BWR Fuel Assembly Redundant Load Chain for Lift Reliability
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Solution Overview
Problem
The existing nuclear fuel assemblies for Boiling Water Reactors (BWRs) face reliability issues during lifting due to the risk of water channel breakage, which can lead to the disconnection of the lower tie plate from the upper tie plate, causing potential damage to other fuel assemblies or generating debris.
Innovation Solution
Incorporation of tie rods forming an auxiliary load chain that connects the lower tie plate to the upper tie plate in case of water channel breakage, with a stopping member that activates only when the main load chain fails, ensuring the fuel assembly remains unitary and prevents parts from falling or generating debris.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If water channels are used as the main load chain to connect lower tie plate to upper tie plate, then the fuel assembly structure is simplified and water channels serve dual purpose (coolant flow and load bearing), but the reliability during lifting deteriorates due to risk of water channel breakage
Solution Approach 1:
The load-bearing function is segmented between two independent systems: water channels for normal operation and tie rods with stopping members for redundancy. This segmentation allows each component to specialize in its function while maintaining overall system reliability.
Solution Approach 2:
The stopping member is positioned in advance at a location that will engage if the water channel fails. This pre-positioned safety mechanism provides immediate protection upon failure without requiring active detection or control systems.
2Reliability
If tie rods are added as auxiliary load chain to prevent downward movement of base, then the reliability during lifting is improved, but the device complexity increases due to additional components
Solution Approach 1:
The tie rods serve multiple functions: they provide structural support during normal operation, act as a redundant load-bearing path during water channel failure, and work with stopping members to prevent base disconnection. This multi-functionality justifies the added complexity.
Solution Approach 2:
The stopping members are strategically positioned only at critical locations where they can prevent catastrophic failure. This localized approach to safety adds minimal complexity while providing maximum protection.
3Reliability
If stopping member is positioned close to abutting surface to activate quickly upon water channel failure, then the reliability is improved by preventing base disconnection, but the manufacturing precision requirement increases to ensure proper spacing
Solution Approach 1:
The stopping member is pre-positioned during assembly at a calculated distance from the abutting surface. This preliminary positioning ensures that upon water channel failure, the stopping member engages within a controlled distance to prevent catastrophic disconnection.
Solution Approach 2:
The spacing between the stopping member and abutting surface is optimized as a design parameter. By carefully selecting this parameter, the system achieves reliable failure response while maintaining reasonable manufacturing tolerances.
Data Source
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AI summary
The fuel assembly extends along a fuel assembly axis (L) and comprises a base (3) including a lower tie plate (4), a head (5) including an upper tie plate (6) and a lift handle (7), a bundle of fuel rods (8) extending axially between the lower tie plate (4) and the upper tie plate (6), and a water channel (10) extending within the bundle of fuel rods (8) with axially connecting the base (3) to the head (5) such that the load of the base (3) is transferred to the head (5) via the water channel (10). The fuel assembly further comprises a tie rod (20) extending between the base (3) and the head (5), the tie rod (20) being axially fixed to the base (3) and connected to the head (5) via a connection assembly (22) comprising a stopping member (30) configured to abut an abutting surface (32) of the head (5) for limiting a downward movement of the base (3) relative to the head (5) during lifting of the fuel assembly (2), in case of a breakage of the water channel (10).