DEMO divertor cassette and plasma facing unit in vessel loss-of-coolant accident

As part of the pre-conceptual design activities for the European DEMOnstration plant, a carefully selected set of safety analyses have been performed to assess plant integrated performance and the capability to achieve expected targets while keeping it in a safe operation domain. The DEMO divertor is the in-vessel component in charge of exhausting the major part of the plasma ions' thermal power in a region far from the plasma core to control plasma pollution. The divertor system accomplishes this goal by means of assemblies of cassette and target plasma facing units modules, respectively cooled with two independentheat-transfer systems. A deterministic assessment of a divertor in-vessel Loss-of-Coolant Accident is here considered. Both Design Basis Accident case simulating the rupture of an in-vessel pipe for the divertor cassette cooling loop, and a Design Extension Conditions accident case considering the additional rupture of an independent divertor target cooling loop are assessed. The plant response to such accidents is investigated, a comparison of the transient evolution in the two cases is provided, and design robustness with respect to safety objectives is discussed

Stardust experimental campaign and numerical simulations: influence of obstacles and temperature on dust resuspension in a vacuum vessel under lova

Activated dust mobilization during a Loss of Vacuum Accident (LOVA) is one of the safety concerns for the International Thermonuclear Experimental Reactor (ITER). Intense thermal loads in fusion devices occur during plasma disruptions, edge localized modes and vertical displacement events. They will result in macroscopic erosion of the plasma facing materials and consequent accumulation of activated dust into the ITER vacuum vessel (VV). These kinds of events can cause dust leakage outside the VV that represents a high radiological risk for the workers and the population. A small facility, Small Tank for Aerosol Removal and Dust (STARDUST), was set up at the ENEA Frascati laboratories to perform experiments concerning the dust mobilization in a volume with the initial conditions similar to those existing in ITER VV. The aim of this work was to reproduce a low pressurization rate (300 Pa s−1) LOVA event in a VV due to a small air leakage for two different positions of the leak, at the equatorial port level and at the divertor port level, in order to evaluate the influence of obstacles and walls temperature on dust resuspension during both maintenance (MC) and accident conditions (AC) (T walls = 25 °C MC, 110 °C AC). The dusts used were tungsten (W), stainless steel 316 (SS316) and carbon (C), similar to those produced inside the vacuum chamber in a fusion reactor when the plasma facing materials vaporize due to the high energy deposition. The experimental campaign has been carried out by introducing inside STARDUST facility an obstacle to simulate the presence of objects, such as divertor. In the obstacle a slit was cut to simulate the limiter–divertor gap inside ITER VV. In this paper experimental campaign results are shown in order to investigate how the divertor and limiter–divertor gap influence dust mobilization into a VV. A two-dimensional (2D) modelling of STARDUST was made using the CFD commercial code FLUENT, in order to get a preliminary overview of the fluid dynamics behaviour during a LOVA event and to justify the mobilization data. In addition, a numerical model was developed to compare numerical results with experimental ones.</jats:p

Scaled experiment for Loss of Vacuum Accidents in nuclear fusion devices: Experimental methodology for fluid-dynamics analysis in STARDUST facility

A recognized safety issue for future fusion reactors fueled with deuterium and tritium is the generation of sizeable quantities of dust. Activated dust mobilization during a Loss of Vacuum Accidents (LOVA) is one of the safety concerns for the International Thermonuclear Experimental Reactor (ITER). Intense thermal loads in fusion devices occur during plasma disruptions, Edge Localized Modes (ELM) and Vertical Displacement Events (VDE). They will result in macroscopic erosion of the plasma facing materials and consequent accumulation of activated dust into the ITER Vacuum Vessel (VV). In order to perform thermo-fluid dynamic analysis a small facility, Small Tank for Aerosol Removal and Dust (STARDUST), was set up at the University of Rome "Tor Vergata", in collaboration with ENEA Frascati laboratories. This facility simulates low pressurization rates (100Pa/s, 300 Pa/s and 500 Pa/s) due to LOVA events in ITER due to a small air inlet at different internal pressure conditions and wall temperatures. The authors will present the experimental results in order to analyze the influence of different pressurization rates in the variation of thermo-fluid dynamic conditions that are strictly connected to dust mobilization

Methodology of the source term estimation for DEMO reactor

tThe problem of source term qualification is one of the most important topics in order to predict possiblereleases of the Activation Products (APs) and Tritium from the DEMO Fusion reactor. The preventionof any possible consequence, which can affect the environment and the population, is the mission ofFusion technology. In the frame of the EUROfusion Work Package of Safety and Environment (WPSAE)a methodology to scale and evaluate the source terms assessed for ITER and the Fusion Power PlantConceptual Study (PPCS) has been studied.This paper refers to the activity currently conducted for the DEMO source terms assessment and thepreliminary results obtained. During activities in the task, the methodology was developed for the evalua-tion of Tritium and APs concentration inventory. The methodology is explained in detail for the predictionof the Tritium and APs concentration in Vacuum Vessel (VV) and in the Breeding Blanket (BB) startingfrom the DEMO current design data and the inventories assumed in ITER, PPCS and SEAFP programs. Theseresults refer to the Helium Cooled Lead Liquid (HCLL) and the Helium Cooled Pebble Bed (HCPB) concepts.The approach is based on the foundations, set in the fission technology safety analysis of the Design BasisAccidents (DBA), Design Extension Conditions (DEC) and Beyond Design Basis Accident (BDBA)

Large eddy simulation of Loss of Vacuum Accident in STARDUST facility

The development of computational fluid dynamic (CFD) models of air ingress into the vacuum vessel (VV) represents an important issue concerning the safety analysis of nuclear fusion devices, in particular in the field of dust mobilization. The present work deals with the large eddy simulations (LES) of fluid dynamic fields during a vessel filling at near vacuum conditions to support the safety study of Loss of Vacuum Accidents (LOVA) events triggered by air income. The model's results are compared to the experimental data provided by STARDUST facility at different pressurization rates (100 Pa/s, 300 Pa/s and 500 Pa/s). Simulation's results compare favorably with experimental data, demonstrating the possibility of implementing LES in large vacuum systems as tokamaks. © 2013 Elsevier B.V

The European contribution to the development and validation activities for the design of IFMIF lithium facility

The International Fusion Materials Irradiation Facility (IFMIF) is an accelerator-driven intense neutron source where candidate materials for fusion reactors will be tested and validated. The high energy neutron flux is produced by means of two deuteron beams (total current of 250 mA, energy of 40 MeV) that strikes a liquid lithium target circulating in a lithium loop of IFMIF plant. The European (EU) contribution to the development of the lithium facility comprises five procurement packages, as follow: (1) participation to the experimental activities of the EVEDA lithium test loop in Oarai (Japan); (2) study aimed at evaluating the corrosion and erosion phenomena, promoted by lithium, for structural fusion reference materials like AISI 316L and Eurofer; (3) design and validation of the lithium purification method with the aim to provide input data for the design of the purification system of IFIMF lithium loop; (4) design and validation of the remote handling (RH) procedures for the refurbishment/replacement of the EU concept of IFMIF target assembly including the design of the remote handling tools; (5) the engineering design of the European target assembly for IFMIF and the safety and RAMI analyses for the entire IFMIF lithium facility. The paper gives an overview of the status of the activities and of the main outcomes achieved so far

Progress in the initial design activities for the European DEMO divertor: Subproject "Cassette"

Since 2014 preconceptual design activities for European DEMO divertor have been conducted as an integrated, interdisciplinary R&D effort in the framework of EUROfusion Consortium. Consisting of two subproject areas, \u2018Cassette\u2019 and \u2018Target\u2019, this divertor project has the objective to deliver a holistic preconceptual design concept together with the key technological solutions to materialize the design. In this paper, a brief overview on the recent results from the subproject \u2018Cassette\u2019 is presented. In this subproject, the overall cassette system is engineered based on the load analysis and specification. The preliminary studies covered multi-physical analyses of neutronic, thermal, hydraulic, electromagnetic and structural loads. In this paper, focus is put on the neutronics, thermohydraulics and electromagnetic analysis