Passive Corium Cooling via Segmented Channel Natural Circulation
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Solution Overview
Problem
Conventional molten core cooling methods in nuclear reactors are prone to equipment failure and operator errors during severe accidents, leading to safety risks due to the need for mechanical operation and potential steam explosions from direct molten core-coolant contact.
Innovation Solution
A passive molten core cooling apparatus featuring a reactor vessel, core catcher, and a channel structure with a coolant channel divided into two sections for spontaneous coolant circulation, where the coolant rises and descends to maintain constant flow without mechanical operation, and a second pipe for vapor discharge to prevent direct contact and steam explosions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a motor-operated valve or mechanical valve is used to supply coolant, then coolant can be supplied to cool the molten core, but equipment failure, loss of operating power, operator misjudgment, or malfunction can occur leading to safety risks
Solution Approach 1:
The system uses natural circulation of coolant driven by temperature differences and gravity to automatically supply coolant to the molten core without requiring external power or operator intervention. The coolant naturally flows from the coolant tank through the coolant channel and back, creating a self-sustaining cooling system that eliminates the need for motor-operated valves or complex mechanical valve operations.
Solution Approach 2:
The patent replaces motor-operated valves and complex mechanical valve systems with a passive natural circulation system. Instead of using powered mechanical components to control coolant flow, the system relies on thermal buoyancy and gravity to drive coolant circulation, thereby eliminating the reliability issues associated with powered mechanical systems.
2Temperature
If coolant is filled into the reactor cavity after the accident to cool the molten core, then cooling can be achieved, but direct contact between high-temperature molten core and low-temperature coolant may cause steam explosion
Solution Approach 1:
The patent introduces an intermediary cooling structure consisting of a coolant channel with heat exchange surfaces. The coolant flows through this channel which is positioned adjacent to the molten core, allowing heat transfer from the molten core to the coolant without direct contact between the two. This intermediary heat exchange mechanism enables effective cooling while preventing steam explosion.
Solution Approach 2:
The cooling system is segmented into separate functional zones: the molten core region, the coolant channel with heat exchange surfaces, and the coolant tank. This segmentation allows the coolant to be kept separate from the molten core while still achieving thermal coupling through the heat exchange surfaces, thereby preventing direct contact and steam explosion.
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
Ensures efficient cooling of the molten core through natural circulation and passive coolant replenishment, preventing equipment failure and operator mistakes, while avoiding direct molten core-coolant contact to prevent steam explosions.
Implementation Method 1
when a severe accident occurs, the coolant rises up along the first channel, and the coolant descends along the second channel, such that the coolant is spontaneously circulated through the coolant channel
Implementation Method 2
a channel structure having a coolant channel located below the core catcher and filled with a coolant
Data Source
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AI summary
The present invention relates to a passively-operated corium cooling apparatus comprising: a nuclear reactor vessel; a core catcher positioned at the lower part of the nuclear reactor vessel; a flow path structure positioned at the lower part of the core catcher, and having a coolant flow path filled with a coolant; and a coolant tank communicating with the flow path structure through a first pipe and supplying coolant to the coolant flow path through the first pipe, wherein the coolant flow path is divided into a first flow path adjacent to the core catcher and a second flow path spaced from the core catcher, and the first flow path and the second flow path are connected to each other.