JPS6120840B2 - - Google Patents

Description

[Detailed description of the invention]

Disposal of large amounts of high-level radioactive waste generated when regenerating spent nuclear reactor fuel is an important issue for nuclear power applications. The most promising method is usually to convert the radioactive waste into a dry solid, which is chemically and thermally stable and does not undergo radiolysis. The ability to maintain the stability of dry solids will determine whether or not we can achieve stability for humans on Earth over a period of more than 20,000 years. For example, radioactive waste contains radioactive isotopes such as Sr ⁹⁰ , which has half-lives of 29, 66,000, and 30 years, respectively.
Contains Pu ²⁴⁰ and Cs ¹³⁷ . Only the radioactive isotopes are so dangerous to human life that they must be converted into a dry solid form that remains stable for thousands of years. The solid radioactive waste requires the radioactive isotopes to remain stationary for thousands of years even when placed in water. The method of fixing radioactive substances into a dry solid body that is hardly affected by leaching etc. is suitable not only for the treatment of radioactive waste but also for the production of radiation sources useful in industry, medicine, and research laboratories. A practical and extremely simple device for safely processing, storing, and immobilizing harmful radioactive materials has not been proposed heretofore. Conventional storage containers do not sufficiently isolate radioactive materials, do not sufficiently prevent environmental influences over long periods of time, and are not sufficiently stable at high temperatures. One of the conventional methods is the so-called dry solid method, for example, a method in which radioactive waste is immobilized in glass by a process of melting the glass. The dry solid method has the advantage of preventing or slowing down the dissipation of radioactive elements when the outer storage container is ruptured. Additionally, glass is more stable at high temperatures than plastics and is chemically more resistant to salt water than metals. The melting temperature of glass, which has excellent chemical durability and low alkali ion conductivity, is extremely high, for example, 1800° C. or higher. Such high-temperature melting treatment is not economically desirable, and furthermore, it is not desirable from a safety standpoint because it causes volatilization of harmful radioactive substances. In general, it is difficult to handle radioactive materials, and in particular, considering the risk of releasing radioactive materials into the atmosphere due to volatilization, glass with a relatively low melting temperature, that is, a glass with a SiO ₂ content of about 27% by weight, is used. Interest was focused on using glass. Although the risk of radioactive material volatilization was reduced, it could not be completely prevented. Furthermore, the chemical durability of low melting temperature glasses has been greatly reduced, and the ion diffusion rate of radioactive substances contained in the glasses has been increased. As the ion diffusion rate increases, the glass becomes unable to hold the radioactive material stationary. Said glasses are unsuitable for keeping radioactive materials confined for long periods of time according to today's safety standards. In addition, conventional methods were unable to trap much of the volatilized radioactive material. It will become clear from the following description that the present invention can provide a glass of a novel composition, a glass container, and a method thereof for confining harmful and dangerous radioactive materials for an extremely long period of time. Unlike the method of melting glass to trap radioactive materials,
Since the method of the present invention does not include the step of heating the radioactive material to a temperature of about 900° C. or higher, there is no risk that the radioactive material will volatilize and be released into the atmosphere. Furthermore, according to the present invention, Kr, I, Xe,
A method for fixing and stationary gaseous radioactive waste such as Ra can be provided. The object of the present invention is to have high chemical durability against corrosion by water, and have a sufficiently small diffusion coefficient of radioactive isotopes.
An object of the present invention is to provide a non-porous glass that functions to prevent radioactive materials such as nuclear waste from being dissipated into the atmosphere. The glass contains at least _SiO2
It is characterized by containing 75 mol% and having a radioactivity greater than 1 mc/cm ³ , preferably greater than 1 c/cm ³ . The radioactive substance in the glass of the present invention is at least 0.1 mol
%, usually at least 5%, preferably at least 5%.
It consists of oxides of 10 types of radioactive elements shown below. It is desirable that the glass of the present invention contains at least 82 mol% _SiO2 , preferably 89 mol% or more. In fact, the maximum amount of radioactive substances contained in non-porous glass is determined by the SiO ₂ concentration in said non-porous glass and B ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , zirconia, alkali metal oxides and the concentration and type of other components present in the non-porous glass such as GO ₂ and the concentration and type of radioactive material trapped in the non-porous glass and the porous structure of the porous glass preform. It can be sufficiently adjusted by the volume ratio and various methods of confining radioactive substances in the non-porous glass. The radioactive substances to be confined and immobilized in the glass base material of the present invention include radioactive elements that exist as natural and artificial isotopes as liquids, solids, or gases;
That is, carbon, rubidium, strontium, lanthanide, cobalt, cadmium, silver, zirconium, molybdenum, technetium, niobium, ruthenium, rhodium, palladium, tellurium, cesium, barium, francium, yttrium, radium, actinide, etc., which normally exist as oxides. Elemental and gaseous krypton, iodine, bromine,
Contains the elements xenon and radon. The present invention is particularly suitable for radioactive waste from nuclear reactors and the like. The present invention provides a glass container with a high confinement capacity, in particular an outer portion of the container containing at least 90 mol %, preferably 95 mol %.
