Current concerns on durability of concrete used in nuclear power plants and radioactive waste repositories

Nuclear power, to most of us, is mystic and somehow scary, and despite its drawbacks, is still playing an important role in the world wide energy supply. However concrete, without mystery as the most widely used materials in construction, is used as a major constituent for nuclear facilities such as radioactive waste repositories and nuclear power plants. Concrete is the only practical material offering a number of advantages including sufficient shielding against the dangers of radiation, good compressive strength, low cost, easy building, and retention of radionuclides limiting their dissipation. The assessment of the long-term durability of such concrete structures is of utmost importance and urgently needed as our knowledge on concrete durability beyond the basis of an expected several decade service life is limited. Within its service environment, these structures undergo chemical degradation processes which are very slow but they significantly change the physical integrity and the chemical conditions of the structures with the passage of time. Current issues on durability of these concrete structures include alkali-silica reaction, delayed ettringite formation, leaching, carbonation, etc. which might be magnified under severe/accelerated conditions (high temperature, radiation, moisture, cyclic loading, and acidic environments). These degradations induce an evolution of the microstructure, cracking and changes in transport properties of concrete which are still unclear due to the limited experimental timeframe available to capture these processes. This paper presents an overview on these concerns with the focus on the long-term chemical degradation aspect and presenting a case study on Ca-leaching.