A borosilicate glass curing agent for treating intermediate and low-level radioactive waste liquids and its application method

Abstract

A borosilicate glass curing agent for treating medium- and low-level radioactive waste liquids and its application method are disclosed. The agent's composition range is: SiO2 45–65%, B2O3 12–25%, Al2O3 0.6–20%, ZnO 0.6–6.5%, ZrO2 0.6–2.5%, RE2O3 0.6–6.5%, and MO 0.6–12, wherein RE2O3 (RE is one or more of La, Nd, and Y) and M is one or more of Mg, Ca, Sr, and Ba. The prepared cured glass contains 20–30% Na2O by mass, and the cured glass product satisfies the following molar ratios: O / (Si+B+Al) 2.0–2.5 and (2ΣM+Na) / (Si+B+Al) 0.5–1.0. The method of use is to weigh and mix the additives and sodium oxide raw materials according to the formula ratio, melt, pour and anneal in an electric melting furnace to obtain high sodium curing glass. This product meets the requirements of curing glass production process, and the process parameters such as viscosity and conductivity are moderate, making it suitable for curing treatment of high sodium medium and low radioactive waste liquid.

Description

Technical Field

[0001] This invention pertains to methods for treating intermediate and low-level radioactive nuclear waste, and relates to a borosilicate curing glass additive with high sodium oxide tolerance and its application method. It is applicable to the curing treatment of high-sodium intermediate and low-level radioactive nuclear waste discharged in the nuclear industry and other fields. Background Technology

[0002] Nuclear power generation produces no air pollution, making it a clean, efficient, and practical energy source. However, the radioactive waste generated during the nuclear fuel cycle is highly toxic and causes significant damage to the ecological environment, making its safe disposal a focus of attention both domestically and internationally. Based on their radioactivity levels, nuclear waste is categorized into high-level, intermediate-level, and low-level radioactive waste. Intermediate- and low-level radioactive liquid waste originates from the three stages of the nuclear fuel cycle (front-end, mid-end or operational, and back-end), accounting for the largest proportion, reaching 97%. Vitrification technology is currently a widely used and feasible method internationally for treating and disposing of intermediate- and low-level radioactive liquid waste. By co-melting intermediate- and low-level radioactive liquid waste with basic glass raw materials to form a glass body, atomic-scale solidification of the waste can be achieved, thereby preventing the migration of radionuclides into the external environment within the glass-solidified body's disposal lifespan.

[0003] Currently, the United States, South Korea, Italy, and Russia all employ vitrification for the treatment of low- and intermediate-level radioactive waste liquids and plan to carry out geological disposal. my country's nuclear waste reprocessing plants urgently need to dispose of solidified acidic and alkaline low- and intermediate-level radioactive vapor residues, which mainly contain UO2(NO3)2 and NaNO3, with NaNO3 accounting for over 99% of the total mass. Research on formulations for solidifying low- and intermediate-level radioactive waste liquids primarily focuses on solidifying high-percentage sodium oxide. Sodium oxide is a highly reactive alkali metal oxide; a large amount of sodium oxide in the vitrified body will inevitably affect its chemical stability. Since the storage of vitrified low- and intermediate-level radioactive waste liquids needs to be maintained for hundreds of years, high requirements are placed on the chemical stability of the solidified glass formulation containing a high percentage of sodium oxide.

[0004] Borosilicate glass curing substrates possess advantages such as good thermodynamic stability, good chemical stability, low radionuclide leaching rate, and small coefficient of thermal expansion. Therefore, borosilicate glass is the preferred curing substrate in large-scale glass curing facilities abroad. Chinese Patent 200980153530.7 discloses an aluminum borosilicate curing glass for treating moderately radioactive waste liquid, in which the highest percentage (by mass) of sodium oxide in the prepared glass curing body is only 15%. References Liu Lijun et al., Nuclear Chemistry and Radiochemistry, 2014, Vol.36, No.3:163-168, disclose a high-sulfur, high-sodium borosilicate curing glass formulation, in which the sodium oxide content in the base glass is 5.21%, and the sodium oxide content in the source term is 45.103%. Based on a source term inclusion rate of 16%, the total sodium oxide content in this curing glass formulation is only 12.37%.