% or more of silica and in which a radioactive substance is confined in the center. The high silica content in the outer part of the glass container significantly increases the chemical durability. The silica content in the center of the glass container is relatively low, at least
75 mol%, preferably 82 mol%, optimally 89 mol%. The present invention relates to a method of manufacturing a glass or a glass container having the above-mentioned composition. Broadly speaking, the present invention includes the steps of impregnating the pores of a porous glass preform with a radioactive substance, and drying if necessary.
heating the porous glass preform until the porous structure is destroyed to confine the radioactive substance in a chemically inert non-porous glass. Regarding. As mentioned above, radioactive isotopes exist as gases, liquids, or solids. Liquid isotopes are usually converted into compounds such as salts, and then dissolved to form a solution in the same way as solid isotopes. Hereinafter, the solution is treated separately from the gaseous isotope. Two embodiments of the invention are described for the solution case. The patent literature fully describes methods of manufacturing porous glass preforms. Porous glass preforms suitable for the method of the invention typically contain SiO ₂ as a major component. When practicing various embodiments of the invention, the concentration of SiO ₂ is at least 75 mol
%, preferably at least 82 mol %, particularly preferably at least 89 mol %, and preferably less than 1 mol % of alkali metal oxides. Glasses of this type are disclosed in the patent literature, for example US Pat. According to a first embodiment, a dopant consisting of a radioactive isotope present as a compound such as a salt, oxide, etc. is diffused into the pores of a porous glass preform, after which the dopant is diffused into the pores of the porous glass preform. The porous glass preform is removed from the additive solution and dried. When the additive-filled porous glass preform is sintered, the salts are decomposed into oxides and impregnated into the glass matrix. Since sintering is normally performed at a temperature much lower than the glass melting temperature, there is no risk of radioactive substances being volatilized and released into the atmosphere. The non-porous glass formed as described above has additives uniformly distributed throughout. According to a second embodiment, an additive solution containing a radioactive compound is diffused into the pores of a porous glass preform, after which said porous glass preform is removed from the additive solution and filled with water, methanol,
The porous glass preform is then soaked in one or more solvents such as ethanol, acetone, nitric acid, etc., after which a preferably thick and largely additive-free region is formed on the surface of the porous glass preform. , removed from the additive solution and dried.
As in the case of the first embodiment, the sintering process ensures that the central part contains the radioactive additive and the outer part contains at least
A non-porous glass containing silica of 90 mol %, preferably 95 mol % or more and substantially free of radioactive substances can be reliably formed. Both embodiments of the invention, detailed below, confine radioactive gas within a glass matrix.
According to a first embodiment, a porous glass preform is dried and then the radioactive gas concentration is trapped in said glass matrix such that the desired radioactive gas, i.e. radioactive waste, is dissolved in said glass matrix. Placed in the radioactive gas at a determined pressure, the pores of the porous glass preform are heated and sintered in the radioactive gas at a high temperature. According to a second embodiment, the porous glass preform is immersed in a solution containing one or more additives, preferably in salt form, prior to drying. Said additives may be selected to increase the surface area, ie increase the solubility of the radioactive gas in the glass, in other words reduce the transition temperature of the glass. The concentration of the additive in the glass may be appropriately selected as desired. After depositing the additives, the porous glass preform is dried and, if necessary, heated to decompose it, generally to an oxidized state. The porous glass preform is then placed in the radioactive gas or radioactive waste at a pressure determined by the radioactive gas concentration trapped within the glass so that the radioactive waste dissolves in the glass matrix. The pores of the preform are sintered by heating to high temperature in the radioactive gas. It is desirable for several reasons to vary the additive concentration and confine radioactive gases or radioactive waste in the porous glass preform prior to drying. If the additive is other radioactive waste, it is desirable to keep the additive concentration as low as possible near the surface of the porous glass preform to prevent leakage to the outside. Next, if the additive used increases the solubility of the radioactive gas in the pores of the porous glass preform, it will reduce the concentration of the radioactive gas dissolved near the surface of the porous glass preform and leak to the outside. In order to reduce the risk of
It is desirable to reduce the concentration of additives near the surface of the porous glass preform. Furthermore, if the additive lowers the transition temperature of the glass matrix and the concentration of the additive is varied from a minimum near the surface of the porous glass preform to a maximum in the center, the concentration of dissolved radioactive gases will decrease. There is a difference in concentration near the surface and in the center of the porous glass preform. In US Pat. No. 3,938,974, which relates to conventional fiber optics, the number of additives that can be used is limited because it requires increased light transmission and does not allow the use of additives that attenuate light. However, the immobilization of radioactive substances of the present invention is not subject to this type of limitation. Additives are compounds deposited within the porous glass. The compounds (elements or molecules in the case of gases) are trapped within the glass when the pores are destroyed, either as such or after being converted into a suitable oxide. In the case of metals, they are often introduced into the pores of porous glass preforms as liquid nitrates, and may even be precipitated as nitrate crystals. When heated, it decomposes into oxide crystals, which are further trapped in the silica structure when the pores of the porous glass preform are crushed. Of course, additives include radioactive substances, alkali metals, alkaline earth elements, boron, germanium, aluminum, titanium, lead, bismuth, phosphorus, rare earth element nitrates, carbonates, acetates, These include hydrates or anhydrides of phosphates, oxides, borates, arsenates, silicates, or mixtures thereof. The porous glass preform contains 75 mol % or more of silica and may be prepared by a method well known to those skilled in the art so as to form a porous glass having a desired shape, preferably cylindrical or rectangular parallelepiped. In the present invention, a cylindrical porous glass preform is prepared according to the method disclosed in US Patent Application No. 635,727 filed on November 26, 1975. To explain briefly,
Add silica, boron trioxide, and two alkali metal oxides (e.g. Na ₂ O and K ₂ O) to the molten glass.
