Control Rod Disconnect Mechanism for Remote CRDM Decoupling
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Solution Overview
Problem
Existing control rod systems in nuclear reactors lack the ability to remotely and efficiently engage and disengage translating control rods from control rod drive mechanisms (CRDMs) during extended shutdown periods for maintenance.
Innovation Solution
A control rod drive mechanism with a torque tube and a disconnect mechanism that includes a connecting rod, a lock cam assembly, and a locking collar, allowing for axial movement of the connecting rod to switch between rotatable and non-rotatable positions relative to the torque tube, enabling remote engagement and disengagement of control rods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control rods are permanently coupled to CRDMs, then reliability of control is improved, but adaptability for remote disengagement during shutdown is lost
Solution Approach 1:
The coupling system is segmented into separable components: the CRDM with torque tube, the connecting rod with lock cam assembly, and the spider with locking collar. This segmentation enables the control rod assembly to be divided into discrete parts that can be independently positioned and reconfigured, allowing permanent coupling during operation and remote disengagement during shutdown periods.
Solution Approach 2:
The coupling mechanism transitions from a static permanent connection to a dynamic system with two distinct states: an engaged state during normal operation where the lock cam and locking collar maintain a secure connection, and a disengaged state during shutdown where the connecting rod can be remotely moved to separate the control rod assembly from the CRDM. This dynamic capability resolves the contradiction between reliability and adaptability.
2Adaptability or versatility
If control rods are detachable from CRDMs, then adaptability for remote engagement/disengagement is improved, but device complexity increases
Solution Approach 1:
The lock cam assembly and locking collar are designed to automatically engage and lock when the connecting rod is in the engaged position, eliminating the need for complex manual locking procedures. The mechanism uses the inherent geometry of the lock cam and locking collar to self-lock, reducing operational complexity while maintaining adaptability for remote engagement and disengagement.
Solution Approach 2:
The lock cam assembly acts as an intermediary element between the connecting rod and the spider assembly. This intermediary mechanism simplifies the overall coupling system by providing a dedicated locking interface that mediates the connection and disconnection processes, making the detachable feature more manageable despite the added complexity of separability.
3Measurement precision
If manual intervention is required for control rod engagement/disengagement, then control precision is improved, but productivity and operational efficiency decrease
Solution Approach 1:
The coupling mechanism is designed to automatically engage and lock when the connecting rod is positioned in the engaged state, eliminating the need for manual intervention to secure the connection. The lock cam and locking collar self-lock through their geometric design, maintaining precise engagement control while significantly improving operational efficiency during both engagement and disengagement operations.
Data Source
AI summary
A control rod drive mechanism having a torque tube, a control rod assembly including a connecting rod and a spider, a lock cam assembly rotatably secured to a bottom end of the connecting rod and including a locking cam, and a locking collar disposed non-rotatably within the spider, the locking collar including a locking recess with an entry slot, wherein in a first axial position the lock cam assembly is rotatable with respect to the torque tube, and a second axial position the lock cam assembly is non-rotatable with respect to the torque tube.