Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/04—Treating liquids
  • G21F9/06—Processing
  • G21F9/16—Processing by fixation in stable solid media
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/28—Treating solids
  • G21F9/30—Processing

Definitions

• the present invention relates to briquettes for glass solidification.
• Radioactive materials such as nuclear power plants and spent fuel reprocessing plants
• This radioactive waste cannot be disposed of in the same manner as general waste, so it is generally solidified with cement or glass, confined in storage containers such as drums or stainless steel canisters, and then disposed of in burial facilities.
• Methods for solidifying radioactive waste include, for example, the Liquid Feed Direct Current Ceramic Melter Method (LFCM Method).
• Patent Document 1 discloses a technology that can reduce the amount of hydrogen gas generated by radiation by solidifying radioactive waste using a geopolymer material and a boron compound.
• Patent Document 2 discloses a technique in which a mixture containing an adsorbent containing titanium that has adsorbed a radioactive element, a SiO2 source, and an M2O source (M is an alkali metal element) is heated and melted to form a vitrified body, thereby making it possible to vitrify the adsorbent containing titanium that has adsorbed a large amount of radioactive elements, and further to suppress the elution of the radioactive elements.
• M2O source M is an alkali metal element
• Patent Document 3 discloses a technology that makes it possible to provide a vitrified radioactive waste body with excellent chemical durability by incorporating iron phosphate glass containing Fe 2 O 3 and P 2 O 5 and a sludge residue from which sulfur components have been removed during vitrification in a specific composition ratio, thereby vitrifying sludge containing sulfate with a high packing effect.
• solidification materials for solidifying radioactive waste have been developed for various purposes.
• Cement, glass, and the like are used as constituent materials for the solidification materials, but glass, which can be preferably used for solidifying both low-level and high-level radioactive waste, has attracted attention from the viewpoint of easily stably containing radioactive materials for a long period of time.
• bulk glass has been used as a solidification material (vitrification material) for solidifying radioactive waste that uses glass as a constituent material.
• the solid glass is melted and mixed with radioactive waste, but bulk glass is difficult to melt, and there is a problem that the glass melting becomes unstable.
• equipment such as a furnace for solidifying and melting radioactive waste, remote automatic operation and stable operation without human intervention are essential due to the strong radioactivity, and it has been required to suppress the glass melting becoming unstable.
• the objective of the present invention is to provide a briquette for vitrifying radioactive waste that can be easily melted.
• the gist of the present invention is as follows.
• a briquette for vitrification of radioactive waste comprising a powdered vitrification material and a binder, the binder including an inorganic borate compound.
• the present invention provides a briquette for vitrifying radioactive waste that can be easily melted.
• FIG. 1 is a diagram showing the evaluation results of the disintegration property of a vitrification material in Experiment I of the embodiment (a photograph as a substitute for a drawing).
• a briquette for vitrification according to one embodiment of the present invention (hereinafter also simply referred to as a "briquette for vitrification” or “briquette”) is a briquette for vitrification of radioactive waste, which contains a powdered vitrification material and a binder, and the binder contains a borate inorganic compound.
• briquette refers to a powdered material that has been compacted and molded.
• spherical bulk glass with a diameter of 1 to 2 mm has been used as a vitrification material (hereinafter also referred to as "solidification material") for melting and solidifying radioactive waste.
• solidification material a vitrification material
• the contact surface where the glass and radioactive waste react is small compared to the volume, and the glass and radioactive waste are difficult to melt, resulting in a problem of a long time required for complete melting.
• powdered glass it is conceivable to use powdered glass as a solidification material.
• the vitrification briquette according to the present embodiment when used as a solidification material and the briquette is put into radioactive waste, the radioactive waste contains nitric acid and the like, so that the dissolution of the binder containing the inorganic borate compound into the radioactive waste proceeds first before the melting of the powdered vitrification material proceeds.
• the collapse of the briquette and the penetration of the radioactive waste into the inside of the briquette occur quickly, and a slurry containing the radioactive waste, the powdered vitrification material, and the inorganic borate compound is obtained.
