Nuclear Spring Apparatus for Fuel Assembly Hold-Down Force
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Solution Overview
Problem
Existing hold-down spring packs in nuclear reactors face challenges in maintaining a consistent downward force on fuel assemblies due to thermal expansion and neutron bombardment, leading to issues such as fuel assembly lift-off or distortion, as they struggle to balance forces across the reactor's life cycle.
Innovation Solution
The improved spring apparatus is designed with a configuration that includes elongated plate-like springs and a support apparatus, where the engagement of springs with the upper core plate varies with temperature, providing tailored load/deflection performance by adjusting the length and spacing of components to maintain optimal compressive force across different operational conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional spring packs are used to provide downward force on fuel assemblies, then hold-down force is provided during reactor operation, but the hold-down force becomes inconsistent due to thermal expansion and neutron bombardment, leading to fuel assembly lift-off or distortion
Solution Approach 1:
The spring pack design incorporates parameters that change in response to thermal and irradiation conditions. The springs are configured with specific initial compressive forces and geometric parameters that allow them to maintain consistent hold-down force despite temperature changes and neutron bombardment effects on the fuel assemblies.
Solution Approach 2:
The spring pack is designed as a dynamic system where the springs can compress and extend to accommodate changes in fuel assembly dimensions due to thermal expansion and irradiation growth. This dynamic capability allows the spring pack to maintain consistent hold-down force throughout the fuel cycle despite changing operational conditions.
2Force
If spring force is increased to prevent fuel assembly lift-off during cold operation, then hold-down force is sufficient during cold conditions, but excessive force causes fuel assembly distortion and handling damage during hot operation
Solution Approach 1:
The spring pack design explicitly accounts for thermal expansion of the fuel assemblies. The springs are configured with initial compressive forces that consider the thermal expansion characteristics of the fuel assembly materials, allowing the hold-down force to be sufficient during cold operation while reducing to appropriate levels during hot operation when the fuel assemblies have expanded.
Solution Approach 2:
The spring pack is pre-configured with specific compressive forces and geometric parameters during manufacturing to anticipate and compensate for thermal and irradiation effects that will occur during reactor operation. This preliminary configuration ensures appropriate hold-down force across the entire fuel cycle without requiring active control adjustments.
3Ease of manufacture
If spring pack design is simplified for ease of manufacture, then manufacturing cost and complexity are reduced, but the ability to maintain consistent hold-down force under varying operational conditions is compromised
Solution Approach 1:
The spring pack is divided into multiple individual springs rather than a single complex mechanism. This segmentation allows each spring to be manufactured using standard, simple processes while the collective arrangement of multiple springs provides the required reliability and consistency of hold-down force under varying operational conditions.
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 reduces compressive forces during hot operation and increases them during cold operation, ensuring a stable downward force on fuel assemblies, thereby preventing lift-off and distortion, and can be customized for specific nuclear installation needs.
Implementation Method 1
a first spring of the plurality of springs is an elongated plate-like spring having a first end and a second end opposite the first end, the first spring being flexible in a longitudinal direction between the first end and the second end
Implementation Method 2
the coefficient of thermal expansion of the Zirconium alloy from which the fuel apparatuses are made is less than that of the stainless steel from which the reactor containment is made
Data Source
Figure 1
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AI summary
A spring apparatus in accordance with the disclosed and claimed concept is usable in a nuclear installation. In one embodiment, the spring apparatus includes a plurality of springs that are in a compressed state and that are compressively engaged with an upper core plate of a nuclear reactor when the reactor is in a cold condition. However, when the reactor is in a hot condition, a spring of the plurality of springs is in a free state wherein a free end of the spring is in an uncompressed state and is disengaged from the upper core plate. In another embodiment, the spring apparatus employs a support apparatus that is also in accordance with the disclosed and claimed concept and that includes one or more bumpers that engage the springs of a spring pack from the underside.