Common Plenum Fuel Assembly for Pool-Type Reactors
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Solution Overview
Problem
The challenge of refueling liquid metal-cooled or salt-cooled reactors is exacerbated by the limited volume of fission gas plenum per linear unit, leading to high internal pressure and embrittlement of fuel rod claddings, which restricts the duration of fuel exposure and increases the cost of fast reactor operations.
Innovation Solution
A common fission gas plenum is positioned above the reactor flow region, connected to a collection header, allowing for a larger plenum volume and reducing the need for plenum space within fuel rods, with each rod connected through one-way valves to prevent backflow, thereby minimizing fuel rod length and internal pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If individual fuel rod plenums are used within the reactor flow region, then each rod can accommodate fission gas, but the plenum volume per linear unit is limited and structural material requirements increase
Solution Approach 1:
Multiple individual fuel rod plenums are merged into a single common plenum located above the reactor flow region. This consolidation achieves several benefits: (1) dramatically increases total plenum volume per linear unit of plenum length, (2) reduces structural material requirements by eliminating redundant plenum walls for each rod, (3) simplifies the overall structure while maintaining the ability to accommodate fission gas from all fuel rods
Solution Approach 2:
The plenum location is moved from the horizontal dimension (within the reactor flow region at rod level) to the vertical dimension (above the reactor flow region). This spatial reconfiguration allows the common plenum to utilize previously-unused reactor vessel space, achieving much larger plenum volume without interfering with the reactor core or coolant flow paths
2Volume of stationary object
If cladding length is increased to accommodate fission gas, then plenum volume is sufficient, but fuel exposure duration is limited due to embrittlement and swelling
Solution Approach 1:
By merging individual rod plenums into a common plenum, the effective plenum volume is dramatically increased without requiring longer cladding. The common plenum acts as a shared reservoir for fission gas from all fuel rods, reducing the volume requirement per unit length and allowing shorter cladding lengths that maintain structural integrity for longer fuel exposure durations
Solution Approach 2:
The plenum pressure parameter is reduced by increasing plenum volume through the common plenum design. Lower plenum pressure decreases the stress on cladding walls, reducing embrittlement and swelling rates, thereby extending the maximum permitted fuel exposure duration
3Ease of manufacture
If common plenum is located within the reactor flow region, then integration is simpler, but plenum volume per length is constrained and bundle flow area is reduced
Solution Approach 1:
The common plenum is positioned in the vertical dimension above the reactor flow region rather than within it. This spatial separation allows the plenum to achieve large volume without constraining the horizontal bundle flow area, while the connection system integrates the plenum with the fuel bundle through the upper end fitting and mast structure
4Reliability
If individual rod plenums are used, then each rod is self-contained, but refueling complexity and cost increase
Solution Approach 1:
Individual rod plenums are merged into a common plenum that serves all fuel rods in the assembly. This consolidation simplifies refueling operations because the entire fuel bundle can be handled as a single unit with a common gas collection system, rather than requiring individual rod manipulation and gas management, thereby reducing refueling complexity and cost
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
This design extends fuel cycle lengths, reduces refueling time pressure, and lowers the stress on fuel rod claddings, enabling longer fuel cycles and increased fuel burnup while simplifying refueling and reducing infrastructure needs.
Implementation Method 1
Each rod may have a one-way valve or fluidic diode to prevent backflow from the plenum, should a rod leak develop
Data Source
AI summary
A fuel assembly for use in a nuclear reactor comprising a fuel bundle, a plenum header connection positioned on the fuel bundle, a mast extending from the fuel bundle, and a common fission gas plenum extending from the mast is disclosed. The reactor includes a vessel and coolant situated within the vessel. The fuel bundle comprises a plurality of fuel elements including nuclear fuel material positioned therein. The plenum header connection comprises a plurality of passageways defined therein that are in fluid communication with the nuclear fuel material. The elongate mast comprises an internal passage connecting the common fission gas plenum to the plurality of passageways of the plenum header connection such that the common fission gas plenum is configured to receive an amount of fission gas generated by the nuclear fuel material during operation. The common fission gas plenum is positioned in an otherwise unused portion of the vessel.