• the contact area between the radioactive waste and the glass increases, so that the glass is melted more easily than in the conventional process in which the melting proceeds gradually from the surface of the bulk glass.
• the facilitation of the melting of the glass means that the melting of the glass proceeds stably and at a high speed.
• the powdered vitrification material which has a smaller volume than the bulk glass body that has been used conventionally, is used as the glass to be melted, the time until all the glass is melted can be shortened.
• the term "bulk glass” is used to refer to glass having a larger volume than a powdered vitrified material.
• radioactive waste contains elements such as molybdenum that are difficult to dissolve in glass, and it is known that these elements that are difficult to dissolve in glass generate water-soluble compounds such as molybdates during the vitrification process. These water-soluble compounds are called yellow phase (YP), and there has been a need to prevent the yellow phase, which does not dissolve in glass, from leaking out of the solidified body.
• the vitrification briquette according to this embodiment is used, the vitrification material is easily melted, which promotes the dissolution of radioactive waste components such as molybdic acid into the glass, making it difficult for a yellow phase to be generated and separated at the end of the melting stage, and suppressing precipitation.
• radioactive waste is roughly divided into low-level radioactive waste and high-level radioactive waste.
• cement or the like is used as a constituent material for the solidification of low-level radioactive waste
• glass or the like is used as a constituent material for high-level radioactive waste, from the viewpoint of stably containing radioactive materials for a long period of time.
• the constituent materials such as glass that can be used for the solidification of high-level radioactive waste can also be used for the solidification of low-level radioactive waste. Therefore, since the briquette of this embodiment confines and solidifies the radioactive waste using glass, it can be used to solidify both low-level radioactive waste and high-level radioactive waste, but is preferably used to solidify high-level radioactive waste.
• the powdered vitrified material is not particularly limited, and may be any vitrified material in a form generally recognized as powdered.
• the vitrified material is a material that is made of components that constitute glass and becomes a part of glass when melted and solidified.
• the vitrified material may be glass itself, or may be a substance made of components that constitute glass, such as silicon dioxide, silica sand, or alumina, and specifically includes glass, silicon dioxide, silica sand, alumina, boric acid, calcium carbonate, zinc oxide, boron oxide, and the like.
• powdered vitrified material for example, only powdered glass may be used, or a mixture of powdered glass and powdered silicon dioxide may be used. It is important that the "powdered vitrified material" is smaller than the bulk glasses conventionally used, and typically has an average particle size (D50) of 500 ⁇ m or less.
• the content of the powdered vitrification material in the briquette is not particularly limited, but is usually 80% by mass or more and 99.9% by mass or less, preferably 85% by mass or more and 99.9% by mass or less, more preferably 90% by mass or more and 99.9% by mass or less, and even more preferably 95% by mass or more and 99.9% by mass or less.
• the upper limit of the content may be 99% by mass or less, 98% by mass or less, 97% by mass or less, or 96% by mass or less.
• the average particle size (D50) of the powdered vitrified material is not particularly limited, but is usually 1 ⁇ m or more and 500 ⁇ m or less, preferably 5 ⁇ m or more and 300 ⁇ m or less, more preferably 10 ⁇ m or more and 250 ⁇ m or less, more preferably 10 ⁇ m or more and 200 ⁇ m or less, even more preferably 10 ⁇ m or more and 150 ⁇ m or less, particularly preferably 10 ⁇ m or more and 100 ⁇ m or less, and most particularly preferably 10 ⁇ m or more and less than 100 ⁇ m.
• the average particle size is equal to or less than the upper limit of the above range, briquetting becomes easy and the melting property into radioactive waste is improved.
• the average particle size is equal to or more than the lower limit of the above range, scattering of the powdered vitrified material during the production of briquettes is easily suppressed.
• the average particle size can be measured by a laser diffraction scattering type measuring device (for example, Microtrack manufactured by Microtrack Bell Co., Ltd.).
