Control Rod Drive Hold-Out Latch for Refueling Without Shaft Removal
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Solution Overview
Problem
The challenge of refueling nuclear reactors is complicated by the impracticality of removing and replacing control rod drive shaft assemblies (CRDSAs) due to their long lengths, which cannot be easily removed through the top of the reactor vessel during refueling, especially in reactors with removable lower vessel portions.
Innovation Solution
A control rod drive mechanism (CRDM) with a drive shaft hold out mechanism (RHO) that suspends the CRDSA at a height above the normal travel range without electrical power, using a passive engagement process involving balls and a sleeve to hold the CRDSA in place during refueling, allowing it to remain in the reactor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the CRDSA is removed during refueling, then the fuel can be replaced, but the CRDSA cannot be removed through the top of the reactor vessel due to its long length
Solution Approach 1:
The invention extracts the CRDSA from the refueling process by leaving it in place within the reactor vessel. Instead of removing the CRDSA through the top of the vessel (which is impossible due to its length), the system allows the CRDSA to remain suspended while only the fuel assemblies are removed and replaced through the top access point.
Solution Approach 2:
The hold out mechanism is pre-positioned within the CRDM to automatically engage with the CRDSA before refueling operations begin. This preliminary engagement ensures the CRDSA is securely held in place at the start of refueling, preventing it from falling into the reactor core when the lower vessel portion is removed.
2Productivity
If the CRDSA remains in the reactor during refueling, then refueling can proceed without removing the CRDSA, but the CRDSA must be held at a height above normal travel range
Solution Approach 1:
The hold out mechanism is designed as a self-actuating system that uses the weight of the CRDSA itself to trigger engagement. When the CRDSA is lowered into the CRDM, its own gravity causes it to engage with the hold out mechanism automatically, raising and suspending itself at the required height without external intervention.
Solution Approach 2:
The invention introduces a passive mechanical intermediary system consisting of balls and a sleeve within the hold out mechanism. These components act as mediators between the CRDSA and the CRDM structure, transferring the load and maintaining the CRDSA at the elevated position through simple mechanical interaction rather than complex active control systems.
3Reliability
If a passive engagement process is used to hold the CRDSA, then electrical power is not required, but the mechanism must reliably engage without active control
Solution Approach 1:
The passive engagement process is self-regulating through gravity and mechanical geometry. The CRDSA's weight automatically drives the engagement sequence, and the mechanical design ensures that once engaged, the system maintains holding position without requiring external power or control systems. The mechanism uses the CRDSA's own mass as the driving force for reliable engagement.
Solution Approach 2:
The passive mechanism incorporates mechanical features that anticipate and accommodate potential misalignments or variations in the engagement process. The design includes tolerance zones and progressive engagement stages that ensure reliable latching even without active control, preventing failure modes before they can occur during refueling operations.
Data Source
AI summary
Techniques for latching a shaft assembly with an integrated system are discussed herein. The integrated system including a nuclear reactor configured to raise a stem of the shaft assembly into a hold out. The hold out can include a sleeve, and metallic balls, the metallic balls being positioned in openings of the sleeve. The hold out can include a housing positioned around the sleeve and the metallic balls. The housing can include a gap that is narrower than a chamber of the housing. The hold out can include a spring coupled to the sleeve. The hold out can include an electromagnetic coil configured to engage the spring and the sleeve to raise the stem until the metallic balls are moved from positions between the gap of the housing and the stem, to positions between the chamber of the housing and the stem.