Electrical Loads and Power Systems for the DEMO Nuclear Fusion Project

EU-DEMO is a European project, having the ambitious goal to be the first demonstrative power plant based on nuclear fusion. The electrical power that is expected to be produced is in the order of 700–800 MW, to be delivered via a connection to the European High Voltage electrical grid. The initiation and control of fusion processes, besides the problems related to the nuclear physics, need very complex electrical systems. Moreover, also the conversion of the output power is not trivial, especially because of the inherent discontinuity in the EU-DEMO operations. The present article concerns preliminary studies for the feasibility and realization of the nuclear fusion power plant EU-DEMO, with a special focus on the power electrical systems. In particular, the first stage of the study deals with the survey and analysis of the electrical loads, starting from the steady-state loads. Their impact is so relevant that could jeopardy the efficiency and the convenience of the plant itself. Afterwards, the loads are inserted into a preliminary internal distribution grid, sizing the main electrical components to carry out the power flow analysis, which is based on simulation models implemented in the DIgSILENT PowerFactory software

Modelling an in-vessel loss of coolant accident in the EU DEMO WCLL breeding blanket with the GETTHEM code

One of the accidents to be analyzed for the operation of the EU DEMO tokamak reactor is the in-vessel Loss-Of-Coolant Accident (LOCA), in which a postulated rupture in the First Wall causes a rapid pressurization of the Vacuum Vessel (VV). To avoid rupture of the VV, a VV Pressure Suppression System (VVPSS) is used, which is aimed at removing the coolant from the VV, preserving its integrity and safely storing the coolant together with the radioactive products contained therein. A system-level tool for the analysis of thermal-hydraulic transients in tokamak fusion reactors, called GEneral Tokamak THErmal-hydraulic Model (GETTHEM), is under development at Politecnico di Torino. This paper presents the GETTHEM module developed for the description of the EU DEMO VVPSS, in the case of a water-cooled Breeding Blanket concept; the code validation against experimental data coming from the Ingress of Coolant Event campaign performed in Japan is shown. The tool is then applied to a parametric analysis relevant for an EU DEMO in-VV LOCA, and the results are presented and discussed

Development of a thermal-hydraulic model for the EU-DEMO Tokamak building and LOCA simulation

The EU-DEMO must demonstrate the possibility of generating electricity through nuclear fusion reactions. Moreover, it must denote the necessary technologies to control a powerful plasma with adequate availability and to meet the safety requirements for plant licensing. However, the extensive radioactive materials inventory, the complexity of the plant, and the presence of massive energy sources require a rigorous safety approach to fully realize fusion power’s environmental advantages. The Tokamak building barrier design must address two main issues: radioactive mass transport hazards and energy-related or pressure/vacuum hazards. Safety studies are performed in the frame of the EUROfusion Safety And Environment (SAE) work package to support design improvement and evaluate the thermal-hydraulic behavior of confinement building environments during accident conditions in addition to source term mobilization. This paper focuses on developing a thermal-hydraulic model of the EU-DEMO Tokamak building. A preliminary model of the heat ventilation and air conditioning system and vent detritiation system is developed. A loss-of-coolant accident is studied by investigating the Tokamak building pressurization, source term mobilization, and release. Different nodalizations were compared, highlighting their effects on source term estimation. Results suggest that the building design should be improved to maintain the pressure below safety limits; some mitigative systems are preliminarily investigated for this purpose

Identification of accident sequences for the DEMO plant

Safety studies are performed in the frame of the conceptual design studies for the European Demonstration Fusion Power Plant (DEMO) to assess the safety and environmental impact of design options. An exhaustive set of reference accident sequences are defined in order to evaluate plant response in the most challenging events and compliance with safety requirements.The Functional Failure Mode and Effect Analysis (FFMEA) has been chosen as analytical tool, as it is a suitable methodology to define possible accident initiators when insufficient design detail is available to allow for more specific evaluation at component level. The main process, safety and protection functions related to the DEMO plant are defined through a functional breakdown structure (FBS). Then, an exhaustive set of high level accident initiators is defined referring to loss of functions, rather than to specific failures of systems and components, overcoming the lack of detailed design information. Nonetheless reference to systems or main components is always highlighted, as much as possible, in order to point out causes and safety consequences. Through the FFMEA a complete list of postulated initiating events (PIEs) is selected as the most representative events in terms of challenging conditions for the plant safety. All the four blanket concepts of the European DEMO reactor have been analysed