• the shape of the powdered vitrified material is not particularly limited, and examples include particles, short fibers (fibers or whiskers), and flakes.
• powdered glass examples include crushed glass (obtained by crushing glass) and cut glass (obtained by cutting glass).
• the type of powdered glass material is not particularly limited, and known glasses can be used, such as borosilicate glass, soda-lime glass, aluminosilicate glass, aluminoborosilicate glass, or phosphate glass. From the viewpoint of availability, borosilicate glass, aluminosilicate glass, aluminoborosilicate glass, or phosphate glass is preferred, and borosilicate glass is more preferred.
• the powdered vitrified material may be manufactured by a known method or a combination of known methods, or a commercially available product may be used.
• the content of powdered glass in the powdered vitrification material is not particularly limited and may be 100% by mass, but is usually 30% by mass or more and 100% by mass or less, preferably 50% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less. If the content is equal to or more than the lower limit of the above range, raw material costs are easily suppressed and vitrification is facilitated.
• the powdered glass may be produced by a known method or a combination of known methods, or a commercially available product may be used. Specifically, commercially available powdered glass may be used, or commercially available glass that has been crushed or cut may be used.
• the briquette contains a binder for binding the powdered vitrification material, and the binder contains an inorganic borate compound.
• the inorganic borate compound has an excellent ability to bind glass, while being easily dissolved in strong acids such as nitric acid, hydrochloric acid, and sulfuric acid. Since radioactive waste contains nitric acid and the like, the inclusion of the inorganic borate compound in the binder can promote the disintegration of the briquette in the radioactive waste, and can promote the formation of a slurry containing the radioactive waste and the powdered vitrification material, and the subsequent melting of the powdered vitrification material.
• the content of the binder in the briquette is not particularly limited, but is usually 0.1% by mass or more and 20% by mass or less, preferably 0.3% by mass or more and 15% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less, and even more preferably 0.5% by mass or more and 5% by mass or less.
• the above content ratio of the binder in the briquette can also be applied as a suitable content ratio of the borate inorganic compound in the briquette.
• the cation contained in the borate inorganic compound is not particularly limited as long as it can form an inorganic compound, and examples thereof include cations of alkali metals such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs); cations of alkaline earth metals such as beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), or barium (Ba); cations such as zinc; etc. These may be used alone or in combination of two or more.
• At least one cation selected from the group consisting of alkali metal cations and alkaline earth metal cations is preferable, at least one cation selected from the group consisting of Li + , Na + , K + , Ca2+ , and Sr2 + is more preferable, and at least one cation selected from the group consisting of Li + and Na + is even more preferable.
• the binder may contain components other than inorganic borate compounds as long as the effects of the present invention are achieved.
• the content of the inorganic borate compound in the binder is not particularly limited, but is usually 50% by mass or more, preferably 75% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. If the content is equal to or greater than the lower limit of the above range, sufficient binding of the powdered vitrified material can be ensured. In addition, there is no need to set an upper limit for the content, and it may be 100% by mass, 100% by mass or less, less than 100% by mass, 99% by mass or less, 95% by mass or less, or 90% by mass or less.
• the solubility of the binder in water is not particularly limited, but from the viewpoint of ease of production and production stability when water is used as a solvent in producing briquettes, the saturated solubility in water at room temperature is preferably 0.1 g/100 mL or more, more preferably 0.5 g/100 mL or more, and even more preferably 1.0 g/100 mL or more. There is no particular upper limit, but it is usually 10 g/100 mL or less, and may be 5 g/100 mL or less.
• the solubility of sodium borate is 4.7 g/100 mL.
• the briquette may contain components other than the powdered vitrified material and binder (hereinafter also referred to as "other components") as long as the effects of the present invention can be obtained.
• the content of other components in the briquette is not particularly limited, and may be 0% by mass, may be more than 0% by mass, may be 0% by mass or more and 10% by mass or less, may be 0% by mass or more and 5% by mass or less, or may be 0% by mass or more and 1% by mass or less.
