Passive Depressurization Valve for LOCA Coolant Isolation
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Solution Overview
Problem
Current safety systems for pressurized water reactors, such as Accumulator Isolation Passive Valve (AIPV) and Automatic Safety Valve for Accumulator Depressurisation (ASVAD), are inadequate for isolating high-pressure, high-temperature water during Loss of Coolant Accident (LOCA) events, and rely on explosive charges or complex control systems, posing safety and cost concerns.
Innovation Solution
A passive depressurization valve with a main valve and secondary valve configuration, utilizing a pilot line and blowdown line with a lower fluid resistance, where the main valve remains closed under normal conditions and opens under extreme conditions, eliminating the need for explosive charges and enhancing safety by allowing complete depressurization of the core circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If explosive charges are used to open the valve (Squib valve), then the valve can be opened reliably, but the risk of spurious operation increases and safety is compromised
Solution Approach 1:
The patent replaces the explosive charge-based mechanical actuation system with a passive thermal-mechanical system. The valve uses a fusible element that melts at a specific temperature to release the valve stem, eliminating the need for explosive charges and their associated control systems. This substitution removes the risk of spurious operation while maintaining reliable valve opening under accident conditions.
Solution Approach 2:
The valve system is designed to automatically respond to temperature increases without external control signals. The fusible element self-activates when the reactor coolant temperature exceeds the melting point, causing the valve to open passively. This self-service mechanism eliminates dependency on external power or control systems, preventing spurious operation while ensuring reliable activation during actual accidents.
2Reliability
If complex control systems are used to prevent spurious operation, then safety is improved, but the system complexity and cost increase
Solution Approach 1:
The patent eliminates complex control systems by replacing them with a passive thermal-mechanical response mechanism. The fusible element directly responds to temperature changes through phase change, converting thermal energy into mechanical valve actuation without intermediaries. This substitution dramatically reduces system complexity while maintaining safety through inherent physical properties rather than active control.
Solution Approach 2:
The valve system performs its own safety function through the fusible element's automatic response to temperature. No external sensors, control logic, or power systems are needed—the system self-regulates based on physical conditions. This self-service approach eliminates complex control infrastructure while ensuring spurious operation prevention through passive physical constraints.
3Reliability
If the valve is designed to open under extreme conditions, then complete depressurization is achieved, but the valve may open during normal operation due to temperature fluctuations
Solution Approach 1:
The patent carefully selects the fusible element's melting point to be significantly higher than normal operating temperatures but below accident condition temperatures. This parameter selection creates a stable operating window where the valve remains reliably closed during normal operation (preventing spurious opening) while ensuring automatic opening when temperature exceeds the melting point during accidents (achieving complete depressurization).
Solution Approach 2:
The design incorporates a temperature buffer zone between normal operating conditions and the fusible element's melting point. This cushioning effect provides a safety margin that accounts for normal temperature fluctuations without triggering valve opening, while still ensuring activation under genuine accident conditions. The buffer prevents premature activation while maintaining protective function.
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 solution ensures reliable and safe depressurization of the coolant circuit during LOCA events, reducing the risk of spurious operation and eliminating the need for complex control systems, thereby enhancing reactor safety and reducing costs.
Implementation Method 1
a pilot line with a secondary valve and a blowdown line, wherein fluid enters the main chamber via the pilot line, which has a lower fluid resistance than the blowdown line
Implementation Method 2
in use the pressure of the fluid in the main chamber maintains the main valve in a closed position
Implementation Method 3
under extreme conditions fluid is prevented from entering the main chamber via a closure of the secondary valve on the pilot line and reduce the pressure from the valve, moving it to its open position
Data Source
AI summary
A depressurisation valve for a cooling system comprising: a main chamber having a main valve, a pilot line having a secondary valve and a blowdown line; the main valve being located to seal a path of the coolant system of the nuclear reactor. The main chamber is connected to the cooling circuit via the pilot line allowing coolant to enter the main chamber, and the blowdown line allows coolant to escape from the main chamber, the pilot line having a lower fluid resistance than the blowdown line. The pressure of coolant in the main chamber maintains the main valve in a closed position, and under elevated temperature and/or pressure conditions fluid is prevented from entering the main chamber via a closure of the secondary valve on the pilot line and reduce the pressure from the valve, moving it to its open position.