[0005] Given the extremely high cost of low-quality treatment of cured glass, it is necessary to improve the sodium oxide tolerance. Therefore, it is essential to develop a cured glass additive with a high sodium oxide tolerance, chemical stability of the cured product that meets the requirements of geological treatment conditions, and suitability for continuous melting production. Summary of the Invention

[0006] To address the requirement for containing high sodium oxide content in the solidification and disposal of existing low- and intermediate-level radioactive waste liquids, a borosilicate curing glass additive with high sodium oxide content and its application method are proposed. The prepared high-sodium cured glass exhibits good glass-forming properties, high chemical stability, and is suitable for continuous solidification treatment of low- and intermediate-level radioactive waste.

[0007] The technical solution of the present invention is as follows:

[0008] The oxide mass percentage composition range of the borosilicate curing glass additive used for curing Na2O is as follows:

[0009]

[0010] Among them, RE2O3 (RE is one or more of La, Nd, and Y) and M is one or more of Mg, Ca, Sr, and Ba.

[0011] The curing of high sodium oxide content glass products using the above-mentioned curing glass additives has the following mass percentage based on the total mass of the cured glass:

[0012]

[0013] Among them, RE2O3 (RE is one or more of La, Nd, and Y), M is one or more of Mg, Ca, Sr, and Ba, and satisfies that the molar ratio of O / (Si+B+Al) is 2.0 to 2.5 and the molar ratio of (2ΣM+Na) / (Si+B+Al) is 0.5 to 1.0.

[0014] The present invention also provides a method for using the above-mentioned borosilicate curing glass additive containing high sodium oxide, comprising the following steps:

[0015] (1) Weigh the raw materials according to the mass percentage of glass additives and sodium oxide, and mix them evenly to obtain a mixture;

[0016] (2) Put the mixture into a crucible and melt it in a furnace at a temperature of 1150-1200℃. Clarify for 1-3 hours to obtain a clear and uniform glass melt.

[0017] (3) The clear and uniform glass melt is poured into a stainless steel mold preheated to 350-450°C and then transferred to an annealing furnace preheated to 450-500°C.

[0018] (4) Keep warm in an annealing furnace for 1 to 5 hours, then cool to room temperature to obtain high borosilicate cured glass.

[0019] In the above preparation method, when weighing the raw materials according to the glass composition and mass percentage in step (1), B2O3 comes from one or more of B2O3 and boric acid; Al2O3 comes from one or more of Al(OH)3, aluminum carbonate, and aluminum nitrate; Na2O comes from one or more of sodium carbonate and nitrate; and MO comes from one or more of alkaline earth metal carbonate and nitrate.

[0020] The present invention will be further described below. The present invention requires the molar ratio of O / (Si+B+Al) to be controlled at 2.0–2.5, and the molar ratio of (2ΣM+Na) / (Si+B+Al) to be 0.5–1.0. The prepared cured glass, after casting and annealing, exhibits an amorphous glass morphology. The main network components in the glass are silicon, boron, and aluminum. When the molar ratios of O / (Si+B+Al) and (2ΣM+Na) / (Si+B+Al) are high, the glass network is insufficient, leading to easy crystallization and reduced chemical stability. Conversely, when the molar ratios are low, the glass modifiers are insufficient, also resulting in phase separation and crystallization.

[0021] Small amounts of ZrO2 participate in the glass network, which is beneficial to improving the chemical stability of the glass. However, if the amount exceeds 2%, it easily leads to crystal nucleation, crystallization, and a decrease in the glass-forming properties. Rare earth oxides such as lanthanum oxide, neodymium oxide, and yttrium oxide can increase the thermal transition temperature of glass, improve its glass-forming properties, and increase its viscosity. Alkali earth metals, as modifiers for glass, can regulate the coordination number, conductivity, and viscosity of the glass.

