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Nuclear plant modeling and control is an important subject in nuclear power engineering, giving the dynamic model from process mechanics and/or operational data as well as guaranteeing satisfactory transient and steady-state operational performance by well-designed plant control laws. With the fast development of small modular reactors (SMRs) and in the context of massive integration of intermittent renewables, it is required to operate the nuclear plants more reliably, efficiently, flexibly and smartly, motivating the recent exciting progress in nuclear plant modeling and control. In this paper, the main progress during the last several years in dynamical modeling and control of nuclear plants is reviewed. The requirement of nuclear plant operation to the subject of modeling and control is first given. By categorizing the results to the aspects of mechanism-based, data-based and hybrid modeling methods, the advances in dynamical modeling are then given, where the modeling of SMR plants, learning-based modeling and state-observers are typical hot topics. In addition, from the directions of intelligent control, nonlinear control, online control optimization and multimodular coordinated control, the advanced results in nuclear plant control methods are introduced, where the hot topics include fuzzy logic inference, neural-network control, reinforcement learning, sliding mode, feedback linearization, passivation and decoupling. Based upon the review of recent progress, the future directions in nuclear plant modeling and control are finally given. [ABSTRACT FROM AUTHOR]

Nonlinear power-level control of nuclear reactors can guarantee wide-range closed-loop stability that is positive for plant load-following capability. Nuclear reactor power dynamics are the tight interconnection of both neutron kinetics and thermal hydraulics, which determines that the corresponding control design model is a complex nonlinear system with large uncertainty. Although nuclear reactor dynamics are complex, it is meaningful to develop simple but effective power-level control methods for easy practical implementation and commissioning. In this paper, a passivity-based control (PBC) is proposed for nuclear reactor power-level dynamics, which has a simple form and relies on the measurement of both neutron flux and average primary coolant temperature. By constructing the Lyapunov function based on the shifted ectropies of neutron kinetics and reactor core thermal hydraulics, the sufficient condition for globally asymptotic closed-loop stability is further given. Finally, this PBC is applied to the power-level control of a nuclear heating reactor, and simulation results show the feasibility and satisfactory performance. [ABSTRACT FROM AUTHOR]

To balance the intermittent renewable energy and cope with the increasing nuclear power installed capacity in China, it is necessary for nuclear power plants (NPPs) to operate with load-following mode for enhancing economic competitiveness. The modular high temperature gas-cooled reactor (MHTGR) is an appropriate candidate for load-following operation due to the advanced features such as robust fuel elements, online fueling and full-power-range temperature negative feedback. The MHTGR-based nuclear steam supply systems (NSSS) which produces superheated steam flow for electricity, is the core for any NPPs. The proper control of NSSS is the prerequisite for the safe, stable and efficient load-following operation. However, in current engineering practice, the set-point trajectories of neutron flux, primary coolant temperature, primary and secondary flowrates are just the curves by linking the referenced steady values from the thermal hydraulic design, which are further determined by the thermal power requirement. Thus, it is meaningful to investigate an optimization-oriented control method to improve the operation efficiency. Motivated by this, two dynamic matrix control (DMC) with cascade structure are presented to improve both thermal power and steam temperature of the MHTGR-based NSSS. The thermal power is optimized by the first DMC through adjusting the set-point of nuclear flux. The second DMC is then designed based on the integration of the NSSS, the proportional-integral-derivative (PID) and the first DMC to improve the steam temperature response by adjusting the feed-water flowrate. The control performance during wide range operation is shown and discussed with the simulation results of a large-scale MHTGR plant model. • Small Modular Reactors are suitable to operate in load following mode. • Two dynamic matrix controls (DMCs) are designed for thermal power control. • Robustness analysis is provided by singular value decomposition. • The performance of DMCs is verified and analyzed by numerical experiments. [ABSTRACT FROM AUTHOR]

