Alain Benjamin Giorla

The extension of service life of Nuclear Power Plants (NPPs) in the United States from 60 to 80 years requires an assessment of the durability of all components under long-term operation conditions, including the concrete structure itself. This, in turns, requires building predictive numerical models able to represent the long-term material behavior.

The U.S. Department of Energy's Office of Scientific and Technical Information

Among various degradation mechanisms possibly affecting the long-term operation of nuclear power plants, the effects of induced expansion and internal degradation occurring in concrete exposed to high-flux neutron radiation require additional research. Notably, using short-term test-reactor data to assess the long-term structural significance of light-water reactor concrete biological shields necessitates properly capturing the concurrent time-dependent effects, e.g., creep and damage caused by radiation-induced volumetric degradation. As this poses significant numerical challenges, a creep-damage algorithm was developed to account simultaneously for the progress of damage and viscoelastic processes in the concrete microstructure. The algorithm uses a time-adaptive scheme in which the instants at which damage occurs are explicitly searched for. This provides a nonlocal continuum damage procedure with very low sensitivity to the time or loading step. The proposed method is then used to simulate creep and restraint effects on radiation-induced degradation in concrete.

Long-term performance of aging concrete in nuclear power plants (NPPs) requires a careful examination of the physical phenomena taking place in the material. Concrete under high neutron irradiation is subjected to large irreversible deformations as well as mechanical damage, caused by a swelling of the aggregates. Mesoscale numerical simulations are performed to separate the underlying mechanisms and their interactions. The cement paste creep-damage model accounts for the effect of the loading rate on the apparent damage properties of the material and uses an event-based approach to capture the competition between creep and damage. The model is applied to the simulation of irradiation experiments from the literature and shows a good agreement with the experimental data.

The U.S. Department of Energy's Office of Scientific and Technical Information