Normal Operation Scenarios Research Articles

Research on optimization of distribution network communication network structure based on invulnerability optimization model

In order to improve the power supply reliability and economy of the distribution network, from the perspective of optimizing its network structure and connectivity, an invulnerability optimization model based on the shortest path multi-scenario and multi-objective is constructed. For the normal operation and various single post-fault scenarios, aiming at the strong destructive and unloading or the minimum load shedding respectively, through the branch exchange method, find the best anti-destructive power of the completed distribution network in each scenario. The network topology provides a new research idea for the optimization of the network structure of medium voltage distribution network. Invulnerability measure index S(G)=1, the strongest invulnerability, the invulnerability measure index of any non-fully connected network is 0<s(G)<1, the larger S(G) is, the more compact the network structure is and the more resistant it is. The optimization results based on the approximate network example of the IEEE33 node distribution network test system show the rationality and practicability of the research method.

NSTX-U Global Thermal Analysis for Bakeout and Normal Operation Scenarios

The NSTX-U recovery project will deploy new plasma-facing components (PFCs) to meet the updated high heat flux requirements, increased heating power, and longer pulse durations compared with NSTX. Many components have been redesigned and replaced. To address the influence of high heat load, heat transfer, and distribution in the whole machine, an ANSYS two-dimensional (2-D) model was built for the global thermal analysis of NSTX-U recovery. This 2-D model includes most of the aspects of the updated design of the center stack casing first wall, new inboard divertor and cooling plate, updated outboard divertor, etc. It models the radiative surfaces of almost all the in-vessel components, vessel, insulation, and cooled coils. It models the convection heat exchange on all the out-of-vessel components and environment. Thee water cooling of coils, casing, and vessel, and helium heating and cooling of PFCs are included, too. Heat loads of normal operation are from the plasma energy deposition of five predefined typical thermal scenarios. Heat sources for bakeout are from Joule heat generation, helium gas, and hot water heating.The results of this global model are used to predict temperature ratcheting and heat distribution of different thermal scenarios, to understand heat transfer and heat removal for bakeout, to evaluate different cooling schemes for operation and heating schemes for bakeout, and to estimate heat loads to the cooling system of the Ohmic heating and Poroidal field coils, heat loss from the system, etc. The temperature and heat flux results are also used as the base and comparison for the detailed thermal analyses of the substructures. This global model is also being converted to a structural model to evaluate thermal growth and thermal stresses. Thermal loads can be mapped to detailed three-dimensional structural models and combined with electromagnetic loads to evaluate different component designs.

Distributed aggregation control of grid-interactive smart buildings for power system frequency support

Grid-interactive smart buildings with thermostatically-controlled loads can be modeled as virtual energy storage systems with dissipation, which have great potentials for providing grid ancillary services such as frequency support. In this paper, a new distributed aggregation control method is proposed for multiple grid-interactive smart buildings in one frequency control area (e.g. a residential community) to provide fast frequency support. The proposed method is based on the distributed sliding mode control via a leader-follower communication scheme. A leader control is designed to provide power and comfort/energy level references for the smart building aggregator based on the area frequency deviation, while references are tracked by each smart building using the proposed distributed sliding mode control. The stability of the proposed control method for grid-interactive smart buildings is proved by the Lyapunov method. With the proposed method, the external characteristics of the aggregated smart buildings will have good power tracking and energy recovery capability, which can effectively improve the system frequency response. In the aggregator, fair and efficient power and comfort/energy level sharing are achieved among all participating grid-interactive smart buildings. The proposed control scheme is tested on a three-area power system considering both system contingency and normal operation scenarios.

Structural integrity assessment of an ITER ECH&CD Upper Launcher mirror (LM1)

The Lower Mirror one (LM1) is part of the in-vessel quasi-optical beam propagation system for the ITER Electron Cyclotron (EC) Upper Launcher (UL), in which each of eight gaussian beams of mm-waves is reflected by a group of four mirrors and radiated into the plasma. Ohmic losses at the mirror surfaces with 60'000 thermal cycles are foreseen at frequencies lower than 3 Hz and power levels up to 1.31 MW per beam.This paper reports the means used to accurately ascertain resistance against the following failure modes: 1) plastic collapse, 2) thermal fatigue and 3) ratcheting. Analyses are carried out in accordance with the design-by-analysis approach. Thermo-mechanical effects are investigated via finite elements to support the assessment during the thermal cycle.This structural integrity study of the LM1 mirror using the American Standard of Mechanical Engineer code (ASME) for pressure vessels and piping confirms the compliance of the proposed design for the Normal Operation (NO) scenario.