• the shape of the briquettes is not particularly limited, and may be, for example, a polygonal columnar shape such as a triangular columnar shape, a square columnar shape, or a pentagonal columnar shape, a spherical shape (including a nearly spherical shape), or a flattened sphere, and from the viewpoint of transportability, a spherical shape is preferable.
• the volume of the briquette is not particularly limited, but is usually 0.1 mm3 or more and may be 15 cm3 or less, 0.1 mm3 or more and 10 cm3 or less, 0.1 mm3 or more and 5 cm3 or less, 1 mm3 or more and 5 cm3 or less, 0.1 cm3 or more and 5 cm3 or less, or 0.3 cm3 or more and 3 cm3 or less.
• the diameter thereof may be 1 mm or more and 3 cm or less, 1 mm or more and 2 cm or less, or 5 mm or more and 2 cm or less.
• the disintegration property when mixed with the waste liquid is excellent, and when the volume is equal to or less than the upper limit of the above range, the melting property of the powdered vitrification material in the radioactive waste can be improved.
• the bulk density of the briquette is not particularly limited, but is usually 1.0 g/ cm3 or more and 1.8 g/ cm3 or less, preferably 1.0 g/ cm3 or more and 1.7 g/ cm3 or less, more preferably 1.2 g/ cm3 or more and 1.5 g/ cm3 or less, and even more preferably 1.2 g/ cm3 or more and 1.4 g/ cm3 or less. If the bulk density is equal to or more than the lower limit of the above range, sufficient hardness can be ensured. Also, if the bulk density is equal to or less than the upper limit of the above range, the melting property of the powdered vitrification material in radioactive waste can be improved. The bulk density can be adjusted by adjusting the particle size of the vitrified material. The bulk density can be evaluated by a liquid gravimetric method.
• the porosity of the briquette is not particularly limited, but is usually 5% to 80%, preferably 10% to 70%, more preferably 20% to 60%, and even more preferably 30% to 50%. If the bulk density is equal to or higher than the lower limit of the above range, the penetration of the waste into the briquette is promoted, and the melting property of the powdered vitrification material can be improved. If the bulk density is equal to or lower than the upper limit of the above range, sufficient hardness can be ensured.
• the above porosity can be adjusted by adjusting the particle size of the vitrified material. The porosity can be evaluated by comparing the bulk density with the true density, and can also be evaluated by mercury intrusion porosimetry.
• Briquettes preferably have a certain degree of hardness since they are not deformed during processes such as transportation where they come into contact with each other or with other members.
• the hardness of a briquette is measured using an index of crushing strength under a parallel plane load measured by a uniaxial pressure test.
• the crushing strength of the briquette measured by the crushing strength test is not particularly limited, but is usually 1 N or more, preferably 3 N or more, more preferably 5 N or more, and even more preferably 10 N or more. If the crushing strength is equal to or higher than the lower limit of the above range, deformation during processes such as transportation is unlikely to occur.
• the above-mentioned crushing strength can be adjusted by the type and amount of the binder.
• the above-mentioned crushing strength can be measured by a uniaxial compression test under the conditions of a compression speed of 1 mm/min and a load of a parallel plane.
• the method for producing the above-mentioned briquettes for vitrification is not particularly limited.
• the method for producing briquettes for vitrification which is another embodiment of the present invention (hereinafter, also simply referred to as "method for producing briquettes for vitrification” or "method for producing briquettes"), specifically, A mixture preparation step for obtaining a mixture containing a powdered vitrification material and a borate inorganic compound; a molding step of molding the mixture to obtain a molded body; A heat treatment step of heat treating the molded body;
• the briquette can be produced by a method for producing a briquette for vitrification of radioactive waste, comprising the steps of:
• the method for producing briquettes according to this embodiment may include steps other than the steps described above as long as the effects of the present invention can be obtained.
• the method for producing briquettes includes a mixture preparation step of obtaining a mixture containing a powdered vitrification material and a borate inorganic compound.
