Axially Heterogeneous Fast Reactor Fuel Assemblies
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Solution Overview
Problem
Current methods for sodium-cooled, metallic fuel fast reactors struggle to flatten power density distribution and increase coolant outlet temperature without degrading reactor core performance, particularly when integrated with heat storage systems using molten salts.
Innovation Solution
The implementation of axially heterogeneous core fuel assemblies with varying internal blanket thicknesses in the inner and outer core regions, where the first fuel assemblies are loaded in the outer core region and the second fuel assemblies are loaded in the inner core region, allowing for a thicker internal blanket in the outer core region compared to the inner core region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the coolant flow rate is reduced to increase coolant outlet temperature, then thermal efficiency is improved, but power density distribution becomes more uneven
Solution Approach 1:
The patent applies local quality by differentiating blanket fuel thickness across different radial zones of the reactor core. The outer core region has a thicker blanket fuel layer compared to the inner core region, creating localized neutron absorption characteristics that compensate for reduced coolant flow rates and enable higher coolant outlet temperatures while maintaining uniform power density distribution.
2Productivity
If blanket fuel thickness is increased to flatten power density distribution, then radial power distribution is improved, but reactor core performance degrades
Solution Approach 1:
The patent implements local quality by spatially varying the blanket fuel thickness according to radial position. The outer core region receives thicker blanket fuel (e.g., 20-30 cm) to enhance neutron absorption and flatten power density, while the inner core region has thinner blanket fuel (e.g., 10-20 cm) to preserve neutron flux and maintain reactor core performance. This non-uniform distribution resolves the contradiction between power density flattening and core performance maintenance.
3Reliability
If metallic fuel is used to improve reactor safety, then safety is improved, but coolant outlet temperature is limited to lower values
Solution Approach 1:
The patent applies parameter changes by modifying the blanket fuel thickness parameter radially across the core. This parameter variation enables the system to operate at higher coolant outlet temperatures (compatible with metallic fuel safety benefits) while maintaining uniform power density distribution through enhanced neutron absorption in the outer core region, thus resolving the temperature limitation imposed by metallic fuel usage.
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 configuration effectively flattens the power density distribution, increases the coolant outlet temperature, and maintains reactor core performance, enhancing compatibility with molten salt heat storage systems and improving thermal efficiency.
Implementation Method 1
Among neutrons generated by nuclear fission reaction occurring inside the fuel assemblies loaded in the core fuel region, neutrons leaked out of the core fuel region are absorbed by depleted uranium (U-238) inside the respective fuel rods of the blanket fuel assemblies loaded in the blanket fuel region
Implementation Method 2
Among neutrons generated by nuclear fission reaction occurring inside the fuel assemblies loaded in the core fuel region
Data Source
AI summary
Disclosed are fuel assemblies that are loaded in the core of a fast reactor including first fuel assemblies and second fuel assemblies being different from the first fuel assemblies. The reactor core has an axially heterogeneous core structure in which an internal blanket region containing depleted uranium fuel is placed around an axially middle section of the core. The first fuel assemblies are loaded in an outer core fuel region extending toward the periphery of the reactor core in a radial direction and the second fuel assemblies are loaded in an inner core fuel region extending around the center of the reactor core in a radial direction. Thickness of an internal blanket in each of the first fuel assemblies in an axial direction of the reactor core is thicker than thickness of an internal blanket in each of the second fuel assemblies in the axial direction of the reactor core.