Fluorinated Coating for Nuclear Fuel Retention
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Solution Overview
Problem
High temperature gas-cooled nuclear reactors face challenges in retaining fission products, particularly silver and caesium, within the nuclear fuel particles due to diffusion issues, which affect the fuel's performance and burnup efficiency.
Innovation Solution
A method involving the deposition of a composite coating around a fissile material kernel, comprising fluorine compounds, silicon carbide, silicon nitride, magnesium, and diamond, using chemical vapor deposition techniques at controlled temperatures and pressures, to create a barrier that reduces fission product diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating is deposited around the fissile material kernel to prevent fission product diffusion, then the retention of fission products is improved, but the manufacturing complexity increases
Solution Approach 1:
The coating is divided into multiple distinct layers with different compositions and functions: an inner layer (silicon carbide, silicon nitride) providing structural integrity and chemical stability, and an outer fluorinated layer providing enhanced diffusion barrier properties. This segmentation allows each layer to be optimized for its specific function while collectively solving the retention problem.
Solution Approach 2:
The invention uses composite coating structures combining multiple materials (silicon carbide, silicon nitride, fluorinated compounds) to achieve properties that single materials cannot provide alone. The composite structure provides both mechanical strength and superior diffusion resistance, resolving the contradiction between reliability and manufacturing simplicity.
2Reliability
If a thick coating is deposited to provide a hard barrier to diffusion, then the retention of fission products is improved, but the fuel particle size increases
Solution Approach 1:
Different regions of the coating have different compositions and thicknesses optimized for their local function. The inner layer is thicker and provides structural support, while the outer fluorinated layer is thinner but provides superior diffusion resistance per unit thickness. This local optimization allows effective barrier properties without excessive overall thickness.
Solution Approach 2:
The invention changes the chemical composition parameters of the coating layers, particularly introducing fluorinated compounds in the outer layer which provide enhanced diffusion barrier properties at reduced thickness compared to conventional coatings, thus maintaining small particle size while improving retention.
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 coated nuclear fuel particles exhibit improved retention of fission products and gas tightness, maintaining performance and reducing burnup at high temperatures, with the fluorine-based coating providing a hard barrier to diffusion.
Implementation Method 1
depositing a mixture of silicon and silicon carbide around a kernel of fissile material followed by fluorinating the silicon and silicon carbide
Implementation Method 2
fluorinating the silicon and silicon carbide
Implementation Method 3
introducing magnesium into the fluorinated silicon and silicon carbide around the kernel
Implementation Method 4
nitriding the silicon and silicon carbide mixture
Implementation Method 5
introducing carbon into the nitrided silicon and silicon carbide mixture
Implementation Method 6
reducing the silicon carbide to carbon, more particularly, to the carbon allotrope of diamond. Preferably, the silicon carbide deposited will be beta polytype silicon carbide. Reducing the silicon carbide may include reacting the silicon carbide with hydrogen chloride or chlorine
Data Source
AI summary
This invention relates to a method of preparing a nuclear fuel including the step of depositing a coating which includes fluorine, or at least one compound thereof, around a kernel (12) of fissile material. The invention extends to a coated nuclear fuel particle (10).