Helically Twisted Fuel Assembly Mixed Grid Pattern
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Solution Overview
Problem
Conventional nuclear reactor fuel assemblies for CANDU reactors have inefficiencies in space utilization and fuel burnup, as they occupy less than optimal areas within the reactor tubes, leading to suboptimal fuel performance and safety concerns.
Innovation Solution
The development of a fuel assembly with helically twisted fuel elements arranged in a mixed grid pattern, including rectangular and triangular patterns, that alternates and is supported by a frame-shaped structure, allowing for improved packing density and self-spacing within the reactor tube, utilizing a shroud to maximize the internal cross-sectional area occupancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional fuel assemblies with square or hexagonal grid patterns are used, then the assembly structure is simple and easy to manufacture, but the space utilization within the reactor tube is suboptimal (occupying only 63.7% or 82.7% of the tube area)
Solution Approach 1:
The patent applies spheroidality by transitioning from conventional square or hexagonal fuel rod arrangements to a circular perimeter configuration. The fuel elements are arranged in concentric circles around a central element, with the outermost elements defining a substantially circular perimeter. This circular arrangement optimizes space utilization within the cylindrical reactor tube, achieving greater than 90% occupancy of the tube's cross-sectional area, compared to 63.7% for square grids and 82.7% for hexagonal grids. The curvature of the circular arrangement allows more efficient packing of fuel elements within the circular boundary of the reactor tube.
2Area of stationary object
If fuel elements are arranged in concentric circles with circular perimeter, then space utilization increases to greater than 90% of tube area, but the manufacturing and assembly complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the fuel assembly into distinct concentric circular layers or rings of fuel elements. The fuel elements are arranged in a central element surrounded by first, second, and third concentric circles of elements. This segmented circular arrangement allows for modular manufacturing and assembly, where each circular layer can be independently prepared and then assembled together, reducing the overall manufacturing complexity despite the advanced geometric configuration.
3Productivity
If conventional fuel rod spacing is used, then the assembly structure is simple, but fuel burnup power and operating time are limited due to suboptimal space utilization
Solution Approach 1:
The patent applies dimensionality change by transitioning from conventional two-dimensional square or hexagonal grids to a three-dimensional concentric circular arrangement. The fuel elements are organized in multiple concentric circles around a central element, creating a radial dimension that optimizes space utilization. This dimensional reorganization allows for greater than 90% occupancy of the reactor tube cross-section, enabling increased fuel burnup power and extended operating time while managing the complexity through systematic radial layering.
Data Source
AI summary
A fuel assembly for use in a core of a nuclear power reactor. The assembly includes a plurality of helically twisted fuel elements supported by a frame in a fuel rod bundle. Each of the fuel elements includes fissile material. When viewed in a cross-section that is perpendicular to an axial direction of the fuel assembly, the outermost fuel elements of the fuel rod bundle define a substantially circular perimeter. The fuel elements are arranged in a mixed grid pattern that includes a first, rectangular grid pattern and a second, triangular grid pattern.