Topology optimisation of the divertor monoblock

  • Oliver Marshall

Student thesis: Phd

Abstract

Nuclear fusion has the potential to provide an energy-dense sustainable electricity supply, however, fusion power plants face a number of design challenges. In-vessel components designed for use inside fusion reactors must be capable of tolerating extreme heat and particle fluxes. This thesis investigates a methodology for re-introducing design freedom to the conceptualisation of in-vessel components for the divertor, a device responsible for handling the highest heat fluxes in the reactor. This is approached through the application of topology optimisation, a process which involves the distribution of material throughout a geometry in order to meet an objective, subject to constraints. The resulting geometries are often complex and may be dependent on progress in novel manufacturing methodologies. A review of divertor design finds that top-down requirements limit material selection, component geometry and coolant fluid choice. Furthermore, the need to tolerate a given heat load creates design challenges which often cannot be managed without driving device size, cost and complexity. Design requirements are also subject to significant uncertainty, caused by a lack of representative testing, the time associated with reactor construction and the large jumps in performance required of successive devices. An investigation into additive manufacturing (AM) of a divertor-relevant alloy (CuCrZr) was conducted as part of an industrial collaboration designed to assess contemporary AM material performance. The work finds the material to exhibit good thermal performance and establishes scope for process optimisation as a means of increasing build speed and reducing cost. Thermal topology optimisation of the divertor monoblock is performed using COMSOL Multiphysics and finds potential for optimised designs to reduce armour temperatures by over 200K during transient high heat flux events and to minimise thermal gradients. The incorporation of thermally induced stress minimisation leads to stress reductions of up to 65% and the potential for heat flux redistribution. The optimised geometries contain transitions between materials which could be interpreted for manufacture using a combination of functional grading and AM. The impact of asymmetric geometries designed to minimise leading edges and multiple attachment scenarios are also investigated, finding substantial differences in optimal design qualities. Finally, the methodology is extended to the treatment of conjugate heat transfer between armour plates and coolant fluid. The optimisation process employs k-epsilon turbulence and maximises heat transfer objectives whilst limiting pressure drop. The optimisation results in the development of internal features which promote convective and conductive heat transfer.
Date of Award1 Aug 2023
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorLee Margetts (Supervisor) & Matthew Roy (Supervisor)

Keywords

  • Topology optimisation
  • Nuclear fusion
  • Divertor

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