Passive Depressurisation Valve for LOCA Pressure Isolation
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Solution Overview
Problem
Existing nuclear reactor safety systems, such as the Accumulator Isolation Passive Valve (AIPV) and Automatic Safety Valve for Accumulator Depressurisation (ASVAD), are inadequate for isolating high-pressure, high-temperature water during a Loss of Coolant Accident (LOCA), and the Squib Valve poses a radiological hazard due to spurious operation, necessitating a simplified passive valve for depressurisation.
Innovation Solution
A passive depressurisation valve with dual control valves that open or close based on predefined pressure thresholds, using a main valve, pilot line, and bleed line configurations to ensure safe depressurisation without external power, incorporating biasing means and latching mechanisms for reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Squib Valve with explosive charge is used to open the valve for depressurisation, then the valve can be opened reliably in emergency situations, but spurious operation could result in a major radiological hazard and requires highly reliable Control and instrumentation system which adds significant cost
Solution Approach 1:
The patent replaces the explosive charge actuation system with a purely mechanical passive valve design. The valve uses a spring-loaded mechanism that automatically opens when system pressure exceeds a predetermined threshold, eliminating the need for electrical control systems, sensors, and explosive charges. This mechanical substitution maintains reliability through passive physics-based operation while dramatically reducing system complexity and cost.
Solution Approach 2:
The valve is designed to operate autonomously without external control systems. The spring mechanism automatically senses pressure conditions and actuates the valve opening when the pressure threshold is exceeded, and automatically closes when pressure normalizes. This self-service capability eliminates dependency on complex control instrumentation while ensuring reliable operation during emergencies.
2Extent of automation
If the Accumulator Isolation Passive Valve (AIPV) is used to isolate the reactor circuit, then the valve can operate passively without external power, but the valve position is proportional to pressure difference and the valve shuts once pressure equalises, preventing complete system depressurisation
Solution Approach 1:
The patent changes the operational parameter from pressure-difference-proportional positioning to pressure-threshold-triggered full opening. Instead of maintaining a proportional relationship between pressure differential and valve position, the valve remains closed until system pressure exceeds a predetermined threshold, at which point it opens fully to allow complete depressurisation. This parameter change enables both passive operation and effective depressurisation.
Solution Approach 2:
The patent inverts the conventional pressure-responsive valve behavior. Rather than opening in response to pressure differential and closing when pressures equalize, this valve remains closed during normal operation and only opens when excessive pressure is detected, reversing the typical pressure-response logic to achieve both passive operation and complete depressurisation capability.
3Extent of automation
If the Automatic Safety Valve for Accumulator Depressurisation (ASVAD) is used to vent gas from the accumulator, then the valve can open when pressure drops below a set level, but the valve is not suitable for isolation of high pressure, high temperature water
Solution Approach 1:
The patent designs a universal passive valve that can handle both gas venting and high-pressure water isolation functions. The valve incorporates a spring-loaded mechanism and pressure-responsive opening capability that works effectively for both gas and liquid applications, including high-pressure, high-temperature water. This multi-functional design eliminates the need for separate specialized valves for different media types.
Solution Approach 2:
The patent modifies the valve design parameters to accommodate high-pressure water service. By adjusting the spring force, seat geometry, and body construction to withstand high pressures and temperatures, the valve transitions from being suitable only for low-pressure gas venting to being capable of isolating and controlling high-pressure, high-temperature water while maintaining automatic pressure-responsive operation.
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 valve effectively isolates and depressurises the coolant system during LOCA events, preventing coolant loss and reducing the risk of radiological hazards, while maintaining system safety and reliability without requiring external power or operator intervention.
Implementation Method 1
the pilot line is operable to transmit fluid pressure from the inlet into the valve dome to apply pressure on a first face of the first piston, the first piston thereby applying a first force to the main valve urging it into the closed position
Implementation Method 2
the second control valve is configured to open and fluidically couple the main dome to a bleed line, to reduce the pressure in the valve dome by releasing fluid from the valve dome through the bleed line
Data Source
AI summary
A depressurisation valve (100) for a pressurised cooling circuit, comprising a main valve (101), a pilot line (104) fluidically coupled to the inlet (110) and closable by a first control valve (105), the first control valve controlled by pressure at the inlet to open above a low pressure threshold, a valve dome (106) containing a first piston (107) coupled to the main valve, the valve dome being fluidically coupled to the pilot line, wherein in normal operation, pressure on the first piston urges the valve into the closed position, and when the pressure in the coolant circuit is lower than the low pressure threshold, the first control valve closes to allow the main valve to open, when the pressure in the coolant circuit is higher than the high pressure threshold, the second control valve is configured to open and reduce the pressure in the valve dome.