It is mixed and added to form a long rod-shaped body. When properly heat-treated, the rods are formed into two phases: a silica-rich phase containing B ₂ O ₃ and alkali metal oxides and a silica-rich phase containing B ₂ O ₃ and alkali metal oxides in larger amounts compared to said phases. It is separated into a phase with a low silica concentration. The heat-treated rod is then immersed in a suitable leachate to decompose and remove the silica-poor phase. When the phase with a low silica concentration is removed and washed, it can be suitably used as a base material for encapsulating radioactive substances. A porous glass preform is obtained, characterized in that the content of SiO ₂ is greater than 90 mol %. In this case, the radioactive substance to be enclosed is a solid
Several treatments are performed depending on whether the liquid or gas is used. 1. When the radioactive substance to be encapsulated is solid or liquid When encapsulating solid or liquid radioactive substances including nuclear waste, the radioactive substance is usually obtained as a mixture of compounds such as hydrated salts of each substance to be encapsulated. . Typically, high-level radioactive waste primarily consists of the aqueous roughinate produced from the first cycle of the well-known Purex process, as well as various waste streams. The composition of radioactive waste can vary widely depending on the situation. Typical compositions are shown in the table. A solvent is added to the radioactive waste until substantially all components are dissolved in the solvent. Some processing plants extract individual components such as Cs and Sr from waste mixtures for specific purposes.

[Table] The terms "rare earth" and "lanthanide" are used here to refer to lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium,
Used interchangeably to refer to the elemental series consisting of gadolinium, terbium, dysprosium, holmium, erbium, thorium, ytterbium, and lutetium. When used in non-waste materials, radioactive elements occur singly or in groups, or as compounds such as salts. In either case, the radioactive material must be dissolved into a solution or melted. A rod-shaped porous glass substrate is immersed in an additive solution containing a radioactive substance for a sufficient time to diffuse the additive solution or filling liquid into the pores. The soaking time depends on the temperature of the filling liquid, the pore structure, and the dimensions of the porous glass matrix. After the filling liquid fills the holes with additives such as radioactive substances, various treatments are performed. According to one method, a porous glass preform is removed from the filling liquid and then the additive impregnated into the pores of said porous glass preform evaporates the solvent by chemical means, reducing the temperature. method or the like into a porous glass preform. If desired, the porous glass preform may be briefly washed to clean the surface. In some cases, the porous glass preform may be soaked for several hours in a cleaning solution, such as a solution that is relatively insoluble in additives. The porous glass preform is then dried, for example in a desiccator, vacuum chamber, etc., preferably at relatively low temperatures. This method results in a non-porous glass having a substantially uniform concentration of waste material upon completion of the drying and sintering steps described below. According to a second method, the porous glass preform is removed from the filling liquid and the additives begin to precipitate, after which the porous glass preform is immersed for several hours in a solution in which the solubility of the additives is moderate. .
This dipping step redissolves the additives into the solution, creating a thick skin on the outer surface of the porous glass preform. The additive is removed from the skin layer by immersing the porous glass preform in several solutions of varying additive solubility in order of decreasing solubility. After completion of the dipping step, the porous glass preform is dried as described above. This method results in a non-porous glass having a skin having a substantially low concentration of additives on the outer surface of the porous glass preform upon completion of the drying and sintering procedure described below. Due to the low concentration of additives in the skin of the porous glass preform, the skin protects the interior from chemical changes and reduces the rate at which radioactive substances that can adversely affect the external environment diffuse from the interior to the skin. cause delay. The drying and sintering process described includes holding the porous glass preform produced by either of the two methods described above in a vacuum at a low temperature for approximately one day, and then substantially drying it in a vacuum. The method includes a step of heating at a rate of 15° C./hr to a temperature higher than the decomposition temperature of the additive and about 100° C. lower than the transition temperature of the porous glass matrix not containing the additive. Here, by heating the porous glass preform to a sintering temperature under appropriate conditions, the redox state of the additive can be brought into a desired state. For example, heating a porous glass preform to the sintering temperature in a vacuum can bring the additives to a reduced state, and heating a porous glass preform to the sintering temperature in a hydrogen atmosphere can bring the additives to a highly reduced state. Alternatively, the additives can be brought to a suitable oxidation state by heating the porous glass preform to the sintering temperature in an oxygen atmosphere under a suitable pressure. Since many radioactive substances, such as acinitide, are hardly soluble in water in the reduced state, being able to change the redox state of the radioactive substance accordingly ensures that the resistance of the glass to external chemical influences is well adjusted. Since the redox state of the radioactive substance can be changed as appropriate, the time until the radioactive substance is dissipated to the outside can be sufficiently prolonged, and safety can be improved. After sintering at high temperature, it is cooled to ambient temperature, thereby forming a non-porous glass that completely encapsulates and immobilizes the radioactive material within the glass structure. In another embodiment, the present invention provides a method for storing and immobilizing an aqueous solution of boric acid contaminated with radioactivity during use as a heat transfer medium in a pressurized water nuclear reactor. In addition to inert gas impurities such as F, the boric acid aqueous solution contaminated with radioactivity contains Co, Cs, Mn, Cr, Sr, and Zn.
