• Nuclear Engineering and Technology
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• 제54권1호
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• pp.226-233
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• 2022

In the present work, a phase-field model was developed to investigate the influence of recrystallization on bubble evolution during irradiation. Considering the interaction between bubbles and grain boundary (GB), a set of modified Cahn-Hilliard and Allen-Cahn equations, with field variables and order parameters evolving in space and time, was used in this model. Both the kinetics of recrystallization characterized in experiments and point defects generated during cascade were incorporated in the model. The bubble evolution in recrystallized polycrystalline of U-Mo alloy was also investigated. The simulation results showed that GB with a large area fraction generated by recrystallization accelerates the formation and growth of bubbles. With the formation of new grains, gas atoms are swept and collected by GBs. The simulation results of bubble size and distribution are consistent with the experimental results.

• Nuclear Engineering and Technology
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• 제35권5호
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• pp.399-411
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• 2003

A model predictive control method is applied to design an automatic controller for thermal power control in a reactor core. The basic concept of the model predictive control is to solve an optimization problem for a finite future at current time and to implement as the current control input only the first optimal control input among the solutions of the finite time steps. At the next time step, the second optimal control input is not implemented and the procedure to solve the optimization problem is then repeated. The objectives of the proposed model predictive controller are to minimize the difference between the output and the desired output and the variation of the control rod position. The nonlinear PWR plant model (a nonlinear point kinetics equation with six delayed neutron groups and the lumped thermal-hydraulic balance equations) is used to verify the proposed controller of reactor power. And a controller design model used for designing the model predictive controller is obtained by applying a parameter estimation algorithm at an initial stage. From results of numerical simulation to check the controllability of the proposed controller at the $5\%/min$ ramp increase or decrease of a desired load and its $10\%$ step increase or decrease which are design requirements, the performances of this controller are proved to be excellent.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.455-465
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• 2021

The Molten Salt Reactor (MSR), one of the six advanced reactor types of the 4th generation nuclear energy systems, has many impressive features including economic advantages, inherent safety and nuclear non-proliferation. This paper introduces a system analysis code named TREND, which is developed and used for the steady and transient simulation of MSRs. The TREND code calculates the distributions of pressure, velocity and temperature of single-phase flows by solving the conservation equations of mass, momentum and energy, along with a fluid state equation. Heat structures coupled with the fluid dynamics model is sufficient to meet the demands of modeling MSR system-level thermal-hydraulics. The core power is based on the point reactor neutron kinetics model calculated by the typical Runge-Kutta method. An incremental PID controller is inserted to adjust the operation behaviors. The verification and validation of the TREND code have been carried out in two aspects: detailed code-to-code comparison with established thermal-hydraulic system codes such as RELAP5, and validation with the experimental data from MSRE and the CIET facility (the University of California, Berkeley's Compact Integral Effects Test facility).The results indicate that TREND can be used in analyzing the transient behaviors of MSRs and will be improved by validating with more experimental results with the support of SINAP.

• Nuclear Engineering and Technology
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• 제26권4호
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• pp.536-547
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• 1994

본 논문에서는 최적제어기법을 이용한 원자로 출력 제어시스템을 다루었다. 시스템 변수들을 상태변수로 표시하면 관측치 뿐만 아니라 시스템 내부의 모든 상태변수를 동시에 다룰 수 있으므로 설계의 자유도가 증가될 수 있다. 따라서 본 논문에서는 원자로의 동특성식과 열수력학적 에너지 평형식을 사용하여 원자로를 모델링한 후 이를 상태변수로 나타내었다. 다음으로는 LQR 및 LQG 시스템을 설계하여 제어봉 및 출력의 거동을 동시에 만족시킬 수 있는 설계조건을 결정하였다. 또한 서보 시스템의 설계를 위해 보통의 휘드백 시스템과 차수를 증가시킨 레귤레이팅 시스템을 만들어 비교하였으며 그 결과 증가차수 레귤레이팅 시스템이 보통의 휘드백 시스템에 비해 우수한 제어 특성이 있음을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제19권3호
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• pp.198-204
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• 1987