[0022] The beneficial effects of this invention are as follows:

[0023] The glass additive provided by this invention can contain a high percentage of sodium oxide, resulting in a transparent, crystal-free cured glass with excellent chemical stability, meeting the chemical stability requirements of the cured body in nuclear industry standard EJ1186-2005. Furthermore, the viscosity and conductivity of the cured glass are suitable for the curing process in continuous melting furnaces using Joule ceramic electric melting furnaces, and it is suitable for the curing treatment of medium- and low-level radioactive waste liquids with high sodium content. Attached Figure Description

[0024] Figure 1 This is a graph showing the element leaching rate of the 28-day chemical stability of six embodiments of the present invention. Detailed Implementation

[0025] The component mass percentages of the high-sodium borosilicate cured glass product for treating medium- and low-level radioactive waste liquid provided in the examples are as follows:

[0026]

[0027]

[0028] Among them, RE2O3 (RE is one or more of La, Nd, and Y), M is one or more of Mg, Ca, Sr, and Ba, and the molar ratio of O / (Si+B+Al) is 2.0 to 2.5, and the molar ratio of (2ΣM+Na) / (Si+B+Al) is 0.5 to 1.0.

[0029] The method of using the glass additive containing high sodium oxide in the above embodiment includes the following steps:

[0030] (1) Weigh the raw materials according to the glass composition and mass percentage, and mix them evenly to obtain a mixture;

[0031] (2) Put the mixture into a crucible and melt it in a furnace at a temperature of 1150-1200℃ depending on the composition and mass percentage. Clarify for 1-3 hours to obtain a clear and uniform glass melt.

[0032] (3) The clear and uniform glass melt is poured into a stainless steel mold preheated to 350-450°C and then quickly transferred to an annealing furnace preheated to 450-500°C.

[0033] (4) Keep warm in an annealing furnace for 1 to 5 hours, and then cool to room temperature at a rate of 1°C / min to obtain the borosilicate cured glass.

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] Table 1 shows the composition of the cured glass products, and the molar ratios of O / (Si+B+Al) and (2ΣM+Na) / (Si+B+Al) for six embodiments of the present invention:

[0036] Table 1

[0037]

[0038]

[0039] Example 1:

[0040] According to the mass percentage composition of oxides in the formulation of Example 1 in Table 1, weigh out 44 g of sodium carbonate, 42 g of silicon dioxide, 17.7 g of boron trioxide, 4 g of aluminum oxide, 3 g of zinc oxide, 1 g of zirconium oxide, 1 g of lanthanum oxide, 1 g of neodymium oxide, 2 g of yttrium oxide, 4 g of light magnesium oxide, and 1.29 g of barium carbonate. Mix them evenly to obtain a mixture. Place the mixture into a silicon dioxide crucible and melt it in a furnace at 1200°C. Clarify for 1 hour to obtain a clear and homogeneous glass melt. Pour the clear and homogeneous glass melt into a stainless steel mold preheated to 390°C and shape it. Then quickly transfer it to an annealing furnace preheated to 500°C. Hold it in the annealing furnace for 2.5 hours to relieve stress, and then cool it to room temperature at a rate of 1°C / min to obtain high-sodium borosilicate glass for solidification treatment of low-to-medium radioactive waste. The high-temperature viscosity of the glass at 1150°C was measured to be 23 Poise using an Orton RSV-16RT high-temperature rotational viscometer. The resistivity was tested according to the method provided in GB / T 10581-2006 "Test Procedure for Resistance and Resistivity of Insulating Materials at High Temperatures", and the conductivity at 1150℃ was calculated to be 0.56 S / cm. According to standard EJ 1186-2005 "Characteristic Identification of Radioactive Waste Bodies and Waste Packages", the normalized elemental leaching rates after static immersion in deionized water at 90℃±1℃ for 28 days are shown in the figure. The leaching rate of each single element is less than 0.2 g / m³. 2 Its chemical stability, viscosity, conductivity, and other process parameters are all suitable for the continuous melting and geological storage of glass cured from low- and medium-level radioactive waste liquids.

