activated concrete, and then cooled and obtained.

  Moreover, you may use the molten slag derived from general waste other than activated concrete as a part of material of the low activated concrete of this embodiment.

  Materials other than the molten slag constituting the low activation concrete of the present embodiment are not particularly limited, and a conventional concrete material or a known low activation concrete material can be applied.

  As the molten slag, as will be described in detail later, molten slag obtained by mixing activated chloride with calcium chloride and heating and melting it can be mentioned. In this case, among the mixed calcium chloride, chlorine is consumed for removal of the radionuclide by chlorination and gasification, so that the calcium component remains in the molten slag.

Examples of the calcium component include CaO (quick lime), Ca (OH) ₂ (slaked lime), CaCO ₃ (limestone), and other calcium compounds. These calcium components are usually used as a concrete material for the purpose of improving the hydration activity or hardening activity of cement in solidification of ready-mixed concrete (concrete material composition).

  When the calcium component is already contained in the molten slag in the present embodiment, low activation concrete may be formed without separately mixing the calcium component. From this viewpoint, 1% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more of calcium is included with respect to the total mass of the molten slag. preferable. Although the upper limit of calcium content is not specifically limited, From a viewpoint of suppressing the strength fall of the concrete formed, it is preferable that it is 30 mass% or less.

Here, the calcium content in the molten slag is calculated not as the calcium compound content but as calcium ions (Ca ²⁺ ). For example, when the content of CaO in the molten slag is 5% by mass, the content of calcium in the molten slag is 5% by mass × (atomic weight of Ca ÷ molecular weight of CaO) = about 3.6% calculate.

When it is technically difficult to quantify all the calcium components in the molten slag, at least one or more analyzable, preferably two, selected from CaO, Ca (OH) ₂ and CaCO ₃ More preferably, the content of the three calcium compounds is measured, and the result obtained by calculating from the content as described above is defined as the calcium content in the molten slag. The reason for paying attention to the above three kinds of calcium compounds is that they are the calcium components that can have the greatest influence on the solidification process of concrete.

  In the low activation concrete of the present embodiment, it is preferable that a composition containing aggregate, one or more kinds of cement and water is solidified, and molten slag is contained in at least one of the aggregate and cement.

  When the molten slag constitutes an aggregate, the aggregate may be a coarse aggregate or a fine aggregate. The molten slag can be crushed by a known method and molded into a size required as a coarse aggregate or fine aggregate and used. When the molten slag does not constitute an aggregate, a known aggregate is applied. You may use together molten slag and a well-known aggregate.

  When an aggregate containing molten slag is used as the material for the low activation concrete of the present embodiment, only molten slag may be used as at least one of coarse aggregate and fine aggregate, or known together with molten slag. Other aggregates may be used in combination. For example, electrobath alumina, limestone and the like known as aggregates having low activation ability can be mentioned. The mixing ratio of the molten slag and other aggregates is not particularly limited, and can be appropriately adjusted within a range of, for example, a mass ratio of 1: 5 to 5: 1.

  When the molten slag constitutes cement, the cement is preferably a mixed cement composed of clinker, gypsum and molten slag. A known cement material is applied to the clinker and the gypsum. Examples thereof include clinker and gypsum that constitute known Portland cement.

  Content of the molten slag with respect to the total mass of mixed cement is not specifically limited, For example, what is necessary is just to adjust suitably in the range of 10-80 mass%. The method for obtaining the mixed cement is not particularly limited, and the molten slag pulverized to an appropriate size may be mixed with a known clinker, gypsum and a blender.

  When the mixed cement containing the molten slag is used as the material for the low activation concrete of the present embodiment, only the mixed cement may be used as the cement, or other known cements may be used in combination with the mixed cement. May be. For example, known Portland cement can be used in combination. The mixing ratio of the mixed cement and other known cements is not particularly limited, and can be appropriately adjusted, for example, within a mass ratio of 1: 5 to 5: 1.

  The low activation concrete of this embodiment is formed by solidifying a concrete material composition (fresh concrete) containing aggregate, one or more kinds of cement, and water. The composition may contain known admixtures, water reducing agents and the like as optional components.