Parametric explorative study of DEMO galleries pressurization in case of ex-vessel LOCA

Abstract Radioactive toxins confinement is a main safety function for fusion power plants, hence the importance of confinement design parameters optimization. Moving from this perspective, two Loss of Coolant Accidents (LOCAs) were analyzed: loss of water from Vacuum Vessel (VV) cooling loop and loss of cryogenic helium from Toroidal Field (TF) cooling loop. In fact these two LOCAs may result into galleries pressurization possibly jeopardizing this second confinement boundary for radioactive toxins. Publicly available ITER data (2000 baseline design) have been scaled to DEMO. A set of sensitivity simulation analyses are performed on main variables (coolant inventories, enthalpy, rooms volume, etc.) in order to derive resulting galleries pressure and temperature conditions. As first design feedback to keep gallery pressure below an assumed design pressure of 120 kPa, the VV H2O LOCA requires pressure reduction (e.g. increase expansion volume, inventory partitioning, sprinkler), while TF He LOCA requires releasable inventory to be limited at about 4.4 tons and Cryo-systems designed against Common Mode Failure (e.g. seismic and fire, quench valve failure)

Energy Analysis for the Connection of the Nuclear Reactor DEMO to the European Electrical Grid

Towards the middle of the current century, the DEMOnstration power plant, DEMO, will start operating as the first nuclear fusion reactor capable of supplying its own loads and of providing electrical power to the European electrical grid. The presence of such a unique and peculiar facility in the European transmission system involves many issues that have to be faced in the project phase. This work represents the first study linking the operation of the nuclear fusion power plant DEMO to the actual requirements for its correct functioning as a facility connected to the power systems. In order to build this link, the present work reports the analysis of the requirements that this unconventional power-generating facility should fulfill for the proper connection and operation in the European electrical grid. Through this analysis, the study reaches its main objectives, which are the definition of the limitations of the current design choices in terms of power-generating capability and the preliminary evaluation of advantages and disadvantages that the possible configurations for the connection of the facility to the European electrical grid can have. In reference to the second objective, the work makes possible a first attempt at defining the features of the point of connection to the European grid, whose knowledge will be useful in the future, for the choice of the real construction site

DEMO fusion power plant: preliminary sizing analysis of power system

EU-DEMO is a European project for the design and construction of the first nuclear reactor able to produce electrical energy thanks to thermonuclear fusion reactions. The electrical power system of this facility is particular demanding for several reasons. First, the electrical power required to operate DEMO is expected to be huge, especially in comparison to a conventional nuclear plant. Moreover, the operations are intrinsically intermittent, thus introducing specific problems in terms of energy balance and grid stability. This paper deals with a first preliminary study about the sizing and the design of the DEMO internal electrical power system, with a specific focus on the steady-state loads necessary to operate the plant. The design results are obtained and verified through a model for power flow analysis, implemented in DIgSILENT PowerFactory

The MEST, a new magnetic energy storage and transfer system: Application studies to the European DEMO

A new Magnetic Energy Storage and Transfer (MEST) system, which can improve the power handling in fusion experiments, has been recently conceived. It is particularly suitable to feed the DEMO Central Solenoid (CS), in principle without the need for resistive switching networks (SNUs), but can be applied to supply the Poloidal Field (PF) coils too. The operating principle of this system, described for one central solenoid circuit, is to pre-charge an additional Superconducting Magnetic Energy Storage (SMES) coil at least up to twice the maximum energy expected in the load (CS) and to transfer the energy from one to the other and viceversa via switched-capacitor. With this approach, the energy is exchanged between the load and the storage system, thus flattening the active power profile to be required from the ac side and substantially nullify the reactive power absorbed. p In this paper, the application of this concept to the European DEMO is studied, starting from the present circuit configuration and from the current and voltage scenario under consideration for the plasma breakdown and ramp-up. A first tentative rating of the system components is reported, discussing also the future R&D steps to explore the industrial feasibility of such a scheme