Reactor Core Coolant Flow Resistance Optimization
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Solution Overview
Problem
Conventional reactor core designs for Boiling Water Reactors face challenges in maintaining thermal margin due to increased power density and the need for frequent fuel assembly exchanges, which leads to reduced thermal margin and increased power generation costs.
Innovation Solution
The reactor core is optimized by dividing fuel assemblies into two groups with different coolant passage resistances, where first fuel assemblies with lower pressure loss are surrounded by second fuel assemblies with higher pressure loss, thereby controlling the coolant flow rate and suppressing power increases, while maintaining or improving thermal margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the flow rate of cooling water is increased to improve thermal margin, then thermal margin is improved, but power of the fuel assembly increases
Solution Approach 1:
The patent applies local quality by differentiating coolant flow control between inner and outer core regions. The outer core region (at least 70% of core radius) uses orifices with a first pore diameter, while the inner core region uses orifices with a second pore diameter that is 0.5 to 2.0 times the first diameter. This localized differentiation allows the outer region to receive increased coolant flow for thermal margin improvement while the inner region maintains appropriate flow rates to prevent excessive power increase.
2Reliability
If pore diameter of orifice in outermost layer region is made smaller to increase inflow resistance, then thermal margin during rated operation is improved, but power density of core decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the pore diameter ratio between inner and outer core region orifices. The second pore diameter (inner region) is set to be 0.5 to 2.0 times the first pore diameter (outer region), with specific ratios selected based on operational requirements. This parameter optimization allows the system to achieve both improved thermal margin and maintained power density by balancing the inflow resistance characteristics across different core regions.
3Productivity
If fuel assemblies are exchanged frequently to maintain core performance, then operational efficiency is maintained, but thermal margin reduces and costs increase
Solution Approach 1:
The patent applies preliminary action by pre-configuring the coolant distribution system with differentiated orifice pore diameters before fuel assemblies are loaded. The outer core region orifices are designed with larger pore diameters to provide higher coolant flow capacity in advance, which compensates for the reduced thermal margin that occurs during extended operation cycles. This allows the reactor to maintain adequate thermal margins even when fuel assemblies are not exchanged frequently.
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 effectively suppresses the power increase rate of fuel assemblies with increased coolant flow, enhancing thermal margin and reducing the need for frequent fuel exchanges, thus improving operational efficiency and cost-effectiveness.
Implementation Method 1
The cooling water is circulated by pump
Implementation Method 2
fuel rods are heated by the heat generated by the nuclear fission of the nuclear fuel material
Data Source
AI summary
A reactor core, comprising:an outermost region; a core region surrounded by said outermost region; a plurality of fuel support members, each of which is disposed at a lower end portion of said outermost region and said core region; and a plurality of fuel assemblies loaded in said outermost region and said core region and supported by said fuel support members,wherein a plurality of fuel assemblies disposed in said core region include a plurality of first fuel assemblies, each of which is inserted into a first coolant passage which is formed in said fuel support member and has a first resistor having an opening, and a plurality of second fuel assemblies, each of which is individually inserted into each of second coolant passage which is formed in said fuel support member and has a second resistor having an opening and a larger pressure loss than that of said first resistor; and,four fuel assemblies, each of which is adjacent to each of four lateral sides of each of a plurality of first fuel assemblies, include either three or four second fuel assemblies.