Numerical assessment of the thermal-hydraulic performances of the ITER Blanket cooling system

This thesis has covered the main research activities carried out during the candidate Ph.D. course of the XXXI Cycle on “Energia e Tecnologie dell’Informazione - curriculum Fisica Tecnica e Ingegneria Nucleare” (Energy and Information Technologies - Applied Physics and Nuclear Engineering curriculum), held at the University of Palermo, in the time frame that goes from the end of 2015 to the end of 2018. In particular, it focusses on the activities carried out at the DEIM in cooperation with the ITER Organisation on the “Hydraulic Analysis of Blanket Cooling System” and it has aimed to investigate the thermal-hydraulic behaviour of the ITER blanket cooling system under nominal steady-state conditions, paying a particular attention to the assessment of the total pressure drop occurring in each module cooling system, together with its spatial distribution along the main circuital components. In addition, the research activity has been intended to fruitfully contribute to: • the assessment of the blanket cooling system effectiveness in terms of mass flow rate distribution as well as of total pressure drop acceptability; • the improvement and potential optimization of the blanket cooling system thermal-hydraulic performances by the assessment of the impact of proposed layout modifications on the investigated cooling circuits steady-state thermal-hydraulic behaviour; • the identification of the potential need for flow regulators within the blanket module cooling systems in order to balance their coolant mass flow rate distribution. The blanket system represents one of the pivotal components of the ITER reactor, because it provides a physical boundary for the plasma transients and contributes to the thermal and nuclear shielding of the vacuum vessel, the superconducting magnets and the external ITER components. Because of its position and functions, the blanket system is foreseen to undergo a significant heat load under nominal conditions. Therefore, the blanket cooling system design results to be particularly demanding since it has to ensure that an adequate cooling is provided to each module and any risk of CHF insurgence is prevented, optimizing mass flow rate distribution and complying with pressure drop limits. Due to the extreme complexity of the flow domain of the blanket module cooling systems to be investigated, the research activity has been carried out following a theoretical-computational approach based on the finite volume method and adopting a suitable release of the ANSYS CFX CFD code, integrated, whenever needed, by the RELAP5 Mod3.3 thermal-hydraulic system code. A proper operative procedure has been outlined to timely and effectively carry out the activity, based on the idea of reducing the assessment of a blanket module cooling system total pressure drop to the proper recombination of those separately calculated for the hydraulic variants of its main components (FW, SB and manifold). The activity has started in 2015 and, according to CAD availability, it was originally conceived to last for 48 months, being articulated in five subsequent phases. In particular, each phase concerns the investigation and optimisation of the nominal steady-state thermal-hydraulic performances of the following quasi-definitive (or frozen) cooling circuits: • 24 SB hydraulic variants; • 10 FW hydraulic variants; • 16 inlet/outlet manifold hydraulic variants; for an overall of 50 frozen hydraulic variants per phase and other still-in-work components. The Ph.D. work has been developed within the context of the first two phases of the activity. Specifically, it has dealt with the investigation and optimisation of the nominal steady-state thermal-hydraulic performances of the following quasi-definitive (or frozen) cooling circuits: • 23 SB hydraulic variants; • 15 FW hydraulic variants; • 31 inlet/outlet manifold hydraulic variants; • 2 plates; for an overall of 71 frozen hydraulic variants. Furthermore, the thermal-hydraulic performances of other still-in-work components have been assessed and optimised under nominal steady-state conditions. Moreover, attention has been focussed also onto the assessment of the steady state fluid-dynamic behaviour of some layout modifications, in order to check their effective impact in the improvement and potential optimization of the blanket cooling system thermal-hydraulic performances, mainly in terms of total pressure drop reduction. As to the results shown in this thesis, they indicate that the total pressure drop of the investigated blanket module cooling systems widely ranges from 0.2696 MPa for the cooling system of BM10-11S01 to a maximum of 0.8553 for the cooling system of BM14S01, as a consequence of the different mass flow rates and layouts characterizing the cooling systems. Concerning the assessment of the steady state fluid-dynamic behaviour of the layout modifications proposed for the FW #14A hydraulic variant, the SB #14A hydraulic variant and their inlet/outlet coaxial connectors, the numerical results obtained have indicated the opportunity to implement the lay-out modifications suggested for the FW #14A, the SB #14A and the inlet coaxial connector, while discouraging the implementation of those proposed for the outlet coaxial connector.