Nuclear Thermal Propulsion Fuel Element with Compliance Structure
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Solution Overview
Problem
Existing nuclear thermal rocket propulsion systems face challenges in maintaining consistent fuel distribution and preventing thermal stress due to the expansion and contraction of nuclear fuel particles during repeated thermal cycling.
Innovation Solution
The fuel element incorporates a compliance structure with bed partitions that separate the fuel bed into segments, allowing for elastic deformation and maintaining consistent fuel distribution, thereby preventing uneven heating and thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If nuclear fuel particles are used in a fuel bed, then thermal energy is released via nuclear fission, but thermal stress and fuel distribution inconsistency occur during repeated thermal cycling
Solution Approach 1:
The fuel bed is divided into multiple segments by bed partitions, creating discrete fuel regions. This segmentation prevents uniform thermal expansion from causing fuel particle migration and maintains consistent fuel distribution throughout the fuel bed during thermal cycling.
Solution Approach 2:
Different regions of the fuel bed are given different structural characteristics through the compliance structure and bed partitions. The compliance structure provides localized flexibility to accommodate thermal expansion, while bed partitions create discrete segments with controlled properties, allowing each region to handle thermal stress differently.
2Duration of action of moving object
If nuclear fuel particles undergo repeated thermal cycling, then propulsion is generated, but thermal stress causes fuel distribution inconsistency
Solution Approach 1:
The compliance structure is designed beforehand to accommodate and cushion the thermal expansion and contraction of fuel particles during thermal cycling. This pre-designed compliance mechanism prevents fuel distribution inconsistency before it occurs, maintaining stable fuel bed composition throughout the propulsion duration.
Solution Approach 2:
By segmenting the fuel bed into discrete regions with bed partitions, the system maintains compositional stability in each segment independently, preventing the propagation of thermal stress effects throughout the entire fuel bed during repeated thermal cycling.
3Temperature
If the fuel bed is allowed to expand freely, then thermal energy is efficiently transferred, but uneven thermal expansion causes cold shell failure
Solution Approach 1:
The compliance structure introduces localized flexibility between the fuel bed and cold shell. This allows regions of the fuel bed to expand and contract independently while maintaining controlled interaction with the cold shell, preventing uneven thermal expansion from causing shell failure while preserving efficient thermal energy transfer.
Solution Approach 2:
The compliance structure acts as an intermediary between the expanding fuel bed and the rigid cold shell. It mediates the thermal expansion forces, distributing them evenly and preventing concentrated stresses that would lead to cold shell failure, while still allowing efficient thermal energy transfer from fuel to propellant.
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 maintains nuclear fuel particles within consistent segments of the fuel bed, ensuring predictable thrust and preventing failure of the cold shell due to uneven thermal expansion.
Implementation Method 1
configured to elastically deform radially and longitudinally to absorb thermal movement of the fuel bed over the range of operating temperatures
Implementation Method 2
The fuel bed includes a set of nuclear fuel particles and configured to release thermal energy via nuclear fission
Implementation Method 3
configured to direct propellant radially inwardly from the moderator bore through the array of cold perforations, and toward the fuel bed
Implementation Method 4
configured to direct propellant, heated by the fuel bed, radially inwardly from the fuel bed into the interior collection volume
Data Source
AI summary
One variation of a reactor assembly for a nuclear thermal propulsion system includes a set of fuel elements arranged within a moderator block. Each fuel element, in the set of fuel elements, includes: a cold shell; a compliance structure; a fuel bed; and a hot shell.