Contains various radioactive impurities such as Currently, the aqueous boric acid solution contaminated with radioactivity is sealed and fixed in a cement container and buried several feet (several meters) underground. However, this treatment method is extremely unsatisfactory since the solubility of boric acid at room temperature is approximately 5% and the capacity of the cement container is therefore low. Moreover, cement is not extremely soluble and will leach into the ground water table. Therefore, it is clear that even the treatment of low-level nuclear fuel waste has harmful effects on humans and the environment. The method of the present invention provides a method for filling a porous glass preform with an aqueous boric acid solution contaminated with such low levels of radioactivity. This filling process is carried out at a temperature that allows several times the amount to be filled compared to when fixing in a cement container. For example 100℃
The solubility of boric acid in water is about 30% by weight, or about 6 times the solubility in water at room temperature when fixed in a cement container. The non-porous glass of this example is characterized in that it encapsulates and fixes a boric acid aqueous solution contaminated with low-level radioactivity emitted from a pressurized water reactor, and the boric acid aqueous solution contaminated with radioactivity is oxidized into boron. Oxides of radioactive contaminants including cobalt and chromium are fixed in the glass matrix. strontium,
Other radioactive contaminants such as cesium, manganese or zinc are also present as oxides. Radioactive contaminants are usually contained as 1% by weight final full oxide. However, in pressurized water reactors, the boric acid aqueous solution can contain relatively large amounts of radioactive contaminants, which is a problem due to leakage. In the experimental example, the additive solution contains only cesium nitrate to briefly verify the effects of the additive and the porous glass. Cesium is chosen because of its high concentration in the waste material and because it is an alkali metal, its diffusion coefficient into glass is greater than other elements except rubidium, which is present in low concentrations. It is expressed in moles below. Cesium has the disadvantage of high vapor pressure at the temperatures required to melt glass, which can be avoided by the method according to the invention. Therefore, of all the radioactive isotopes in nuclear reactor waste, Cs poses the most problems when sealed in glass, and is likely to contaminate the environment at the earliest stage after being sealed and fixed. Therefore, the method of immobilizing cesium on a glass base material may solve the problems associated with the encapsulation and immobilization of other radioactive isotopes. Therefore, using the method of immobilizing cesium, other radioactive isotopes can also be immobilized without difficulty. In the following examples and cases, the molecular "filling" process of the examples is carried out. In the case of the experimental example,
The filling liquid contains SrNO ₃ which, like CsNO ₃ , is present in hazardous waste liquids. The example solution simulates low-level radioactive waste in boric acid.
Each solution in the experimental examples is similar to untreated radioactive waste actually discharged from a nuclear reactor. Main ingredients are used. Experimental example: Porous glass preform contains 60.2mol of SiO ₂
%, _{B2O3 32.8mol} %, _Na2O3.6mol %, _K2O3.4mol
% glass composition is placed in a platinum crucible and heated to approximately 1400℃.
a step of homogenizing the molten glass using a platinum stirrer, a step of elongating the molten glass using a glass bait, and a step of elongating the elongated glass to a diameter. 7
A step of cutting the glass rod into a cylinder or rod with a length of 30.5 cm, a step of heat treating the cut glass rod at 550° C. for 1.5 to 2 hours, and a step of cooling the heat treated glass rod. , washing the cooled glass rod in a 2.5% aqueous solution of HF for 60 seconds, and washing the washed glass rod in 3NHCl.
and 15 to 20% of NH ₄ Cl, and washing the leached glass rod with water. The formed porous glass preform is characterized by connected pore structure and contains 95mol% _SiO2 , 5mol _{% B2O3}
%, and has a component composition of less than 0.1 mol% of alkali metal oxides. The rod-shaped porous glass preform formed as described above is then filled with a so-called "fill" containing waste material.
The concentration of liquid, in this case _CsNO3 , is 65% by weight
Add the filling solution to the _CsNO3 aqueous solution for at least 3 hours.
