بهینه سازی شکل ارزش میله های کنترل قدرت محوری متغیر با روش بهینه سازی شبیه سازی برای مانور قدرت راکتورهای فشرده شده آب

In this research, the optimization of the worth shape of axially variable strength control rods (AVSCRs) is performed to provide optimal performance to the AVSCRs for the power maneuvering of PWRs. The optimization objective is minimizing axial offset (AO) violation of target boundaries during the power maneuvering, and the objective functions for the optimization are relationships between AO variation and axial worth shape of the AVSCRs. However, in this case, an analytic objective function does not exist, and the response for input can only be evaluated by computer simulation. Therefore, a simulation optimization methodology is used. The response surface methodology (RSM) is adopted and objective functions are evaluated with a typical 100-50-100%, 2-6-2-14 h pattern of daily load-follow power maneuvering using reactor simulation code. The optimization result shows that the optimized AVSCRs have good performance on the AO control. The violation of the AO target boundary during the power maneuvering is minimized, and consequently the AO is regulated well within the AO target band during the power maneuvering.

During the power maneuvering of a nuclear power plant, the reactor core is in a transient state induced by transient effects of xenon. The reactivity change that causes change in reactor power makes variation of xenon concentration and axial distribution, and a change in xenon axial distribution causes xenon oscillation, which makes the reactor able to reach an uncontrollable state or trip. Therefore, in order to prevent a xenon oscillation, maintaining the axial power distribution within some prescribed range is required during the power maneuvering. The axial power distributions in a reactor are represented by a variable called axial offset (AO) where PT is the power in the top half of the core, PB is the power in the bottom half of the core. This is simply the normalized difference between the power in the top half of the core and the power in the bottom half of the core. However, the reactivity change using the existing mechanisms has difficulties in maintaining this AO within the prescribed range. In a previous study, therefore, axially variable strength control rods (AVSCRs) are suggested, and lower shifted worth control rods (LSWCRs) are devised as a kind of AVSCRs to mitigate variation of axial power distribution during the power maneuvering. Through this work, the utilities of LSWCRs are identified such that these rods have good characteristics for controlling the AO during the power maneuvering of PWRs, and the power maneuvering without reactivity compensation by change of boron concentration is accomplished (Kim and Seong, 2003). However, the objectives of developing these LSWCRs were showing feasibility for the use of control rods that have axially varying worth shape, and the LSWCRs were developed intuitively as a kind of AVSCRs. Therefore, in this work, the optimization of the worth shape of the AVSCRs is performed to find optimal worth shape that provides the AVSCRs with optimal performance for the power maneuvering of PWRs. The suggested AVSCRs are axially three-sectioned control rods that are divided into three sections which have different strengths in relation to each other. The optimization objective is minimizing AO violation of target boundaries during the power maneuvering, and the objective functions for the optimization are relationships between AO variation and axial worth shape of the AVSCRs. However, in this case, an analytic objective function does not exist, and the response for input can only be evaluated by computer simulation using reactor simulation code. Therefore, a simulation optimization methodology is used. A simulation optimization problem is an optimization problem where the objective function and some constraints are responses that can only be evaluated by computer simulation

In this research, AVSCRs are suggested, and the optimization of the worth shape of the AVSCRs is performed to provide the AVSCRs with optimal performance for the power maneuvering of PWRs. The suggested AVSCRs are axially three-sectioned control rods. This control rod is divided into three sections which have different strengths in relation to each other. The optimization objective is minimizing AO violation of target boundaries during the power maneuvering. The objective functions for the optimization are relationships between AO variation and axial worth shape of the AVSCRs. However, in this case, an analytic objective function does not exist, and the response for input can only be evaluated by computer simulation using reactor simulation code. Therefore, a simulation optimization methodology is used. A simulation optimization problem is an optimization problem where the objective function and some constraints are responses that can only be evaluated by computer simulation. The simulation optimization methodologies are classified into the six major categories, and among the six methods, in this work, the RSM is used as the simulation optimization algorithm for the optimization of the worth shape of the AVSCRs. The RSM is a procedure for fitting a series of regression models to the output variable of a simulation model by evaluating it at several input variable values and optimizing the resulting regression function. The process starts with a first-order regression function and the steepest ascent/descent method. After reaching the vicinity, higher degree regression functions are employed. Then the optimization of the worth shape is performed and a typical 100-50-100%, 2-6-2-14 h pattern of daily load-follow power maneuvering is adopted based on the demand pattern in Korea. The optimization result shows that the optimized AVSCR has good performance on the AO control. The violation of the AO target boundary during the power maneuvering is minimized, and consequently, the AO is regulated well within the AO target band during the power maneuvering. Through this work, the optimization of the worth shape of AVSCRs, in order to provide these rods with the optimal performance for the power maneuvering, is performed. For implementation to real nuclear power plants, the safety analyses remain as future works considering several constraints such as regulation guides, shutdown margin, etc.