Sapphire Fuel Cladding Creep Forming
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Solution Overview
Problem
Conventional fuel cladding materials for nuclear reactors are inadequate for supercritical water conditions due to high neutron absorption, corrosion, and inability to retain fission products during severe accidents, while existing sapphire tubes have ridged inner surfaces that hinder thermal contact with fuel pellets.
Innovation Solution
The method involves heating sapphire tubes to thermal creep temperatures and using thermal creep drawing or differential expansion moulding to smooth the inner and outer surfaces, maintaining crystalline structure, and employing infrared-absorbing aluminium nitride for joining sapphire parts to create a smooth, uniform cladding with improved thermal contact and stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fuel cladding materials are used, then manufacturing is easier and cost is lower, but neutron absorption is high and corrosion resistance is poor
Solution Approach 1:
The patent changes the material parameter from conventional metals to sapphire (Al2O3), which fundamentally alters the physical and chemical properties to achieve low neutron absorption and high corrosion resistance while maintaining manufacturability through appropriate processing methods
Solution Approach 2:
The patent uses composite construction with sapphire cladding tube, aluminium nitride coating layer, and graphite or metal end plugs, combining materials with complementary properties to achieve both nuclear performance and manufacturing feasibility
2Reliability
If sapphire tubes are used for fuel cladding, then neutron absorption is low and corrosion resistance is high, but the inner surface has ridges that reduce thermal contact with fuel pellets
Solution Approach 1:
The patent applies preliminary action by coating the inner surface with aluminium nitride before fuel insertion, which fills the ridge valleys and creates a smooth thermal interface, thereby improving thermal contact without requiring post-manufacturing surface refinement
Solution Approach 2:
The aluminium nitride coating acts as an intermediary substance between the sapphire tube and fuel pellets, filling surface irregularities and providing a continuous thermal contact path that enhances heat transfer while maintaining the structural integrity of the sapphire tube
3Productivity
If sapphire tubes with ridges are used, then manufacturing is simpler, but thermal contact with fuel pellets is poor leading to inefficient heat transfer
Solution Approach 1:
The patent applies preliminary action by coating the inner surface with aluminium nitride before fuel insertion, which fills the ridge valleys and creates a smooth thermal interface, thereby improving thermal contact without requiring post-manufacturing surface refinement
Solution Approach 2:
The patent replaces mechanical surface finishing operations with a chemical/coating process, using aluminium nitride deposition to achieve the desired surface smoothness and thermal contact quality without complex mechanical grinding or polishing equipment
4Reliability
If conventional cladding materials are used, then manufacturing is easier, but the cladding cannot retain fission products during severe accidents
Solution Approach 1:
The patent changes the material parameter from conventional metals to sapphire (Al2O3), which has fundamentally different physical and chemical properties including high melting point, chemical inertness, and low neutron absorption, enabling it to retain fission products and maintain structural integrity during severe accidents
Solution Approach 2:
The patent uses composite construction with sapphire cladding tube, aluminium nitride coating layer, and graphite or metal end plugs, combining materials with complementary properties to achieve both nuclear performance and manufacturing feasibility
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 enhances the thermal contact between fuel pellets and cladding, ensuring efficient heat transfer and maintaining structural integrity under supercritical conditions, reducing the risk of hydrogen production and fission product release during accidents.
Implementation Method 1
heating the tube to thermal creep temperatures and slowly drawing and/or pushing the heated tube through a plug and die set to reduce heights of ridges on respective inner and outer surfaces of the tube
Implementation Method 2
providing at a joint interface between juxtaposed surfaces of the parts an infrared absorbing interstitial layer of aluminium nitride, and heating the layer by infrared illumination to the melting temperature of the juxtaposed surfaces of the sapphire parts
Implementation Method 3
heating the layer by infrared illumination to the melting temperature of the juxtaposed surfaces of the sapphire parts, such that the aluminium nitride reacts with sapphire to form aluminium oxy-nitride compounds that, on cooling, provide required joining of the parts
Data Source
AI summary
A method of fine surface finishing a cladding tube for a nuclear fuel element comprising a cladding tube containing fuel pellets, comprises heating the tube to thermal creep temperatures (e.g., 1750-2000 degrees Celsius) for sapphire and forming inner and outer surfaces of the tube to reduce ridge heights while limiting changes in the crystalline structure of the bulk of the tube. Alternatively, the tube may be placed in a mould and heating the tube-mould assembly to the range of the creep temperature of the sapphire at which differential thermal expansion of the mould and tube cause pressure at an interface between the sapphire and the mould. Maintaining the assembly at an upper end of the creep temperature range allows creep to progress and relieve stresses resulting from the pressure; and cooling the assembly to allow the sapphire tube to part from the mould and be withdrawn.