The need for long-term predictions of the performance of old nuclear power plants concrete shielding all around the world has recently relaunched the issue of predictive modeling of the deterioration ...mechanisms associated to irradiated concrete, both theoretically and numerically. A robust numerical model for describing concrete affected by prolonged nuclear irradiation, based on a coupled thermo-hydro-mechanical formulation, is proposed and the main features that are phenomenologically responsible for the degradation of concrete material at the mesoscale level are discussed. The study is conducted at the mesoscale to account for the antagonist action of the cement paste and aggregates when irradiated. Radiation-induced damage is assimilated to mechanical damage in the proposed formulation in that radiation-induced volumetric expansion of aggregates is conceived as the source of triggering of damage in the surrounding paste. The numerical results for plain concrete samples exposed to severe radiation fluences and high temperature are juxtaposed with experimental data, showing that the model agrees satisfactorily with the general tendency of the irradiated concrete stiffness evolution and dehydrated water mass of the sample. On the other hand, the model tends to underestimate its global radiation-induced volumetric expansion.
In recent years, gravitational wave observatories have conquered the world science scene due to their unprecedented capability to observe astrophysical signals. Those first observations opened up ...multimessenger astronomy and called for a tremendous R&D effort to improve the sensitivity of future detectors. One of the many issues to be solved, not to affect the desired sensitivity, is the noise induced by the use of room temperature mirrors, especially for the low-frequency detection range. The use of cryogenic mirrors to reduce such a noise source has been individuated as a viable solution to obtain the desired sensitivity at low frequency. Cryogenically cooled mirrors, routinely operating at 10 K, present a number of extraordinary challenges, one being the cryogenic vacuum system hosting the cold mirrors. Gases composing the residual vacuum will tend to cryosorb and build a contaminant ice layer ("frost") on the mirror surface. Depending on such ice layer thickness, various unwanted detrimental effects may occur affecting mirror performances. This paper analyzes the consequences of hosting a cryogenically cooled mirror in a vacuum system and sets new limits for an acceptable operating pressure to avoid frost formation in a given period of continuous data taking. Since ice formation can be reduced but not avoided, we analyze potential mitigation methods to cure such a phenomenon. Thermal and nonthermal methods are analyzed and compared. Electron stimulated desorption is also considered as an alternative method to desorb the ice layer on mirrors. Finally, we briefly discuss further studies needed to validate the various methods with special care on their effects on the mirror perfection and optical properties.
► We present the effect of radiation on concrete as shielding material. ► The coupling between hydro-thermal-mechanical fields and radiation damage is shown. ► Attention is focused on numerical ...modelling of concrete in 3D domains. ► A new estimate of the radiation damage parameter is given. ► A risk assessment of concrete-radiation interactions is developed.
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.
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