The mass ratio of water and cement constituting the composition may be appropriately adjusted in consideration of the use and compressive strength of the concrete, as with the water cement ratio (W / C) in conventional concrete formation, For example, what is necessary is just to adjust suitably in the range of 20/80-80/20.
Content of the coarse aggregate and the fine aggregate with respect to the total mass in the composition is not particularly limited, and may be appropriately adjusted in consideration of the use of concrete, compressive strength, and the like. What is necessary is just to adjust suitably in the range.
The total content of water and cement, excluding aggregates and optional components, with respect to the total mass in the composition may be appropriately adjusted in consideration of the use and compressive strength of the concrete, as in the case of conventional concrete, For example, what is necessary is just to adjust suitably in the range of 10-50 mass%.
The amount of air in the composition is not particularly limited, and may be adjusted in the same manner as in the past in consideration of the size of the coarse aggregate and the fine aggregate. For example, it can be adjusted in the range of 1 to 10% by volume. it can.

  Examples of optional components include high-performance water reducing agents, AE water reducing agents, fluidizing agents, thickeners, rust inhibitors, antifreezing agents, shrinkage reducing agents, setting modifiers, silica, alumina, fine limestone powder, colemanite, Examples include one or more of clay minerals such as zirconia, boron carbide, and bentonite, anion exchangers such as hydrotalcite, and fibrous substances such as vinylon fibers, acrylic fibers, and carbon fibers. Content of an arbitrary component is not specifically limited, What is necessary is just to adjust suitably in consideration of the use of concrete, compressive strength, etc.

  In addition, when preparing the said concrete material composition, it can also use as a mortar which consists of a fine aggregate, water, and cement, without mixing a coarse aggregate. Moreover, when preparing the said composition, it can also be used as a cement paste which consists of water and a cement, without mixing a coarse aggregate and a fine aggregate. The mixing ratio of the materials constituting the mortar and the cement paste may be the same as the mixing ratio of the materials constituting the conventional mortar and the cement paste.

  The low activation concrete of this embodiment can be formed by performing each process, such as kneading | mixing of the said concrete material composition, conveyance, placement, and curing, by a well-known method.

  Since the low activation concrete of this embodiment has previously removed cobalt and europium as chlorides in the process of producing molten slag as will be described later, even if it is exposed to neutrons for a long time in a radiation handling facility, etc. And the radionuclide of europium is not generated and is difficult to activate. The contents of cobalt and europium in the low activation concrete of the present embodiment can be quantified by ICP-MS measurement after pretreatment according to, for example, JIS R2522.

  An example of the manufacturing process of the low activation concrete of this embodiment is shown in FIG. First, in the melting process described later, molten slag is obtained from activated concrete as waste. The molten slag is crushed to an appropriate size to obtain coarse aggregate and fine aggregate, and cement obtained by pulverizing the molten slag is obtained. A concrete material composition prepared by mixing this cement with Portland cement, coarse aggregate and fine aggregate, water (not shown) and optional components is prepared, and it is as low as the method for forming ordinary concrete. Activated concrete is obtained.

<Manufacture of molten slag>
The molten slag used as the material for the low activation concrete of the present embodiment is obtained by a heating process, a collection process, and a solidification process described below. Details of each step will be described below, but steps or processes other than these steps may be included.

<Heating process>
The heating step is a step of heating activated concrete containing at least one radionuclide of cobalt 60, europium 152 and europium 154 to 1000 ° C. or higher in the presence of chlorine in the furnace.
By heating the activated concrete under the above-mentioned conditions, the activated concrete can be melted and gas component vaporization and evaporation can be promoted.

The temperature at which the activated concrete is heated is not particularly limited as long as it is equal to or higher than the temperature at which the concrete melts, and is usually 1000 ° C or higher, preferably 1200 ° C or higher, more preferably 1300 ° C or higher, further preferably 1400 ° C or higher, 1500 degreeC or more is especially preferable.
By heating above the above temperature, the activated concrete can be reliably melted, the radionuclide can be sufficiently chlorinated, and vaporization and evaporation of the chloride can be sufficiently promoted.
The upper limit of the heating temperature is not particularly limited, and can be set to, for example, about 1500 ° C. to 2000 ° C. in consideration of the durability of the heating furnace.

  The time for heating at the above temperature is not particularly limited and is appropriately set according to the amount of the activated concrete. For example, from the viewpoint of sufficiently generating and vaporizing the radionuclide chloride, the molten state is 0.5. Heating is preferably performed so as to continue for about 3 hours.

  Generally, activated concrete contains at least one of cobalt 60, europium 152, and europium 154. These are considered to be present in the concrete as oxides. By heating the activated concrete in the presence of chlorine, the oxide can be converted to chloride and vaporized.

