Numerical structural analysis and flow-induced vibration study in support of the design of the EU-DEMO once-through steam generator mock-up for the STEAM experimental facility

ENEA, as part of the EUROfusion consortium, is working at the realization of STEAM, an experimental facility integrated into the Water-cooled lithium lead-thermal-HYDRAulic (W-HYDRA) platform, envisaged for the qualification of the EU-DEMO steam generator during the different operational phases of a fusion reactor. It will aim at testing and qualifying the technological solutions to be adopted for the Primary Heat Transport System (PHTS) of the Water-Cooled Lead Lithium Breeding Blanket (WCLL BB). In particular, a mock-up of the Once-Through Steam Generator (OTSG) foreseen for the PHTS of the DEMO WCLL BB will be designed, installed and tested within STEAM. In this regard, a campaign of numerical structural analyses and a preliminary flow-induced vibration study have been carried out at the University of Palermo, in close collaboration with ENEA Brasimone. Firstly, a pipe stress analysis has been conducted focussing on the structural performances of the surge line devoted to connecting the STEAM facility to the pressurizer, looking at the stress and displacement arising under the nominal operating conditions so to propose proper design modifications. Secondly, in order to investigate the structural performances of the DEMO OTSG mock-up in the envisaged nominal operating scenario, a 3D steady-state thermo-mechanical FEM analysis has been carried out. The outcomes have allowed selecting the most critical regions in view of the adopted structural design code. Lastly, in order to preliminarily assess the potential onset of vibration-induced issues within the tubes of the DEMO OTSG mock-up, a preliminary analytical study has been carried out adopting formulae available in literature. The scope has been to establish if vibration-induced issues in the tubes can be reasonably excluded or if they could represent a tangible concern, to be further assessed. Models, assumptions and outcomes are provided and critically discussed.