Maintain and soak at 105℃. For the experimental example,
The filling liquid of CsNO ₃ is exchanged with a mixture of cold water and methanol for several minutes until precipitation of CsNO ₃ occurs within the porous structure, and then the glass rod is immersed in methanol for 3 hours. In the case of the experimental example, the fill liquid is replaced with a mixture of cold water and methanol for a period of time until precipitation of CsNO ₃ occurs, ie less than 2 minutes. The glass rod is then soaked in water for about 3 hours at 2°C and then in methanol for an additional at least 3 hours at 0°C. Through these two immersion treatments, a skin layer with a thickness of about 1 mm is formed on the cylindrical surface of the glass rod. CsNO ₃ is not present in the cortical layer. In both the experimental examples, after being kept at a temperature of 0°C in a vacuum of about 0.1 mmHg for 24 hours, the glass rod-shaped body was freed of solvent, water, and methanol, and the additive, that is, cesium nitrate, was decomposed into oxides. The material is dried in a vacuum while gradually increasing the temperature from 0°C to 625°C. The heating rate is 15°C/hr. It is further heated in an oxygen atmosphere to 840° C., which is the sintering temperature of the glass rod or rod-shaped porous glass preform. Once the porous structure is destroyed, the encapsulation is considered complete and the sintered non-porous glass rod is removed from the furnace and returned to ambient temperature. Thereafter, the cesium concentration and the refractive index associated with the cesium concentration of the second non-porous glass rod-shaped body formed in Experimental Example 2 were measured. In the experimental example, the composition of the center of each glass rod-shaped body formed by SiO ₂ 92.1 mol%, B ₂ O ₃ 4.9 mol%, Cs ₂ O
It was approximately 3 mol% (corresponding to a refractive index of 1.487), and a trace amount of alkali metal oxide. In the experimental example,
The above composition was substantially maintained up to a depth of more than 1 mm below the surface. As a result of analyzing the non-porous glass rod-shaped body formed in the experimental example, it was found that the thickness was 1 mm.
The refractive index of the cortical layer was found to be 1.458. This refractive index indicates that there is no measurable Cs ² O additive present in the cortical region. The figure was obtained from an experimental example compared to a glass that seals and fixes radioactive waste obtained by molten glass technology from the Battelle Pacific Northwest Laboratory in Richland, Washington State, USA. It shows the weight fraction of waste material released into the environment after 20000 years of storage of sintered non-porous glass. In order to obtain an estimate of the diffusivity of cesium ions so that the amount of radioactive material dissipated as a function of time can be estimated, two non-porous glasses formed by the above-mentioned experimental example and Battel Pacific Northwest were used. The electrical conductivity of the glasses obtained in the laboratory, ie by the melting process, was measured in each case. The measurement results are shown in the table below.

[Table] (1) These values were obtained from the Stokes-Einstein relationship and are only estimated values. (2) The data regarding the experimental examples are only for the cortical layer. The values in the center are the same as in the experimental example. (3) Battel-Pacific Northwest Research Institute, Litchiland, Washington; This glass was less than half the cesium concentration of the additive encapsulated in the glass formed by the experimental example. In the table, the diffusivity is estimated from the conductivity using the Stokes-Einstein relation. Looking at the numerical values in the table, when compared with glass formed by the melting method at Battel Pacific Northwest Research Institute at room temperature,
The diffusivity of the non-porous glass in the experimental example is several orders of magnitude smaller than that of the Battelle glass, even though the non-porous glass in the experimental example contains more than twice as much additive as the Battelle glass. The theoretical loss weight, that is, the most pessimistically estimated theoretical loss weight, after 20,000 years of contact exposure to a substance that does not accumulate a complete sink, that is, dissipated molecules or atoms at the interface, is formed by the method of the experimental example. The storage temperature coefficients for non-porous glass rods obtained from the values in the table are shown in the figure. Experimental example A rod-shaped porous glass preform, that is, a glass rod-shaped body prepared as shown in the experimental example, has a diameter of 100.
Contains Sr( _NO3 ) ₂ at a rate of 95g per ml of water60
immersed in a solution that is maintained at °C. The glass rod was immersed in this solution for 4 hours, then removed and placed in isopropanol at room temperature.
Precipitation of _SrNO3 progresses slowly within the porous structure,
It took 2 to 3 hours to complete. Next, the glass rod was heated to 0°C to remove SrNO ₃ from the cortical layer.
It was immersed in a mixture of 66% ethanol and 34% water for 5 hours. Finally, the glass rod was immersed in a mixture of 90% ethanol and 10% water at room temperature, and then into isopropanol at room temperature. After that, the glass rod-like body is 0 as in the experimental example.
The subsequent steps are performed by maintaining the product in vacuum at ℃ for 24 hours, followed by drying and further sintering. Strontium was contained in the glass structure at the center of the glass rod-shaped body taken out of the furnace after sintering, but on the other hand, almost no strontium was contained in the skin layer. EXPERIMENTAL EXAMPLE A rod-shaped porous glass preform, i.e., a glass rod, prepared as shown in the experimental example, is made of H ₃ BO ₃
25g, Fe(NO ₃ ) ₃・9H ₂ O 0.27g, Cs
(NO ₃ ) 0.27g, Sr(NO ₃ ) ₂ 0.27g, Co
(NO ₃ ) ₂・6H ₂ O, 0.27 g, Cr(NO ₃ ) ₃・9H ₂ O
0.27 g, 80 ml of water, and 1 ml of HNO ₃ , i.e.