As a method for heating the activated concrete in the presence of chlorine, a method in which calcium chloride (CaCl ₂ ) and activated concrete are mixed and heated in a furnace is preferable. The radionuclide chloride is produced in the molten concrete heated at a high temperature. Since the vapor pressure and boiling point of the radionuclide chloride are lower than when it is an oxide, it is easily vaporized and evaporated.

  As another method of heating the activated concrete in the presence of chlorine, a method of introducing hydrogen chloride gas or chlorine gas into the furnace and heating the activated concrete together with the activated concrete can be mentioned. Also, hydrogen chloride gas can be generated in the furnace by mixing hydrochloric acid with activated concrete instead of hydrogen chloride gas. Since hydrogen chloride gas and chlorine gas are corrosive, calcium chloride is preferably mixed from the viewpoint of improving the durability of the furnace.

The amount of calcium chloride mixed with the activated concrete is not particularly limited, but considering the content of the radionuclide in the activated concrete, for example, the amount of calcium chloride mixed with the mass of activated concrete (100 parts by mass) is 1-30 mass parts is preferable, 5-20 mass parts is more preferable, 10-15 mass parts is still more preferable.
By mixing 1 part by mass or more of calcium chloride with respect to 100 parts by mass of the activated concrete, the radionuclide chloride can be sufficiently generated.

  Although the upper limit of the calcium chloride to mix is not specifically limited, From a viewpoint of reusing the molten slag after cooling, for example, 30 mass parts or less with respect to 100 mass parts of activated concrete, More preferably, 20 mass parts or less, Furthermore, Preferably it is 15 mass parts or less. It is possible to prevent the calcium component remaining in the molten slag from becoming excessive, and to suppress a decrease in the structural strength of the concrete that reuses the molten slag.

  The activated concrete put into the furnace is preferably crushed in advance before heating. Since melting by heating is facilitated and mixing with calcium chloride is facilitated, generation of the radionuclide chloride can be promoted. The degree of crushing is not particularly limited. For example, it is preferable to make the size of a so-called concrete glass having a diameter of about 1 cm to 50 cm. Moreover, you may make it a granule of less than 1 cm. Usually, the smaller the diameter of the crushed material, the higher the heat conduction efficiency and the contact efficiency with calcium chloride.

  The furnace for heating and melting the activated concrete is not particularly limited, and is preferably a furnace capable of melting concrete glass and concrete particles, and more preferably a closed furnace capable of collecting exhaust gas and fly ash. As such a furnace, a known furnace for melting inorganic waste such as concrete can be applied. For example, a gasification and fusion integrated type such as a shaft furnace type gasification melting furnace, a thermoselect type gasification melting furnace, etc. And gasification / melting / separation type furnaces such as kiln type gasification / melting furnace and fluidized bed type gasification / melting furnace.

<Collection process>
The collection step of the present embodiment is a step of vaporizing the radionuclide chloride generated in the molten activated concrete, and cooling and collecting the chloride exhausted to the outside of the furnace.

The volatilized chloride is discharged out of the furnace by a gas supplied into the furnace, for example, a combustion gas supplied from a burner for heating. The exhaust gas containing the discharged chloride is cooled on the exhaust path. It is preferable to collect the condensed or solidified chloride by a predetermined collector installed on the exhaust path. As a collector, well-known dust collectors, such as a bag filter and a ceramic filter, are mentioned, for example. A pre-stage of a known dust collector is often provided with a cooling mechanism for cooling high-temperature exhaust gas to about 200 ° C., for example. Such a cooling mechanism is also useful in this embodiment.
The collected chloride is disposed of by a known method in accordance with laws and regulations.

  As an example, a concrete glass activated by a melting process including a heating step is heated in a melting furnace at 1500 ° C. in the presence of chlorine, and a cooling mechanism is provided for cobalt and europium chloride contained in the discharged gas. Collect with filter. The collected coagulum is separated from the filter and the cobalt and europium chlorides are dissolved in water or a low concentration of acid. Next, alkali is added to precipitate, for example, cobalt and europium radionuclides as hydroxides. The precipitate can be collected by filtration or the like, dried and pressed, and disposed of as high-level radioactive waste.

<Solidification process>
The solidification process of this embodiment is a process of obtaining a solidified molten slag by cooling a melt made of molten activated concrete.
Since the radionuclides Cobalt 60, Europium 152, and Europium 154 are evaporated as chlorides, the melt that has been sufficiently heated and chlorinated does not substantially contain the radionuclides. Can handle up to. By cooling such a melt, a volume-reduced molten slag can be obtained.