[0041] Example 2:

[0042] According to the mass percentage composition of oxides in the formulation of Example 2 in Table 1: 51.3 g of sodium carbonate, 50 g of silicon dioxide, 26.6 g of boric acid, 0.5 g of aluminum oxide, 2 g of zinc oxide, 2 g of zirconium oxide, 0.5 g of lanthanum oxide, and 7.1 g of strontium carbonate were weighed and mixed evenly to obtain a mixture. The mixture was placed in a silicon dioxide crucible and melted in a furnace at 1200°C. After clarifying for 1 hour, a clear and homogeneous glass melt was obtained. The clear and homogeneous glass melt was poured into a stainless steel mold preheated to 390°C and then quickly transferred to an annealing furnace preheated to 500°C. The glass was held in the annealing furnace for 2.5 hours to relieve stress and then cooled to room temperature at a rate of 1°C / min to obtain high-sodium borosilicate glass for solidification treatment of low-to-medium radioactive waste. The viscosity of the glass at 1150°C was measured to be 40 Poise using an Orton RSV-16RT high-temperature rotational viscometer. The resistivity was tested according to the method provided in GB / T 10581-2006 "Test Procedure for Resistance and Resistivity of Insulating Materials at High Temperatures", and the conductivity at 1150℃ was calculated to be 0.13 S / cm. According to standard EJ 1186-2005 "Characteristic Identification of Radioactive Waste Bodies and Waste Packages", the normalized elemental leaching rates after static immersion in deionized water at 90℃±1℃ for 28 days are shown in the figure. The leaching rate of each single element is less than 0.2 g / m³. 2 Its chemical stability, viscosity, conductivity, and other process parameters are all suitable for the continuous melting and geological storage of glass cured from low- and medium-level radioactive waste liquids.

[0043] Example 3:

[0044] According to the mass percentage composition of oxides in the formulation of Example 3 in Table 1, weigh out 34.2 g of sodium carbonate, 55 g of silicon dioxide, 23.1 g of boric acid, 15.3 g of aluminum hydroxide, 0.5 g of zinc oxide, 2 g of zirconium oxide, 1 g of lanthanum oxide, 1 g of neodymium oxide, 3 g of yttrium oxide, 2 g of light magnesium oxide, and 7 g of calcium carbonate. Mix thoroughly to obtain a mixture. Place the mixture into an alumina crucible and melt it in a furnace at 1200°C. Clarify for 1 hour to obtain a clear and homogeneous glass melt. Pour the clear and homogeneous glass melt into a stainless steel mold preheated to 390°C and shape it. Then quickly transfer it to an annealing furnace preheated to 500°C. Hold it in the annealing furnace for 2.5 hours to relieve stress, and then cool it to room temperature at a rate of 1°C / min to obtain high-sodium borosilicate glass for solidification treatment of low-to-medium radioactive waste. The viscosity of the glass at 1150°C was measured to be 33 Poise using an Orton RSV-16RT high-temperature rotational viscometer. The resistivity was tested according to the method provided in GB / T 10581-2006 "Test Procedure for Resistance and Resistivity of Insulating Materials at High Temperatures", and the conductivity at 1150℃ was calculated to be 0.7 S / cm. According to standard EJ 1186-2005 "Characteristic Identification of Radioactive Waste Bodies and Waste Packages", the normalized elemental leaching rates after static immersion in deionized water at 90℃±1℃ for 28 days are shown in the figure. The leaching rate of each single element is less than 0.17 g / m³. 2 Its chemical stability, viscosity, conductivity, and other process parameters are all suitable for the continuous melting and geological storage of glass cured from low- and medium-level radioactive waste liquids.

