Effect of temperature on the time-dependent behavior of blended concrete used for nuclear waste disposal

According to the Belgian geological disposal concept for high-level nuclear waste, waste is disposed of in so-called disposal galleries (tunnels) lined with high-strength concrete at a depth of a few hundred meters below the ground. The waste generates high amounts of heat due to radioactive decay, leading to temperatures in the region of 70 °C at the intrados of the concrete liners, which may affect their structural integrity, especially during the operational phase, lasting for several decades. Furthermore, similar hightemperature conditions are also observed in nuclear reactor containment structures of existing NPPs, warranting studies on the high-temperature behaviour of concrete. In particular, this paper examines the physical and mechanical properties of a high-strength concrete subjected to high temperatures, including compressive strength, flexural tensile strength, dynamic modulus of elasticity, water permeability, pore structure, creep and shrinkage. It has been observed that when concrete is cured for 90 days and then exposed to a high temperature of 85 °C under sealed conditions, the accessible porosity, cumulative nano pores and water permeability increase by 5.8%, 47.2%, and 9.5%, respectively. Meanwhile, the compressive strength, flexural tensile strength, and dynamic modulus of elasticity decrease by 3.0%, 6.5%, and 3.0%, respectively.