Passive Thermal Shutdown System for Small Nuclear Reactors
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Solution Overview
Problem
Conventional nuclear reactor shutdown systems are not easily adaptable for use in small-sized nuclear reactors, which lack a primary cooling system and rely on solid-state heat conduction.
Innovation Solution
A nuclear reactor shutdown system comprising a housing vessel with neutron absorbers, a shielded path extending through the reactor core fuel, and a communicating part that opens the housing vessel when reaching a threshold temperature, allowing the neutron absorbers to fall into the shielded path and shut down the reactor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nuclear reactor shutdown systems are used, then shutdown reliability is improved, but adaptability to small-sized reactors deteriorates
Solution Approach 1:
The shutdown system is segmented into independent components: a housing vessel containing neutron absorbers, a shielded path through the reactor core, and a communicating part. This segmentation allows the system to be adapted to small-sized reactors by adjusting the size and configuration of these modular components while maintaining the core shutdown function.
Solution Approach 2:
The housing vessel serves multiple functions: it houses the neutron absorbers, provides a sealed environment, and includes an opening for neutron absorber release. The communicating part serves as both a seal and a temperature-responsive release mechanism. This multi-functionality reduces the number of separate components needed, making the system more adaptable to compact reactor designs.
2Volume of moving object
If small-sized nuclear reactors without primary cooling systems are used, then reactor size is reduced, but shutdown system complexity increases
Solution Approach 1:
The communicating part is designed to automatically respond to temperature changes by opening the housing vessel opening when a threshold temperature is reached. This self-service mechanism eliminates the need for external control systems, actuators, or complex control logic, thereby reducing shutdown system complexity while maintaining effective shutdown capability in compact reactors.
Solution Approach 2:
The temperature-responsive opening mechanism replaces complex mechanical or electronic control systems with a passive thermal response system. The communicating part utilizes thermal expansion, melting, or phase change to automatically open the housing vessel, eliminating the need for sensors, controllers, and actators that would increase system complexity.
3Device complexity
If passive neutron absorber release mechanism is used, then system simplicity is improved, but response speed may deteriorate
Solution Approach 1:
The communicating part is designed with specific material properties and geometric dimensions that optimize its thermal response characteristics. By carefully selecting the material's melting point or phase change temperature to match the reactor's critical temperature, and by optimizing the opening size and shape, the system achieves rapid response while maintaining simplicity.
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 system enables safe and quick shutdown of small-sized nuclear reactors by passively releasing neutron absorbers into the reactor core upon temperature increase, without requiring special control functions.
Implementation Method 1
a communicating part that is disposed so as to close the opening and causes the housing vessel and the shielded path to communicate with each other when the communicating part reaches or exceeds a threshold temperature
Implementation Method 2
causing the neutron absorbers housed in the housing vessel to fall down into the shielded path through the opening when the communicating part reaches or exceeds the threshold temperature
Data Source
AI summary
A nuclear reactor shutdown system includes a housing vessel that is disposed above a reactor core fuel housed in a nuclear core vessel in a hermetically sealed manner, houses a plurality of neutron absorbers, and has an opening enabling the neutron absorbers to pass through at a bottom, a shielded path that passes through the reactor core fuel to extend in an up-and-down direction, an upper end of the shielded path communicating with the opening of the housing vessel and a lower end of the shielded path being closed, and a communicating part that is disposed so as to close the opening and causes the housing vessel and the shielded path to communicate with each other when the communicating part reaches or exceeds a threshold temperature.