[0045] Example 4:

[0046] According to the mass percentage composition of oxides in the formulation of Example 4 in Table 1: 41 g of sodium carbonate, 35 g of silicon dioxide, 35.5 g of boric acid, 18.3 g of aluminum hydroxide, 5 g of zinc oxide, 1.5 g of zirconium oxide, 2 g of yttrium oxide, and 3.7 g of magnesium hydroxide were weighed and mixed evenly to obtain a mixture. The mixture was placed in an alumina crucible and melted in a furnace at 1200°C. After clarifying for 1 hour, a clear and homogeneous glass melt was obtained. The clear and homogeneous glass melt was poured into a stainless steel mold preheated to 390°C and then quickly transferred to an annealing furnace preheated to 500°C. The glass was held in the annealing furnace for 2.5 hours to relieve stress and then cooled to room temperature at a rate of 1°C / minute to obtain high-sodium borosilicate glass for solidification treatment of low-to-medium radioactive waste. The viscosity of the glass at 1150°C was measured to be 22 Poise using an Orton RSV-16RT high-temperature rotational viscometer. The resistivity was tested according to the method provided in GB / T 10581-2006 "Test Procedure for Resistance and Resistivity of Insulating Materials at High Temperatures", and the conductivity at 1150℃ was calculated to be 0.6 S / cm. According to standard EJ 1186-2005 "Characteristic Identification of Radioactive Waste Bodies and Waste Packages", the normalized elemental leaching rates after static immersion in deionized water at 90℃±1℃ for 28 days are shown in the figure. The leaching rate of each single element is less than 0.18 g / m³. 2 Its chemical stability, viscosity, conductivity, and other process parameters are all suitable for the continuous melting and geological storage of glass cured from low- and medium-level radioactive waste liquids.

[0047] Example 5:

[0048] According to the mass percentage composition of the oxides in Example 5 of Table 1, 34.2 g of sodium carbonate, 55 g of silicon dioxide, 28.9 g of boric acid, 0.5 g of alumina, 1 g of zinc oxide, 0.5 g of zirconium oxide, 2 g of neodymium oxide, 4.3 g of strontium carbonate, and 5.2 g of barium carbonate were weighed and mixed evenly to obtain a mixture. The mixture was placed in an alumina crucible and melted in a furnace at 1200°C. After clarifying for 1 hour, a clear and homogeneous glass melt was obtained. The clear and homogeneous glass melt was poured into a stainless steel mold preheated to 390°C and then quickly transferred to an annealing furnace preheated to 500°C. The glass was held in the annealing furnace for 2.5 hours to relieve stress and then cooled to room temperature at a rate of 1°C / minute to obtain high-sodium borosilicate glass for solidification treatment of low-to-medium radioactive waste. The viscosity of the glass at 1150°C was measured to be 75 Poise using an Orton RSV-16RT high-temperature rotational viscometer. The resistivity was tested according to the method provided in GB / T10581-2006 "Test Procedure for Resistance and Resistivity of Insulating Materials at High Temperatures", and the conductivity at 1150℃ was calculated to be 0.55 S / cm. According to standard EJ 1186-2005 "Characteristic Identification of Radioactive Waste Bodies and Waste Packages", the normalized elemental leaching rates after static immersion in deionized water at 90℃±1℃ for 28 days are shown in the figure. The leaching rate of each single element is less than 0.16 g / m³. 2 Its chemical stability, viscosity, conductivity, and other process parameters are all suitable for the continuous melting and geological storage of glass cured from low- and medium-level radioactive waste liquids.