It is immersed for 3 hours in a solution at 100°C containing only 13.4 mol%. The glass rods are removed from the mixture and then placed in water at 0°C for 30 minutes and dried in vacuum at 0°C for 24 hours. The glass rods are then heated to 625°C at a rate of 15°C/hr in vacuum to remove residual solution and decompose metal nitrates, and further heated to 50°C in vacuum to destroy pores and sinter. /hr to 850℃. The sintered glass rod contains oxides of Cs, Sr, Fe, Co and Cr as part of the matrix and
It is a non-porous glass containing SiO ₂ and B ₂ O ₃ . The water soaking step that follows the soaking or filling step reduces the additive concentration in the skin of the glass rod. The glass rod may be immersed in methyl acetate or acetone after being removed from the filling liquid to form a skin layer with a low additive concentration. However, glass rods made by immersing them in methyl acetate or acetone tend to crack longitudinally during the drying and sintering process;
Not harmful with respect to quiescence. Experimental example: 12.9 g of Sr(NO ₃ ) ₂ , 18 g of Rb(NO ₃ ), Ba
(NO ₃ ) ₂ 15.9g, Zr(NO ₃ ) ₄・5H ₂ O 104.1g,
153.6g of Fe(NO ₃ ) ₃・9H ₂ O, Co(NO ₃ ) ₂・
4.2 g of 6H ₂ O, 21.3 g of Ni(NO ₃ ) ₂ 6H ₂ O, Cs
(NO ₃ ) 12.3g, rare earth nitrate mixture 89.4g,
and a fill solution consisting of sufficient water to decompose these metal additives at about 100°C. A rod-shaped porous glass preform or glass rod prepared as shown in the experimental example was immersed in the filling liquid for 3 hours. The glass rods were then removed from the filling liquid and placed in 3NHNO ₃ solution at 0° C. for 10 minutes. The glass rods were then placed in acetone at 0° C. for 2 hours and placed in a drying chamber at 0° C. equipped with a vacuum pump system running for 24 hours to remove the solvent. Afterwards, the glass rod-shaped body was heated at 15℃/hr in a vacuum.
It was heated to 625℃ at a rate of . The glass rod is
It is maintained in vacuum at 625°C for 24 hours and then slowly heated to 840°C in vacuum to strongly reduce the waste additives impregnated into the porous structure. The glass rods are sintered at around 840°C to yield a solid, non-porous glass containing waste material as part of the matrix. Experimental example A filling liquid containing 10 main components obtained from a typical radioactive waste labeled PW8a is used here. The relative concentration of each of the 10 components is expressed as three times that of the waste liquid component. The filling liquid is Fe
(NO ₃ ) ₃・9H ₂ O 148.8g, UO ₂ (NO ₃ ) ₂・6H ₂ O
21.3g, NaNO ₃ 33.6g, Zr(NO ₃ ) ₄・5H ₂ O
18.6g, 19.8g of Nd( _NO3 ) ₃・_5H2O , Ce
(NO ₃ ) ₃・6H ₂ O 9.0 g, La (NO ₃ ) ₃・6H ₂ O 4.2
g, 4.2 g of CsNO ₃ , 2.4 g of Sr(NO ₃ ) ₂ , Ba
It contains 3.0 g of (NO ₃ ) ₂ , 264.9 g of HNO ₃ , and only 150 ml of water. Sufficient water and nitric acid were added to keep the metal nitrates dissolved in the fill liquid. The filling liquid was prepared by adding the components one by one at different temperatures. The final temperature at this time was 99°C. Six rod-shaped porous glass preforms, i.e., glass rods, prepared as shown in Experimental Example, were immersed in a filling solution at 99°C for 3 hours and heated at 20°C for 5 seconds.
℃ water and then placed in a desiccator maintained at 20°C for 16 hours. Therefore, since no skin layer is formed on the glass rod-like body, it is hereinafter referred to as a skinless glass rod-like body. The three skinless glass rods are taken out of the desiccator and then subjected to a dipping process to form a skin layer near the surface (hereinafter referred to as a skin glass rod) with a lower concentration of additives, ie, waste materials, than the center. 8 wt% Uo ₂ (NO ₃ ) ₂ ·6H ₂ O and 4 wt % Ce(NO ₃ ) ₂ ·6H ₂ O and 2 wt % La
(NO ₃ ) 30 in isopropanol containing _{3.5H 2} O
A 30 minute immersion step was carried out, followed by a 30 minute immersion step in another solution consisting of 80% chloroform and 20% isopropanol. The skinned glass rods were then dried in a vacuum at 0° C. with a pressure of less than 1 mmHg for 24 hours, and then placed in an oven at room temperature with the remaining three skinless glass rods to remove the solvent. Furthermore, the additives, i.e., metal nitrates, are decomposed into metal oxides by 15°C in a vacuum.
It was heated to 625°C at a rate of °C/hr. They were divided into three groups, each containing one non-cortical glass rod and one cortical glass rod. Each set has a different environment, namely: (1) Atmosphere containing 95% N ₂ and 5% H ₂ at 1 atm (strong reducing condition) (2) Vacuum atmosphere below 1 mmHg (moderate reducing condition) (3) It was heated at a rate of 50°C/hr in an air atmosphere of 1 atm (oxidizing conditions).
