Fluence Control Structures for Nuclear Reactor Core Protection
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Solution Overview
Problem
Nuclear power operations face issues with neutron flux over time causing component brittling and failure, particularly in flux-sensitive components like the core shroud and reactor pressure vessel, and existing solutions such as separate reflector/absorber structures or smaller cores with water perimeters create additional installation and maintenance challenges or reduce power generation.
Innovation Solution
The implementation of fluence control structures positioned around nuclear fuel assemblies to limit neutron flux, using materials with high absorption cross sections and strategically placed to create a flux boundary at the core perimeter, which can be integrated into existing fuel assemblies without requiring additional installation within the reactor core.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate reflector/absorber structures are installed to reduce neutron flux, then component brittling and failure is prevented, but installation and maintenance complexity increases
Solution Approach 1:
The fluence control structure is integrated into the fuel assembly itself, merging the flux reduction function with the fuel assembly structure. This eliminates the need for separate reflector/absorber structures and their associated installation and maintenance operations, while still providing protection against neutron-induced component brittling
Solution Approach 2:
The fuel assembly serves multiple functions: it provides fuel for power generation and simultaneously acts as a fluence control structure to reduce neutron flux. This multi-functionality eliminates the need for dedicated flux-reducing components, simplifying the overall system while maintaining component reliability
2Reliability
If smaller cores with water perimeters are used to reduce neutron flux, then component failure is prevented, but power generation capability is reduced
Solution Approach 1:
The fluence control structure is positioned at specific locations within the fuel assembly (at the periphery) where neutron flux is highest and most damaging to surrounding components. This localized approach reduces neutron flux where it is most harmful while maintaining the full core size and power generation capability
3Ease of operation
If fluence control structures are integrated into fuel assemblies, then installation and maintenance operations are simplified, but manufacturing complexity increases
Solution Approach 1:
The fluence control structure is nested within the fuel assembly structure, with the flux-reducing material positioned inside or integrated with the fuel rod cladding. This nesting approach allows the fluence control function to be incorporated during standard fuel assembly manufacturing without requiring separate assembly steps
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 approach effectively reduces neutron flux and fluence over time, preventing component failure while maintaining compatibility with various reactor types and power generation levels, without the need for separate installation or maintenance, and allows for flexible reactivity patterns and power control.
Implementation Method 1
fluence control structures limit neutron flux at particular positions through the use of appropriate material, dimensioning, and placement in fuel assemblies
Data Source
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AI summary
Nuclear fuel assemblies include at least one fluence control structure (112,114,120) for use in a nuclear reactor core (35) with other nuclear fuel assemblies (110). Such flux-limiting assemblies and structures may be positioned outside of or around the other nuclear fuel assemblies in the core so as to reduce neutron flux beyond the fluence controlled nuclear fuel assemblies, and fluence control structures may be positioned at an outside edge of the core. Fluence control structures limit neutron flux with non-fuel materials in structures like fuel rods and inserts, channels, shield curtains, etc. at particular positions in fuel assemblies. An engineer may select and/or install fluence-limiting fuel assemblies with flux-limiting characteristics in cores having neutronics profiles expected to benefit from such flux limitation.