Radioactive Waste Packaging Process Using CaO-SiO2-Al2O3 Composition
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Solution Overview
Problem
Current processes for conditioning radioactive waste, such as those involving FA/MA waste, face challenges in achieving high incorporation rates, compressive strength, insolubility, and reduced cooling times, while also retaining volatile radioactive elements, due to issues like high silica content leading to viscosity problems and the need for annealing and high thermal constraints.
Innovation Solution
A process that adjusts the composition of radioactive waste to achieve a target composition in the ternary system CaO-SiO2-X2O3, where X2O3 includes trivalent oxides like Al2O3, Fe2O3, and B2O3, allowing for the formation of a vitreous or vitro-crystalline rock with improved mechanical properties and reduced cooling times, achieving incorporation rates greater than 2 and meeting regulatory standards for compressive strength and solubility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the composition is adjusted to achieve ternary eutectic (high silica content 59-65%), then the melting temperature is reduced below 1300°C, but the viscosity of the melt becomes too high making homogenization difficult and bubble escape impossible
Solution Approach 1:
The patent modifies the chemical composition parameters by replacing a portion of silica (SiO2) with alumina (Al2O3) to achieve an optimal balance. Specifically, the silica content is reduced from 59-65% to 40-50%, while alumina is increased from 10-16% to 20-30%. This parameter change reduces melt viscosity while maintaining low melting temperature, enabling effective homogenization and bubble escape during melting.
Solution Approach 2:
The patent creates a composite glass composition combining multiple oxides (CaO, SiO2, Al2O3, and optionally Fe2O3 or B2O3) in specific proportions. This composite approach leverages the low-melting-point特性 of alumina and boric anhydride while using silica as a network former, achieving both low melting temperature and manageable viscosity through the synergistic interaction of different materials.
2Temperature
If the silica content is high (59-65%) to achieve ternary eutectic composition, then the melting temperature is lowered, but the cooling time becomes excessively long (one month) due to thermal constraints
Solution Approach 1:
The patent changes the chemical composition to reduce silica content and increase alumina content, which fundamentally alters the cooling behavior. This composition modification enables faster cooling rates while maintaining structural integrity, reducing cooling time from one month to a practical industrial timeframe without compromising the low melting temperature benefit.
3Temperature
If the composition is adjusted to ternary eutectic, then the melting temperature is reduced, but the incorporation rate of waste remains low (not exceeding 2) due to inhomogeneity requiring much higher melting temperatures
Solution Approach 1:
The patent optimizes the composition parameters by increasing alumina content to 20-30% and reducing silica to 40-50%, creating a melt that is both fluid enough for homogenization and hot enough to melt heterogeneous waste efficiently. This balanced composition enables effective waste incorporation at practical melting temperatures, achieving incorporation rates greater than 2.
4Ease of manufacture
If mortar slurry is used to condition waste, then the process is simple, but the incorporation rate is very low (0.2-0.5) and storage costs increase due to large final volume
Solution Approach 1:
The patent utilizes the phase transition from solid waste to molten glass during high-temperature melting, enabling complete mixing and incorporation of waste into the final product. This thermal processing approach achieves incorporation rates greater than 2, compared to 0.2-0.5 for mortar slurry methods, while the final glass monolith occupies significantly less volume, reducing storage costs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process achieves high incorporation rates of radioactive waste, ensures the resulting monoliths have sufficient compressive strength and are insoluble, and allows for rapid cooling without thermal constraints, effectively addressing the limitations of existing methods.
Implementation Method 1
said supplemented radioactive waste is melted
Implementation Method 2
after cooling, a monolith of mineral, vitreous or vitrocrystalline rock is obtained
Implementation Method 3
the calcium carbonate dissociates around 900°C to become lime (CaO) by degassing CO2
Implementation Method 4
the water evaporates from 100°C
Implementation Method 5
the organic materials burn between 300 and 500°C
Data Source
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AI summary
The present invention relates to a process for packaging radioactive wastes, in which the following successive steps are carried out: a/ radioactive wastes, the solids content of which comprises at least 90% of compounds chosen from CaCO2, Fe2O3, SiO2, Al2O3 and B2O3, are supplemented so as to achieve a target composition of said supplemented wastes after calcination, and b/ said supplemented radioactive wastes are melted and c/ said molten pool is poured into a container so as to obtain, after cooling, a product comprising a vitreous or vitreous-crystalline synthetic rock having said target composition, characterized in that said target composition corresponds to the following definition, in a CaO, SiO2 and X2O3 ternary system, in which X2O3 is a trivalent oxide or a mixture of trivalent oxides chosen from Al2O3, Fe2O3 or B2O3, Pc and Ps being the weight percentages of CaO and SiO2: - Pc is from 35 to 60%, and - Ps is from 10 to 45%.