At about 860°C, the sintered pores of the glass rod were destroyed. Analysis of three sets of sintered non-porous glass rods revealed that the metal oxides were in appropriately different oxidation states. It will be clear that, according to the invention, it is possible to provide a chemically inert, non-porous glass capable of enclosing and immobilizing radioactive substances, such as akinitide, in a low oxidation state for very long periods of time, for example centuries. 2 When the radioactive substance to be encapsulated is a gas The above-described embodiments of the present invention are applied to a method of encapsulating and fixing a radioactive gas in glass. The first method is shown in Experimental Example. In this case, a rod-shaped porous glass, i.e., a glass rod, is partially dried in a vacuum at 0° C. for about 24 hours, and then 50° C. above the transition temperature of the host, additive-free, unsintered glass. Dry by slow heating in vacuum to a drying temperature between 150°C and 150°C lower. This drying temperature is approximately
It is 625℃. At 625°C one or more radioactive gases are introduced into a sealed chamber in which a glass rod is placed. The temperature is maintained at 625°C for about 24 hours, and then the glass rod is sintered in an atmosphere of radioactive gas at a rate of about 50°C/hr to 835°C to 835°C, where the gas dissolved in the glass matrix is sintered. Heated to 900℃.
The heating rate and holding temperature may be changed as desired. Rapid heating may damage the glass rod-like body, but this does not adversely affect the encapsulation and immobilization of radioactive gas within the glass base material. In the second method, a porous glass rod is immersed in a solution containing one or more additives. If desired, the additives may be selected to increase the solubility of the radioactive gas within the glass rod. After the additive has been diffused into the pores of the glass rod, the glass rod is removed from the additive solution and immersed in an additive-free solvent. If desired, the concentration of additives in the pores of the glass rod may be varied in a variety of ways. First, if there is no change in the additive concentration within the glass rod, the solvent solution is selected so that the additive is evenly precipitated within the pores of the glass rod. The solvent is then removed and the glass rod is dried. If it is then desired to form an additive-free skin layer on the surface of the glass rod (see example experiment), the additive is precipitated in the same manner as described above, but prior to the drying step, the glass rod is The cortical additives are transferred into one or more other solvents to dissolve and remove them. If it is then desired to create a gradient in additive concentration, the glass rod is first immersed in a solvent which serves to prevent the additive from precipitating, but to allow it to diffuse out of the pores. The glass rod is then transferred to one or more other solvents that precipitate the additives and then dried. If desired, the drying step may begin at a temperature of 0° C. in a vacuum. The glass rod is then slowly placed in vacuum, i.e. at a rate of 15°C/hr, at 625°C to remove residual solvent and decompose the additives.
heated up to. At 625°C one or more radioactive gases are introduced into the heating chamber in which the glass rods are placed and the temperature is maintained at 625°C for about 24 hours. Further, the glass rod-shaped body is heated to 835°C to 900°C so that sintering occurs at a rate of 50°C/hr and the radioactive gas dissolved in the glass matrix is encapsulated. In the case of the third method, the concentration of the additive, ie, the radioactive gas, impregnated into the glass rod can be varied depending on the distance from the axis. In this case, the rod-shaped porous glass, ie the glass rod, is impregnated with a substance capable of lowering the transition temperature, such as potassium nitrate. After the additive has completely diffused into the pores of the glass rod, the additive is precipitated into the pores by cooling the glass rod or by introducing it into a solvent in which the additive has very low solubility. Next, the glass rod-shaped body has a solubility of the additive of 5 to remove the additive from the cortical layer.
% to 10% of the solvent. After drying the solvent, the additive concentration inside the glass rod is higher inside and lower in the cortical layer. Therefore, the sintering temperature of the glass rod-shaped body is high in the skin layer and low in the interior. A glass rod-shaped body has a temperature of about 24°C in a vacuum at 0°C.
It takes time to dry. The glass rod is then heated in vacuum to 600°C at a rate of 15°C/hr. At 600°C one or more radioactive gases are introduced into a heating chamber in which a glass rod is placed. The temperature is slowly increased until the interior of the porous glass rod is sintered, and is maintained at a temperature at which the skin of the glass rod is sintered. The radioactive gas is then removed from around the glass rod and the temperature is raised until the skin is sintered. According to this method, dissolved radioactive gas is sealed inside the glass rod-shaped body, while the cortical layer contains almost no dissolved radioactive gas. EXPERIMENTAL EXAMPLE A rod-shaped porous glass preform or glass rod prepared as shown in the experimental example was immersed in methanol at ambient temperature for about 3 hours. The glass rod was then transferred to a drying room maintained at 0° C. and equipped with a vacuum pump for 24 hours to dry. The glass rods were heated to 650°C at a rate of 50°C/hr to ensure complete drying. Kr gas at 650°C and 1 atm was introduced into the heating chamber in which the glass rod was placed. Furthermore, the glass rod-shaped body was placed in a Kr atmosphere at 650°C.
It was maintained for a time and then heated to 880° C. to achieve sintering in a Kr atmosphere and then to encapsulate the dissolved Kr gas within the glass matrix. Experimental example The process of the experimental example is 1/10 instead of krypton.
