Spent Fuel Storage Rack Passive Cooling Design
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Solution Overview
Problem
Current spent fuel storage systems face challenges in maintaining effective cooling and subcriticality during prolonged nuclear plant station blackout conditions, leading to potential overheating and radionuclide release, with issues such as human error in fuel assembly placement and degradation of components over time.
Innovation Solution
A system comprising a support structure with cells and compartments that allow for coolant circulation between fuel assemblies, using perforations to facilitate unimpeded coolant flow and maintain neutron separation, and an intermediate barrier to manage coolant levels, ensuring continuous cooling and subcriticality without relying on active systems or fixed neutron absorbers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid neutron absorbers (e.g., boron-carbide plates) are incorporated between fuel assembly storage positions, then criticality control is improved, but device complexity and potential degradation issues increase
Solution Approach 1:
The patent removes solid neutron absorbers from the storage rack structure, extracting the criticality control function from passive structural components. Instead, criticality is controlled through the geometric arrangement of fuel assemblies and natural neutron absorption by the coolant, eliminating degradation-prone solid absorber materials while maintaining safety
Solution Approach 2:
The system uses the coolant itself to provide neutron absorption, making the coolant serve dual purposes: heat removal and criticality control. The water in the pool naturally absorbs neutrons, eliminating the need for separate solid neutron absorber components and their associated maintenance issues
2Reliability
If soluble boron is added to the fuel storage pool to maintain subcriticality, then criticality control is improved, but potential harmful effects and water chemistry management complexity increase
Solution Approach 1:
The patent eliminates soluble boron additives from the pool water, removing the chemical method of criticality control. Instead, it relies on geometric spacing of fuel assemblies and the natural neutron absorption properties of water, avoiding water chemistry degradation and associated maintenance requirements
Solution Approach 2:
The system changes the approach from chemical parameter control (soluble boron concentration) to physical parameter control (fuel assembly spacing and pool geometry). By adjusting the physical arrangement rather than chemical composition, it achieves criticality control without water chemistry management issues
3Temperature
If preferential loading of hotter fuel assemblies with colder fuel assemblies is implemented, then heat exchange between adjacent assemblies is reduced, but human error in placement increases
Solution Approach 1:
The patent divides the pool into distinct cooling channels with intermediate compartments that physically separate fuel assemblies. This segmentation creates natural thermal zones where hot and cold assemblies are automatically positioned by the flow pattern, eliminating the need for manual preferential loading while maintaining thermal management
Solution Approach 2:
The coolant flow pattern automatically manages thermal distribution through the segmented channels, with water naturally flowing from regions with hotter assemblies to regions with colder assemblies. This self-organizing flow pattern achieves thermal balance without human intervention or complex placement requirements
4Productivity
If stacked fuel racks are used to increase storage capacity, then productivity is improved, but cooling effectiveness may be compromised
Solution Approach 1:
The patent extends the cooling system into the vertical dimension with stacked racks, each having through-channels that allow coolant flow from top to bottom. This three-dimensional cooling architecture maintains effective heat removal while maximizing storage density by utilizing vertical space
Solution Approach 2:
The intermediate compartments serve multiple functions: they provide neutron absorption, facilitate coolant distribution to multiple rack levels, and create thermal separation between adjacent fuel assemblies. This multi-functionality enables stacked configuration without compromising cooling effectiveness
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 system effectively maintains coolant circulation and neutron separation, preventing overheating and radionuclide release, even in the absence of liquid coolant, through passive means, thereby ensuring the safety and stability of spent fuel storage.
Implementation Method 1
provide passageways for coolant entering a bottom end of the support structure to remove heat from the nuclear fuel assemblies
Implementation Method 2
remove heat from the nuclear fuel assemblies
Implementation Method 3
A first perforation transfers coolant between the first cell and one or more of the compartments, and a second perforation transfers coolant between the second cell and one or more compartments
Implementation Method 4
Additives such as soluble boron may be provided in a fuel storage pool in order to help maintain subcriticality of spent fuel
Data Source
AI summary
A system for storing nuclear fuel assemblies includes a plurality of cells housed within a support structure. A first cell may house a first fuel assembly and a second cell may house a second fuel assembly. A plurality of compartments separate the plurality of cells and provide passageways for coolant entering a bottom end of the support structure to remove heat from the nuclear fuel assemblies. A first perforation transfers coolant between the first cell and one or more of the compartments, and a second perforation transfers coolant between the second cell and the one or more compartments. At least a portion of the coolant entering the bottom end of the support structure is transferred between the plurality of cells and the plurality of compartments. Two or more fuel storage racks may be stacked together in alternating fuel patterns to facilitate cooling the fuel assemblies with liquid or air.