• the method for mixing the powdered vitrified material and the inorganic borate compound is not particularly limited, and any known method can be used.
• the powdered vitrified material and the inorganic borate compound are placed in a container and mixed using a mixing device such as a ball mill, a mortar and pestle mixer, or a shaker mixer.
• a mixing device such as a ball mill, a mortar and pestle mixer, or a shaker mixer.
• the powdered vitrified material may be one produced by a known method or a combination of known methods, or a commercially available product may be used.
• the crushing method is not particularly limited, and for example, a method such as a jet mill, a bead mill, a ball mill, a hammer mill, a turbo mill, a sand mill, or freeze crushing may be used.
• the inorganic borate compound may be produced by a known method or a combination of known methods, or a commercially available product may be used.
• a dispersion medium or solvent When mixing, a dispersion medium or solvent may be used.
• the dispersion medium or solvent include water. These may be used alone or in combination of two or more. These solvents may be removed from the briquette before the briquette is finally manufactured, but may remain in the briquette to the extent that the effects of the present invention can be obtained.
• the constituent materials of the vitrification briquette and the dispersion medium or solvent may be mixed at the same time, but from the viewpoint of ease of manufacture, the constituent materials of the vitrification briquette and a portion of the dispersion medium or solvent may be mixed first and then the remainder may be added, for example, the binder may be dissolved in a solvent such as water and then the other constituent materials may be added.
• the method for producing briquettes according to the present embodiment includes a molding step of molding the mixture to obtain a compact. This molding may be performed with or without pressure.
• the method for molding the mixture to obtain a molded product is not particularly limited, and for example, the molding can be performed using a mold. In this case, methods such as press molding, extrusion molding, and injection molding may be used.
• the molding temperature in the molding process is not particularly limited and may be, for example, 0°C or higher and 30°C or lower.
• the number of times molding is performed is not particularly limited, and may be one time or two or more times, and is preferably two or more times.
• the molding step may include at least a step of molding the mixture to obtain a molded body of a first shape, and then further molding the molded body of the first shape to obtain a molded body of a second shape.
• the method for producing briquettes according to the present embodiment may include a freezing step of freezing the above-mentioned compact.
• this freezing step the dispersion medium or solvent in the mixture is frozen, thereby increasing the adhesion and integrity between the constituent materials of the briquettes, and the compacts can be obtained with a good yield.
• the freezing temperature is not particularly limited, but is preferably equal to or lower than the melting point of the dispersion medium or solvent.
• the method for producing briquettes according to the present embodiment includes a heat treatment step of heat-treating the above-mentioned molded body.
• the heat treatment step can dry the molded body, specifically, can reduce the content of moisture, dispersion medium, solvent, etc. in the molded body.
• the method for heat treating the molded body is not particularly limited, and for example, a method for heat treating the molded body using an electric furnace or a gas furnace can be adopted.
• the number of times of heat treatment in the heat treatment step is not particularly limited, and may be one time or two or more times.
• the heat treatment temperature in the heat treatment step is not particularly limited, and may be, for example, above room temperature and below the boiling point of the dispersion medium or solvent.
• FIG. 1 Another embodiment of the present invention is the use of the above-mentioned vitrification briquette for vitrification of radioactive waste.
• the above-mentioned vitrification briquette is used, so that melting of glass for vitrification is easier than in the case of using conventional vitrification materials, and efficient solidification is possible.
• the method of using the vitrification briquette for vitrification of radioactive waste can be the same as the method of using a known vitrification material for vitrification of radioactive waste.
• the vitrification briquette is used by mixing it with radioactive waste while heating it to obtain a mixture of the vitrification briquette and radioactive waste to be solidified, as described in the method of producing a vitrified body of radioactive waste described later.
• the method for mixing the vitrification briquettes with the radioactive waste is the same as that described in the method for producing a vitrified body of radioactive waste described below.
