Distinct Effects of Irradiation on the Structure and Chemical Reactivity of Silicates and Carbonates

Concrete in nuclear power plants (NPP) is subject to sustained exposure to neutron irradiation. The interaction of neutrons with crystalline components of concrete, e.g.., the mineral aggregates, may result in its premature degradation by, for example, alkali-silica reaction leading to cracking. In this collection of studies, we investigated the effects of irradiation on the structure and reactivity of a wide variety of minerals typical of concrete aggregates. The silicates quartz (SiO ₂ ), albite (NaAlSi ₃ O ₈ ), and almandine (Fe ₃ Al ₂ (SiO ₄ ) ₃ ), and the carbonates calcite (CaCO ₃ ) and dolomite (CaMg(CO ₃ ) ₂ ) were irradiated using Ar+ ions at 400 keV. Molecular dynamics simulations enabled the characterization of network rigidity of pristine and irradiated samples from the magnitudes of radial and angular bond excursions. Dissolution rates quantified using vertical scanning interferometry showed that the minerals underwent various degrees of enhancement in reactivity upon irradiation, ranging from nearly unchanged (i.e., calcite and dolomite) to a factor of 1000 (i.e., quartz). The observed increase in dissolution rates for a variety of aqueous environments depended on the nature and magnitude of the relative decrease in network rigidity upon irradiation, as well on the specific dissolution mechanism of the phase. The dominance of ionic bonding in carbonates rendered the phase resilient to irradiation, whereas the breakage of Si—O bonds in the percolated silicates albite and quartz resulted in structural disorder. In addition, the trends in reactivity alterations are consistent with the corresponding changes in density. These findings can help guide assessments of susceptibility of concrete to irradiation-induced damage and inform selections of durable aggregates.