Thermomechanical engineering of water-cooled plasma-facing components in fusion reactors

Nuclear fusion is the reaction that fuels our Sun an the other stars. Adopting fusion on Earth as an energy source for electricity production offers unique advantages, such as: virtually unlimited and widely available fuel, intrinsic safety (no chain-reaction is possible), no production of green-house gases and no long-term radioactive waste. However, building a fusion reactor able to deliver power to the grid presents engineering challenges yet to be solved. One of the main issues is linked to the so-called Plasma Facing Components (PFCs), whose main goal is to both shield the internal parts of the reactor and exhaust the plasma heating power, which is the thermal power continu ously fed to the fuel to sustain the fusion reactions. The design of such components has very stringent requirements due to the harsh environment in which they operate. In fact, PFCs are subjected to extreme loads of charged particles, neutrons and photons, which intrinsically makes the design of these heat exchangers a multidisciplinary labor. For this reason, key notions to the design of PFCs, being often spread among multiple specialized manuals (when existent) or academic papers, are not readily available to the engineers. This thesis was written with the intention of filling this gap, with main focus dedi cated to the steady-state thermomechanical design of PFCs. The thesis is divided into 3 parts. Chapter 1 provides a global overview on the requirements of PFCs, attempting to list all the engineering constraints while giving the references for a more detailed treatment. Chapter 2 focuses on the thermomechanical modelling of PFCs. Starting from the definition of the thermal problem, reduced models will be presented for the estimation of the most relevant engineering parameters for the design. Simple models will be derived to evaluate the stresses inside PFCs, divided in primary and secondary. For the derivation of the latter, fundamentals of thermoelastic theory will be reported, with a complementary discussion on possible stress free layouts of PFCs. This chapter will end with considerations about the engineering of the interlayer, particularly re garding its role as a compliant layer. Chapter 3 presents a design study of an advanced PFCs, namely a steel-based first wall. Design criteria for PFCs will be reported, as well as technology considerations regarding the relevant fabrication techniques.