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The overall thermo-hygro-mechanical behavior of concrete is to be investigated, because its bearing capacity is required together with its shielding properties, specifically when concrete structures are exposed to high-energy neutron fluxes, which represent the next generation facilities designed for the production of high energy radioactive ion beams in physics research. Irradiation in the form of either fast and thermal neutrons, primary gamma rays or gamma rays produced as a result of neutron capture, are learnt to affect concrete as well as neutron fluences of the order of 10^19 n/cm^2 and gamma radiation doses of 10^10 rad seem to become critical for concrete strength. The collection of data on concrete samples, variously exposed to neutron radiation, has allowed for defining a law for radiation damage within the FEM research code NEWCON3D, assessing the 3D coupled thermo-hygro-mechanical behavior of concrete, modeled as a multiphase porous medium, both at the macroscale and the mesoscale level. The required damage law is thought to be a function of the neutron flux impinging the concrete shielding wall, and a good estimate of this quantity has been provided by means of a Monte Carlo code developed by CERN and the National Institute of Nuclear Physics of Milan, Italy; this code handles radiation transport calculations and represents at this day one of the most reliable procedures for dealing with the interaction of radiation and matter. The suggested procedure for the radiation damage evaluation has allowed for discussing on differences between mesolevel and macrolevel approaches. Stochastic contour maps of the expected radiation field, properly interfaced with the numerical FE code, have allowed for obtaining a more precise evaluation of the radiation damage front as well as its evolution in time

Concrete is a relatively cheap material and easy to be cast into variously shaped structures. Its good shielding properties against neutrons and gamma-rays, due to its intrinsic water content and relatively high-density, respectively, make it the most widely used material for radiation shielding also. Concrete is so chosen as biological barrier in nuclear reactors and other nuclear facilities where neutron sources are hosted. Theoretical formulas are available in nuclear engineering manuals for the optimum thickness of shielding for radioprotection purposes; however they are restricted to one-dimensional problems; besides the basic empirical constants do not consider radiation damage effects, while its long-term performance is crucial for the safe operation of such facilities. To understand the behaviour of concrete properties, it is necessary to examine concrete strength and stiffness, water behavior, volume change of cement paste, and aggregate under irradiated conditions. Radiation damage process is not well understood yet and there is not a unified approach to the practical and predictive assessment of irradiated concrete, which combines both physics and structural mechanics issues. This paper provides a collection of the most distinguished contributions on this topic in the past 50 years. At present a remarkable renewed interest in the subject is shown.

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Concrete is commonly used as a biological shield against nuclear radiation. As long as, in the design of nuclear facility, its load carrying capacity is required together with its shielding properties, changes in the mechanical properties due to nuclear radiation are of particular significance and may have to be taken into account in such circumstances. The study presented here allows for reaching first evidences on the behavior of concrete when exposed to nuclear radiation in order to evaluate the consequent effect on the mechanical field, by means of a proper definition of the radiation damage, strictly connected with the strength properties of the building material. Experimental evidences on the decay of the elastic modulus of concrete have allowed for implementing the required damage law within a 3D F.E. research code which accounts for the coupling among moisture, heat transfer and the mechanical field in concrete treated as a fully coupled porous medium. The upgrade of the numerical model allows for assessing the durability of concrete under the effects of a radioactive environment; considerations on the ultimate strength resource in the lifetime of a nuclear structure can finally lead to its restoration in the damaged parts of the concrete slabs to preserve their load bearing capacity. The development of the damage front in a concrete shielding wall is analyzed under neutron radiation and results within the wall thickness are reported for long-term radiation spans and several concrete mixtures in order to discuss the resulting shielding properties