Cooling Circuit Depressurisation Valve for Passive LOCA Blowdown
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Solution Overview
Problem
Current safety systems in pressurized water reactors, such as the Squib Valve, rely on explosive charges and complex instrumentation, posing risks and increasing costs, while existing passive valves like Accumulator Isolation Passive Valve (AIPV) and Automatic Safety Valve for Accumulator Depressurisation (ASVAD) fail to ensure complete depressurization during Loss of Coolant Accident (LOCA) events due to pressure and temperature dependencies.
Innovation Solution
A passive depressurization valve system using a poppet valve and blowdown line configuration that opens based on temperature and pressure conditions, eliminating the need for explosive charges and providing complete depressurization of the core circuit, with the option to position the valve upstream or within the main chamber, and utilizing a magnovalve or alternative thermal valves for secondary isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If explosive charges (Squib Valve) are used to open the depressurisation valve, then the valve can be reliably opened, but the risk of spurious operation increases and operational costs increase
Solution Approach 1:
The invention removes the explosive charge mechanism from the valve system entirely. Instead of using explosive charges to force the valve open, the design relies on passive thermal expansion of a bimetallic strip that automatically opens the valve when temperature thresholds are exceeded, eliminating the harmful spurious operation risk associated with explosive charges
Solution Approach 2:
The valve system uses self-activating thermal mechanisms (bimetallic strip and fusible plug) that automatically respond to temperature conditions without external intervention. The valve opens itself when thermal thresholds are reached, eliminating the need for external control systems and reducing the risk of spurious operation from control system failures
2Ease of operation
If complex instrumentation and control systems are used to operate the depressurisation valve, then the valve operation can be controlled, but the device complexity increases
Solution Approach 1:
The valve system is designed to be completely passive and self-activating. Thermal conditions directly trigger mechanical responses through the bimetallic strip and fusible plug mechanisms, eliminating the need for sensors, control systems, power supplies, or manual intervention. The system monitors and responds to temperature automatically through inherent physical properties
Solution Approach 2:
The invention replaces complex electronic control and instrumentation systems with simple passive mechanical and thermal mechanisms. The bimetallic strip and fusible plug provide automatic temperature-responsive valve operation without requiring any electronic sensors, processors, or control circuits
3Extent of automation
If pressure-dependent valves (AIPV, ASVAD) are used for depressurisation, then the valve can operate passively, but complete depressurisation cannot be achieved during LOCA events
Solution Approach 1:
The invention changes the activation parameter from pressure-dependent to temperature-dependent mechanisms. The bimetallic strip responds to temperature changes by changing its curvature, and the fusible plug responds to temperature by melting, allowing the valve to open based on thermal conditions rather than pressure conditions. This enables complete depressurisation during LOCA events when temperature rises occur
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 safe and reliable depressurization of the reactor coolant system during LOCA events, reducing the risk of spurious operation and operational costs by using a simpler, temperature- and pressure-activated valve mechanism that maintains safety without external power or manual intervention.
Implementation Method 1
The valve will automatically open when the temperature of the coolant exceeds a threshold and will remain open until the temperature falls below a second threshold
Implementation Method 2
utilizing a magnovalve or alternative thermal valves for secondary isolation
Data Source
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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.