Integral PWR Passive Cooling via Natural Circulation
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Solution Overview
Problem
Small modular pressurized water reactors face challenges in passive cooling after a trip, particularly in minimizing auxiliary systems while maintaining safety and functionality, especially in the event of a loss of coolant accident or main steam line break, where existing designs rely on active safety systems that require external power and complex configurations.
Innovation Solution
A modular nuclear reactor system with an in-containment pool system for passive recirculation of coolant, a depressurization system to equalize pressures, and a passive residual heat removal system using natural circulation and heat exchangers to cool the reactor core over an extended period without external intervention, integrated into a simplified design within a compact containment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active safety systems with emergency AC power and pumps are used to cool the reactor after a trip, then the reactor can be cooled down, but the system requires external power and complex configurations
Solution Approach 1:
The reactor cooling system is designed to operate autonomously using passive safety mechanisms. The natural circulation system automatically circulates coolant through the core without requiring external power or operator intervention. The gravity-driven cooling system uses the weight of the coolant itself to drive circulation, and the heat exchangers automatically transfer heat from the reactor core to the environment. This self-service approach eliminates the need for complex active safety systems with emergency AC power and electric pumps.
Solution Approach 2:
The patent replaces active mechanical cooling systems (electric pumps, motors, and control systems) with passive physical mechanisms. Natural circulation replaces electric pumps by using density differences in the coolant to drive flow. Gravity-driven cooling replaces mechanical lifting systems. Thermal conduction and convection replace active heat transfer systems. This substitution of mechanical systems with fundamental physics-based mechanisms simplifies the overall system while maintaining reliable cooling capability.
2Ease of operation
If passive safety systems using natural circulation and gravity-driven cooling are implemented, then external power and operator intervention are eliminated, but the system design becomes more complex
Solution Approach 1:
The patent combines multiple passive safety functions into an integrated system. The natural circulation loop integrates coolant flow, heat transfer, and thermal management into a single unified mechanism. The gravity-driven cooling system merges storage, circulation, and heat rejection functions. The heat exchangers are designed to simultaneously perform heat transfer, thermal storage, and flow regulation. This merging of functions reduces the number of separate components and simplifies the overall system architecture while maintaining ease of operation without operator intervention.
3Volume of moving object
If the reactor is designed as a small modular integral pressurized water reactor with all primary loop components inside the vessel, then space is minimized and cost is reduced, but the number of auxiliary systems must be minimized without compromising safety
Solution Approach 1:
The patent implements a nested configuration where the primary reactor components are housed within the pressure vessel, and passive safety systems are integrated within the containment structure. The natural circulation cooling system is nested within the reactor vessel, with coolant channels and heat exchangers positioned inside the pressure boundary. The gravity-driven cooling reservoirs are integrated into the containment structure. This nested arrangement minimizes the overall footprint while maintaining all necessary safety functions within the compact design.
Solution Approach 2:
The patent designs components to perform multiple functions simultaneously. The primary coolant serves both as the reactor cooling medium and as the natural circulation fluid for passive safety cooling. The pressure vessel contains both the reactor core and the passive safety system components. The heat exchangers perform both normal operation heat transfer and emergency cooling functions. This multi-functionality reduces the number of auxiliary systems needed while maintaining safety functionality within the minimized volume.
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
Enables continuous cooling of the reactor core for approximately seven days without operator action or external power, simplifying the design and reducing spatial and cost requirements while maintaining safety margins by utilizing natural circulation and gravity-driven recirculation of coolant.
Implementation Method 1
means for passively recirculating reactor coolant within the in-containment pool system and the sump into the reactor pressure vessel
Implementation Method 2
utilizing natural circulation and gravity-driven recirculation of coolant
Implementation Method 3
a depressurization system to equalize the pressure within the reactor pressure vessel and the containment pressure vessel
Implementation Method 4
a passive residual heat removal system using natural circulation and heat exchangers to cool the reactor core
Data Source
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AI summary
An integral pressurized water reactor that combines all of the components typically associated with a nuclear steam supply system, such as the steam generator, reactor coolant pumps, pressurizer and the reactor, into a single reactor pressure vessel. The reactor pressure vessel is itself enclosed in a containment pressure vessel that also houses a number of safety systems, such as the core make-up tanks, the primary side of residual heat removal heat exchangers, an automatic depressurization system and a recirculation system that enables continuous core cooling through natural circulation over an extended period of time. Actuation of the passive systems is done by single actuation of valves, powered from redundant batteries.