Deflector Shield Reduces Gas Entrainment in ECCS Pump Suction
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Solution Overview
Problem
During a Loss of Coolant Accident (LOCA), gases such as steam and non-condensable gases are entrained in the suction of Emergency Core Cooling System (ECCS) pumps, leading to cavitation, pump damage, and reduced flow to the reactor core, compromising the safety and availability of the cooling system.
Innovation Solution
The implementation of specially designed deflector shields or baffles between the drywell-to-wetwell vent downcomer and the ECCS pump suction strainer, which directs gases away from the suction structure, reducing gas entrainment and preventing cavitation, includes a container with a venting arrangement and a suction structure with a deflector to shield the liquid extraction process from uncondensed gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the ECCS pump suction strainer is positioned to extract liquid from the suppression pool, then the pump can maintain the pool level and provide cooling function, but gases may become entrained along with the liquid into the suction, causing loss of suction and decreased flow to the reactor core
Solution Approach 1:
A deflector shield is introduced as an intermediary component between the suction strainer and the gas source (drywell vent downcomer). The deflector intercepts gases before they can reach the suction inlet, allowing liquid to pass through while blocking gas entrainment. This mediator resolves the contradiction by selectively preventing gas entry while maintaining liquid extraction capability.
2Reliability
If the ECCS pump operates during a LOCA to maintain suppression pool level, then cooling function is provided to the reactor core, but non-condensable gases cause cavitation and pump damage
Solution Approach 1:
The deflector shield is positioned to preemptively block gases from reaching the suction inlet before cavitation can occur. By establishing this protective barrier in advance, the system prevents the harmful effect of gas entrainment that would otherwise lead to cavitation and pump damage during LOCA conditions.
3Stress or pressure
If gases are vented into the suppression pool to manage pressure during LOCA, then pressure control is achieved, but the venting gases elevate the suppression pool level and increase gas entrainment risk
Solution Approach 1:
The deflector acts as an intermediary that allows the venting function to continue (pressure control) while preventing the harmful consequence (gas entrainment). It selectively blocks gases at the suction inlet while allowing liquid to pass, thus decoupling the pressure management function from the gas entrainment problem.
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
This solution effectively mitigates gas entrainment, ensuring the continued operation and safety of ECCS pumps by preventing gas from reaching the suction of the ECCS pumps, thereby maintaining adequate flow to the reactor core during a LOCA, and reducing the risk of pump damage.
Implementation Method 1
A deflector may be disposed between the suction structure and the venting arrangement within the container. The deflector may be configured to reduce the entrainment of uncondensed gases during the extraction of the liquid.
Implementation Method 2
A suction structure may extend into the lower portion of the container. The suction structure may be configured to carry out an extraction of the liquid from the container.
Implementation Method 3
A venting arrangement may extend into the container. The venting arrangement may be configured to direct gases into the container.
Data Source
AI summary
An entrainment-reducing assembly may include a container configured to hold a liquid. A venting arrangement may extend into an upper portion of the container and be configured to direct condensable and non-condensable gases into the container. A suction structure may extend into a lower portion of the container and be configured to carry out an extraction of excess liquid from the container caused by condensed gases. A deflector may be disposed between the suction structure and the venting arrangement within the container. As a result, an entrainment of uncondensed gases during the extraction of the liquid by the suction structure may be reduced or prevented, thereby protecting the pump from cavitation and failure.