Abstract Since nuclear power still fulfills nearly 11% of world electricity demand nowadays, the flexible operation of nuclear reactors can be positive to improve the penetration level of intermittent renewable energy (IRE) sources. Meanwhile, the operational flexibility of nuclear reactors results in the frequent variation of reactor process variables such as the neutron flux, fuel temperature and primary coolant pressure and temperature, which may fasten the degradation of equipment, and further leads to the necessity of developing performance monitoring methods for nuclear reactors in the context of fast and deep IRE penetration. Motivated by the importance of performance monitoring, an adaptive state observer (ASO) for nuclear reactors is newly proposed, which only needs the measurements of neutron flux and coolant temperature at reactor inlet and can provide globally asymptotic estimation for the normalized concentrations of delayed neutron precursors, 135Xe and 135I, the average temperatures of fuel elements and primary coolant as well as the total reactivity disturbance. The ASO is then applied for reconstructing the unmeasurable state variables and total reactivity disturbance of a nuclear heating reactor (NHR). Numerical simulation results verify the theoretical analysis, and show the satisfactory observation performance with its influence given by the ASO parameters. Furthermore, a hardware-in-loop (HIL) verification experiment is performed, and the corresponding results show that this newly-built ASO is not sensitive to the measurement noises, which leads to the feasibility of deploying the ASO on those digital control system platforms. Highlights • Deep penetration of renewables to the grid needs the flexibility of nuclear power. • Monitoring is necessary for the reliability of flexible reactors for grid balancing. • An adaptive state observer (ASO) of nuclear reactors is given for state monitoring. • Globally convergent estimation of states and disturbance can be provided. • The performance of ASO is verified through numerical and HIL experiments. [ABSTRACT FROM AUTHOR]

The modular high temperature gas-cooled reactor (MHTGR) is a typical small modular reactor (SMR) with inherent nuclear safety, which has a low average power density about 3 MW/m 3 , uses TRISO particle based fuel elements, and adopts helium as coolant and graphite as both moderator and structure material. Based upon the multimodular scheme, i.e. multiple MHTGR-based nuclear steam supply system (NSSS) modules driving a single turbine/generator system, the MHTGR-based nuclear power plants (NPPs) with inherent safety as well as any desired power ratings can be realized. However, since multiple NSSS modules are coupled together by the common secondary-circuit, the operation and control of multimodular NPPs is quite different from those classical single modular NPPs. For the design and verification of operation and control strategies of a NPP, it is necessary to develop the dynamical model of this NPP, and to study its open-loop and closed-loop dynamics. In this paper, a lumped-parameter dynamical model of the six-modular MHTGR-based NPP HTR-PM600 is proposed based on the conservation laws of mass, energy and momentum, which is composed of the MHTGR-based NSSS modules and the common secondary-circuit. Then, both the open-loop responses to exterior disturbances and the closed-loop behavior in power-level maneuver are given by numerical simulation, which shows not only the feasibility of this model but also the coupling effect of the modules caused by the common secondary-circuit. [ABSTRACT FROM AUTHOR]

Nuclear superheated-steam supply systems (Su-NSSS) produces superheated steam flow for electricity generation or process heat. Although the current Su-NSSS control law can guarantee satisfactory closed-loop stability, which regulates the neutron flux, primary coolant temperature and live steam temperature by adjusting the control rod speed as well as primary and secondary flowrates, however, the control performance needs to be further optimized. Motivated by the necessity of optimizing the thermal power response, a novel multi-layer perception (MLP) based model predictive control (MPC) is proposed in this paper, which is constituted by a MLP-based prediction model and the control input designed along the direction opposite to the gradient of a given performance index. It is proved theoretically that this MLP-based MPC guarantees globally-bounded closed-loop stability. Finally, this newly-built MLP-based MPC is applied to the thermal power control of a Su-NSSS, whose implementation is given by forming a cascaded feedback control loop with the currently existing Su-NSSS power-level control in the inner loop for stabilization and with this new MPC in the outer loop for optimization. Numerical simulation results verify the correctness of theoretical result, and show the satisfactory improvement in optimizing the thermal power response. [ABSTRACT FROM AUTHOR]

The modular high temperature reactor (MHTGR), which uses helium as coolant and graphite as both moderator and structural material, has inherent safety features. It is multi-modular, i.e. the superheated steam produced by multiple MHTGR-based nuclear supplying system (NSSS) modules are combined to drive a common thermal load. The inherent safety feature of MHTGR can applied to a large-scale nuclear plant of any desired power ratings by adding modules. Since the plant power control technique of classical single-modular plants cannot be directly applied to multi-modular plants, it is necessary to design a new power control system for multi-modular plants. In this paper, the coordinated control system is presented for the two-module HTR-PM plant, the first multi-modular high temperature gas-cooled nuclear plant to be constructed in the world. The control system design is tested on the full-scale simulator of HTR-PM plant for the cases of power and high ramp down pressure heater bypass. The results demonstrate the feasibility of control system design and the acceptable transient performance of the multi-module plant. [ABSTRACT FROM AUTHOR]