• a method for producing a vitrified radioactive waste according to another embodiment of the present invention comprises: a melting step of mixing the above-mentioned vitrification briquettes with liquid radioactive waste while heating them, or mixing them and then heating them to obtain a mixed molten liquid; a solidification step of cooling and solidifying the mixed molten liquid to obtain a vitrified body;
• the present invention relates to a method for producing a vitrified form of radioactive waste, comprising the steps of:
• the method for producing briquettes according to this embodiment may include steps other than the steps described above as long as the effects of the present invention can be obtained.
• the method for producing vitrified bodies according to this embodiment includes a melting step of obtaining a mixed molten liquid by a process of mixing the above-mentioned vitrification briquettes and liquid radioactive waste while heating them (hereinafter also referred to as the "first process”), or by a process of mixing them and then heating them (hereinafter also referred to as the "second process").
• the method for mixing the vitrification briquette and the liquid radioactive waste is not particularly limited, and may be, for example, a method in which the vitrification briquette and the liquid radioactive waste are charged into a known container such as a melting furnace and mixed therein.
• a method in which the vitrification briquette and the liquid radioactive waste are charged into a container separate from the melting furnace and mixed therein may be used, and in this case, the mixture obtained here may be charged into a container such as a melting furnace and subjected to the next heating treatment.
• the heating method is not particularly limited, and heating can be performed by a known method.
• the radioactive waste is not particularly limited as long as it contains radioactive material, but it is preferably in liquid form.
• the above-mentioned vitrification briquettes can be used to solidify both low-level radioactive waste and high-level radioactive waste, and although the radioactive waste may be either low-level or high-level radioactive waste, application to high-level radioactive waste is preferred from the viewpoint of the high need to stably contain radioactive materials for a long period of time and from the viewpoint of the relatively high concentration of nitric acid.
• the temperature at which the above-mentioned vitrification briquettes and liquid radioactive waste are mixed is not particularly limited, and is usually 20°C or higher and 150°C or lower, and may be 20°C or higher and 100°C or lower. If the temperature is within the above range, the radioactive waste can be handled stably.
• the heating temperature in the first and second processes is not particularly limited, and may usually be 900°C or higher and 1300°C or lower. If the temperature is within the above range, the briquette for glass solidification can be stably melted.
• the method for producing a vitrified body according to this embodiment includes a solidification step of cooling and solidifying the above-mentioned mixed molten liquid to obtain a vitrified body.
• the cooling is preferably performed with the mixed molten liquid confined in a storage container for storing the final solidified body. Therefore, the method for producing a vitrified body according to the present embodiment preferably includes a step of storing the mixed molten liquid in a storage container such as a stainless steel canister after the melting step and before the solidification step.
• the method for cooling and solidifying the mixed melt is not particularly limited, and any known method can be used. For example, a method of cooling a storage container containing the mixed melt using a cooling liquid, or a method of cooling the storage container or the mixed melt using a cooling gas can be used.
• volume of vitrification material The volume of the vitrification material was calculated by weight and density conversion.
• alkali metal elements such as Cs and Rb: 0.26 mol/L
• alkaline earth metal elements such as Sr: 0.06 mol/L
• transition metal elements such as Cr and Fe: 0.15 mol/L
• rare earth metal elements such as La and Ce: 0.30 mol/L
• platinum group elements such as Ru: 0.10 mol/L
• other elements such as
• the nitrate chemical reagents of each element were dissolved in a 2 mol/L nitric acid aqueous solution to produce a simulated solution of radioactive waste.
• a load of 30 g was applied to one vitrification material using a glass rod, and the simulated solution of radioactive waste was poured in so that half of the vitrification material was immersed, and the collapse of the vitrification material in the simulated solution of radioactive waste was observed.
• the time from the time when the simulated solution of radioactive waste was poured in to the time when the glass rod with a load of 30 g started to collapse the vitrification material is shown in Table 1.
• the observation results for Experiment I are shown in Figure 1.