Optimal Energy Storage Sizing for Networked Microgrids Considering Reliability and Resilience

In this paper, an optimal energy storage sizing method is proposed for networked microgrids (NMGs) considering reliability and resilience enhancement. A bi-level optimization model for energy storage sizing is developed. The upper-level model is focused on the optimal energy storage sizing problem, aiming at maximizing annual profit. The lower-level problem is aimed at operation optimization for profit maximization under multiple operating scenarios, i.e., normal operation, typical fault, and extreme fault scenarios. The bi-level model is converted into a mixed-integer linear program (MILP), which can be solved by off-the-shelf optimization solvers such as CPLEX. For comparison, the optimal energy storage size schemes are obtained for the NMGs and non-networked microgrids (NNMGs), respectively. The results indicate that the required energy storage size can be reduced while the operating profit is improved by interconnecting the microgrids (MGs). The results also indicate that the energy interaction in NMGs enables the enhancement of both reliability and resilience during grid outages.

Voltage quality in delta Egypt network and its impact in oil industry

The electrical energy is transmitted from the generating stations to the consumers through a transmission network. The effectiveness of improving voltage profile yields high transmission network efficiency and increase the capacity of transmission lines, also decrease power losses, voltage drop and unplanned shut down in the big industrial and strategic loads like (oil refining industry). This paper objective presents the suggested solutions for improving voltage profile in electrical network of delta Egypt to achieve a voltage quality. The methodology of suggested solutions are applied on delta Egypt network with voltage levels (66, 11, 6.6, 0.4) kV, the simulations were performed using digital simulation and electrical network calculation (DIgSILENT power factory software) to study the voltage profile. The validation of results was performed by comparing the voltage profile of proposed four different scenarios: 1st: power flow in normal operation (without using any voltage improving devices), 2nd: using Automatic Tap Changer (ATC) of transformers, 3rd: installing a Static Volt Ampere Reactive (VAR) System(SVS) with (ATC), 4th: installing a (SVS), (ATC) and shunt reactive power compensation devices (parallel capacitor / inductor). The best voltage profile achieved by using scenario 4, which supported and improved the voltage profile of all system and brings the magnitudes of all buses in permissible voltage level from (0.79-0.99 P.U.) at normal operation (scenario 1) to (0.9-1.04 P.U.) at (scenario 4). So the system can be operated with more efficiently, stability and improving the capacity of the network after applying the solution stated in scenario 4. • This paper studied the voltage profile in delta Egypt network. • A relation between voltage quality and catastrophic events in oil refining industry. • High quality grid must have voltage stability with in accepted levels at each bus. • Network construction was performed by (DIgSILENT power factory software). • The voltage profile was performed by proposed four different scenarios. Scenario 1: power flow (PF) study in normal operation (base case). Scenario 2: (PF) study using automatic tap changer (ATC). Scenario 3: (PF) study using (ATC)& static Var system (SVS). Scenario 4: (PF) study using (ATC), (SVS) and shunt reactive power control devices. • A comparison between all scenarios results have done to get the optimum solution. • The best voltage profile had achieved by using scenario 4.

Phenomena identification and categorization by the required level of multiphysics coupling in FHR modeling and simulation

This study identifies the phenomena that impact the accuracy of the multiphysics analysis of fluoride salt-cooled high temperature reactors (FHR) and categorizes the level of coupling needed to model these phenomena with sufficient accuracy in the context of three scenarios, namely, normal operation, station blackout, and simultaneous withdrawal of all control rods. Such a study is a necessary step prior to developing or extending existing multiphysics modeling and simulation tools. The identified multiphysics phenomena are categorized into the groups requiring “tight” and “loose” coupling. “Tight” coupling refers to phenomena that require iterative feedback between multiple physics modules/methods whereas “loose” coupling refers to phenomena that require only data from other physics that can be pre-calculated and shared in tabular or functional form.For the station blackout scenario, it was determined that no identified phenomena required tight coupling. For the rod withdrawal and normal operation scenarios, it is found that there is a large number of phenomena that require tight coupling between neutronics and thermal hydraulics.

