1,720,984 research outputs found
Innovative control strategy for fast runback operational transient applied to SMRs
No full textThe recent interest in the Small Modular Reactor (SMR) for its potential increased economic competitiveness has focused attention in part on reducing operational costs to offset those plant costs that do not benefit from the economies of scale of large traditional units. Plant operation and maintenance economics are significantly driven by plant availability, which can be enhanced by means of innovative control strategies by avoiding unnecessary plant or unit trips. In this context, an effective strategy for achieving fast runback of a sodium-cooled SMR has been developed. In this work, after having defined and modeled a suitable control strategy by adopting the Petri nets formalism, a Model-based Predictive Control regulator has been developed in order to reduce as promptly as possible the power level, without scramming the reactor (fast runback) and possibly limiting the control rod contribution. Such flexibility could lead to significant savings in the operational costs of the reactor while also improving the system availability. The proposed procedure has been characterized by simulating the operational transients on both an oxide-fueled reactor and on a metal-fueled reactor, comparing the responses of the two different configurations and the respectively needed control rod contribution
A preliminary approach to the ALFRED reactor control strategy
Full text linkIn this paper, a preliminary approach to the definition of a suitable control strategy for the Advanced Lead Fast Reactor European Demonstrator (ALFRED), developed within the European 7th Framework
Program, has been undertaken. The Generation IV reactors offer new challenges for what concerns the
nuclear power plant control since several constraints both on primary and secondary loops have to be
faced, differently from the conventional Light Water Reactors. A simulator of the ALFRED plant has been
developed in a previous work (Ponciroli et al., 2014) with the main purpose of studying the system free
dynamics and stability features in a control-oriented perspective. Based on the outcomes of these investigations, in the present work, the possibility of adopting decentralized control schemes has been
investigated. Accordingly, Single Input Single Output control laws have been applied directly to the selected couples of inputeoutput variables, which have been identified first on the basis of the preliminary plant dynamics analyses, and then confirmed by the indications of the Relative Gain Array
method. Afterwards, two different control schemes have been studied depending on the number of
available inputs, and then implemented and compared in order to evaluate the effect of each control
action on the associated potential control strategy effectiveness. As a last step, the ALFRED control system has been finalized. The regulator design has been set up based on a simultaneous feedforward-feedback scheme incorporating four closed feedback loops. A controlled power reduction and a controlled overpower transient have been simulated in order to assess the performance of the two proposed control
schemes. Results show that both the adopted control strategies can assure an efficient control of the
thermal power while guaranteeing an effective control of lead and steam temperatures as well. In addition, some non-negligible differences between the two schemes have been observed and discussed
in the simulation results of control and controlled variables
Analytical models for a small LFR core dynamics studies
No full textAnalytical models for the study of a small Lead-cooled Fast Reactor (LFR) demonstrator (DEMO) core dynamics, in a control-oriented perspective, have been developed aimed at providing a useful, very flexible and straightforward tool allowing relatively quick transient design-basis and stability analyses. A simplified approach has been developed consisting in a lumped-parameter modeling of the coupled neutronics and thermal-hydraulics. The reactor transient responses following both postulated accident initiators such as Unprotected Transient of OverPower (UTOP), Loss of Heat Sink (ULOHS) and Loss of Flow (ULOF), and an emergency SCRAM event have been studied in MATLAB/SIMULINK® environment. A benchmark analysis has been then performed by means of the SAS4A/SASSYS-1 Liquid Metal Reactor Code System with the purpose of providing verification for the analytical outcomes of the nonlinear model and indicating how the latter relate to more realistic one-dimensional calculations. As a general result, responses concerning the main core characteristics (namely, power, reactivity, etc.) have turned out to be mutually consistent in terms of both steady-state absolute figures and transient developments, showing discrepancies of the order of only few per cents. DEMO dynamic behavior has been studied through a linear approach as well, so as to enable the use of linear analysis tools allowing to verify the system stability, thanks to the possibility of expressing a physical model in terms of transfer functions or state–space representation. The impact of linearization and point-kinetics one-precursor-group approximation has been further evaluated by examining the respective transient predictions, which have been compared to the nonlinear reference ones for increasing perturbations. An asymptotic stability analysis, according to Lyapunov's definition, is finally presented
An Object Oriented Approach to Simulation of Triga Mark II Dynamic Response
No full textThis paper deals with the development of a model for the nuclear research reactor TRIGA Mark II operating at University of Pavia. The purpose of the modeling is to reproduce the dynamic behavior of the reactor on the entire operative power range, i.e. 0÷250 kW, using the object oriented approach, implemented by the Modelica language. The main advantage is the a-causal formulation of the model, based on equations instead of statement assignment
Development of an Object-Oriented Dynamics Simulator for a LFR DEMO
No full textA control-oriented dynamics simulator for a Generation IV Lead-cooled Fast Reactor (LFR) demonstrator (DEMO) has been developed aimed at providing a flexible, simple and fastrunning
tool allowing to perform design-basis transient and stability analyses, and to lay the foundations for the study of the system control strategy. For such purposes, a model representing a
compromise between accuracy and straightforwardness has been necessarily sought, and in this view an object-oriented approach based on the Modelica language has been adopted. The reactor
primary and secondary systems have been implemented by assembling both component models already available in a specific thermal-hydraulic library, and ad hoc developed nuclear component models suitably modified according to the specific DEMO configuration. The resulting overall plant simulator, incorporating also the balance of plant, consists in the following essential parts: core, integrated steam generator/primary pump block, cold and hot legs, primary coolant cold pool, turbine, heat sink, secondary coolant pump. Afterwards, the reactor response to typical transient initiators has been investigated: feedwater mass flow rate and temperature enhancement, turbine admission valve coefficient variation, increase of primary coolant mass flow rate, and transient of overpower have been simulated; results have been compared with the outcomes of analogous analyses performed by employing a lumped-parameter DEMO plant model
