Beatrice Pomaro

Radiation damage evaluation on concrete within a facility for Selective Production of Exotic Species (SPES Project), Italy

Concrete is commonly used as a biological shield against nuclear radiation. As long as, in the design of nuclear facilities, 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 mechanical 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 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.

A Review on Radiation Damage in Concrete for Nuclear Facilities

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.

Dynamic Stability of Elastic Rectangular Plates with Viscoelasto-Damaged Constraints

AbstractThe problem of dynamic instability of rectangular plates with complex constraints at the edges is here solved starting from a theory in the literature; the suggested approach allows for the definition of generic, nonperfect constraint configurations for the regions of instability due to in-plane compression loads as diagrams that are expressed in function of the applied dynamic force and its frequency. The novelty of the work stands in (1)xa0the study of viscoelasticity, combined with damage, at the constraints, which allows for the discussion of the performance of a rectangular plate with regards to dynamic instability at varying degrees of damping and damage, and (2)xa0the analytical approach developed to solve the associated eigenvalue problem for rectangular plates with generic viscoelasto-damaged constraints at two opposite edges and simply supported at the other edges. Regarding the second point, the differential equation of motion of such a system is derived and, via the variable separation met...