Nuclear Control Element Interlocks Against Simultaneous Withdrawal

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Solution Overview

Problem

Computerized control systems in nuclear reactors face an increased risk of malfunction and non-operation due to errors such as incorrect automated responses, malware, and cyber threats, leading to potential quick and simultaneous over-withdrawal of control elements without operator intervention, resulting in unwanted excess reactivity and plant damage.

Innovation Solution

Implementing a hardware-based withdrawal controller interfaced with interlocks that use non-software, processor-based logic circuits to generate output signals, ensuring that only a subset of control elements can be withdrawn at a time, and requiring a trusted release command from the controller to disengage interlocks, preventing full withdrawal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If computerized control systems are used to automate control element movement, then operational efficiency and speed are improved, but the risk of malfunction and errors increases

Engineering Contradiction:

Improveoperational efficiencyVSAvoidrisk of malfunction

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

A hardware interlock device is introduced as an intermediary between the computerized control system and the control element drive mechanism. This interlock physically prevents simultaneous withdrawal of multiple control elements by using mechanical latches and release mechanisms that can only be activated through trusted controller signals, thereby isolating the harmful effects of software errors while preserving automated operation benefits

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces purely software-based control with a hybrid system where critical safety functions are implemented through hardware mechanics. The interlock device uses mechanical latches, springs, and levers that physically enforce withdrawal limitations, substituting the mechanical safety system for vulnerable software control logic

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Speed

If multiple control elements can be withdrawn simultaneously, then response time to reactor conditions is improved, but the risk of excess reactivity and plant damage increases

Engineering Contradiction:

Improveresponse timeVSAvoidexcess reactivity

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The control element withdrawal function is segmented into individual controlled actions rather than a simultaneous batch operation. Each control element has its own interlock mechanism that independently evaluates and controls its withdrawal, preventing the harmful effect of simultaneous withdrawal while maintaining individual response capability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The interlock device applies preliminary anti-action by physically blocking the withdrawal path of control elements before erroneous simultaneous withdrawal can occur. The mechanical latches prevent the harmful action from happening in the first place, rather than attempting to correct it after occurrence

Inventive Principle:

Principle #9Preliminary anti-action

3Reliability

If hardware interlocks are added to prevent control element withdrawal errors, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improveprevention of withdrawal errorsVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The interlock device merges multiple safety functions into a single integrated hardware unit that combines latches, release mechanisms, and signal interfaces. This consolidation reduces the overall complexity compared to implementing separate independent safety systems, while maintaining reliable prevention of withdrawal errors through unified hardware control

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20250226124A1Systems and methods for limiting control element movement in nuclear power plants

Publication Date: 2025.07.10 GE HITACHI NUCLEAR ENERGY AMERICAS LLC

AI summary

Systems and methods provide reliable checks on nuclear core reactivity increases by proscribing certain types of removal of control elements. Controllers are associated with one or more limiters on control elements to stop withdrawal as needed, such as in erroneous or dangerous element movement scenarios. Controllers may use hardware not subject to software reprogramming to monitor, select, and control limiters and resultant element movement. Limiters may physically interrupt control elements and/or drives for the same, such as by being positioned in their normal operating ranges or eliminating their power. Limiters may use a reliable command from the controller to disengage and allow withdrawal; however, insertion or otherwise decreasing reactivity may be possible in any limiter state. Limiters and controllers may be installed in any plant and element configuration with proper positioning and sizing. Other reactor operations and element manipulations may not be affected, only unwanted or dangerous control element removals.