Due to its inherent nuclear safety, modular high temperature gas-cooled reactor (MHTGR) is promising in building the next generation nuclear plants which provide safe and clean power or heat supply. It is clear that power-level control technique is crucial in guaranteeing safe, stable and efficient operation of MHTGRs. Since MHTGR dynamics is complexly nonlinear, it is necessary to develop nonlinear power-level control laws. The stepper motor is a satisfactory choice for driving the control rods of MHTGRs, and has already been applied to under-construction HTR-PM plant. Since a stepper motor itself is a nonlinear dynamic system that can deeply influence power-level control performance, it is meaningful to develop nonlinear power-level control laws of MHTGRs by considering the stepper motor dynamics. Motivated by this and based upon the backstepping technique and physically-based control design approach, a novel nonlinear power-level control is proposed by regarding the MHTGR and stepper motor as an entire dynamical system. It is proved theoretically that this newly-built power-level controller can guarantee globally asymptotic closed-loop stability by generating proper motor stator voltages. Numerical simulation results show not only the feasibility of this novel control law but also the relationship between regulation performance and controller parameters. [ABSTRACT FROM AUTHOR]

Because of its inherent safety feature and potential economic competitiveness, modular high temperature gas-cooled reactor (MHTGR) has been seen as one of the best candidates for building the next generation nuclear plants. As a typical small modular reactor (SMR), MHTGR can be incorporated with new energy resources to build micro-grids, and can also be utilized to build large nuclear energy systems having inherent safety feature at any power rating. The nuclear steam supplying system (NSSS) of MHTGR-based plants is composed of an MHTGR and a once-through steam generator (OTSG). The NSSS coordinated control is crucial for providing the load-following function. Motivated by this, a nonlinear coordinated control for MHTGR-based NSSSs is proposed in this paper. Based upon theoretical analysis, sufficient conditions for this newly-built control law to guarantee globally asymptotic closed-loop stability are given. The feasibility of this novel coordinated control strategy is verified through numerical simulation, and simulation results show that this new control law can provide satisfactory regulating performance for the NSSS by properly choosing its feedback gains. Moreover, this coordinated control has a very simple form, which means that it can be easily implemented in practical engineering. [ABSTRACT FROM PUBLISHER]

The modular high temperature gas-cooled reactor (MHTGR), which has the inherent safety feature, high thermal efficiency and satisfactory economic feasibility, can be applied for electricity and process heat production. Power-level control is an important technique for providing both the stable operation and load-following performance. Since the coolant temperature sensors of an MHTGR are usually installed near the primary side of the corresponding steam generator, there must be time-delay effect in the feedback loop of the coolant temperatures. Moreover, the measurement signal transducing may also induce time-delay effect. Therefore, it is meaningful to give the power-level control design method by considering this time-delay effect. In this paper, a simple output-feedback power-level control is proposed for the MHTGRs by using the delayed measurement signal of average reactor coolant temperature. In the aspect of theoretical analysis, a sufficient condition, under which it is well guaranteed that this newly-built power-level control is a globally asymptotic stabilizer, is firstly given. In the aspect of verification, numerical simulation results not only verify the feasibility of the theoretical results but also show the relationship between the performance and values of parameters of this novel power-level controller. The meaning of this work lies in two aspects. The first one is deeply revealing the relationship between the closed-loop stability and values of the controller parameters. The second one is giving the approach of designing a simple and effective power-level control strategy to suppress the negative influence induced by the time-delay in the feedback loop of the coolant temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Nuclear fission energy is currently the sole energy that can substitute fossil in a centralized way and great amount with commercial availability and economic competitiveness. Power-level control is one of the key techniques which provide safe, stable and efficient operation for nuclear power plants. The physically-based regulation theory is definitely a promising trend of modern control theory, which can provide a control design method that suppresses the unstable part of the system dynamics and remains the stable part. Usually, control laws designed by the physically-based control theory have a simple form and high performance. Stimulated by this, a novel nonlinear dynamic output feedback power-level control law is established in this paper for the pressurized water nuclear reactors (PWRs) based upon its natural dynamic features. This newly-developed controller guarantees not only the globally asymptotic closed-loop stability but also the satisfactory transient performance through properly adjusting the feedback gains. Furthermore, this controller has the L 2 disturbance attenuation performance. Numerical simulation results not only verify the correctness of the theoretical results but also illustrate the high control performance. [Copyright &y& Elsevier]

