Modular Integrated Head Assembly for PWR Refueling
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Solution Overview
Problem
The existing integrated head assemblies for pressurized water reactors require complex and costly procedures for refueling, involving heavy components that concentrate loads on reactor vessel closure head lifting lugs, leading to potential damage and instability, and do not efficiently manage cooling of control element drive mechanisms.
Innovation Solution
A two-part integrated head assembly that distributes loads across a ring beam and lift rods attached to the reactor vessel closure head, with a shroud for radiation shielding and a forced air cooling system, allowing the upper portion to be supported by containment walls, reducing the weight on the reactor vessel and enabling separate removal and storage of components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy components are concentrated on the reactor vessel closure head lifting lugs, then the components can be supported by the lifting lugs, but the lifting lugs and reactor vessel closure head may be damaged due to excessive load concentration
Solution Approach 1:
The head assembly is divided into an upper portion and a lower portion that can be separated. The lower portion attaches to the reactor vessel closure head while the upper portion contains the heavy components (missile shield, cooling system, seismic support). This segmentation allows the heavy components to be supported by the lower portion during operation, reducing direct loads on the lifting lugs during refueling operations.
Solution Approach 2:
The upper portion of the head assembly is designed to be removable and storable separately from the lower portion. During refueling operations, the upper portion can be removed and stored in containment, eliminating the need to disassemble heavy components from the reactor vessel closure head and reducing the complexity and time of refueling procedures.
2Adaptability or versatility
If all components are supported by lift rods attached to the reactor vessel closure head, then the components can be integrated into a modular assembly, but the lift rods are subjected to unstable compressive, bending, and torsional stresses
Solution Approach 1:
The head assembly is segmented into upper and lower portions that can be independently supported. The lower portion is supported by the reactor vessel closure head lifting lugs, while the upper portion is supported by the lower portion during operation. This segmentation reduces the span and stress concentration on individual lift rods.
Solution Approach 2:
The lower portion acts as an intermediary structure between the reactor vessel closure head and the upper portion containing heavy components. During operation, the lower portion supports the upper portion, distributing loads more effectively and reducing direct stresses on the lift rods from the full weight of all components.
3Weight of moving object
If the upper portion is supported by containment walls, then the weight on the reactor vessel is reduced, but additional support structures are required
Solution Approach 1:
The head assembly is segmented into upper and lower portions with distinct support functions. The lower portion attaches to the reactor vessel closure head and supports the upper portion during operation. The upper portion is designed to be removable and storable in containment, allowing the reactor vessel to support only the lower portion weight during refueling operations.
Solution Approach 2:
The support configuration is dynamic rather than static. During normal operation, the upper portion is supported by the lower portion which attaches to the reactor vessel. During refueling operations, the upper portion is removed and stored in containment, changing the load distribution on the reactor vessel. This dynamic configuration allows the reactor vessel to be optimized for its primary support function without permanent additional structures.
4Reliability
If complex procedures are followed for refueling operations, then safety is ensured, but the critical path time and radiation exposure to personnel increase
Solution Approach 1:
The head assembly is segmented into upper and lower portions that can be independently handled during refueling operations. The lower portion remains attached to the reactor vessel closure head while the upper portion is removed and stored in containment. This segmentation eliminates the need to disassemble heavy components from the reactor vessel, significantly reducing the number of steps and time required for refueling operations while maintaining safety through controlled procedures.
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 minimizes the critical path time and radiation exposure during refueling, reduces the need for polar crane upgrades, and allows for efficient cooling of control element drive mechanisms while maintaining structural integrity and stability, without requiring additional support from the reactor vessel.
Implementation Method 1
a forced air cooling system, allowing the upper portion to be supported by containment walls
Data Source
AI summary
A two-part integrated head assembly (100) is disclosed wherein the lower portion (110) attaches to, and is supported by, the reactor vessel closure head (90), and the upper portion (160) is fluidly connected to the lower portion, but is supported externally from the reactor vessel closure head. In the disclosed embodiment, the upper portion includes transverse support beams (170) that engage containment walls (92), for example steam generator walls, to support the upper portion. A duct (150) releasably connects a fan plenum (165) in the upper portion with an annular plenum in the lower portion, such that fans (166) can draw heated air from around the CEDMs (95). In one embodiment, a chiller (168) is provided in the fan plenum to cool the air prior to expelling it in containment. A missile shield (169) is also provided in the upper portion.