  The method of cooling the melt is not particularly limited, and granulated slag may be obtained by rapidly cooling and solidifying the melt into cooling water, blowing air into the melt, or air cooling naturally. Air cooling slag may be obtained by cooling and solidifying, and gradually cooling while controlling the temperature of the melt, and cooling and solidifying while growing inorganic crystals inside to obtain slow cooling slag Also good. Any molten slag can be obtained by known methods.

<Co and Eu removal process>
Incinerated ash 100g (100 parts by mass) (primary material) containing Co and Eu is mixed with 30 g (30 parts by mass) calcium chloride as an additive, heated at 1300-1500 ° C. for 30 minutes, and then slowly And treated ash (slag) (secondary material) was obtained.
As shown in Table 1, the amount of each element of Co and Eu contained in incinerated ash and treated ash was measured by ICP-MS manufactured by Agilent, and as shown in Table 1, it was 98.5% or more Co and 24.2% or more. Eu was removed. This indicates that Co and Eu were volatilized as chlorides. In addition, it can be seen that heating at a higher temperature is sufficient to further increase the Eu removal rate. It was confirmed separately that these volatilized chlorides could be recovered by cooling. Therefore, it is clear that when the activated concrete containing radioactive Co and Eu is processed by the above-described method, a molten slag having a sufficiently reduced radioactivity can be obtained.

<Preparation of fine aggregate and coarse aggregate>
The concrete waste material was melt-processed by the above-mentioned method, cobalt and europium were removed, and molten slag (secondary material) was obtained. This was crushed to obtain fine aggregates and coarse aggregates as materials for molten slag aggregate concrete.

<Production of concrete specimen>
175 parts by weight of water, 350 parts by weight of Portland cement, 845 parts by weight of molten slag fine aggregate, 971 parts by weight of molten slag coarse aggregate, 0.70 parts by weight of AE water reducing material, 1.40 parts by weight of AE auxiliary, Molded and cured by a conventional method, a specimen of molten slag aggregate concrete (MG-MS) was obtained.

  Specimens of recycled aggregate concrete (RG-RS) by the same method as above except that known aggregates obtained by dismantling existing structures were used as fine aggregates and coarse aggregates. Got.

  A specimen of ordinary aggregate concrete (NG-NS) was obtained by the same method as described above except that ordinary aggregate newly produced by a conventional method was used as the fine aggregate and coarse aggregate.

<Evaluation of concrete specimen>
The uncured specimen after aging was room temperature 20 ° C., humidity 60% R.D. H. Was dried in a room, and the change in drying shrinkage strain with age was measured according to JIS A1129-1 (comparator method). The measurement period was a material age of 1 day to 85 days. From the results of FIG. 2, it was found that molten slag aggregate concrete (MG-MS) has a property that it is less likely to shrink than recycled aggregate concrete (RG-RS) and ordinary aggregate concrete (NG-NS). At an age of 85 days, the dry shrinkage strain of molten slag aggregate concrete was about one-fourth that of ordinary aggregate concrete.

  The uncured specimen after aging was room temperature 20 ° C., humidity 60% R.D. H. Was dried in a room, and the change in compressive strength with age was measured in accordance with JIS A1108 (Concrete compressive strength test method). The measurement period was 7 to 91 days. From the results in Fig. 3, molten slag aggregate concrete (MG-MS) shows the same compressive strength as recycled aggregate concrete (RG-RS), which is about 20% less than ordinary aggregate concrete (NG-NS). It was found to exhibit a high compression strength. Along with the progress of age, all specimens tended to increase in compressive strength.

  The configurations and combinations thereof in the embodiments described above are examples, and additions, omissions, substitutions, and other modifications of known configurations are possible without departing from the spirit of the present invention.

  The present invention can be widely applied to the field of handling activated concrete.

Claims (3)

Cobalt or europium were included to the primary material, a low-activation Concrete Using secondary material obtained by performing chemical treatment to remove these elements,
Molten slag is included as the secondary material,
The molten slag is
Activated concrete containing at least one radionuclide of cobalt 60, europium 152 and europium 154 is heated in the presence of chlorine;
Low-activation concrete characterized in that it is slag obtained by cooling after the radionuclide chloride has been vaporized and removed from molten activated concrete. The low activation concrete according to claim 1 , wherein the molten slag contains 1 mass% or more of calcium. A composition comprising aggregate, one or more types of cement and water is solidified,
The low activation concrete according to claim 1 or 2 , wherein the molten slag is contained in at least one of the aggregate and the cement.

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