After the Fukushima nuclear accident, much more attention has to be drawn on the safety issues. The improvement of safety has already become the focus of the developing trend of the nuclear energy systems. Due to the inherent safety feature and the potential economic competitiveness, the modular high temperature gas-cooled reactor (MHTGR) has been seen as the central part of the next generation of nuclear plant (NGNP). Power-level control is one of the key techniques that guarantee the safe, stable and efficient operation for nuclear reactors. Since the MHTGR dynamics has the features of strong nonlinearity and uncertainty, in order to improve the operation performance, it is meaningful to develop the nonlinear adaptive power-level control law for the MHTGR. Based on using the natural dynamic features beneficial to system stabilization, a novel nonlinear adaptive power-level control is given for the MHTGR in this paper. It is theoretically proved that this newly-built controller does not only provide globally asymptotic closed-loop stability but is also adaptive to the system uncertainty. This control law is then applied to the power-level regulation of the pebble-bed MHTGR of the HTR-PM power plant. Numerical simulation results show the feasibility of this control law and the relationship between the performance and controller parameters. [ABSTRACT FROM PUBLISHER]

Both intermittent renewable energy (IRE) and nuclear fission energy can provide carbon-free electric power to the grid. The electric power generation from the intermittent renewable energy (IRE) sources such as the wind and solar are strongly dependent on the climatic conditions, geographical location and large land footprint. While, nuclear plants can provide consistent and clean power supply with small land footprint. Due to the strong complementarity between the IRE and nuclear, it is attractive to interconnect them to build nuclear-renewable hybrid energy systems (NRHESs) which are defined as the integrated facilities comprised of nuclear reactors, renewable energy generation and industrial processes. The flexibility of a NRHES for grid balance can be provided by actively adjusting the electric power output of nuclear cogeneration plants (NCPs), which leads to the frequent redistribution of main steam flow to the turbine and cogeneration process. For the main steam redistribution, it is necessary to guarantee the stability of grid frequency and main steam pressure, which heavily relies on the flexible control strategy of NCPs. In this paper, a new flexible control of NCPs with saturated main steam is proposed based on the idea of actively suppressing the total disturbance to the dynamics of grid frequency and main steam pressure. The stabilization problems of pressure and frequency are transferred to the disturbance attenuation Problem of a second-order disturbed dynamical system, and an active disturbance rejection control (ADRC) is then originally proposed for system stabilization. This ADRC is applied to the flexible control of a NCP composed of a nuclear heating reactor (NHR), a turbine-generator set and a multi-effect-desalination and thermal-vapor-compression (MED-TVC) process for seawater desalination. Numerical simulation results in the cases of load stepping and maneuvering show that the flexibility of this NCP is satisfactory in balancing the grid. • Flexibility of nuclear plants can be provided by cogeneration. • Flexible control is transferred to frequency and steam pressure stabilization. • Stabilization is guaranteed by a novel active disturbance rejection control. • Application to a nuclear plant cogenerating electricity and water is given. • Simulation results show the satisfactory performance. [ABSTRACT FROM AUTHOR]

