Parametric FE model for the thermal and hydraulic optimization of a Plasma Facing Component equipped with sacrificial lattice armours for First Wall limiter application in EU-DEMO fusion reactor

In EU DEMO reactor, components exposed to burning plasma are subject to extreme conditions due to short and extremely strong thermal transients, which impact their lifetime and functional integrity. Due to this energy, surface vaporization, melting and resolidification may lead to excessive degradation and frequent extraordinary maintenance. For this reason, in view of DEMO and future reactors, one of the most challenging aspects of fusion reactor technology is to devise FW (First Wall) sacrificial limiters that will prevent excessive damage of the otherwise un-shadowed FW modules during extreme plasma transients. Rather than dense armours, W-lattice structures can contribute to this purpose, since they can be optimized to have a thermal conductivity that ensures, at steady state, effective heat dissipation and at the same time a thermal diffusivity that, in transients, maximizes the vapour shielding effect. The objective of the research activity here presented was to identify, through a parametric model, the optimized component configurations to be considered for this sacrificial limiter, in order to maximize its functional effectiveness. Based on the two elementary cell morphologies developed in previous studies, the parametric model allowed to investigate the combinations of relevant parameters, above all component size and geometries, armour/heat sink materials and thicknesses. Thermal optimization regarded both normal operation and two possible transient scenarios: an unmitigated plasma disruption or the Ramp Down phase. By scanning all possible combinations of parameters, those able to provide the best performances thus satisfying the user-defined functional requirements of the limiter have been identified. The thermal optimization phase was followed by CFD (Computational Fluid Dynamics) analyses in order to evaluate the potential integration of the limiter cooling circuits within the divertor Primary Heat Transfer System (PHTS) from a thermal–hydraulic point of view

Pre-conceptual design of a PFC equipped with a W lattice armour for first wall limiters in the EU-DEMO fusion reactor

amongst the engineering challenges of power exhaust in DEMO and future reactors, an effective wall protection strategy is regarded as a crucial one. It aims at strongly mitigating the degradation of conventional plasma-facing components (PFCs) during plasma transients and disruptions [1]. amongst the solutions for the EU-DEMO reactor, sacrificial first wall limiters provided with innovative tungsten (W) lattices are envisaged as the last protection resource of the otherwise unshadowed wall during such extreme events. Their design must comply with conflicting requirements, e.g. adequate heat exhaust during normal operation but acceptable lifetime, i.e. vapour shielding and thermal insulation of the heat sink (HS), during transients. For this purpose, porous W lattices are preferred to dense armours, as the former provide larger design flexibility, pronounced HS insulation and promoted vapour shielding [2]. Additive manufacturing was employed to realize samples with the envisaged properties for material characterization and testing. In this work, we report on the recent research activities towards the development of a pre-conceptual design of a small-scale prototype of the sacrificial limiter. Above all, thermo-mechanical finite element (FE) analyses, implemented in support of the design phase, helped to assess and optimize parametrically the response of the lattice armour and component layout. In this context, an original MAPDL routine was employed to account for armour degradation and phase change of W during extreme events. Results suggest that a PFC provided with an optimized lattice armour could promote vapour shielding and prevent HS overloading during transients, at the same time ensuring adequate heat exhaust and acceptable thermal stresses during normal operation. Accurate measurements of thermo-physical and mechanical properties of W lattices helped improve our simulations. Dipping tests highlighted the technical viability of joining the lattice to copper-based substrates by infiltrating melt copper in the open pores of W lattices. This might significantly ease the mock-up and component fabrication, as one could rely on conventional joining methods, such as copper-copper brazing, industrially available and well-established for fusion applications

Limiters for DEMO wall protection: Initial design concepts & technology options

Off-normal macroscopic plasma instabilities which possibly occur in a fusion power plant represent the most critical operational accidents and pose a serious risk to economically viable exploitation of fusion power. During such an instability, a huge amount of plasma energy is rapidly deposited onto the plasma-facing first wall in form of extreme heat flux. Such heavy thermal shocks can cause severe damages or a fatal failure of the first wall even by a single event. This issue is a serious design concern raising the requirement of a wall protection strategy. To cope with this issue, the European DEMO project adopted the limiter concept. The limiters equipped with tungsten sacrificial armor shall be installed at those wall areas where plasma contact is expected to be probable. To implement the limiter concept, comprehensive engineering studies have been conducted including conceptual design of the plasma facing component and technology R&D for armor material and joining. In this overview paper, the background of the wall protection issue and its implication on design and materials are explained and the outcomes from the recent project period (2019-20) are reported. The focus is placed on the technology achievement related to the development of novel lattice-type tungsten armor material fabricated by an innovative additive manufacturing process. Interim results from the extreme and medium heat flux tests and the joining trials for tungsten-to-heat sink material (copper or steel) are also addressed. The design rationale and the interpretation of the test data are supported by computational simulations

Divertor Tokamak Test facility project: status of design and implementation

An overview is presented of the progress since 2021 in the construction and scientific programme preparation of the Divertor Tokamak Test (DTT) facility. Licensing for building construction has been granted at the end of 2021. Licensing for Cat. A radiologic source has been also granted in 2022. The construction of the toroidal field magnet system is progressing. The prototype of the 170 GHz gyrotron has been produced and it is now under test on the FALCON facility. The design of the vacuum vessel, the poloidal field coils and the civil infrastructures has been completed. The shape of the first DTT divertor has been agreed with EUROfusion to test different plasma and exhaust scenarios: single null, double null, X-divertor and negative triangularity plasmas. A detailed research plan is being elaborated with the involvement of the EUROfusion laboratories