Uranium-Dioxide Pellet Grain Growth via La-Al-Si Liquid Phase
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Solution Overview
Problem
Current uranium-dioxide pellets with added oxides face limitations in promoting grain growth and effectively adsorbing cesium, a nuclear fission material, due to volatilization of silicon oxide compounds during sintering, which reduces their ability to enhance safety and operational margins in nuclear reactors.
Innovation Solution
Incorporating a sintering additive mixture of lanthanum oxide (La2O3), aluminum oxide (Al2O3), and silicon oxide (SiO2) into uranium dioxide pellets to form a stable liquid phase at high temperatures, accelerating uranium ion movement and promoting grain growth while effectively adsorbing cesium through the additive's application on grain boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If silicon oxide (SiO2) is added to promote grain growth and cesium adsorption, then grain size increases and cesium adsorption improves, but silicon oxide volatilizes during sintering reducing effectiveness
Solution Approach 1:
The patent combines silicon oxide with aluminum oxide and lanthanum oxide to form a composite sintering additive system (Al-Si-La). This composite approach creates a synergistic effect where the combination of materials provides both the grain growth promotion and cesium adsorption capabilities of silicon oxide while the aluminum and lanthanum components reduce silicon volatilization and enhance liquid phase stability during sintering.
Solution Approach 2:
The patent optimizes the compositional parameters of the sintering additive, specifically controlling the ratios of Al2O3, SiO2, and La2O3 within defined ranges. By adjusting these chemical composition parameters, the system achieves optimal balance between grain growth promotion, cesium adsorption capacity, and resistance to silicon volatilization during the sintering process.
2Strength
If oxide additives are used to increase grain size, then PCI damage resistance improves, but nuclear fission gas adsorption capability decreases due to reduced grain boundary area
Solution Approach 1:
The patent creates local quality differentiation by concentrating the sintering additive (Al-Si-La composite) specifically at the grain boundaries. This localized distribution ensures that grain boundaries retain their adsorption functionality for nuclear fission gases and cesium, while the overall microstructure develops large grains for PCI damage resistance. The additive forms a liquid phase that preferentially locates at grain boundaries during sintering.
Solution Approach 2:
The composite Al-Si-La additive system provides multiple functions simultaneously: aluminum oxide and lanthanum oxide promote grain growth for PCI resistance, while silicon oxide provides cesium adsorption capacity. The composite nature allows the system to overcome the trade-off by having different components serve different functions within the same additive package.
3Shape
If sintering temperature is increased to promote grain growth, then grain size increases for PCI damage resistance, but silicon oxide volatilization increases reducing cesium adsorption
Solution Approach 1:
The patent introduces aluminum oxide and lanthanum oxide as intermediary substances that mediate between the high sintering temperature environment and silicon oxide stability. These intermediary materials form a more stable liquid phase complex that suppresses silicon volatilization even at high temperatures, while still allowing grain growth to proceed. The Al-Si-La composite acts as a thermal buffer that maintains silicon oxide effectiveness.
Solution Approach 2:
The composite Al-Si-La sintering additive system enables high-temperature sintering to proceed while maintaining silicon oxide content. The synergistic interaction among aluminum oxide, silicon oxide, and lanthanum oxide creates a stable liquid phase that reduces silicon volatility, allowing the system to achieve both large grain size and retained cesium adsorption capacity after sintering.
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 approach results in uranium-dioxide pellets with increased grain size and improved cesium adsorption capabilities, enhancing safety and operational margins by reducing PCI damage and nuclear fission gas leakage during reactor operations.
Implementation Method 1
accelerating uranium ion movement and promoting grain growth
Implementation Method 2
form a stable liquid phase at high temperatures
Implementation Method 3
effectively adsorbing cesium through the additive's application on grain boundaries
Data Source
AI summary
The present disclosure relates to a pellet containing an oxide additive to improve a nuclear-fission-gas-adsorption ability of a uranium-dioxide pellet used as nuclear fuel and increase the grain size thereof, and to a method of manufacturing the same. A La2O3—Al2O3—SiO2 sintering additive is added to uranium dioxide so that mass movement is accelerated due to the liquid phase generated during sintering of the uranium-dioxide pellet, which promotes the growth of grains thereof. Further, since less volatilization occurs during sintering due to the low vapor pressure of the liquid phase, efficient additive performance is exhibited, so the liquid phase surrounding the grain boundary effectively adsorbs cesium, which is a nuclear fission gas.