A numerical model accounting for the effects of neutron irradiation on concrete at the mesoscale is detailed in this paper. Irradiation experiments in test reactor (Elleuch et al., 1972), i.e., in accelerated conditions, are simulated. Concrete is considered as a two-phase material made of elastic inclusions (aggregate) subjected to thermal and irradiation-induced swelling and embedded in a cementitious matrix subjected to shrinkage and thermal expansion. The role of the hardened cement paste in the post-peak regime (brittle-ductile transition with decreasing loading rate), and creep effects are investigated. Radiation-induced volumetric expansion (RIVE) of the aggregate cause the development and propagation of damage around the aggregate which further develops in bridging cracks across the hardened cement paste between the individual aggregate particles. The development of damage is aggravated when shrinkage occurs simultaneously with RIVE during the irradiation experiment. The post-irradiation expansion derived from the simulation is well correlated with the experimental data and, the obtained damage levels are

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A review of the current state of knowledge on the effects of radiation on concrete in nuclear power production applications is presented. Emphasis is placed on the effects of radiation damage, as reflected by changes in engineering properties of concrete, in the evaluation of the long-term operation and for plant life or aging management of nuclear power plants (NPPs) in Japan, Spain, and the United States. National issues and concerns are described for Japan and the United States followed by a discussion of the fundamental understanding of the effects of radiation on concrete. Specifically, the effects of temperature, moisture content, and irradiation on ordinary Portland cement paste and the role of temperature and neutron energy spectra on radiation-induced volumetric expansion (RIVE) of aggregate-forming minerals are described. This is followed by a discussion of the bounding conditions for extended operation; the significance of accelerated irradiation conditions; the role of temperature and creep; and how these issues are being incorporated into numerical and meso-scale models. From these insights on radiation damage, analyses of these effects on concrete structures are reviewed, and the current status of work in Japan and the United States is described. Also discussed is the recent formation of a new international scientific and technical organization, the International Committee on Irradiated Concrete, to provide a forum for timely information exchanges among organizations pursuing the identification, quantification, and modeling of the effects of radiation on concrete in commercial nuclear applications. The paper concludes with a discussion of research gaps, including (1) interpreting test-reactor data, (2) evaluating service-irradiated concrete for aging management and to inform radiation damage models with the Zorita NPP (Spain) serving as the first comprehensive test case, (3) irradiated-assisted alkali-silica reactions, and (4) RIVE under constrained conditions.

Among the various degradation mechanisms possibly affecting the long-term operation of nuclear power plants, the effects of induced expansion and internal degradation that occur in concrete exposed to high-flux neutron radiation require additional research. Notably, the utilization of short-term test-reactor data to assess the long-term structural significance of light water reactor concrete biological shields necessitates to properly capture the concurrent time-dependent effects, e.g., creep and damage caused by radiation-induced volumetric damage. As this poses significant numerical challenges, a creep-damage algorithm was developed to account simultaneously for the progress of damage and visco-elastic processes in the concrete microstructure. The algorithm uses a time-adaptative scheme in which the instants at which damage occurs are explicitly searched for. This provides a non-local 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.