RWST Standpipe Flow Tailoring for 72-Hour Passive Core Cooling
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Solution Overview
Problem
In nuclear reactors, the refueling water storage tank (RWST) is designed to provide emergency core cooling (ECC) but faces challenges in maintaining sufficient water levels to remove decay heat effectively during a loss of coolant accident (LOCA), leading to reduced heat removal capacity below the design basis of 72 hours.
Innovation Solution
The implementation of a standpipe with multiple orifices or cross-connection pipes in the RWST, combined with a float valve, tailors the flow of water to match the decay heat profile over time, ensuring adequate water supply to the reactor core for extended periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If water flows freely from the RWST to the pressure vessel, then the initial cooling capacity is high, but the water level drops too quickly reducing the duration of effective cooling
Solution Approach 1:
The standpipe is segmented with multiple orifices at different heights, creating distinct flow paths that activate at different water levels. This segmentation allows the system to provide high initial flow when water levels are high, then transition to sustained lower flow as levels drop, resolving the contradiction between initial cooling capacity and duration of cooling.
2Duration of action of moving object
If the RWST volume is increased to extend cooling duration, then the duration of cooling is improved, but the device complexity and space requirements increase
Solution Approach 1:
The standpipe acts as an intermediary device between the RWST and pressure vessel, mediating the water flow through its multi-orifice structure. This intermediary component enables extended cooling duration without requiring a larger RWST, as the standpipe's geometry and orifice distribution passively regulate flow to match decay heat profiles over time.
3Manufacturing precision
If multiple orifices are added to the standpipe to tailor flow, then the flow matching precision is improved, but the manufacturing complexity increases
Solution Approach 1:
The invention changes geometric parameters of the standpipe (orifice locations, diameters, and distributions) to achieve precise flow tailoring. By optimizing these parameters during design, the system achieves accurate matching of water flow to decay heat profiles without requiring complex manufacturing processes, as the precision is achieved through geometric configuration rather than complex fabrication.
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 approach maintains the reactor core immersed in water for the designed 72 hours by optimizing water flow, preventing excessive loss through the break and ensuring continuous decay heat removal.
Implementation Method 1
The RWST is located above the reactor core so that the passive ECC system can operate by gravity-driven water flow
Implementation Method 2
a float valve configured to regulate flow through one of the two or more orifices, the float valve including a float disposed in the standpipe
Implementation Method 3
Boiling heat transfer removes decay heat generated in the fuel assemblies and the resulting steam is subsequently vented through depressurization lines
Implementation Method 4
The required RWST volume can be computed based on the latent heat capacity of water (i.e., the amount of thermal energy that is removed per liter of liquid water converted to steam)
Data Source
AI summary
A nuclear reactor comprises a pressure vessel containing a nuclear reactor core. A reactor core cooling system comprises a standpipe including a plurality of orifices in fluid communication with a refueling water storage tank (RWST) to drain water from the RWST into the standpipe, and an injection line configured to drain water from the standpipe to the pressure vessel. In some embodiments the standpipe is disposed in the RWST, while in other embodiments the standpipe is disposed outside of the RWST and cross-connection pipes connect the plurality of orifices with the RWST. The reactor core cooling system may further comprise a valve configured to control flow through one orifice of the plurality of orifices in fluid communication with the RWST based on water level in the standpipe. The valve may comprise a float valve having its float disposed in the standpipe.