The steps were repeated except that the iodine pellets were boiled to create a bar iodine gas atmosphere and the iodine gas was introduced into the heating chamber at 650°C. The glass rods were held in the 650° C. iodine atmosphere for 18 hours to sinter the glass rods and, in turn, melt the non-porous glass into the glass matrix, as evidenced by the pink coloration of the non-porous glass. It was heated to 880°C to enclose iodine gas. Experimental Example This experimental example involves encapsulating both a solid additive and a gaseous additive dissolved in a glass matrix. The rod-shaped porous glass preform, that is, the glass rod-shaped body created as shown in the experimental example, is
It was immersed in a 67 wt% _CsNO3 solution at 105°C for 4 hours. Further, the glass rod-like body is transferred and immersed in pure water at 0° C. to precipitate cesium nitrate in the holes. It took 30 seconds for complete precipitation. The glass rod-shaped body was left in water at 0° C. for 3 hours to change the concentration of cesium nitrate in the pores, thereby forming a skin layer substantially free of cesium nitrate near the surface. The glass rod-shaped body was transferred to methanol at 0° C. and immersed for 3 hours to further reduce the cesium nitrate concentration in the cortex. After this value, the glass rod was inserted into a vacuum chamber at 0° C. and the drying process was started and continued for 24 hours. The glass rods were then heated to 625°C at a rate of 15°C/hr to complete the drying process and decompose the cesium nitrate to cesium oxide. Further, the glass rod was kept in a vacuum at 625°C for 24 hours. Krypton gas was then introduced into the vacuum chamber until the pressure reached 1 atmosphere. The glass rod-shaped body was kept in a krypton atmosphere at 625℃ for another 24 hours, and then heated to the sintering temperature at a rate of 50℃/hr to encapsulate and fix the krypton dissolved in the glass base material like Cs. It was done. According to the present invention, radioactive materials, especially radioactive waste emitted from nuclear reactors, can be suitably encapsulated, so that these radioactive materials can be used beneficially without endangering human life on the ground. Some useful applications are listed below. By sintering the porous glass, the radioactive element is completely encapsulated within the glass matrix. Since these radioactive elements are chemically bonded and immobilized within the glass container, radioactive waste streams from highly dangerous nuclear reactors can be safely contained for extremely long periods of time. The new glass container can be moved without risk of leaking radioactive isotopes into the environment. These glass containers can be stored for long periods in underground storage rooms. Preferably, the storage chamber is located at a depth of 1000 feet (approximately 300 meters) or more. Some, but not all, radioactive isotopes resulting from radioactive waste can be put to beneficial use in addition to being stored. For example, by killing microorganisms such as bacteria and viruses, it can be used to sterilize food and medicine, and can also be used in the fields of medicine, industry, education, and research. When used for disinfection purposes, glass containers containing selected isotopes such as radioactive cesium, strontium, and cobalt can be used to store food or recover nutrients from sewage sludge as food. It is. These examples include preventing contamination of food with radioactive isotopes;
In addition, it is necessary to develop a container suitable for preventing radiation damage that may occur when the contaminated food is ingested, so it has not yet become commercially popular. According to the present invention, by completely encapsulating the radioactive material as described above, food can be sterilized and sterilized using the radioactive material released in large quantities from the nuclear reactor. According to the present invention, radioactive waste can be completely enclosed in a glass container, so a radiation source is required for quality control equipment that detects damage in materials by ionization, sterilization, patient irradiation, or gamma ray irradiation. It can be used in medical, industrial, educational and research equipment.

[Brief explanation of the drawing]

The figure shows the relationship between weight fraction, storage temperature and concentration of glass rods according to the invention.

Claims (1)

[Scope of Claims] 1. A non-porous glass in which a radioactive substance is encapsulated and immobilized in a glass matrix, which (a) contains at least 75 mol% SiO ₂ , (b) contains 1 mc/cm ³ or more of SiO 2 . It has radioactivity, (c) it has high chemical durability against aqueous solutions, and (d) the oxide in which the radioactive substance is chemically contained and fixed in the silica structure leaks out at ambient temperature. Non-porous glass is characterized by being able to prevent this for an extremely long time. 2 (i) The cortical layer contains at least 90 mol % of SiO ₂ and is substantially free of radioactive substances, and (ii) The interior contains at least 75 mol % of SiO ₂ and a radioactive substance sealed and fixed. Non-porous glass according to claim 1. 3. In a method for storing radioactive nuclear waste for a long period of time, (a) the pores of the connected porous structure of the porous glass preform are decomposed into oxides at a temperature below the sintering temperature of the porous glass preform; (b) precipitating the radioactive material into the pores of the connected porous structure of the porous glass preform; (c) impregnating the porous glass preform with a solution of radioactive nuclear waste containing radioactive material; (d) converting the radioactive material to an oxide at a temperature below the sintering temperature of the porous glass preform; and (e) destroying the pores of the interconnected porous structure of the porous glass preform. (f) heating the porous glass preform to a sintering temperature so that the radioactive substance existing as an oxide is encapsulated and fixed in the silica structure; (f) encapsulating and fixing the radioactive substance as an oxide in the silica structure; and obtaining a non-porous glass that prevents leakage to the outside at ambient temperature for an extremely long period of time. 4 (i) A porous glass preform with radioactive material precipitated in the pores is placed in a solution in which the radioactive material has a lower solubility than the solution in step (a) to form a skin layer that does not substantially contain radioactive material. (ii) obtaining a non-porous glass having a skin layer substantially free of radioactive substances and an interior in which radioactive substances as oxides are sealed and fixed in the silica structure; The method according to claim 3, comprising: