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

The molten reactor core-concrete interaction, which describes the effect of molten reactor spread on the concrete floor of the reactor cavity, is a very complex process to simulate and predict, but the knowledge of this process is of major importance for planning the emergency counteractions for severe accidents with respect to the Stress Tests requirements after the Fukushima-Daiichi accident. The key issue is to predict the rate and most probable focusation of the melt-through process which is affected by the concrete composition, especially by the aggregate type. A limited number of small-scale experiments have been conducted over the past years along with accompanying numerical models which focused mainly on the siliceous type of aggregate. It is common for the concrete structures that the limestone type or the mixture of these two types of aggregate are used as well. Then, the objective of this paper is to extend the knowledge gained from the experiments with the siliceous aggregate to the concrete structures which are made of limestone aggregate or their combination, such as limestone sand and siliceous gravel. The proposed one-dimensional model of the melt-through process is based on the fuzzylogic interpretation of the thermodynamic trends which reflect the aggregate type. This approach allows estimating the asymptotic cases in terms of the melt-through depth in the concrete floor over time with respect to the aggregate type, which may help to decide the rather expensive further experimental efforts.

The worldwide need for nuclear power plant (NPP) lifetime extension to meet future national energy requirements while reducing greenhouse gases raises the question of the condition of concrete structures exposed to ionizing radiation. Although research into the effects of radiation has a long history and the phenomenon of deterioration of concrete due to irradiation is not yet completely understood, the main assumed degradation mode is radiation-induced volumetric expansion of aggregates. There are experimental data on irradiated concrete obtained over decades under different conditions; however, the collection of data exhibits considerable scatter. Fuzzy logic modeling offers an effective tool that can interconnect various data sets obtained by different teams of experts under different conditions. The main goal of this work is to utilize available data on irradiated concrete components such as minerals and aggregates that expand upon irradiation. Furthermore, aggregate radiation-induced volumetric expansion gives an estimate of the change in mechanical properties of aggregate after years of reactor operation. The mechanical properties of irradiated aggregate can then be used for modeling irradiated concrete in the actual NPP structure based on the composition of concrete, the average temperature on the surface of the biological shield structure, and the neutron dose received by biological shield.

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This paper presents the possibility to utilize the 3D printing technology in civil engineering field specifically for concrete structures. Since this technology is booming last years and spreads in different fields of industry, the tools to analyse structures in such a way is important. Many research groups worldwide try to develop cement-based material suitable for 3D printing so that it might be used for civil engineering structures. Moreover, this technology brings necessity to check the safety of the structure at early ages of concrete. Therefore, the modelling and simulation of the digitally printed concrete structure would be of great help for such effort. The software tool that enables simulation of digitally printed concrete structure using a nonlinear FEM analysis is presented. ATENA is well established tool for such analyses of civil engineering structures made of concrete. The new module for digital printing simulation is developed as an additional feature of ATENA software. The 3D extrusion technology is supported. The paper describes the whole procedure how to model and analyse such structures and stress out all the differences compared to analyses of structures produced by traditional manner. The structure itself is modelled as usual in FE software, whereby based on velocity of printing head the time of printing, i.e. production of each element is calculated. It is later used to activate the elements during analysis and it also influence the material behaviour, such as shrinkage, strength etc.