발전소 과도현상과 비냉각재 상실사고를 모의할 수 있는 가압경수로발전소 모의코드 MCSIM을 개발하였다. 원자로 냉각재계통은 에너지 방정식과 운동량 방정식을 분리 취급하면서 Drift Flux 2상 유동모델, 적분 운동량 방정식 등을 사용하여 모델링하였다. 증기발생기의 모사는 Pot Boiler 모델을 사용하였고, 2차계통을 위해서는 분리 취급된 정상상태 에너지 방정식과 운동량방정식을 핵출력 계산을 위해서는 점 동특성 방정식을 사용하였다. 현재의 코드성능을 시험하기 위해 완전 냉각재 유동상실사고와 제어봉 집합체 인출 사고를 계산하여 그 결과를 원자력 5/6호기 최종 안전 보고서의 결과와 비교하였다.

• Nuclear Engineering and Technology
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• 제52권7호
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• pp.1443-1451
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• 2020

The objective of this study is to design a robust power control system for a small pressurized water reactor (PWR) to achieve stable power operations under conditions of external disturbances and internal model uncertainties. For this purpose, the multiple-input multiple-output transfer function models of the reactor core at five power levels are derived from point reactor kinetics equations and the Mann's thermodynamic model. Using the transfer function models, five local reactor power controllers are designed using an H infinity (H_∞) mixed sensitivity method to minimize the core power disturbance under various uncertainties at the five power levels, respectively. Then a multimodel approach with triangular membership functions is employed to integrate the five local controllers into a multimodel robust control system that is applicable for the entire power range. The performance of the robust power system is assessed against 10% of full power (FP) step load increase transients with coolant inlet temperature disturbances at different power levels and large-scope, rapid ramp load change transient. The simulation results show that the robust control system could maintain satisfactory control performance and good robustness of the reactor under external disturbances and internal model uncertainties, demonstrating the effective of the robust power control design.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1644-1651
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• 2022

This paper focuses on the power-level control of nuclear power plants (NPPs) in the presence of lumped disturbances. An adaptive second-order nonsingular terminal sliding mode control (ASONTSMC) scheme is proposed by resorting to the second-order nonsingular terminal sliding mode. The pre-existing mathematical model of the nuclear reactor system is firstly described based on point-reactor kinetics equations with six delayed neutron groups. Then, a second-order sliding mode control approach is proposed by integrating a proportional-derivative sliding mode (PDSM) manifold with a nonsingular terminal sliding mode (NTSM) manifold. An adaptive mechanism is designed to estimate the unknown upper bound of a lumped uncertain term that is composed of lumped disturbances and system states real-timely. The estimated values are then added to the controller, resulting in the control system capable of compensating the adverse effects of the lumped disturbances efficiently. Since the sign function is contained in the first time derivative of the real control law, the continuous input signal is obtained after integration so that the chattering effects of the conventional sliding mode control are suppressed. The robust stability of the overall control system is demonstrated through Lyapunov stability theory. Finally, the proposed control scheme is validated through simulations and comparisons with a proportional-integral-derivative (PID) controller, a super twisting sliding mode controller (STSMC), and a disturbance observer-based adaptive sliding mode controller (DO-ASMC).

• Nuclear Engineering and Technology
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• 제19권3호
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• pp.192-197
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• 1987

다량의 중수반사체를 가진 조밀한 노심에서는 핵분열시 발생하는ｒ선과 중수소와의 (ｒ,n) 반응에 의해 지발 광중성자가 다량 생성되므로 이러한 계통을 기술하기 위하여 광중성자와 그 모핵종의 공간적 분리에 역점을 두어 2-점노 운동방정식을 정립하였다. 여러 반응도를 주입하여 출력 천이를 모사계산하므로써 노심과 반사체사이의 관련 효과를 조사하였다. 이 모델에 의한 모사계산 결과와 공간 종속 운동방정식에 의한 계산결과를 비교하였다. 반사체 영역에서의 광중성자 효과가 포함되므로써, 이를 포함하지 않은 모델에 비해 출력 천이현상을 감소시켰다. 실제로 출력을 측정하는 계측기는 이러한 공간적 분리영 향을 제거하기 위하여 노심 내부에 위치하여야 한다.