• Figure 1 shows that collapse began at 2.0 minutes in Example 1, collapse began at 2.0 minutes in Example 2, and no collapse occurred even after 30 minutes in Comparative Examples 1 and 2.
• the measurement results of each vitrification material are shown in Table 1.
• the notation "-" in Table 1 means that no collapse occurred even after 30 minutes.
• the porosity of vitrification material was calculated from the bulk density and the true density of the powdered glass. The measurement results for each glass material are shown in Table 1. The true density was calculated by the Archimedes method for bulk glass that does not contain voids.
• Example 1 ⁇ Production of vitrification material> (Example 1-1)
• the glass was pulverized using a ball mill to obtain powdered glass (average particle size (D50): 10.08 ⁇ m).
• 40 g of the above powdered glass as a raw glass, 0.3 g of sodium borate as a binder, and 14 g of water were charged into a polypropylene container (disposable cup) and mixed using a planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro) to obtain a mixture.
• a planetary centrifugal mixer Thinky Corporation's Awatori Rentaro
• the mixture was packed into a hemispherical Teflon (registered trademark) mold capable of obtaining a spherical molded body with a volume of 0.52 cm3 (radius 0.5 cm), and press-molded into a sphere by combining the molds at a molding temperature of 20°C.
• the molded body was filled in the mold and placed in a freezer maintained at -4°C for at least one day to freeze the solvent, and the spherical molded body was removed from the mold.
• the molded body was kept at 25°C for 24 hours, at 50°C for 1 hour, and at 85°C for 3 hours in a thermostatic dryer, and then returned to room temperature to produce a vitrification material (briquette).
• the content ratio of each component in the vitrification material is shown in Table 1.
• "-" in the column for a component indicates that the component is not added. This is also true in Table 2 described later.
• Example 1-2 A vitrification material (briquette) was produced in the same manner as in Example 1-1, except that the amount of sodium borate added was changed from 0.3 g to 1.0 g. The content ratio of each component in the vitrification material is shown in Table 1.
• Example 1-1 The same powdered glass as in Example 1-1 was used as a raw glass material. 40 g of the powdered glass, 0.4 g of water glass as a binder, and 14 g of water were charged into a polypropylene container (disposable cup) and mixed using a planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro) to obtain a mixture. A vitrification material was produced in the same manner as in Example 1-1, except that the mixture in Example 1 was changed to the above mixture. The content ratio of each component in the vitrification material is shown in Table 1.
• Comparative Example 1-2 A vitrification material (briquette) was produced in the same manner as in Comparative Example 1-1, except that the amount of water glass was changed from 0.4 g to 1.2 g. The content ratio of each component in the vitrification material is shown in Table 1.
• Example 2-1 A vitrification material (briquette) was produced in the same manner as in Example 1-1. The content of each component in the vitrification material is shown in Table 2.
• Example 2-2 A vitrification material (briquette) was produced in the same manner as in Example 1-2. The content of each component in the vitrification material is shown in Table 2.
• Comparative Example 2-1 A vitrification material (briquette) was produced in the same manner as in Comparative Example 1-1. The content ratio of each component in the vitrification material is shown in Table 2.
• Example 2-4 A vitrification material (briquette) was produced in the same manner as in Comparative Example 2-1. The content of each component in the vitrification material is shown in Table 2.
• One vitrification material (briquette) was placed in a glass settling tube together with a simulated solution of radioactive waste, and the vitrification material was immersed in the simulated solution, and the settling tube was placed in a silicon oil bath maintained at 200° C. for one minute. The vitrification material inside the settling tube was then observed using an X-ray CT scanner, and the results of the evaluation of disintegration are shown in Table 2.
• the criteria for assessing collapse are as follows: A: No structure having a spherical shape or a shape that appears to be a part of the molded product was observed, and the molded product collapsed. B: Structures having a spherical shape or a shape that appeared to be a part of the molded product were observed, and disintegration was insufficient.
• the present invention provides a briquette for vitrification of radioactive waste that can be melted more easily than conventional vitrification materials.

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