Investigations on Detecting Potential Nuclear Material Diversion from a Pyroprocessing Facility

Under normal operating conditions, a pyroprocessing facility removes highly radioactive and nonradioactive fission product waste from used nuclear reactor fuel to recycle the remaining uranium (U), plutonium (Pu), and other actinides contained in it. The products from this facility are separate ingots of U and mixed transuranic elements (TRUs)–uranium (TRU-U). Uranium in both ingots will be depleted U with 235U enrichment less than 1%. The TRU-U ingot will contain neptunium, Pu, americium (Am), and curium (Cm) mixed with U with an approximate TRU:U ratio of 1:1. Four scenarios of nuclear material diversion by potential misuse of the pyroprocessing facility operations are analyzed and compared with the scenario of normal operating condition when the electrowinning process or the TRU-U ingot manufacturing process is misused. These diversion scenario analyses are carried out to understand the proliferation potential and to recommend safeguards measures. The four scenarios of nuclear material diversion analyzed are (1) 50 g Pu, (2) 100 g Pu, (3) 200 g Pu, and (4) all Pu, i.e., 452 g in the 1-kg TRU-U ingot. Plutonium cannot be diverted by itself because other TRUs (Am and Cm) will be simultaneously extracted with Pu. This is because the reduction potentials of those actinides are not distinguishably different from that of Pu on a liquid cadmium cathode of the electrowinning step of the pyroprocess. Hence, in addition to Pu, simultaneous diversion of respective amounts of Am and Cm for the four diversion scenarios are considered. The diversion scenario analysis also considered the concealment of Pu and Cm removal from the TRU-U ingot by adding an equivalent amount of 252Cf to replenish the neutron source emissions. These five scenarios (four nuclear material diversion scenarios and one normal operation scenario) are modeled and simulated using the Monte Carlo N-Particle (MCNP6) radiation transport computer code by incorporating the model of a NaI gamma radiation detection system. The results show that the presence and absence of Pu in the TRU-U ingot can be confirmed by the NaI gamma radiation detection system. However, identifying the presence of U in the TRU-U ingot is difficult using the NaI gamma radiation detection system due to interference from TRU gamma radiation. To identify the U presence in the TRU-U ingot, an application of nuclear magnetic resonance (NMR) is studied. The NMR technology employs a numerical calculation approach based on density functional theory (DFT) simulation. The DFT calculation results show that the detection of U in a pyroprocess is feasible by NMR technology. In addition, these four nuclear material diversion scenarios are analyzed through MCNP6 simulations by incorporating the model of a coincidence neutron detection system. To conceal the nuclear material diversion, the simulations are performed by replacing the diverted Pu and Cm by an appropriate mass of 252Cf neutron source that is equivalent to the neutron source strengths of the diverted mass. Simulation results show that this concealment (misuse) results in a deceived Pu mass estimate in the TRU-U ingot if the Pu-to-244Cm–ratio method (proposed method in the literature) is used.

An Unsupervised Approach to Leak Detection and Location in Water Distribution Networks

Abstract The water loss detection and location problem has received great attention in recent years. In particular, data-driven methods have shown very promising results mainly because they can deal with uncertain data and the variability of models better than model-based methods. The main contribution of this work is an unsupervised approach to leak detection and location in water distribution networks. This approach is based on a zone division of the network, and it only requires data from a normal operation scenario of the pipe network. The proposition combines a periodic transformation and a data vector extension together with principal component analysis of leak detection. A reconstruction-based contribution index is used for determining the leak zone location. The Hanoi distribution network is employed as the case study for illustrating the feasibility of the proposal. Single leaks are emulated with varying outflow magnitudes at all nodes that represent less than 2.5% of the total demand of the network and between 3% and 25% of the node’s demand. All leaks can be detected within the time interval of a day, and the average classification rate obtained is 85.28% by using only data from three pressure sensors.

