VVER Fuel Assembly Cladding Reduction for Neutronic Yield
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Solution Overview
Problem
The existing nuclear reactor fuel assemblies for VVER-440, VVER-1000, and VVER-1200 reactors have a low water-to-uranium ratio, which limits their energy yield and neutronic performance.
Innovation Solution
The solution involves reducing the outer diameter of the fuel element cladding while maintaining the same fuel pellet diameter, thereby increasing the water-to-uranium ratio. This is achieved by adjusting the fuel element spacing and using a 2-stage spring lock to secure the fuel pellets within the cladding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the outer diameter of fuel element cladding is reduced, then the water-to-uranium ratio increases, but the structural strength and rigidity of the fuel assembly may deteriorate
Solution Approach 1:
The patent changes the geometric parameters of the fuel assembly by reducing the outer diameter of the cladding from 9.1 mm to 8.6 mm and adjusting the fuel pellet diameter to 7.57-7.60 mm. This parameter optimization increases the water-to-uranium ratio from 1.41-1.47 to the optimal value of 1.9, while maintaining structural integrity through careful selection of new parameter combinations
Solution Approach 2:
The fuel assembly design integrates multiple functions: the cladding provides both containment and structural support, the spring lock mechanism provides both fuel pellet retention and compression force, and the spacer grids provide both positioning and rigidity. This multi-functionality allows the system to achieve improved neutronic characteristics without sacrificing structural strength
2Loss of substance
If the outer diameter of fuel element cladding is reduced, then metal consumption decreases, but the mechanical stability of fuel pellets may worsen
Solution Approach 1:
The patent optimizes the cladding outer diameter parameter to 8.6 mm (reducing from 9.1 mm) and adjusts the fuel pellet diameter to 7.57-7.60 mm. This parameter change reduces metal consumption for cladding while the spring lock mechanism compensates for mechanical stability by providing continuous compression force on the fuel pellets
Solution Approach 2:
The spring lock mechanism acts as an intermediary between the cladding and fuel pellets. It transfers and maintains the compression force necessary for mechanical stability, allowing the cladding to be thinner while still ensuring proper fuel pellet support and positioning throughout the reactor operation
3Quantity of substance
If the grid spacing of fuel elements is increased, then the water-to-uranium ratio increases, but the transverse rigidity of the fuel assembly deteriorates
Solution Approach 1:
The patent increases the grid spacing parameter from 12.2-12.3 mm to 12.6-12.75 mm, which increases the water-to-uranium ratio. Simultaneously, the cladding outer diameter is reduced to 8.6 mm and the fuel pellet diameter is optimized to 7.57-7.60 mm, creating a new parameter balance that maintains rigidity while improving neutronic characteristics
Solution Approach 2:
The patent applies different local qualities to different parts of the fuel assembly: the cladding has optimized thickness and diameter for neutron economy, the spacer grids maintain appropriate spacing for water flow, and the spring lock provides localized compression. This local optimization allows increased grid spacing without sacrificing overall structural rigidity
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
The proposed design significantly increases the water-to-uranium ratio, reduces metal consumption, and enhances the neutronic characteristics and energy yield of the fuel assemblies.
Implementation Method 1
a 2-stage spring lock resting on the cladding of the fuel element, pressing the fuel pellets in the axial direction
Implementation Method 2
sealed with a plug and a tip using butt resistance welding
Data Source
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AI summary
The invention relates to the field of nuclear engineering, and more particularly to fuel assemblies for VVER-type nuclear reactors. The present fuel assembly comprises a bundle of fuel elements arranged in a regular triangular pattern with a spacing of 12.2-12.3 mm within spacer grids connected to a central tube, a hexagonal casing connected to a top nozzle and bottom nozzle, and a debris filter. The outside diameter of the cladding of the fuel elements is 0.720-0.733 of the spacing of the pattern, the diameter of the fuel pellets being 7.57-7.60 mm. In a second embodiment, the fuel assembly has a regular triangular pattern with a spacing of 12.60-12.75 mm and a reinforcing structure of spacer grids connected by longitudinal tubes and corner elements, wherein the outside diameter of the cladding of the fuel elements is 0.695-0.710 of the spacing of the pattern, the diameter of the fuel pellets being 7.57-7.60 mm. The invention makes it possible to increase the water-to-uranium ratio of fuel assemblies, reduce the metal requirement of such assemblies, and improve their neutronic characteristics and energy yield.