Passive Reactor Cooling via Gravity-Driven Natural Convection
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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, as seen in the Fukushima disaster, and lack passive cooling mechanisms to manage decay heat after reactor shutdown.
Innovation Solution
A passive reactor cooling system using gravity-driven fluid circulation and a submerged bundled cooling system, combined with a double-walled containment structure and annular water reservoir, to reject heat without the need for pumps or external power, 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 from the reactor, then heat rejection efficiency is improved, but system reliability deteriorates due to dependence on external power supply and vulnerable pumps
Solution Approach 1:
The system uses natural convection currents generated by temperature differences to drive coolant circulation through the heat exchanger, eliminating the need for external power sources or mechanical pumps. The thermal energy itself creates the driving force for heat rejection, making the system self-sufficient and reliable during power outages
Solution Approach 2:
The patent replaces the mechanical pump-based forced circulation system with a passive natural convection system. Instead of using motors and pumps to move the coolant, the system relies on buoyancy-driven flow where heated coolant rises and cooler coolant sinks, creating continuous circulation without mechanical components
2Strength
If massive reinforced concrete containment structures are built to withstand aircraft impact, then structural strength is improved, but heat insulation worsens causing excessive heat accumulation inside containment
Solution Approach 1:
The patent introduces an intermediate heat rejection system consisting of heat exchangers positioned within the containment structure. These heat exchangers act as mediators between the internal reactor components and the external environment, transferring heat through their surfaces while the thick concrete walls provide structural protection. This allows the containment to maintain both strength and effective heat management
3Reliability
If station black out occurs forcing reactor scram, then safety response is improved, but decay heat removal capability deteriorates due to loss of pump power
Solution Approach 1:
The passive heat rejection system automatically activates during station black out conditions without requiring external power. The temperature differential between the hot reactor components and the cooler external environment naturally drives convection currents through the heat exchangers, enabling continuous decay heat removal even when all electrical systems fail
Solution Approach 2:
The system ensures continuous heat rejection operation by eliminating mechanical components that can fail. The natural convection process operates continuously as long as there is a temperature difference, providing uninterrupted decay heat removal capability from reactor scram through station black out scenarios
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 provides a reliable, pump-independent means to manage reactor decay heat, maintaining containment integrity and safety by utilizing gravity-driven fluid flow and passive heat rejection, capable of operating indefinitely without human intervention.
Implementation Method 1
a primary coolant heated by the fuel core... 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
A heat exchanger includes an inventory of a liquid third coolant and a tube bundle... the secondary coolant steam... condenses forming condensate
Implementation Method 4
The primary coolant circulates in a first closed flow loop... The secondary coolant circulates via gravity flow in a second closed flow loop
Implementation Method 5
a reactor vessel housing a nuclear fuel core inside, the reactor vessel containing a primary coolant heated by the fuel core
Data Source
Figure 1
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Figure 4
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.