Neutron Shielding Material Selection via Figure of Merit
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Solution Overview
Problem
Current neutron shielding technologies in tokamak fusion reactors face challenges in achieving efficient neutron attenuation while minimizing the thickness of the shielding to maintain compact reactor designs.
Innovation Solution
A method is developed to select materials of specific isotopic composition for neutron shielding by calculating an overall figure of merit using absorption and scattering coefficients, weighted by criteria such as neutron flux, dose, and heating effects, to identify optimal materials like scandium borohydride and nickel hydride.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional neutron shielding materials and thicknesses are used, then adequate neutron protection is achieved, but the reactor size increases and efficiency decreases
Solution Approach 1:
The patent applies parameter changes by systematically varying material composition parameters (isotopic ratios, elemental composition) and thickness parameters to optimize shielding performance. The figure of merit calculation evaluates multiple parameters simultaneously to identify the optimal combination that provides adequate neutron protection with minimal thickness, directly resolving the contradiction between protection reliability and reactor volume.
Solution Approach 2:
The patent employs composite materials by evaluating shielding effectiveness of material combinations rather than single materials. The figure of merit methodology assesses how different materials work together in layered or mixed configurations, allowing the design of composite shielding structures that achieve superior neutron attenuation per unit thickness compared to conventional single-material shields.
2Productivity
If shielding thickness is reduced to improve compactness, then reactor efficiency increases, but neutron attenuation capability deteriorates
Solution Approach 1:
The patent uses parameter changes to enhance the neutron interaction properties of shielding materials. By optimizing isotopic composition and material density parameters, the figure of merit identifies configurations that maximize neutron cross-sections for absorption and scattering, thereby achieving high attenuation capability in reduced thickness and improving reactor efficiency without sacrificing protection.
Solution Approach 2:
The patent applies local quality by tailoring the isotopic composition and material properties at specific locations within the shielding structure. Different regions of the shield can have different material compositions optimized for the local neutron flux spectrum and direction, allowing maximum attenuation efficiency per unit thickness and resolving the contradiction between compactness and neutron attenuation.
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 allows for improved neutron attenuation with reduced shielding thickness, enhancing the efficiency and compactness of tokamak fusion reactors, and identifies new candidate materials like nickel hydride and scandium borohydride that offer superior performance.
Implementation Method 1
determining a figure of merit for each neutron energy group based on absorption and scattering coefficients of the material for each neutron energy group
Implementation Method 2
determining a figure of merit for each neutron energy group based on absorption and scattering coefficients of the material for each neutron energy group
Data Source
AI summary
A method of selecting one or more materials of specific isotopic composition for use in a neutron shield. A first list of materials is provided, each material having a different isotopic composition. Values of incident neutron fluxes ϕg0 that the neutron shield will encounter in use are provided. A set of criteria is provided, the set of criteria including one or more of: neutron flux, neutron dose, heating of a target protected by the neutron shielding, damage to the target, gas production within the target, tritium production within the target, and transmutation of the target. For each criterion, an overall weight βcriteria is defined, and an intrinsic weighting factor αg is defined for each of a plurality of neutron energy groups based on the incident neutron fluxes. Using a computing system, an overall figure of merit Λ is calculated for each material in the first set of materials, wherein the overall figure of merit Λ for each material is based on: determining a figure of merit Λg for each neutron energy group based on absorption and scattering coefficients of the material for each neutron energy group; for each criterion, determining a figure of merit Λcriteria for the criterion based on the figures of merit for each neutron energy group, weighted by the intrinsic weighting factors for the criterion; determining an overall figure of merit Λ based on the figures of merit for each criterion, weighted by the overall weight for the criterion. A second list of materials is selected based on the overall figures of merit Λ of the materials, wherein the second list is a subset of the first list.