A numerical approach to assess durability of irradiated concrete

Given the increasing use of concrete for radiation shielding and the aging nuclear power plants, there is a need to efficiently optimize concrete mix designs and assess their durability for structural and radiation safety. In this thesis, after a brief introduction (Chapter 1), Chapter 2 summarizes the current state of the art regarding the modeling of irradiated concrete. It is organized into two main sections: aggregate and mortar matrix, based on the mesoscale of concrete material. Then, Chapter 3 presents a Finite Element-based formulation to assess the behavior of cementitious materials irradiated in operational scenarios, by combining thermo-mechanical and neutron diffusion processes. Specifically, the mathematical model resorts to a two-group neutron diffusion theory in association with the heat conduction theory. At the end of this chapter, it is validated against the literature results. For the purposes of investigating material durability, the proposed numerical formulation is extended to the mesoscale in Chapter 4, and different aggregate materials are compared. The radiation field, temperature, and stress states in irradiated concrete at operational conditions are evaluated, proving to serve as a versatile tool for the structural assessment of irradiated facilities at the wider structural level. In Chapter 5, the aggregate sieving effects on the concrete shielding performance are investigated from the aspects of aggregate distribution, size, and contents. The proposed model is extended in the application of the radiation protection field in Chapter 6. The shielding capacity of a dry-stacked concrete structure after earthquakes is analyzed. Different levels of effective dose are obtained and compared with the standard requirement. The last chapter summarizes all the contributions of this thesis and provides future directions for the research in this field.