Integral Vessel Isolation Valve for Nuclear Reactor Coolant Containment
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Solution Overview
Problem
Light water nuclear reactors face challenges in preventing coolant loss during pipe breaks, as integral reactor designs still utilize small bore piping that can lead to loss of coolant accidents (LOCA), necessitating effective valve solutions to block outward flow when pressure differentials exceed thresholds.
Innovation Solution
The implementation of an isolation valve with a mounting flange and a moveable valve member biased to an open position, which automatically seals against a valve seat when a pressure differential across the valve exceeds a threshold, preventing coolant flow from the pressure vessel in case of a pipe break or sudden pressure change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If small bore connecting piping is used in integral reactor designs, then compactness and reduced number of pressure vessel penetrations are achieved, but the risk of loss of coolant accident (LOCA) increases due to potential pipe breaks
Solution Approach 1:
The isolation valve is designed with a self-actuating mechanism that automatically closes in response to pressure differential changes without requiring external control systems. The spring-loaded valve member is biased to close the valve when pressure inside the pressure vessel exceeds pressure outside, enabling the valve to serve itself in detecting and responding to LOCA conditions
Solution Approach 2:
The isolation valve acts as an intermediary device positioned at the connection between small bore piping and the pressure vessel. It mediates the potential harm of pipe breaks by providing an automatic shutdown mechanism that isolates the pressure vessel from external piping failures, thus protecting the main coolant system
2Speed
If automatic pressure-differential-actuated valves are implemented, then rapid response to LOCA events is achieved, but valve complexity increases
Solution Approach 1:
The valve employs a self-actuating mechanism where the pressure differential itself provides the actuating force. The spring-loaded valve member automatically transitions between open and closed states based on pressure conditions, eliminating the need for external actuators, control systems, or power sources while achieving rapid response
Solution Approach 2:
The complex control system, actuators, sensors, and power supply typically associated with automatic valves are extracted and replaced with a simple spring-loaded mechanism. Only the essential closing function remains, achieved through direct pressure differential action on the valve member with spring bias
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 isolation valve effectively blocks coolant flow from the pressure vessel during LOCA events, ensuring containment and minimizing the consequences of pipe breaks by maintaining the valve in a closed position until the pressure differential is mitigated, thus enhancing nuclear reactor safety.
Implementation Method 1
a biasing member that biases the valve member towards the open position
Implementation Method 2
The vessel isolation valve is configured to block outward flow from the pressure vessel when a pressure differential across the valve exceeds prescribed criteria
Data Source
AI summary
A nuclear reactor comprises a nuclear reactor core disposed in a pressure vessel. An isolation valve protects a penetration through the pressure vessel. The isolation valve comprises: a mounting flange connecting with a mating flange of the pressure vessel; a valve seat formed into the mounting flange; and a valve member movable between an open position and a closed position sealing against the valve seat. The valve member is disposed inside the mounting flange or inside the mating flange of the pressure vessel. A biasing member operatively connects to the valve member to bias the valve member towards the open position. The bias keeps the valve member in the open position except when a differential fluid pressure across the isolation valve and directed outward from the pressure vessel exceeds a threshold pressure.