Passive Reactor Heat Removal with Fluidic Diode Bypass Cooling
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Solution Overview
Problem
Current nuclear reactors face challenges in effectively managing decay heat during shutdown and startup processes, as existing residual heat removal systems are primarily safety systems designed for emergency use and do not efficiently handle heat removal during these phases without active pumping mechanisms.
Innovation Solution
A passive heat removal system utilizing natural circulation through an intermediate coolant loop with a fluidic diode and air heat exchanger, allowing heat to be dumped during low-power conditions, both during startup and shutdown, without the need for active pumping, thereby ensuring continuous heat removal without safety-grade design requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a passive heat removal system is used to remove decay heat during shutdown, then safety requirements and design complexity are reduced, but the system cannot actively control heat removal rate
Solution Approach 1:
The system uses natural circulation where the coolant automatically flows through the heat exchanger based on density differences created by temperature variations, eliminating the need for external pumps or active control mechanisms. The heated coolant rises and the cooler coolant sinks, creating a self-sustaining circulation loop that removes decay heat passively.
Solution Approach 2:
The patent replaces the mechanical pumping system with a gravity-driven natural circulation system. Instead of using motor-driven pumps to force coolant through the heat exchanger, the system relies on buoyancy forces generated by temperature-induced density differences to drive the flow, thereby simplifying the mechanical complexity.
2Device complexity
If natural circulation is used for heat removal, then active pumping is eliminated, but heat removal efficiency during high-power operation is reduced
Solution Approach 1:
The system dynamically adapts its heat removal capability to the reactor's power level. During low-power operation and shutdown, natural circulation efficiently removes decay heat. During high-power operation, the increased temperature differential enhances the natural circulation driving force, allowing the system to scale its heat removal efficiency according to the thermal load without requiring active pumping.
Solution Approach 2:
The system changes the flow rate parameter automatically based on temperature differential. As the reactor power increases, the temperature difference between the hot and cold legs increases, which increases the natural circulation flow rate proportionally, maintaining effective heat removal across different operating conditions.
3Productivity
If a fluidic diode is added to prevent thermal energy mixing, then heat removal effectiveness is improved, but device complexity increases
Solution Approach 1:
The fluidic diode acts as an intermediary element in the coolant loop that selectively allows flow in the desired direction while blocking reverse flow. This passive flow control mechanism prevents thermal energy mixing between the hot and cold legs without requiring complex active control systems or multiple valves, maintaining simplicity while improving heat removal effectiveness.
4Reliability
If the system is designed as a safety system, then reliability is improved, but manufacturing cost and design requirements increase
Solution Approach 1:
The passive heat removal system is designed to serve multiple functions: it acts as a safety system for decay heat removal during shutdown, provides heat removal during startup procedures, and can supplement the primary cooling system during low-power operation. This multi-functionality allows the system to meet safety requirements while being manufactured to commercial rather than strict safety-grade standards, reducing costs.
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 system effectively manages decay heat and reactor output heat during low-power conditions, promoting natural circulation and reducing thermal energy mixing, ensuring safe and efficient operation by leveraging gravity-driven fluid flow and asymmetric fluidic diode resistance, thus enhancing reactor safety and operational efficiency.
Implementation Method 1
The natural circulation of fluid is promoted, by relying on gravity to cause the higher density cold fluid to fall and the lower density heated fluid to rise, causing natural circulation through the intermediate coolant loop through a heat exchanger
Implementation Method 2
relying on gravity to cause the higher density cold fluid to fall and the lower density heated fluid to rise
Implementation Method 3
a fluidic diode disposed along the bypass flowpath between to asymmetrically restrict fluid flow along the bypass flowpath
Implementation Method 4
an air heat exchanger disposed along a bypass flowpath between the hot leg and the cold leg of the intermediate coolant loop
Implementation Method 5
dumping reactor output heat during a low-power startup operating condition
Data Source
AI summary
A nuclear reactor is configured with an intermediate coolant loop for transferring thermal energy from the reactor core for a useful purpose. The intermediate coolant loop includes a bypass flowpath with an air heat exchanger for dumping reactor heat during startup and/or shutdown. A fluidic diode along the bypass flowpath asymmetrically restricts flow across the bypass flowpath, inhibiting flow in a first flow direction during a full power operating condition and allowing a relatively uninhibited flow in a second direction during a startup and/or shut down low power operating condition.