Thermo-mechanical analysis on the full module of water cooled ceramic breeder blanket for CFETR

As one of blanket candidates for Chinese Fusion Engineering Test Reactor (CFETR), the concept design of the Water Cooled Ceramic Breeder (WCCB) blanket is being carried out and the analyses of the neutronics and thermal hydraulics have been finished. To investigate the thermo-mechanical behavior of the current WCCB blanket design version under normal operation and accidental operation scenarios (e.g. in-box loss of coolant accident (LOCA)), the finite element thermo-mechanical analyses of a full blanket module were performed by using ANSYS Multiphysics code. The stress results were assessed referring to ITER SDC-IC code. Under normal operation scenario, the blanket shows a satisfying mechanical behavior withstanding 15.5MPa coolant pressure on its cooling channel walls and thermal deformations. However, under in-box LOCA scenario, the blanket fails to withstand 15.5MPa coolant pressure on its internal walls at normal operation thermal level. In this situation, the relief valve is proposed as a mitigation measure to release coolant pressure to maintain the structural integrity of blanket box under in-box LOCA accident.

Development of computational algorithms for pump operations and their applications to the system dynamics modelling of a water supply system

ABSTRACTIn this study, computational algorithms for the simulations of the operations of pumps for water distribution storage tanks were developed. The developed algorithms include pump operating rules for different electricity price schemes and operating situations such as normal and emergency conditions. The algorithms were programmed into System Dynamics modelling modules that can be used as basic building blocks when an SD model is constructed for the simulations of complex real-world water supply systems. Based on the basic SD modelling modules, a dynamic computer simulation model was developed for the simulations of the water supply system in Young-Jong island in South Korea where multiple local water sources are to be utilised. The developed model dynamically simulated the water levels in the water distribution storage tanks and estimated the pumping costs of the system according to the normal and emergency operational scenarios. During the emergency situation it was assumed that the local water sources will not be able to supply the assigned portion of demand. STELLA system dynamics modelling software was used for the modelling.

A Schedule-Control Aided Strategy for Charging Large Number of EVs Under Normal and Line Failure Scenarios

Electric vehicle (EV) becomes a popular choice for its zero air pollutant and high energy efficiency. Nevertheless, the massive penetration of EVs can cause problems, including voltage drop and peak amplification. The charging pattern of EVs also poses a challenge to the reconfiguration work of the power system when failure occurs. Therefore, an EV schedule-control-based strategy is designed to address these issues in order to achieve voltage regulation and load shifting under both normal operation and failure scenarios. The framework involves two agents: 1) a two-stage voltage control agent schedules EVs to perform load shifting and voltage regulation under normal condition and 2) a fault control agent deals with line failure scenarios to recover the power supply of out-of-service basic and EV loads. A three-level queue table mechanism is designed to collaboratively perform EV scheduling. The influence of EV charging locations on the voltage variations of other nodes is considered and alleviated through a voltage sensitivity analysis method. Moreover, graph theory is employed to perform the network reconfiguration process to deal with line failure situations. The effectiveness of the scheme to restore the power supply while maintaining reliable system voltage level has been verified with the simulation results based on a modified IEEE 30 nodes test feeder.

European DEMO divertor target: Operational requirements and material-design interface

Recently, an integrated program of conceptual design activities for the European DEMO reactor was launched in the framework of the EUROfusion Consortium, where reliable power handling capability was identified as one of the most critical scientific as well as technological challenges for a DEMO reactor. The divertor is the key in-vessel plasma-facing component being in charge of power exhaust and removal of impurity particles. The DEMO divertor target will have to withstand extreme thermal loads where the local peak heat flux is expected to reach up to 20 MW/m2 during slow transient events in DEMO. To assure sufficient heat removal capability of the divertor target against normal and transient operational scenarios under expected cumulative neutron dose of up to 13 dpa is one of the fundamental engineering challenges imposed on target design. To develop the design of the DEMO divertor and related technologies, an R&D work package ‘Divertor’ has been set up in this consortium. The subproject ‘Target Development’ is devoted to the development of the conceptual design and the core technologies of the plasma-facing target. Devising and implementing novel structural heat sink materials (e.g. W/Cu composites) to advanced target design concepts is one of the major objectives of this subproject. In this paper, the underlying design requirements imposed by the envisaged power exhaust goal and the prominent material-design interface issues are discussed. In addition, the candidate design concepts being currently considered are presented together with the related material issues. Finally, the first results achieved so far are presented.