To suppress the fluctuation from both load side and intermittent renewable energy (IRE), nuclear power plants (NPPS) should be operated in load-following mode to improve economic competitiveness. The modular high temperature gas-cooled reactor (MHTGR) belongs to the category of small nuclear reactor (SMRs) and is suitable for load-following by the virtue of online refueling ability and inherent safety. To realize economies of scale for MHTGR, multi-modular scheme that multiple nuclear steam supply system (NSSS) modules are connected in parallel providing superheated steam for common turbine is recommended to achieve desired power ratings. However, because of the large heat capacity in the pebble-bed of MHTGR and thermal coupling of different NSSSs through common secondary loop fluid network, the current control strategy which suppresses the nuclear power, coolant temperatures measurement from their set-points without considering thermal dynamic of NSSS itself, may not favorable for heat transfer in the NSSS. To improve the load-following ability, a multivariable dynamic matrix control (DMC) is constituted to dynamic compensate the thermal energy variation of NSSS. The implementation of the DMC has a typical cascade structure, where DMC revises the set-points of NSSS module in outer loop and the existing PID control law is adopt for stabilization in inner loop. Numerical results show that this cascade DMC can improve the transient of thermal power under power maneuvering, and can also attenuate the nuclear power, helium flowrate set-points and feed-water temperature step disturbance. • A multivariable dynamic matrix control (MDMC) is given for nuclear plants. • The MDMC can effectively improve plant load-following capability. • The MDMC gives the setpoints for local PID controllers. • Simulation results show the feasibility and satisfactory performance. [ABSTRACT FROM AUTHOR]

The sixth edition of the International Conference on “Advancements in Nuclear Instrumentation Measurement Methods and their Applications” (ANIMMA) was held in Portorož, Slovenia, from June 17–21, 2019. The conference attracted almost 300 participants from 32 different countries, coming from academy, research institutes, and industry to discuss new scientific and technical prospects in all fields where nuclear instrumentation and measurements techniques play a major role. The scientific program included 25 invited talks, 125 oral presentations, and 77 poster presentations on the following topics: fundamental physics; fusion diagnostics and technology; nuclear power reactors monitoring and control; research reactors; nuclear fuel cycle; decommissioning, dismantling, and remote handling; safeguards and homeland security; severe accident monitoring; environmental and medical sciences; and education, training, and outreach. [ABSTRACT FROM AUTHOR]

• Reinforcement learning is introduced to energy system dynamic optimization. • A novel multilayer perception based reinforcement learning control is proposed. • This new algorithm approximates the optimal control online without system model. • Application to the optimized thermal power control of a nuclear reactor is given. • Simulation results show the feasibility and satisfactory performance. Energy system optimization is important in strengthening stability, reliability and economy, which is usually given by static linear or nonlinear programming. However, the challenge faced in real-life currently is how to give the optimization by taking naturally existed energy system dynamics into account. To face this challenge, a multi-layer perception (MLP) based reinforcement learning control (RLC) method is proposed for the nonlinear dissipative system coupled by an arbitrary energy system and its local controllers, which can be able to optimize a given performance index dynamically and effectively without the accurate knowledge of system dynamics. This MLP-based RLC is composed of a MLP-based state-observer and an approximated optimal controller. The MLP-based state-observer is given for identification, which converges to a bounded neighborhood of the system dynamics asymptotically. The approximated optimal controller is determined by solving an algebraic Riccati equation with parameters given by the MLP-based state-observer. Based on Lyapunov direct method, it is further proven that the closed-loop is uniformly ultimately bounded stable. Finally, this newly-built MLP-based RLC is applied to the supervisory optimization of thermal power response for a nuclear steam supply system, and simulation results show not only the satisfactory performance but also the influences from the controller parameters to closed-loop responses. [ABSTRACT FROM AUTHOR]

The modular high temperature gas-cooled reactor (MHTGR) based nuclear steam supplying system (NSSS) is constituted by an MHTGR, a once-through steam generator (OTSG) and can generate superheated steam for industrial heat or electric power generation. The wide range closed-loop stability is achieved by the recently proposed coordinated control law, in which the neutron flux and the temperatures of both main steam and primary coolant are chosen as controlled variables, and the flowrates of both primary and secondary loop and the control rod speed are chosen as manipulated variables. However, the thermal power is only controlled in open loop manner and hence could be further optimized through feedback. Motivated by this, a dynamic matrix control (DMC) is proposed for optimizing the thermal power of MHTGR based NSSS. A simple step-response model with the thermal power response data is utilized in designing the DMC. The design objective of DMC is to optimize the deviation of the thermal power from its reference under its rate constraint. Then, by the virtue of strong stability of existing control law and optimization ability of DMC, a cascade control structure is implemented for the thermal power optimization, with the coordinated control law in the inner loop and DMC in the outer loop. Numerical simulation results show the satisfactory improvement of thermal power response. This cascade control structure inherits the advantages of both proportional-integral-differential (PID) control and DMC, by which the zeros offset and the short settling time of thermal power are realized. [ABSTRACT FROM AUTHOR]