Reactor Shutdown System Redundant Control Pathways
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Solution Overview
Problem
Conventional reactor shutdown systems face difficulties in safely shutting down a reactor during malfunctions, particularly when a common cause failure occurs in the safety protection-system device, making it challenging to activate the reactor trip breaker effectively.
Innovation Solution
A reactor shutdown system that includes a power converter with a storage unit, a main stop-control device, and an auxiliary stop-control device, where the auxiliary device can take over power interruption if the main device fails, using a detection sensor to determine shutdown signals and a delay circuit to manage signal transmission, ensuring the reactor can be safely shut down by various means.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a digital safety protection-system device is used to control the reactor trip breaker, then the control precision and reliability are improved, but the system becomes vulnerable to common cause failures that prevent activation of the breaker
Solution Approach 1:
The shutdown control function is segmented into two independent pathways: the main stop-control device controlling the breaker, and the auxiliary stop-control device controlling the power converter. This segmentation ensures that a failure in one pathway does not prevent shutdown capability, as the other pathway remains operational.
Solution Approach 2:
The power converter acts as an intermediary component between the auxiliary stop-control device and the control-rod drive unit. By controlling the power converter instead of directly controlling the breaker, the system provides an alternative shutdown pathway that bypasses failures in the main control system.
2Speed
If the main stop-control device is used to control the breaker for shutdown, then the shutdown response is direct and fast, but the system fails to shut down when the main device malfunctions
Solution Approach 1:
The auxiliary stop-control device and power converter are prepared in advance as a backup shutdown pathway. When the main stop-control device fails, the auxiliary device can immediately take over and control the power converter to achieve shutdown, ensuring both speed and reliability.
Solution Approach 2:
The system incorporates a redundant auxiliary shutdown pathway that cushions against the risk of main control device failure. This prior cushioning ensures that even if the main device malfunctions, the shutdown capability is preserved through the auxiliary pathway.
3Reliability
If a redundant auxiliary stop-control device and power converter are added to the system, then the shutdown reliability under failure conditions is improved, but the device complexity increases
Solution Approach 1:
The power converter serves multiple functions: it acts as a power conversion device during normal operation and as a shutdown control component when the main stop-control device fails. This multi-functionality reduces the need for completely separate redundant systems, thereby limiting the increase in complexity.
Solution Approach 2:
The auxiliary stop-control device utilizes the existing power converter infrastructure to achieve shutdown functionality, rather than requiring entirely separate shutdown mechanisms. This self-service approach leverages existing components to provide redundancy, reducing overall system complexity.
Data Source
AI summary
A reactor shutdown system includes a reactor, a control-rod drive unit that can drive a control rod in pulling and inserting directions with respect to a fuel assembly, a power source that can supply power to the control-rod drive unit, and a power converter that is provided between the control-rod drive unit and the power source, in which when power supply is cut off, the control-rod drive unit inserts the control rod into the fuel assembly to stop nuclear reaction in the reactor, and the reactor shutdown system includes a reactor trip breaker provided between the power converter and the control-rod drive unit, a safety protection-system device that controls the reactor trip breaker to cut off power supply to the control-rod drive unit, and a CCF device that controls the power converter to cut off power supply to the control-rod drive unit.