Passive Cooling Device for Ex-Vessel Corium Using Mechanical String Actuation
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Solution Overview
Problem
Existing ex-vessel corium cooling devices face reliability issues due to active device failures and measurement instrument integrity failures during severe accidents, leading to potential cooling water injection failures.
Innovation Solution
A passively operating cooling device that uses the tension of a string to mechanically open a cooling water injection valve, eliminating the need for a power supply and measurement instruments, with a fusible plug and string system to trigger water injection by gravity when the corium penetrates and damages the plug.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a motor driven valve (MOV) powered by DC battery is used for cooling water injection, then the valve can be actuated remotely, but the system reliability decreases due to active device failure and power supply dependency
Solution Approach 1:
The patent replaces the motor-driven valve system with a purely mechanical valve actuation system. The valve is opened by the mechanical action of falling corium that cuts the tension member, eliminating motors, batteries, and electrical systems. This substitution of mechanical for electromechanical systems resolves the contradiction by maintaining remote actuation capability through passive mechanical means while dramatically improving reliability by removing active components that can fail.
Solution Approach 2:
The system uses the corium itself as the actuating force for the valve. The falling corium directly cuts the tension member and opens the valve through its own gravitational energy, without requiring external power sources or control systems. This self-service mechanism eliminates dependency on external power supplies and complex control systems, thereby improving reliability while maintaining operational capability.
2Measurement precision
If temperature measuring instruments are installed to detect corium temperature, then the temperature can be monitored, but the system reliability decreases due to measurement instrument integrity failure in severe accident conditions
Solution Approach 1:
The patent replaces temperature measuring instruments with a mechanical temperature-responsive element (the tension member with fusible plug). Instead of using electrical or electronic sensors that can fail in severe accident conditions, the system uses a purely mechanical element that responds to temperature through material property changes (softening, melting, or deformation). This mechanical substitution eliminates measurement instrument integrity issues while maintaining the ability to detect temperature conditions.
Solution Approach 2:
The system changes the detection parameter from electrical or electronic temperature measurement to mechanical property changes of the tension member material. The tension member's material properties (strength, stiffness, melting point) change with temperature, providing a reliable passive indication of thermal conditions without requiring functional measurement instruments that can fail.
3Ease of operation
If active control systems are used for cooling water injection, then the injection can be controlled precisely, but the device complexity increases due to power supply and control instrumentation requirements
Solution Approach 1:
The patent extracts and removes all active control systems, power supplies, and measurement instruments from the cooling water injection system. Only the essential passive mechanical components (valve, tension member, cooling water supply) are retained. This extraction eliminates the complex infrastructure of motors, batteries, sensors, and control electronics while preserving the core function of controlled cooling water injection through passive mechanical means.
Solution Approach 2:
The system eliminates the need for external power supplies and control systems by using the corium's own gravitational energy and thermal energy to actuate the valve. The falling corium directly opens the valve through mechanical action, and the temperature-responsive tension member provides automatic control based on thermal conditions. This self-service approach dramatically reduces device complexity while maintaining operational control.
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
This solution ensures reliable cooling water injection without power or measurement failures, minimizing steam explosion risks and allowing for easier inspection, as the system is driven solely by mechanical means and string tension.
Implementation Method 1
after the corium released from the reactor pressure vessel reaches the core catcher, cooling water is directly or indirectly supplied to remove decay heat of the corium
Implementation Method 2
the cooling water injection valve is interlocked with a string so as to be opened according to a temperature, of which the value exceeds a set value, and is mechanically driven using the tension of the string
Implementation Method 3
injecting, by gravity, cooling water for cooling corium, by the water supply source of an in-containment refueling water storage tank when a cooling water injection valve is opened
Implementation Method 4
cooling water is directly or indirectly supplied to remove decay heat of the corium
Data Source
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AI summary
The present invention relates to a passively operating cooling device for ex-vessel corium, the passively operating cooling device having a core catcher 3 provided below a reactor pressure vessel 2 in a reactor cavity area so as to prepare for severe accidents damaging to the reactor pressure vessel, and injecting, by gravity, cooling water for cooling corium, by the water supply source of an in-containment refueling water storage tank 4 when a cooling water injection valve 5 is opened, wherein the cooling water injection valve is interlocked with a string so as to be opened according to a temperature, of which the value exceeds a set value, and is mechanically driven using the tension of the string.