Passive Reactor Cooling Barrier for LOCA Water Retention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In a loss of coolant accident (LOCA), the emergency core cooling (ECC) system in nuclear reactors faces challenges with steam loss and potential contamination, particularly due to the reliance on sump pumps that can fail and the inefficiency of water flow dynamics, leading to incomplete immersion of the reactor core and inadequate heat removal.
Innovation Solution
Implementing a barrier mechanism within the reactor's central riser and pressurizer to suppress the flow of liquid water during depressurization, using methods such as counterflow injection, bypass valves, and modified flow paths to manage the two-phase steam/water mixture, ensuring the reactor core remains immersed and effectively cooled.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a sump pump is used to recirculate water back into the RWST, then water recirculation is achieved, but the system becomes susceptible to failure if power sources fail and contamination may be transferred
Solution Approach 1:
The patent implements a passive recirculation system that uses natural convection and density differences to circulate water without mechanical pumps. The system allows steam and non-condensable gases to rise and condense naturally, creating a self-sustaining circulation loop that eliminates dependence on powered equipment.
Solution Approach 2:
The invention replaces the mechanical sump pump system with a passive thermal-hydraulic system that relies on natural convection currents and phase change dynamics. This substitution eliminates mechanical components that require power and maintenance while achieving the same water recirculation function.
2Temperature
If water is injected into the pressure vessel by the ECC system, then core cooling is achieved, but steam is lost from the break and does not recirculate effectively
Solution Approach 1:
The patent captures the previously lost steam and non-condensable gases and uses them as a beneficial resource. By allowing these gases to accumulate and then condense in the upper portion of the vessel, the system creates a natural circulation driver that promotes water recirculation and maintains pressure, converting what was previously a loss into a useful function.
Solution Approach 2:
The invention utilizes phase transitions of water between liquid, vapor, and condensed states to drive the recirculation process. Steam rises, condenses on cooler surfaces, and the resulting condensate flows back down to the core area, creating a continuous natural circulation loop that maintains cooling without requiring external power.
3Ease of operation
If the RWST is located above the reactor core for gravity-driven flow, then passive ECC operation is enabled, but liquid water may flow out through the vessel penetration break during depressurization
Solution Approach 1:
The patent introduces a barrier or interface region in the upper portion of the pressure vessel that separates the liquid water reservoir from the steam and gas phase. This intermediary zone allows the system to maintain the high RWST location for passive operation while preventing direct liquid water egress through the break, as the barrier captures and redirects liquid flow.
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 barrier mechanism enhances the efficiency of the ECC system by maintaining core immersion and prolonged heat removal without relying on sump pumps, thereby preventing contamination and ensuring safe reactor operation during LOCA scenarios.
Implementation Method 1
The suppressing may include generating a counterflow in the pressure vessel during the draining in a direction opposite a flow of coolant water in the pressure vessel during the operating, for example by injecting the water from the body of water into the central riser
Implementation Method 2
The suppressing additionally or alternatively may comprise shunting a portion of the upward flow of coolant water in the central riser through holes in the central riser and into a lower portion of the downcomer annulus without the shunted water reaching a top of the central riser
Implementation Method 3
The suppressing additionally or alternatively may comprise directing surge flow between a pressurizer volume and the remainder volume of the pressure vessel outboard toward a downcomer annulus
Implementation Method 4
the nuclear reactor core is to be kept immersed in water so as to provide for removal of decay heat
Implementation Method 5
a barrier configured to operate concurrently with the emergency core cooling system to suppress flow of liquid water from the pressure vessel out the vessel penetration break at the top of the pressure vessel
Data Source
AI summary
In a pressurized water reactor (PWR), emergency core cooling (ECC) responds to depressurization due to a vessel penetration break at the top of the pressure vessel by draining water from a body of water through an injection line into the pressure vessel. A barrier operates concurrently with the ECC to suppress flow of liquid water from the pressure vessel out the vessel penetration break. The barrier may comprise one or more of: (1) an injection line extension passing through the central riser to drain water into the central riser; (2) openings in a lower portion of a central riser to shunt some upward flow from the central riser into a lower portion of the downcomer annulus; and (3) a surge line providing fluid communication between a pressurizer volume at the top of the pressure vessel and the remainder of the pressure vessel which directs water outboard toward the downcomer annulus.