Dual-Threshold Depressurisation Valve for LOCA Coolant 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 Loss of Coolant Accident (LOCA) events, 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, ensuring safe depressurisation by isolating the coolant circuit during LOCA events, preventing spurious operation and reducing reliance on complex control systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Squib Valve with explosive charge is used for depressurisation, then the valve can be opened reliably in emergency situations, but the risk of spurious operation increases creating a major radiological hazard
Solution Approach 1:
The explosive charge mechanism is completely removed from the valve system. Instead, the valve is opened passively by the natural pressure differential between the high-pressure coolant and the low-pressure atmosphere when the isolation valve opens, eliminating the radiological hazard while maintaining reliable depressurisation functionality
Solution Approach 2:
The valve design enables self-opening through the inherent pressure difference that occurs during LOCA events. The high-pressure coolant automatically forces the valve open when the isolation valve isolates the accumulator, requiring no external explosive charges or complex control systems
2Extent of automation
If the Accumulator Isolation Passive Valve (AIPV) is used, then the valve operates passively without external power, but the valve shuts when pressure equalises preventing complete system depressurisation
Solution Approach 1:
The valve transitions from a static pressure-balanced design to a dynamic latching mechanism. Once the valve opens due to pressure differential, the latch mechanism maintains the open state even when pressures equalise, allowing complete depressurisation while retaining passive operation throughout the sequence
3Adaptability or versatility
If the Automatic Safety Valve for Accumulator Depressurisation (ASVAD) is used, then the valve can vent gas from the accumulator, but the valve is not suitable for isolating high pressure, high temperature water
Solution Approach 1:
The valve design integrates multiple functions into a single device: it can handle both gas and high-pressure liquid coolant, provides isolation capability, and enables depressurisation. The robust sealing surfaces and pressure-activated opening mechanism make it suitable for both gas venting and high-pressure water isolation applications
4Measurement precision
If complex control systems with instrumentation and actuators are used for valve operation, then precise control of valve positions is achieved, but the system complexity and cost increase significantly
Solution Approach 1:
The valve system uses the inherent physical conditions of the coolant (pressure and temperature) to automatically control valve positions. The high-pressure coolant itself acts as the actuating force, opening the depressurisation valve when needed, eliminating the need for external instrumentation, control systems, and electrical actuators
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 passive depressurisation valve effectively isolates the coolant circuit during LOCA events, reducing the risk of spurious operation and maintaining reactor safety without complex control systems, thereby enhancing safety and reducing costs.
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 closed position preventing fluid flow through the main valve from the inlet to the outlet
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 main 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, a second control valve opens to transmit fluid pressure to apply a second force to the main valve opposing the first force to urge the main valve to the open position.