Development, verification and validation of an FPGA-based core heat removal protection system for a PWR

To reach high confidence and ensure reliability of nuclear FPGA-based safety system, life cycle processes of discipline specification and implementation of design as well as regulations verification and validation (V&V) are needed. A specific example on how to conduct life cycle development process and V&V on FPGA-based core heat removal (CHR) protection system for CPR1000 pressure water reactor (PWR) is presented in this paper. Using the existing standards and guidelines for life cycle development and V&V, a simplified FPGA-based CHR protection system for PWR has been designed, implemented, verified and validated. Diversified verification and simulation languages and tools are used by the independent design team and the V&V team. In the system acceptance testing V&V phase, a CPR1000 NPP operation principle simulator (OPS) model is utilized to simulate normal and abnormal operation scenarios, and provide input data to the under-test FPGA-based CHR protection system and a verified C code CHR function module. The evaluation results are applied to validate the under-test FPGA-based CHR protection system. The OPS model operation outputs also provide reasonable references for the tests. Using an OPS model in the system acceptance testing V&V is cost-effective and high-efficient. A dedicated OPS, as a commercial-off-the-shelf (COTS) item, would contribute as an important tool in the V&V process of NPP I&C systems, including FPGA-based and microprocessor-based systems.

On the optimization of the first wall of the DEMO water-cooled lithium lead outboard breeding blanket equatorial module

Within the framework of EUROfusion R&D activities a research campaign has been carried out at the University of Palermo in order to investigate the thermo-mechanical performances of the DEMO water-cooled lithium lead (WCLL) breeding blanket first wall (FW). The research campaign has been mainly focused on the optimization of the FW geometric configuration in order to maximize the heat flux it may safely withstand fulfilling all the thermal, hydraulic and mechanical requirements foreseen by safety codes. Attention has been focused on the FW flat concept endowed with square cooling channels and the potential influence of its four main geometrical parameters on its thermo-mechanical performances has been assessed performing a parametric analysis by means of a qualified commercial finite element method code. A set of 5929 different FW geometric configurations has been considered and the thermal performances of each one of them have been numerically assessed in case it undergoes 26 different values of heat flux on its plasma-facing surface. The resulting 154154 thermal analyses have allowed to select those cases fulfilling the adopted thermal-hydraulic requirements, whose thermo-mechanical performances have been numerically assessed under both normal operation and over-pressurization steady state loading scenarios to check whether they met the mechanical requirements prescribed by the pertaining SDC-IC safety rules. Four optimized FW configurations have been found to safely withstand a heat flux up to 2MW/m2 fulfilling all the rules prescribed by safety codes. Finally, the thermo-mechanical performances of these FW optimal configurations have been further investigated under both normal operation and over-pressurization steady state loading scenarios setting-up more realistic 3D FEM models. Results obtained, herewith presented and critically discussed, have allowed to select one promising FW geometrical configuration.

Assessment of the Thermo-mechanical Performances of a DEMO Water-Cooled Liquid Metal Blanket Module

Within the framework of DEMO R&D activities, a research cooperation has been launched between ENEA-Brasimone, CEA-Saclay and the University of Palermo to investigate the thermo-mechanical behaviour of the outboard equatorial module of the DEMO1 Water-Cooled Lithium Lead (WCLL) blanket, both under normal operation and over-pressurization steady state scenarios. The research campaign has been carried out following a theoretical-computational approach based on the finite element method (FEM) and adopting a qualified commercial FEM code. In particular, two different three-dimensional FEM models of the WCLL blanket module have been set-up to be used for normal operation and over-pressurization analysis, respectively. The former reproduces realistically the WCLL blanket module central poloidal–radial region, including one breeder cell in the toroidal direction and all the five cells in the radial one. The latter simulates the entire module segment box, without including the breeder and its cooling tubes. Two set of uncoupled steady state thermo-mechanical analyses have been carried out with reference to the investigated loading scenarios. In particular, under normal operation scenario (level A) the module has been supposed to undergo both 15.5 MPa coolant pressure on its cooling channels walls and thermal deformations due to the flat-top plasma operational state thermal field, while under over-pressurization scenario (level D) it has been assumed to experience 15.5 MPa coolant pressure on its segment box internal walls while operating at normal operation thermal level. Results obtained are presented and critically discussed according to the SDC IC code.

