Digital Control Rod Positioning With Redundant Sensor Channels
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Solution Overview
Problem
Existing control rod drives in nuclear reactors lack precision, with analog sensors reducing accuracy and representing a failure risk due to lack of redundancy, particularly in large reactors like ESBWRs that require finer reactivity control.
Innovation Solution
A fully digital control rod drive system using redundant digital transducers and a motor control system with radiation-hardened components, eliminating analog-to-digital converters and enabling precise control element positioning with millimeter accuracy and self-braking capabilities, ensuring high reliability and redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog sensors are used for position detection, then device complexity is reduced, but measurement precision and reliability deteriorate
Solution Approach 1:
The patent replaces analog sensors with digital transducers (incremental or absolute encoders) in the motor control system. This substitution eliminates the need for analog-to-digital converters and associated analog circuitry, directly improving measurement precision while reducing overall system complexity through native digital signaling.
Solution Approach 2:
The patent introduces a radiation-hardened interface circuit that acts as an intermediary between the digital transducer and the control system. This interface handles signal conditioning and protection without requiring analog conversion stages, maintaining measurement precision while simplifying the system architecture by eliminating analog-to-digital conversion components.
2Reliability
If redundant digital transducers are implemented, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent segments the position detection function into multiple independent digital transducers (redundant encoders). Each transducer operates independently, and their outputs are processed separately by the control system, allowing fault isolation and continued operation even when one transducer fails, thus improving reliability without requiring complex integrated solutions.
Solution Approach 2:
The patent implements feedback processing of redundant digital transducer signals within the digital control system. The controller continuously monitors and compares outputs from multiple transducers, using logical operations to detect inconsistencies and maintain accurate position control even when one transducer provides erroneous data, thereby improving reliability through systematic feedback rather than hardware complexity.
3Measurement precision
If analog-to-digital converters are eliminated, then measurement precision is improved, but adaptability deteriorates
Solution Approach 1:
The patent changes the fundamental parameter of signal transmission from analog to digital at the sensor level. Digital transducers output discrete encoded position data directly, eliminating analog voltage signals and the need for analog-to-digital conversion. This parameter change improves measurement precision by avoiding analog signal degradation while the digital interface maintains adaptability through programmable control logic that can handle various encoder types (incremental or absolute).
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
The digital control rod drive system achieves precise control element positioning with redundancy, reducing failure risks and enhancing reliability in nuclear environments, capable of handling both fine and large movements with improved resistance to noise and vibration.
Implementation Method 1
A magnetic coupling 17 pairs internal and external magnets to rotate ball screw 11 across a pressure barrier
Implementation Method 2
During scram, hollow piston 16 may be lifted off ball nut 12 by hydraulic pressure in the outer tube
Data Source
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AI summary
Control rod drives include all-digital monitoring, powering, and controlling systems for operating the drives. Each controlling system includes distinct microprocessor-driven channels that independently monitor and handle control rod drive position information reported from multiple position sensors per drive. Controlling systems function as rod control and information systems with top-level hardware interfaced with nuclear plant operators other plant systems. The top-level hardware can receive operator instructions and report control rod position, as well as report errors detected using redundant data from the multiple sensors. Positional data received from each drive is multiplexed across plural, redundant channels to allow verification of the system using independent position data as well as operation of the system should a single channel or detector fail. Control rod drives are capable of positioning and detecting position of control elements in fine increments, such as 3-millimeter increments, with plural position sensors that digitally report drive status and position.