Thin Core Catcher for ABWR Natural Circulation Cooling
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Solution Overview
Problem
Conventional core catchers in boiling water nuclear reactors face challenges in accommodating their size within the limited space of the lower dry well of conventional ABWRs, which affects seismic resistance and increases construction costs, and struggle to maintain sufficient cooling water flow rates due to the height constraints, leading to potential core debris release and reduced safety.
Innovation Solution
A thin core catcher design with a main body height of 1.6 m or less, featuring inclined cooling channels, a distributor, and chimney pipes connected to the suppression pool, allowing for natural circulation and immediate cooling during accidents without interfering with control rod drive handling equipment, and maintaining a higher water head for enhanced flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional core catcher design is installed in a conventional ABWR, then the core catcher can provide cooling function, but it increases the reactor building height and reduces seismic resistance
Solution Approach 1:
The core catcher utilizes the radial dimension by extending cooling channels in radial directions from the central basin, rather than relying solely on vertical height. This dimensional shift allows efficient heat removal while maintaining a compact vertical profile that fits within conventional ABWR height constraints.
Solution Approach 2:
The core catcher employs natural circulation dynamics where cooling water automatically circulates through the cooling channels without requiring external pumps. The system dynamically adjusts water flow based on temperature differences and pressure gradients, providing adaptive cooling while maintaining a compact structure.
2Reliability
If a conventional core catcher design is installed in a conventional ABWR, then the core catcher can provide cooling function, but it increases construction costs
Solution Approach 1:
The core catcher is designed to perform multiple functions within a single integrated structure: the basin collects core debris, the cooling channels provide heat removal, and the natural circulation system provides pump-independent water flow. This multi-functionality reduces the number of separate components needed, simplifying construction and reducing costs.
3Length of stationary object
If the core catcher height is reduced to fit in conventional ABWR, then it can be installed without increasing building height, but it becomes difficult to maintain sufficient cooling water flow rates
Solution Approach 1:
The core catcher divides the cooling function into multiple radial cooling channels distributed around the central basin. This segmentation allows each channel to efficiently cool debris in its sector while collectively providing sufficient total cooling capacity, maintaining effective flow rates despite reduced overall height.
Solution Approach 2:
The design changes the cooling water flow parameters by utilizing natural circulation driven by density differences between heated and cool water. This parameter change from pump-driven flow to buoyancy-driven flow enables sufficient cooling water movement within a compact height configuration.
4Ease of operation
If radial cooling channels are used with natural circulation, then cooling water can be circulated uniformly without active pumps, but the system requires sufficient height for water head
Solution Approach 1:
The system transitions from relying primarily on vertical height for natural circulation to utilizing radial extension of cooling channels. By extending channels radially outward from the central basin, the design creates sufficient water head and circulation path length without requiring increased vertical height, enabling pump-independent operation in compact configurations.
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
Enables the core catcher to be installed in conventional ABWRs without increasing the reactor building height, ensures continuous cooling water flow, and prevents core debris release by maintaining a stable natural circulation flow rate, thus enhancing safety and reducing construction costs.
Implementation Method 1
This recirculation of cooling water is natural circulation, and does not require active pumps
Implementation Method 2
the cooling water in the upper part of the core catcher is recirculated, efficiently removing the decay heat generated in the debris
Data Source
AI summary
According to an embodiment, a core catcher has: a main body including: a distributor arranged on a part of a base mat in the lower dry well, a basin arranged on the distributor, cooling channels arranged on a lower surface of the basin connected to the distributor and extending in radial directions, and a riser connected to the cooling channels and extending upward; a lid connected to an upper end of the riser and covering the main body; a cooling water injection pipe open, at one end, to the suppression pool, connected at another end to the distributor; and chimney pipes connected, at one end, to the riser, another end being located above the upper end of the riser and submerged and open in the pool water.