Nuclear Fuel Assembly Spacing With Flexible Oval Tubes
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Solution Overview
Problem
Existing fuel assembly designs for nuclear reactors face issues with increased hydraulic resistance, corrosion, and local stress in fuel element claddings due to complex structures and rigid spacing elements, leading to potential vibration, fretting, and accelerated corrosion.
Innovation Solution
The design incorporates thin-walled round tubes with longitudinal through slots as spacing elements, allowing for transverse compression to form an oval cross section in contact zones with the jacket, increasing spacing contacts and reducing local stresses, and using a method that compresses the fuel element bundle during assembly to achieve optimal spacing tension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple grids and rigid spacing elements are used to retain and space fuel elements, then fuel element spacing reliability is improved, but hydraulic resistance increases and heat transfer conditions worsen
Solution Approach 1:
The patent removes the complex system of multiple rigid grids and spacing elements, extracting only the essential spacing function. Fuel elements are retained solely by the end grids, eliminating intermediate spacing grids that caused hydraulic resistance issues while maintaining spacing reliability through the simplified structure.
Solution Approach 2:
The patent introduces flexible retaining elements made of materials with high elastic properties (such as phosphor bronze or beryllium copper) that can deform elastically under load. These flexible elements adapt to fuel element dimensional changes without requiring rigid structural support, reducing hydraulic resistance while maintaining spacing stability.
2Reliability
If multiple grids and retaining elements are installed along the fuel assembly axis, then fuel element retention reliability is improved, but the structure complexity and metal intensity increase
Solution Approach 1:
The patent extracts and eliminates the complex system of multiple retaining grids and spacing elements installed along the fuel assembly axis. Only the end grids remain for retention functions, dramatically simplifying the structure while maintaining reliability through the flexible retaining elements that compensate for dimensional changes.
Solution Approach 2:
The end grids are designed to perform multiple functions: they provide structural support, retain fuel elements, and work in conjunction with flexible retaining elements that adapt to thermal and radiation-induced dimensional changes. This multi-functional design eliminates the need for separate intermediate retaining structures.
3Stability of the object's composition
If rigid spacing elements are used to maintain fuel element geometry, then spacing stability is improved, but corrosion and radiation-induced creep increase due to geometric changes
Solution Approach 1:
The patent replaces rigid static spacing elements with dynamic flexible retaining elements made of elastic materials. These elements can deform and adapt to gradual dimensional changes in fuel elements caused by thermal expansion and radiation-induced creep, maintaining contact stability without generating stress concentrations that lead to corrosion and fretting.
Solution Approach 2:
The patent changes the material parameters of the retaining elements, selecting materials with high elastic properties (phosphor bronze, beryllium copper) that can accommodate dimensional changes in fuel elements. This parameter change allows the retaining elements to maintain stable spacing while adapting to thermal and radiation effects, preventing corrosion and fretting.
4Strength
If a complex frame structure with jacket, central pipe, and tie bars is used, then fuel assembly strength and rigidity are improved, but the flow section for coolant passage is reduced and hydraulic resistance increases
Solution Approach 1:
The patent extracts and eliminates the complex frame structure including the jacket, central pipe, and tie bars. The fuel assembly relies on the simplified end grid structure combined with flexible retaining elements to provide necessary strength and rigidity, dramatically increasing the coolant flow section and reducing hydraulic resistance.
Solution Approach 2:
The patent uses flexible retaining elements as thin-walled structures that provide necessary mechanical function with minimal material. These elastic retaining elements maintain fuel element spacing and assembly integrity without the bulk of rigid frame structures, preserving coolant flow paths and reducing hydraulic resistance.
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 design enhances the reliability of fuel element spacing, reduces local stresses, and decreases the probability of corrosion and deformation, improving the operational stability and neutronic parameters of the reactor core.
Implementation Method 1
thin-walled round tubes with longitudinal through slots as spacing elements, allowing for transverse compression to form an oval cross section in contact zones with the jacket
Implementation Method 2
using a method that compresses the fuel element bundle during assembly to achieve optimal spacing tension
Data Source
AI summary
A fuel assembly design for nuclear reactors that is used in fast neutron reactor cores to provide more reliable spacing of a fuel element bundle in a fuel assembly and reduced local stress in the cladding of the fuel elements in the region where the elements are in contact with spacing elements. The fuel assembly has a top nozzle and a bottom nozzle which are connected to one another by a jacket. A bundle of rod-type fuel is elements arranged in the fuel assembly with the aid of a grid and spiral spacer elements wrapped around the cladding of each fuel element. At least the peripheral fuel elements in the bundle are provided with spacer elements in the form of thin-walled tubes with longitudinal through slots, wherein the elements have a substantially oval cross section in the regions where they are in contact with the jacket.