Control Rod Insertion Time Simulation Using CFD Variable Grids
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Solution Overview
Problem
Conventional methods for calculating control rod insertion time in nuclear reactors are overly conservative due to the lack of consideration for three-dimensional thermal-hydraulic effects, resulting in significant calculation errors and inaccurate insertion time measurements.
Innovation Solution
A simulation method using computational fluid dynamics (CFD) to model the three-dimensional thermal-hydraulic phenomenon within the nuclear reactor, including the control rod, guide tube, impact absorption tube, and drainage, with variable and aligned grid systems to accurately calculate the insertion time, considering hydraulic drag, friction, and weight, and adjusting cell sizes to minimize error within a 5% margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one-dimensional codes are used to calculate control rod insertion time, then the calculation is simple, but the measurement precision is low due to ignoring three-dimensional hydraulic effects
Solution Approach 1:
The patent transitions from one-dimensional calculation codes to three-dimensional CFD simulation to accurately capture the thermal-hydraulic effects inside the guide tube. This dimensional upgrade allows the simulation to model the complex fluid dynamics, pressure distributions, and flow patterns that occur during control rod insertion, thereby resolving the contradiction between calculation simplicity and measurement precision.
Solution Approach 2:
The patent creates a virtual three-dimensional model that replicates the physical nuclear reactor system, including the guide tube, control rod, and surrounding structures. By copying the geometric and physical characteristics of the actual system into the CFD simulation environment, the measurement precision is significantly improved while maintaining computational feasibility through optimized meshing and boundary conditions.
2Measurement precision
If three-dimensional CFD simulation is used to model thermal-hydraulic phenomena, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The three-dimensional simulation domain is divided into discrete computational cells or mesh elements that represent different regions of the guide tube and surrounding structures. This segmentation allows the complex continuous physical domain to be broken into manageable discrete units, enabling accurate modeling of local thermal-hydraulic phenomena while keeping the computational complexity tractable through systematic grid generation and boundary condition application.
3Reliability
If conservative evaluation is applied to ensure safety, then the reliability is improved, but the measurement precision deteriorates due to exaggerated conservatism
Solution Approach 1:
The CFD simulation provides detailed feedback on the actual thermal-hydraulic conditions during control rod insertion, including pressure gradients, flow velocities, and temperature distributions. This feedback mechanism allows for accurate prediction of insertion time based on real physical phenomena rather than conservative assumptions, thereby improving measurement precision while maintaining safety through physically-based predictions.
Solution Approach 2:
The patent changes the fundamental parameters used in the evaluation from conservative simplified assumptions to actual physical parameters obtained through CFD simulation, such as accurate pressure distributions, flow rates, and thermal conditions. By using these realistic parameter values instead of conservative estimates, the measurement precision is improved while the reliability is maintained through the physical accuracy of the simulation results.
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 provides a highly accurate estimation of control rod insertion time, reducing conservatism and providing valuable information for reactor design and operation, including drop speed, pressure distributions, and flow rates, applicable to both new and existing reactors.
Implementation Method 1
the control rod freely falls down to the nuclear reactor core with the gravity
Implementation Method 2
simulating a three-dimensional thermal-hydraulic phenomenon using the computational fluid dynamics (CFD)
Implementation Method 3
the calculation of the simulation estimated value for the insertion time... by calculating the thermal-hydraulic phenomenon
Implementation Method 4
The one-dimensional codes consider factors such as hydraulic resistance of a fluid, friction, and weight of a control rod assembly
Data Source
AI summary
Provided is a method of the simulation construction for measurement of the control rod insertion time including a three-dimensional modeling operation of an inside wall of the nuclear reactor, a control rod, etc; a flow field configuration operation wherein the flow field is differentially configured by a variable grid system comprising variable cells which change the configuration and by an aligned grid system comprising fixed cells which maintains the configuration; a calculation operation of simulation estimated value for the insertion time by analyzing the thermal-hydraulic phenomenon using the three-dimensional CFD; and a cell change operation, wherein an error between the estimated value and the actual value is verified whether the error lies within the reference range, and, when the error exceeds the reference range, the size of the variable cell and/or of the size of the fixed cell is changed.