U-Mo Fuel Pellet Processing for Uniform Molybdenum Distribution
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Solution Overview
Problem
Existing methods for producing uranium-molybdenum alloy fuel pellets for nuclear reactors face issues such as uneven molybdenum distribution, high pressure requirements, two-stage pressing, significant power consumption, and reduced uranium intensity, leading to safety concerns and inefficiencies.
Innovation Solution
A method involving the preparation of uranium-molybdenum powder with specific enrichment and molybdenum content, followed by heating, pressing at controlled pressures, and sintering in an inert atmosphere to achieve uniform distribution and high density pellets, enhancing uranium intensity and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cold pressing is performed without binder on uranium and molybdenum powders, then the alloying elements fully react with each other, but there is an uneven distribution of molybdenum throughout the volume and high pressure is required
Solution Approach 1:
The patent applies preliminary action by pre-mixing uranium and molybdenum powders with a binder (stearic acid) before pressing. This preliminary mixing ensures uniform distribution of molybdenum particles throughout the uranium matrix, preventing the uneven distribution problem that occurs when pressing without binder. The binder facilitates homogeneous mixing and maintains particle distribution during the subsequent pressing and sintering operations.
Solution Approach 2:
The patent uses a binder (stearic acid) as an intermediary substance during the cold pressing stage. This intermediary allows the powder mixture to be pressed at lower pressures while maintaining particle distribution and enabling complete alloying during sintering. The binder acts as a temporary medium that facilitates processing without compromising the final reaction completeness, as it is removed during the sintering process.
2Ease of manufacture
If two-stage pressing is performed on uranium dioxide pellets, then the pellets can be produced, but the process complexity increases and a plasticizer must be used
Solution Approach 1:
The patent applies preliminary action by incorporating a binder (stearic acid) into the powder mixture before the single pressing stage. This preliminary addition of binder enables the powder to be pressed into pellets in a single stage without requiring subsequent plasticizer treatment or additional pressing operations. The binder provides the necessary plasticity and binding strength during the pressing operation itself, eliminating the need for complex two-stage pressing processes.
3Ease of manufacture
If significant pressing force is applied to produce ceramic fuel pellets, then the pellets can be formed, but the power consumption increases
Solution Approach 1:
The patent uses a binder (stearic acid) as an intermediary that reduces the pressing force required to form pellets. The binder acts as a lubricant and binding agent, allowing powder particles to consolidate into pellet form at lower pressures. This significantly reduces the mechanical work and power consumption during the pressing operation compared to pressing binder-free powder mixtures, while still achieving complete alloying during the subsequent sintering process.
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 produces uranium-molybdenum pellets with increased density and thermal conductivity, reducing heat buildup and improving reactor safety by increasing uranium mass and resilience to accidents.
Implementation Method 1
sintering pellets in a gaseous atmosphere
Implementation Method 2
uniform distribution of molybdenum throughout the volume
Implementation Method 3
thermal removal of the binder
Data Source
AI summary
The invention relates to the nuclear industry and can be used for producing fuel pellets from uranium-molybdenum metal powders enriched to 7% uranium 235 for nuclear reactor fuel elements. The pellets are sintered in an inert atmosphere of argon at a temperature ranging from 1100° C. to 1155° C., and the initial powder is a uranium-molybdenum powder having a fraction size of 160 μm and a molybdenum con⊥tent of 9.0 to 10.5 wt %. The powder is pre-heated at a temperature of 500° C. for 10-20 hours (in an atmosphere of argon) and is subsequently cold pressed into pellets in a die under a force of up to 950 MPa. In an alternative emb⊥odiment for producing uranium-molybdenum pellets with a binder (plasticizer), the step of sintering is preceded by heating the pellets in an atmosphere of argon at 300° C. to 450° C. for 2-4 hours to remove the binder. The invention makes it possible to increase the uranium intensity of the fuel, reduce the amount of heat buildup in a reactor core, and lower the amount of energy released in the event of abnormalities in the operation of a nuclear reactor, thus providing increased reactor safety and resilience to accidents.