THERMAL-HYDRAULIC STUDY IN SUPPORT OF THE DESIGN OF THE DEMO BALANCE OF PLANT

The European Research Roadmap to the Realisation of Fusion Energy, foresees that the Demonstration Fusion Power Reactor (DEMO) is going to be the successor of ITER reactor in the pathway towards the exploitation of nuclear fusion to produce electric energy on an industrial scale. It will, hence, have to deliver hundreds MW of electric power ensuring an adequate availability and reliability of operation over a reasonable time span. EU-DEMO pre-conceptual design is being conducted by research institutions and universities from 26 countries of European Union, Switzerland and Ukraine, with the main aim to provide electric energy to the grid from nuclear fusion reactions by 2050. However, where exactly DEMO should be located in between ITER and a commercial fusion power plant depends on the resources, the gaps towards a commercial plant as well as the development risks that can be accepted and the time scale to fusion deployment. It is worth to say that, due to the inherent different mission between the two machines, some of the technical solutions adopted for ITER are not DEMO relevant and a return of design and operational experiences cannot be expected from ITER in certain fields. For instance, as DEMO has been conceived to deliver net electric power to the grid, the reactor design must be more oriented toward the Balance of Plant (BoP) issues than it is in ITER, where the heat power, available at a rather low temperature level, will be wasted to the environment heat sink without any energy conversion intended to civil applications and/or exploitation. Therefore, since the early phase of the DEMO project, emphasis has been given to those engineering aspects and design integration issues that actually affect the architecture of a nuclear power plant, e.g. technology readiness, power conversion features, safety and related licensing aspects etc. Within the framework of the R&D activities DEMO-oriented, promoted and supported by the EUROfusion Consortium, it has been carried out the research activity relevant to the XXXII cycle of the Ph.D. course in Energy and Information Technologies. In particular, the main objective of the theoretical research campaign has been to outline a pre-conceptual design of the Primary Heat Transfer System for the helium-cooled Breeding Blanket concept. The choice of the Breeding Blanket option, thus of the primary coolant, plays a pivotal role in the whole reactor Balance of plant architecture having a strong influence on plant operation, safety and maintenance. The studies have been articulated in two main phases: in the first part of the work it has been carried out a thermal-hydraulic and mechanical design of the main system components following and developing analytical/semi-analytical procedures by the adoption of the methodologies commonly used for this purpose; the second half of the activities has intended to verify the effectiveness of these procedures as well as the robustness of the design, therefore an assessment of the thermal-hydraulic behaviour of the primary heat transfer system has been made by means of a theoretical-computational approach based on the Finite Volume Method and adopting suitable releases of both 1-D and 3-D codes. The Ph.D. activities, which were led from the end of 2016 to the second half of 2019, are going to be extensively described in this thesis.