Additive Thermal Conduction Structures in Nuclear Fuel Compacts
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Solution Overview
Problem
Nuclear fuels, such as uranium dioxide, exhibit low thermal conductivity, leading to high temperature gradients and thermal stresses, which can cause cladding failure due to swelling and excessive fission gas release, necessitating improved heat transfer methods within nuclear fuel pellets.
Innovation Solution
A method involving the formation of a three-dimensional additive structure within a fuel matrix using additive manufacturing techniques like powder bed fusion or binderjet printing, which is then thermally processed to create a densified nuclear fuel compact with enhanced heat transfer and fission product trapping capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If uranium dioxide fuel pellets are used, then high melting point and chemical inertness are achieved, but thermal conductivity remains very low causing high temperature gradients and thermal stresses
Solution Approach 1:
The patent applies composite materials by combining uranium dioxide fuel matrix with high thermal conductivity additives (such as graphite, boron carbide, or metallic particles) to create a composite fuel structure. This composite approach maintains the high melting point and chemical inertness of uranium dioxide while introducing pathways for improved heat conduction, thereby reducing temperature gradients and thermal stresses that lead to cladding failure.
Solution Approach 2:
The patent implements local quality by creating non-uniform distributions of high thermal conductivity additives within the fuel pellet, including radial gradients where additive concentration varies with distance from the center, and axial variations near the pellet ends. This localized enhancement of thermal conductivity targets the regions with highest temperature gradients, efficiently reducing thermal stresses while maintaining fuel performance.
2Temperature
If additives are uniformly dispersed in fuel pellets, then heat transfer is improved, but uniform dispersion is difficult to achieve and heat transfer from fuel center remains insufficient
Solution Approach 1:
The patent employs local quality by designing specific spatial distributions of additives rather than uniform dispersion. Radial gradients concentrate additives where they are most needed for heat conduction, while axial variations address hot spots near pellet ends. This non-uniform approach achieves superior heat transfer efficiency while avoiding the manufacturing difficulties of uniform dispersion.
Solution Approach 2:
The patent applies dimensionality change by transitioning from uniform three-dimensional dispersion to structured distributions that vary in radial and axial dimensions independently. This creates a multi-dimensional additive architecture that optimizes heat transfer pathways from the fuel center to the cladding, achieving both improved heat transfer and manufacturability.
3Quantity of substance
If high density pellets are used, then fuel density is achieved, but thermal conductivity decreases and fission gas release increases
Solution Approach 1:
The patent uses composite materials by incorporating high thermal conductivity additives into the dense uranium dioxide fuel matrix. This composite structure maintains the high fuel density required for efficient fission while introducing thermal conduction pathways that reduce centerline temperatures and associated thermal problems.
Solution Approach 2:
The patent applies porous materials concepts by creating controlled porosity or interconnected void structures that can serve as thermal conduits or accommodate fission gases. This approach allows maintenance of high overall fuel density while providing pathways for heat transfer and gas management.
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 method significantly improves heat transfer from the fuel center and allows for efficient utilization of burnable absorbers, reducing thermal stresses and cladding failure risks by using continuous high thermal conductivity structures within the fuel compact.
Implementation Method 1
The additive structure may include multiple arm segments that extend generally radially for conducting heat outwardly toward an exterior surface of the nuclear fuel compact
Implementation Method 2
Thermal processes can include sintering, hot-pressing (including direct current, spark plasma, field assisted, etc.), or infiltration
Data Source
AI summary
A method for manufacturing a nuclear fuel compact is provided. The method includes forming an additive structure, consolidating a fuel matrix around the additive structure, and thermally processing the fuel matrix to form a fuel compact in which the additive structure is encapsulated therein. The additive structure optionally includes a vertical segment and a plurality of arm segments that extend generally radially from the vertical segment for conducting heat outwardly toward an exterior of the fuel compact. In addition to improving heat transfer, the additive structure may function as burnable absorbers, and may provide fission product trapping.