[0049] Example 6:

[0050] According to the mass percentage composition of oxides in Example 6 of Table 1, weigh out 39.2 g of sodium carbonate, 42 g of silicon dioxide, 19.5 g of boric acid, 15 g of alumina, 3 g of zinc oxide, 1 g of zirconium oxide, 3 g of neodymium oxide, 2 g of light magnesium oxide, and 1.42 g of strontium carbonate. Mix thoroughly to obtain a mixture. Place the mixture into an alumina crucible and melt it in a furnace at 1200°C. Clarify for 1 hour to obtain a clear and homogeneous glass melt. Pour the clear and homogeneous glass melt into a stainless steel mold preheated to 390°C and then quickly transfer it to an annealing furnace preheated to 500°C. Hold in the annealing furnace for 2.5 hours to relieve stress, and then cool to room temperature at a rate of 1°C / min to obtain high-sodium borosilicate glass for solidification treatment of low-to-medium radioactive waste. The viscosity of the glass at 1150°C was measured to be 25 Poise using an Orton RSV-16RT high-temperature rotational viscometer. The resistivity was tested according to the method provided in GB / T10581-2006 "Test Procedure for Resistance and Resistivity of Insulating Materials at High Temperatures", and the conductivity at 1150℃ was calculated to be 0.45 S / cm. According to standard EJ 1186-2005 "Characteristic Identification of Radioactive Waste Bodies and Waste Packages", the normalized elemental leaching rates after static immersion in deionized water at 90℃±1℃ for 28 days are shown in the figure. The leaching rate of each single element is less than 0.18 g / m³. 2 Its chemical stability, viscosity, conductivity, and other process parameters are all suitable for the continuous melting and geological storage of glass cured from low- and medium-level radioactive waste liquids.

Claims

1. A method for solidifying treatment of medium- and low-level liquid radioactive waste, characterized by, The high content of Na2O is solidified by using a glass solidification aid for medium and low radioactive waste liquid treatment, and the mass percentage of Na2O in the solidified glass is 20-30%, wherein the oxide mass percentage components of the borosilicate glass solidification aid for medium and low radioactive waste liquid treatment are as follows: RE is one or more of La, Nd and Y, and M is one or more of Mg and Sr.

2. The method of solidifying a liquid medium of medium- or low-level radioactive waste according to claim 1, characterized in that, The solidification method comprises the following steps: Step (1). The raw materials are weighed according to the following mass percentages and mixed uniformly to obtain a mixture; RE is one or more of La, Nd and Y, M is one or more of Mg, Ca, Sr and Ba, the molar ratio of O / (Si+B+Al) is 2.0-2.5, and the molar ratio of (2ΣM+Na) / (Si+B+Al) is 0.5-1.0; Step (2). The obtained mixture is put into a crucible and placed in a melting furnace to be melted and clarified to obtain a clarified and uniform glass melt; Step (3). After the glass melt is cast into a shape, annealing treatment is carried out in a preheated annealing furnace to obtain high-sodium borosilicate solidification glass.

3. The method of solidifying a liquid medium of medium- or low-level radioactive waste according to claim 1 or 2, characterized in that, The high-sodium borosilicate solidification glass is in a glass amorphous state, and the network body in the glass is silicon, boron and aluminum.

4. The method of solidifying a liquid high-level radioactive waste according to claim 1 or 2, characterized in that, The melting temperature is 1100-1200℃, and the melting time is 1-3 hours.

5. The method of solidifying a liquid high-level radioactive waste according to claim 1 or 2, characterized in that, The electrical conductivity of the glass melt at 1150 degrees is 0.1-0.7 S / cm, and the viscosity is 20-80 Poise.

6. The method of solidifying a liquid high-level radioactive waste according to claim 1 or 2, characterized in that, The normalized leaching rate of single element of the cured glass is less than 1 g / (day·m 2 ) after static immersion in deionized water at 90℃±1℃ for 28 days.

7. The method of solidifying a liquid high-level radioactive waste according to claim 1 or 2, characterized in that, The B2O3 is from one or more of B2O3 and boric acid; the Al2O3 is from one or more of Al(OH)3, carbonates and nitrates of aluminum; and the MO is from one or more of carbonates and nitrates of alkaline earth metals.

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