energies Article Electrical Loads and Power Systems for the DEMO Nuclear Fusion Project Simone Minucci 1, Stefano Panella 2, Sergio Ciattaglia 3, Maria Carmen Falvo 2 and Alessandro Lampasi 4,* 1 Department of Economics, Engineering, Society and Business Organization, University of Tuscia, 01100 Viterbo, Italy; [email protected] 2 Department of Astronautics, Energy and Electrical Engineering, University of Rome Sapienza, 00184 Rome, Italy; [email protected] (S.P.); [email protected] (M.C.F.) 3 EUROfusion Consortium, 85748 Garching bei München, Germany; [email protected] 4 National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), 00044 Frascati, Italy * Correspondence: [email protected] Received: 16 March 2020; Accepted: 22 April 2020; Published: 4 May 2020 Abstract: 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. Keywords: balance of plant; DEMO; electric loads; nuclear fusion; plasma; power flow; power supply; power systems 1. Introduction EU-DEMO (the DEMOnstration fusion power reactor proposed by the European Union), or simply DEMO, is a unique European project, as it will be the first demonstrative nuclear fusion power plant able to produce and distribute electrical power throughout Europe, thanks to a connection with the European High Voltage (HV) electrical grid (typically at 400 kV) [1–3]. To accomplish this challenging purpose, the European Union set up the EUROfusion Consortium, whose main goals and tasks are summarized in the “European Research Roadmap to the Realisation of Fusion Energy” [4]. The schedule and the milestones of the Roadmap are sketched in Figure1. Even though other alternative approaches are being investigated in EUROfusion [4] and in another research facility [5], the EUROfusion Roadmap is based on two tokamak projects: DEMO and ITER [6]. The latter is currently under construction in Cadarache (France) with a worldwide contribution and aims at: Producing 500 MW of fusion power for pulses of at least 400 s. • Energies 2020, 13, 2269; doi:10.3390/en13092269 www.mdpi.com/journal/energies Energies 2020, 13, 2269 2 of 21 Energies 2020, 13, x FOR PEER REVIEW 2 of 23 Demonstrating the integrated operation of technologies for a fusion power plant. • • Demonstrating the integrated operation of technologies for a fusion power plant. Achieving a deuterium-tritium plasma where reactions are sustained through internal heating. • • Achieving a deuterium-tritium plasma where reactions are sustained through internal heating. Testing tritium breeding. • • Testing tritium breeding. • Demonstrating the safety characteristics of a fusion device, both for human and environment. • Demonstrating the safety characteristics of a fusion device, both for human and environment. FigureFigure 1. 1.Overview Overview of of the the European European RoadmapRoadmap to the realization of of Fusion Fusion Energy Energy [4 []4. ].The The reported reported datesdates are are still still indicative. indicative. TheseThese goals goals are are importantimportant and and partially partially common common with with the DEMO the DEMO project project,, so that so it can that use it ITER can use- ITER-likelike solutions solutions for possible for possible future future issues issues.. However, However, DEMO DEMO will be will bigger be bigger than ITER than in ITER terms in of terms size of sizeand and of required of required services services,, also because also because it will itbe will connected be connected to the grid to to the deliver grid tothe deliver produced the electrical produced electricalenergy, energy, unlike ITER unlike. Also ITER. the Also time the required time required for the realization for the realization of these two of these projects two is projects different: is di whilefferent: whileit is itforeseen is foreseen to start to start ITER ITER first firstexperiments experiments by 2025 by 2025and to and operate to operate with withdeuterium deuterium and tritium and tritium by by2035, 2035, DEMO DEMO is is expected expected to tobe be in inoperation operation around around by by2050. 2050. InIn the the past, past, fusion fusion devices devices were were generallygenerally not regarded as as nuclear nuclear facilities facilities and and did did not not need need a a nuclearnuclear license. licens However,e. However, ITER ITER and and DEMO DEMO are muchare much more more critical critical in terms in terms of tritium of tritium inventory, inventory, neutron flux,neutron pulse flux, duration, pulse duration, stored magnetic stored magnetic energy, coolingenergy, cooling system system enthalpy enthalpy and amount and amount of helium of helium at 4 K. ITERat 4 demonstrated K. ITER demonstrated its safety andits safety obtained and the obtained nuclear the license nuclear to start license the construction.to start the constructi Nevertheless,on. specificNevertheless, nuclear specific regulations nuclear are regulations likely to be are introduced likely to be forintroduced next-generation for next-generation devices, also devices, depending also depending on the host country. As DEMO is expected to have more neutronic flux and more on the host country. As DEMO is expected to have more neutronic flux and more inventory of inventory of tritium than ITER, a license from authorities will be necessary before starting the tritium than ITER, a license from authorities will be necessary before starting the construction of construction of safety-classified systems. safety-classified systems. As a nuclear facility, a specific design is necessary for the DEMO Balance of Plant (BoP), that is As a nuclear facility, a specific design is necessary for the DEMO Balance of Plant (BoP), that is the nuclear engineering term referred to all the supporting and auxiliary systems needed for energy the nuclear engineering term referred to all the supporting and auxiliary systems needed for energy conversion and delivering, excluding all the nuclear components. Therefore, EUROfusion is conversionpromoting and a multidisciplinary delivering, excluding research all theand nuclear engineering components. activity that Therefore, is approaching EUROfusion the design is promoting of the a multidisciplinaryDEMO BoP [7,8], even research moving and from engineering the experience activity of the that other is approaching experimental the tokamaks design and of the nuclear DEMO- BoPfission [7,8], power even moving plants. One from of the the experience most critical of thepart other of the experimental BoP is the electrical tokamaks power and nuclear-fissionsystem, also powerbecause plants. this Onesystem of theis not most trivial critical both partin terms of the of BoPsize isand the of electrical complexity. power system, also because this system is not trivial both in terms of size and of complexity. Energies 2020, 13, 2269 3 of 21 The present paper introduces the preliminary studies for the feasibility and realization of the electrical system of the nuclear fusion power plant DEMO. In particular, the results of the following activities are described: Characterization and classification of the expected of the electrical loads belonging to the specific • DEMO systems by analyzing literature data, technical specifications and design progresses of DEMO itself and of previous tokamak plants, especially ITER and its satellites JT-60SA [9] and DTT [10]. Preliminary design of part of the internal distribution network and preliminary sizing of the main • electrical components of part of the internal distribution grid (conception and development of simulation models for the power flow analysis) then implemented in the DIgSILENT PowerFactory software environment. The loads characterization and classification is the starting point for first electrical designs and is expected to provide more realistic data than those in previous analyses based on theoretical considerations [11]. This paper is organized in seven sections. Section2 introduces the relevant DEMO figures and explains possible configurations and operation phases. Section3 presents the preliminary layout of the DEMO site as used for the electrical analysis. Section4 introduces the main options of the BoP and the basic principles for the design of the electrical systems. Section5 is focused on the survey of the main DEMO subsystems and electrical loads and on the results