Pilot-Operated Depressurization Valve for Passive LOCA Response
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Solution Overview
Problem
Current safety systems for pressurized water reactors, such as the Squib Valve, rely on explosive charges and complex control systems, posing risks and increasing costs, and existing passive valves do not effectively isolate high-pressure, high-temperature water during Loss of Coolant Accident (LOCA) events.
Innovation Solution
A 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 coolant 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 mechanism with a purely mechanical spring-loaded valve system. The valve is held closed by a spring force during normal operation and opens automatically when the upstream pressure drops below the downstream pressure, eliminating the need for explosive charges and their associated spurious operation risks.
Solution Approach 2:
The valve system is designed to be self-activating based on pressure differential. When a LOCA occurs and upstream pressure drops, the pressure difference automatically overcomes the spring force and opens the valve without requiring external control signals, explosive charges, or operator intervention, making the system inherently safer and more reliable.
2Ease of operation
If complex control systems are used to operate the valve, then precise control is achieved, but the system complexity and cost increase
Solution Approach 1:
The valve system requires no external control systems, operators, or power sources. It automatically responds to pressure changes by opening when upstream pressure drops below downstream pressure, providing precise control through inherent mechanical response to the actual system conditions.
Solution Approach 2:
The patent extracts and eliminates the complex control system, instrumentation, and power requirements from the valve operation, retaining only the essential mechanical function of opening when needed based on pressure differential.
3Use of energy by stationary object
If existing passive valves are used, then no external power is required, but they cannot effectively isolate high-pressure, high-temperature water during LOCA events
Solution Approach 1:
The valve is designed to respond to extreme parameter changes (pressure drop and temperature increase) by opening when upstream pressure drops below downstream pressure and/or temperature exceeds a threshold, making it effective for LOCA events while requiring no external power.
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 provides a reliable and cost-effective means for depressurization, reducing the risk of spurious operation and enhancing safety by ensuring the valve opens during LOCA events, independent of external power or operator input, thus preventing fuel damage and radioactive releases.
Implementation Method 1
a spring located in the main chamber, the spring being biased in an opening direction of the main valve
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
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 including 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.