Grid-friendly wind power systems based on the synchronverter technology

Back-to-back PWM converters are becoming a realistic alternative to conventional converters in high-power wind power applications. In this paper, a control strategy based on the synchronverter technology is proposed for back-to-back PWM converters. Both converters are run as synchronverters, which are mathematically equivalent to the conventional synchronous generators. The rotor-side converter is responsible for maintaining the DC link voltage and the grid-side converter is responsible for the maximum power point tracking (MPPT). As the two converters are operated using the synchronverter technology, the formed wind power system becomes more friendly to the grid. Extensive real-time digital simulation results are presented to verify the effectiveness of the proposed method under normal operation and grid-fault scenarios.

Experimental Investigation of a Scaled Water-Cooled Reactor Cavity Cooling System

The Very High Temperature Gas-Cooled Reactor (VHTR) is one of the next-generation nuclear reactors designed to achieve high temperatures to support industrial applications and power generation. Because of the high temperature reached during normal operation, new safety features were added to its design. The reactor cavity cooling system (RCCS) is a passive safety system that will be incorporated in the VTHR. The system was designed to remove the heat from the reactor cavity and maintain the temperature of structures and concrete walls under desired limits during normal operation (steady state) and accident scenarios. A small-scale (1:23) water-cooled experimental facility was scaled, designed, and constructed in order to study the thermal-hydraulic phenomena taking place in the RCCS during steady-state and transient conditions. The facility represents a portion of the reactor vessel with nine stainless steel coolant risers and utilizes water as coolant. The facility was equipped with instrumentation to measure temperatures and flow rates. A steady-state experimental run was conducted to study the behavior of the coolant under this condition. The experimental results obtained confirmed the capabilities of the system in removing the heat from the cavity and helped in identifying phenomena that may occur in this type of passive system.

Modeling the thermal–hydraulic behavior of the reactor cavity cooling system using RELAP5-3D

The Very High Temperature Gas-Cooled Reactor (VHTR), one of the six proposed designs for the next generation nuclear reactor, was conceived to achieve high temperatures to support industrial applications and power generation. Due to the high temperature reached during normal operation, the design included new passive safety systems. The Reactor Cavity Cooling System (RCCS) is a new passive safety system designed to remove the heat from the reactor cavity during normal operation (steady-state) and accident scenarios. Computational tools such as system codes have been selected to simulate the reactor system and, in particular, the new safety components. The capabilities of these codes are being investigated to verify their ability in predicting the phenomena involved in the RCCS operation during steady-state and accident conditions. A RELAP5-3D input model of a small scale water-cooled experimental facility was prepared to simulate steady-state. The simulation results were compared with data produced during the experimental steady-state run. The results obtained and presented in the paper showed a good agreement of the code prediction with the experimental data. The paper also provides a set of modeling techniques to overcome some of the limitations of the current version of the computer code in simulating complex geometries with combined heat transfer mechanisms in the reactor cavity of the VHTR.

Measurement of tokamak error fields using plasma response and its applicability to ITER

The nonlinear response of a low-beta tokamak plasma to non-axisymmetric fields offers an alternative to direct measurement of the non-axisymmetric part of the vacuum magnetic fields, often termed ‘error fields’. Possible approaches are discussed for determination of error fields and the required current in non-axisymmetric correction coils, with an emphasis on two relatively new methods: measurement of the torque balance on a saturated magnetic island, and measurement of the braking of plasma rotation in the absence of an island. The former is well suited to ohmically heated discharges, while the latter is more appropriate for discharges with a modest amount of neutral beam heating to drive rotation. Both can potentially provide continuous measurements during a discharge, subject to the limitation of a minimum averaging time. The applicability of these methods to ITER is discussed, and an estimate is made of their uncertainties in light of the specifications of ITER's diagnostic systems. The use of plasma response-based techniques in normal ITER operational scenarios may allow identification of the error field contributions by individual central solenoid coils, but identification of the individual contributions by the outer poloidal field coils or other sources is less likely to be feasible.