Control approach to the load frequency regulation of a Generation IV Lead-cooled Fast Reactor
Full text linkOne of the most pressing issues in the study of the power generation and distribution is the characterization of the grid behavior, whether a relevant fraction of the connected power plants relies on Renewable Energy Sources. Indeed, because of the discontinuous power supply and the limited presence of energy accumulators, concerning power imbalances may take place on the grid. The power plants ensuring high reliability performance should be ready to feed the loads when the Renewable Energy Sources are not available. In order to ensure the grid stability and the sustainability of nuclear energy, the possibility of operating Generation-IV nuclear reactors in a flexible way should be considered, i.e., the Nuclear Power Plants should adjust the mechanical power produced so as to comply with the sudden grid frequency variations. In the present work, this opportunity is assessed for the Lead-cooled Fast Reactors, adopting the Advanced Lead Fast Reactor European Demonstrator (ALFRED) as a representative of Lead-cooled Fast Reactor technology. For this reactor concept, because of the large thermal inertia that characterizes the system, the adoption of the ‘‘reactor-follows-turbine’’ scheme (currently employed in the Pressurized Water Reactors) is not feasible. An alternative solution is proposed, i.e., the set-point for the thermal power produced in the core is kept constant at the nominal value (or slowly variable), and the set-point for the mechanical power available to the alternator is adjusted according to the load demands. In order to assess the performance of the developed control scheme, two case studies are simulated. In the first one, a frequency profile of the synchronous Continental European grid is provided. In the second simulation, the possibility of performing the islanding operational transient is evaluated. Such an operational transient needs the connected power plants to perform relevant power variations in few seconds in order to deal with the abrupt change in the grid powered configuration. The simulation outcomes show that the proposed control scheme allows achieving prompt mechanical power variations. As for the quantitative results, in both simulations the frequency value is maintained below the upper safety threshold (50.8 Hz). On the other hand, the control scheme complies with the technological constraints set for the safe operation of the primary circuit of the ALFRED reactor. In particular, the Balance of Plant pressure-induced feedbacks on the primary circuit dynamics are effectively dampened, i.e., the temperature in the cold leg is effectively maintained close to its set-point (i.e., 400 °C) and the plant is almost insensitive to the variations of the grid power demands
Innovative Control Strategy for the Fast-Runback Transient in a Sodium-Cooled Small Modular Reactor
No full textThe recent interest in the Small Modular Reactors for their potential increased economic competitiveness has focused attention in part on reducing operational costs to offset those plant costs that do not benefit from the economies of scale of large traditional units. Plant economics is significantly driven by plant availability, which can be enhanced by means of innovative operating strategies that act to avert plant or unit trips. A strategy that involves fast runback of the power plant to avert a turbine trip following a disconnection from the grid has been developed and assessed for a typical sodium-cooled SMR (adopted for proof-of-principle demonstration). A classic control approach based on PID feedback controllers has been adopted for establishing a baseline for performance improvement. Simulations outcomes have shown that although the reactor power level can be appropriately reduced, the net result is a global cooling of the system circuits. Such system conditions do not facilitate the objective of a rapid reconnect to the grid once the issue has been resolved. Moreover, the classic approach requires relatively large control rod motion. An alternative MIMO (Multiple Input Multiple Output) control scheme on the other hand provides additional regulation flexibility by allowing for coordinated control actions on the mass flow rates and on the control rods. A Model-based Predictive Control implementation of the MIMO approach has ensured prompt power level reduction with reduced overcooling and control rod motion, facilitating a quicker reconnect to the grid. Such flexibility could lead to improved system availability. An investigation of the metal-fuel form as an alternate to the oxide fuel form and its wider experience base has been performed for the same operational transient. By comparing the plant response for these two different fuel forms, it has been possible to evaluate the favorable properties in terms of inherent safety and plant operation of the metal-fuelled core configuration
Safety Issues Affecting the Feasibility of an Early High-Flux LFR Technology Demonstrator
No full textEvaluation of the Coolant Reactivity Coefficient Influence on the Dynamic Response of a Small LFR System
No full textAn assessment of the coolant reactivity feedback influence on a small Lead-cooled Fast Reactor (LFR) dynamics has been made aimed at providing both qualitative and quantitative insights into the system transient behavior depending on the sign of the above mentioned coefficient. The need of such an investigation has been recognized since fast reactors cooled by heavy liquid metals show to be characterized by a strong coupling between primary and secondary systems. In particular, the coolant density and radial expansion coefficients have been attested to play a major role in determining the core response to any perturbed condition on the Steam Generator (SG) side. The European Lead-cooled SYstem (ELSY)-based demonstrator (DEMO) has been assumed as the reference LFR case study. As a first step, a zero-dimensional dynamics model has been developed and implemented in
MATLAB/SIMULINK® environment; then typical transient scenarios have been simulated by incorporating the actual negative lead density reactivity coefficient and its opposite. In all the examined cases results have shown that the reactor behaves in a completely different way when considering a positive coolant feedback instead of the reference one, the system free dynamics resulting moreover considerably slower due to the core and SG mutually
conflicting reactions. The outcomes of the present analysis may represent a useful feedback for both the core and the control system designers
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