Passive Reactor Cooling via Gravity-Driven Natural Circulation
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Solution Overview
Problem
Current nuclear reactor containment systems rely on pumped heat rejection systems that are vulnerable to power outages and extreme environmental conditions, such as seen during the Fukushima disaster, and fail to passively manage decay heat after reactor shutdown.
Innovation Solution
A passive reactor cooling system utilizing gravity-driven fluid flow and a submerged bundled cooling system, combined with a double-walled containment structure and auxiliary air cooling, to remove decay heat without relying on electric power or pumps, ensuring continuous operation during accidents like LOCA or station blackouts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If pumped heat rejection systems are used to remove decay heat, then heat rejection capability is improved, but system reliability deteriorates due to vulnerability to power outages and extreme environmental conditions
Solution Approach 1:
The system uses natural convection and gravity-driven flow to circulate coolant through the reactor core and heat exchangers, eliminating the need for external power sources or control systems. The coolant automatically flows from the reactor vessel through the steam generator and back, using density differences created by temperature variations to drive the cooling process indefinitely without human intervention or electrical power.
Solution Approach 2:
The patent replaces the mechanical pump-based cooling system with a passive natural circulation system. Instead of using electrically-powered pumps to force coolant flow, the system relies on natural convection currents and gravity to move the coolant through the reactor core and heat rejection pathways, substituting mechanical actuation with physical principles that operate autonomously.
2Strength
If thick concrete containment walls are used to withstand aircraft impact, then structural strength is improved, but heat rejection capability deteriorates due to thermal insulation properties
Solution Approach 1:
The containment system is segmented into multiple functional layers: the thick concrete containment structure provides mechanical strength and impact resistance, while separate integrated heat exchanger systems provide thermal management. The heat exchangers are positioned within or attached to the containment structure, allowing the concrete to fulfill its primary structural role while dedicated thermal pathways handle heat rejection independently.
Solution Approach 2:
The patent merges the containment structure with the heat rejection system by integrating heat exchangers within or attached to the containment vessel. This combination allows the thick concrete walls to simultaneously provide structural strength against aircraft impact and serve as a mounting structure for thermal management components, resolving the conflict between structural integrity and heat dissipation.
3Reliability
If passive gravity-driven cooling system is implemented, then system reliability is improved by eliminating pump dependencies, but device complexity increases due to multiple flow loops and heat exchangers
Solution Approach 1:
The steam generator serves multiple functions: it acts as a heat exchanger to transfer heat from the primary coolant to the secondary coolant, serves as a condenser for the secondary steam, and functions as a storage vessel for the secondary coolant inventory. This multi-functionality reduces the number of separate components needed, thereby reducing overall system complexity while maintaining the passive safety features.
Solution Approach 2:
The patent employs a nested configuration where the tube bundle heat exchanger is submerged within the secondary coolant inventory in the steam generator vessel. The primary coolant tubes are nested within the secondary coolant chamber, creating a compact integrated structure that reduces spatial requirements and simplifies the overall system layout while maintaining effective heat transfer pathways.
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 and autonomously manages reactor heat rejection indefinitely, maintaining containment integrity and safety without the need for active components, even in the absence of power, thus enhancing reactor safety and resilience against severe events.
Implementation Method 1
The primary coolant circulates in a first closed flow loop between the reactor vessel and steam generator, the primary coolant transferring heat to the secondary coolant in the steam generator
Implementation Method 2
The secondary coolant steam is extracted from the steam generator and flows in the second closed flow loop to the tube bundle, condenses forming condensate
Implementation Method 3
The secondary coolant circulates via gravity flow in a second closed flow loop between the submerged tube bundle and the steam generator
Data Source
AI summary
A nuclear reactor cooling system with passive cooling capabilities operable during a reactor shutdown event without available electric power. In one embodiment, the system includes a reactor vessel with nuclear fuel core and a steam generator fluidly coupled thereto. Primary coolant circulates in a flow loop between the reactor vessel and steam generator to heat secondary coolant in the steam generator producing steam. The steam flows to a heat exchanger containing an inventory of cooling water in which a submerged tube bundle is immersed. The steam is condensed in the heat exchanger and returned to the steam generator forming a closed flow loop in which the secondary coolant flow is driven by natural gravity via changes in density from the heating and cooling cycles. In other embodiments, the cooling system is configured to extract and cool the primary coolant directly using the submerged tube bundle heat exchanger.